ECOLOGY
Ecology is the study of the relationship between living organisms and the
environment or surrounding.
The living organisms are the flora and fauna. Ecological studies can be directly
towards a particular organism or a single species, communities or an ecosystem.
The word ecology originates from a Greek word ‘oikos’ meaning a home. Two types
of ecological studies namely autecology and synecology are commonly carried out.
Autecology is the study of the relationship between a single species and the
environment in relation to its environment.
Synecology is the study of the relationship between communities or different
populations of organisms in a given environment i.e. the study of the relationship
between all plants and animals in a particular area to the environment.
Description of ecological terms
1. Species
This is a group of organisms or individuals capable of interbreeding to produce
fertile off springs.
2. Population
This is a group of organisms or individuals of the same species which occupy a
particular area or habitat at the same point and time. The population size of a
given species changes with time and changes in environmental factors.
3. Habitat
This is a place or physical area where the organism or species lives in an
ecosystem.
4. Community
This refers to all populations that occupy a particular area at a given time. This
implies that all plants, animals and fungi in a particular area form a community
therefore a community is a group of plants and animals of different species living
together in a certain environment i.e. plant and animal community.
5. Ecological niche
Is the role and position any species has within its habitat, and its interactions with
living and non-living environment.
A niche describes how an organism meets its need for food and shelter, how it
survives, and how it reproduces; therefore reduces intra specific competition for
resources.
An ecological niche describes the functional position and role of an organism
within its environment
An ecological niche will be comprised of various components, including:
1 | Ecology Endriyo Phillip.




The habitat in which the organism lives
The activity patterns of the organism (e.g. periods of time during which it is
active)
The resources it obtains from the environment (e.g. food source, territorial
boundaries, etc.)
The interactions that occur with other species in the region (e.g.
competition / predator-prey relationships)
Types of Niches
Some species may not be able to occupy their entire niche due to the presence or
absence of other species


The fundamental niche is the entire set of conditions under which an
organism can survive and reproduce (i.e. where it can live)
The realised niche is the set of conditions actually used by a given organism
after interactions with other species are taken into account (i.e. where it
does live)
Fundamental versus Realised Niche
Niche Differentiation
Niche differentiation describes the way by which competing species use the
environment differently in order to exist
If two species with identical niches compete, two distinct outcomes are possible:


Competitive exclusion: One species will use the resources more efficiently
and drive the other species to local extinction
Resource partitioning: Two species will alter their use of the niche to
avoid direct competition, allowing for co-existence
2 | Ecology Endriyo Phillip.
Species interaction
In nature no species exists in total isolation – all organisms interact with both the
abiotic environment and other organisms


If two species interact directly within a shared environment, they share a
positive association (they co-exist)
If interactions within an environment are mutually detrimental to both
species, they share a negative association (do not co-exist)
Positive Associations
1. Predator-Prey Relationships


Predation is a biological interaction whereby one organism (predator) hunts
and feeds on another organism (prey)
Because the predator relies on the prey as a food source, their population
levels are inextricably intertwined
3 | Ecology Endriyo Phillip.
If the prey population drops (e.g. due to over-feeding), predator numbers will
dwindle as intra-specific competition increases
If the prey population rises, predator numbers will increase as a result of the overabundance of a food source
Predator-Prey Relationships (Arctic Fox vs Snowshoe Hare)
2. Symbiotic Relationships



Symbiosis describes the close and persistent (long-term) interaction
between two species
Symbiotic relationships can be obligate (required for survival) or facultative
(advantageous without being strictly necessary)
Symbiotic relationships can be beneficial to either one or both organisms in
the partnership:
o Mutualism – Both species benefit from the interaction (anemone
protects clownfish, clownfish provides fecal matter for food)
o Commensalism – One species benefits, the other is unaffected
(barnacles are transported to plankton-rich waters by whales)
o Parasitism – One species benefits to the detriment of the other
species (ticks and fleas feed on the blood of their canine host)
Types of Symbiotic Relationships
4 | Ecology Endriyo Phillip.
Negative Associations
1. Competition



Competition describes the interaction between two organisms whereby the
fitness of one is lowered by the presence of the other
Competition can be intraspecific (between members of same species) or
interspecific (between members of different species)
Limited supplies of resources (e.g. food, water, territory) usually triggers
one of two types of responses:
o Competitive exclusion – One species uses the resources more
efficiently, driving the other species to local extinction
o Resource partitioning – Both species alter their use of the
environment to divide the resources between them
Competitive Exclusion vs Resource Partitioning
5 | Ecology Endriyo Phillip.
6. Ecosystem
An ecosystem is an ecological unit consisting of a community of living organisms
and its physical environment. Such a unit will consist of plants, animals and microorganisms as well as non-living components like water, soil, air and light. Or
An ecosystem refers to the interaction between living organisms and non-living
components of the environment or habitat to form a self-supporting system e.g. in
a pond or aquatic ecosystem. It consists of phytoplanktons, saprophytes,
zooplanktons as the biotic component (living) whose interaction with dead
decaying organic matter or recycle for self-sustainability.
7. Biosphere
This is part of the earth inhabited by living organisms. The biosphere comprises of
terrestrial and aquatic ecosystem.
The biosphere is subdivided into bio-geographical regions each inhabited by species
of plants and animals that are favored by unique conditions of such areas.
Bio-geographical regions are also subdivided into particular areas called
biomass/biomes’.
Biome refers to a large recognizable community formed as a result of interaction
between regional climates with regional biomes e.g. tropical rain forests, tropical
savanna, desert, temperate region. The biome is divided into zones e.g. forests
biome forms the ground level and canopy. The lake forms the limnetic zone,
littoral zone, benthos and profundal zone, each zone supporting a particular type
of organisms.
Terrestrial biomes
The two most important environment variables for life on land are rainfalls and
temperature.
Basing on these facts the terrestrial biome is further subdivided into;
(a) Tropical rain forests
These are formed whenever, it’s hot [24-280C] and wet throughout the year. The
vegetation of tropical rain forest has a distinctive structure, with very tall tree
which project above the rest of the forest canopy, beneath these emergent is a
second layer of large tree which, together with emergent make up a continuous
canopy. A third tree layer is made up of smaller tree which complete their cycle
without ever reaching the canopy. Still nearer the ground are young trees, palms
vine and herbs. By the time sunlight reaches the forest floor, most of it has already
been intercepted so that it’s dark with relatively sparse vegetation. Many
organisms live in the canopy.
The soils of tropic rain forest are generally poor probably because decomposition
occurs very quickly due to high temperature and any other available nutrient are
rapidly taken up by plant or leached due to high rainfall.
(b) Temperate deciduous forest.
The north temperature zone lies between tropical of Cancer and artic cycle. The
southern temperature zone lies between tropical of Capricorn and Antarctic cycle.
6 | Ecology Endriyo Phillip.
In these two zones is where the temperature deciduous forest likely to be found,
dominated by oak, hazel, beech
The major problem in this biome is that half of the year is winter when the
temperature is too low for life. To survive in this condition, organisms have
developed the following adaptations.
a) Loss of leaves by the trees in winter to reduce on water loss by guttation.
b) small animals hibernate
c) birds migrate to tropics during winter
d) some animals have accumulated a lot of fast to prevent heat loss in winter
e) some have short life cycle in of 3-6 months and survive in a dormant stage in
winter
(c) Desert
For example, Sahara Desert in Northern Africa is characteristic by scarce irregular
rainfall and sandy soil.
To survive in the desert organism have developed the following adaptations.
i. Small plants and animals have got very short life cycle; For instance, plants
may germinate, mature, flower in a few weeks following occasioned
rainfall, and then survive in form of seeds during the long dry spell.
ii. To overcome shortage of water, the camel; use metabolic water and its
body is very resistant to dehydration; certain frogs can survive for years
without water by burying themselves deep into the sand. When it rains they
dig themselves out, mate, and lay their eggs in shallow puddles. Here the
tadpole grows very quickly, metamorphosing into adults before the puddle
disappears.
iii. The camel has got broad feet not to sink in the sand.
iv. Some plant such cactus store water in their fleshly stems.
(d) Tundra
It occurs in northern Canada and Asia. It is characterized by long winter and very
short growing season. For this reason, it contains no tree neither small mammals
but plants with very short life cycle and bigger animals with a lot of fats deposits
e.g., Reindeer
Aquatic biomes
7 | Ecology Endriyo Phillip.
Most important variable that affect organism which live in water are





Salinity
nutrient availability
depth of water
how permanent is the water body
tide strength
Salinity
Aquatic organisms have got a problem of osmoregulation at different salinities.
Consequently, organisms are only adapted differently to this problem in freshwater
and marine water. And those that can survive in freshwater cannot survive in
marine water and vice versa
Nutrient availability
The most important nutrient in water are the nitrates and phosphate. Lake with
low phosphate and nitrate (oligotrophic) contain more species than lakes with high
levels of nitrates and phosphates (eutrophic lakes)
In eutrophic lakes, the high levels of nitrates and phosphate promote high growth
rates of algae and other photosynthetic organisms. This, in turn, supports a large
number of aerobic bacteria that decompose the dead photosynthetic organisms.
However, the aerobic bacteria take up more oxygen from water thus oxygen
concentration may fall below that, can support the life of big organisms.
Depth of water
Shallow water may not be able to support big animals like whales. Small ponds may
dry up which has a profound effect on the organism that can only survive in water.
Tidal strength
Distribution of organism on the shores is affected tide strength; very strong tides,
it prevents the growth of plant near the lake and big animals in water.
Ecotones are boundary zone between two biomes or ecosystem where one merges
into the other.
ECOSYSTEM
It is natural unit of environment composed of living (biotic) and non-living (abiotic)
components whose interactions lead to a self-sustaining system.
(i) Water (aquatic) ecosystems may be fresh water bodies (e.g. lakes, ponds,
rivers) or marine water bodies (e.g. sea, ocean).
Organisms in water may be of large size (nektons) e.g. fish, whales, turtles or very
tiny (planktons) e.g. phytoplanktons and zooplanktons.
(ii) Land (terrestrial) ecosystems include forests, deserts, savanna, etc
8 | Ecology Endriyo Phillip.
THE MAJOR COMPONENTS OF AN ECOSYSTEM
a) Abiotic / non-living things: these are physical and chemical factors that
influence living organisms on land (terrestrial) ecosystems and in water (aquatic).
Examples of abiotic components:
 climatic factors, which include; Temperature, Light, Wind, Humidity,
rainfall etc
 soil (edaphic) factors e.g. Soil pH, Soil air, Inorganic particles, Soil water ,
Organic matter (dead organic matter and living organisms), Soil temperature
etc
 Topography
 Other physical factors e.g fire and wave action etc
Question. How do abiotic factors affect the distribution and abundance of
organisms?
(i) Climatic factors
Temperature
a. Affects physiological processes (respiration, photosynthesis, and growth etc)
in organisms which in turn influence their distribution.
b. Ultimate heating and cooling of rocks cause air to break and crack into small
pieces and finally form soil.
c. These changes in turn may result into migration of organisms’ e.g birds to
avoid over heating or freezing.
d. Low temperatures inactivate enzymes while excessive temperatures
denature enzymes.
e. High temperature increase transpiration and sweating
f. Low temperatures break dormancy of some plants.
g. Temperatures stimulate flowering in some plants e.g cabbage (vernalisation)
h. Exposure to low temperature (stratification) stimulate germination in some
seeds after imbibitions.
Organisms have evolved to have structural, physiological and behavioral
adaptations to maintain their temperature in an optimum range.
(i) Adaptations of animals for life in hot and dry deserts.
Structural adaptations,
a) Large body extremities e.g ear lobes; to increase surface area over which
heat is lost.
b) Small sized; to increase the surface area to volume ratio, for heat loss
c) Some animals like the camel, have long skinny non fatty legs to increase
heat loss during locomotion
d) Little or no fur to reduce on insulation, and increase amount of heat lost
e) Thin subcutaneous fat layer under the skin to increase heat loss from the
body
f) Have tissues tolerant to extreme temperature changes, maintaining the
body’s main functions
Physiological adaptations
 Enzymes work under a high optimum temperature range to maintain
metabolism during day and night.
Behavioral adaptations
9 | Ecology Endriyo Phillip.




Most are nocturnal, i.e. most active at night, when temperatures are
relatively low
Aestivation(seasonal response by animals to drought or excessive heat
during which they become dormant, and the metabolic rate followed by
body temperature fall to the minimum required for maintaining the vital
activities of the body) ; allows them to survive extremes of hot
temperatures e E.g. African lungfish burrows into mud till the dry season
ends, earthworms , garden snails , desert rats, termites also aestivate
Movement with some body parts raised to minimize direct contact with hot
grounds e.g desert snakes
Salivation of the neck and legs ; increasing heat loss by evaporation e.g in
tortoise
(ii).adaptations of animals for life in cold environments
Structural adaptations
 Thick layer of fat under the skin; to increase on insulation by avoiding heat
loss
 Small body extremities to reduce the surface area over which heat is lost
 Large sized; thus small surface area to volume ratio; reducing amount of
heat lost to the surrounding
 Thick fur; to increase on insulation
 Tissues tolerant to extreme changes in temperature; maintaining their
normal functions in the body
Physiological adaptations
 Enzymes work under a high optimum temperature range to maintain
metabolism during day and night
Behavioral adaptations
 Hibernation (is seasonal response by animals to cold temperature during
which they become dormant, body temperature and metabolic rate fall to
the minimum required for maintaining the vital activities of the body) The
animals, said to be in ‘deep sleep’ ably reduce energy needs to survive the
winter when food is scarce allowing them survive extreme cold conditions
e.g in polar bears.
 Gathering in groups to warm themselves e.g. penguins
Rain fall;
Amount of rainfall in a given area determines the abundance, distribution and
types of plants in the area
Ecological significances of water
 Habitat for many aquatic organisms e.g. frogs, fish etc.
 Raw material for photosynthesis; main energy source for body processes of
other organisms
 High thermal capacities; acting as cooling agent for terrestrial organisms e.g
plants during transpiration, some animals during sweating.
 Agent for fruit, seed, spore, larva and gamete dispersal
 Condition for germination
 Highly transparent; therefore allowing light to reach aquatic organisms, for
photosynthesis; and aquatic predators to locate their prey
10 | Ecology Endriyo Phillip.

Important factor in decay and decomposition; therefore increases in
recycling of nutrients in an ecosystem.
Humidity;
Amount of water in the atmosphere;
Affects the rate at which water evaporates from organisms i.e. Low humidity
results to increasing evaporation while high humidity causes low rate of
evaporation; through stomata of leaves in plants. Accordingly, organisms within
areas of low humidity are adapted to avoid excessive loss of water by;




Having reduced number of sweat glands e.g in kangaroo rat
Presence of leaf spines in cactus plants; to reduce surface area over which
water is lost through transpiration.
Controls other activities of animals like feeding, hunting, and movements
e.g earth worms experience a larger ecological niche when the environment
is humid.
Controls opening and closure of stomata; therefore affecting rate of
photosynthesis and transpiration.
Wind / air currents;
It influences the following,
 Dispersal or migration of flying mammals, winged insects; thus reducing the
level of competition.
 Pollination
 Dispersal of seeds and spores; increasing the spread of non-motile
organisms’ e.g fungi and some bacteria.
 Takes part in rain formation
 Current and wave formation in seas and lakes enables distribution of
mineral salts.
 Increase transpiration; thus promoting water and mineral salt uptake from
the soil by plant roots
 Increases evaporation and reduces sweating.
 Causes physical damage to vegetation and soils e.g soil erosion.
 Increases dissolution of oxygen in aquatic bodies; thereby increasing aerobic
activities of organisms.
Light (intensity, quality, and duration)
Influences many physiological activities of organisms’ i.e.
 It is a source of energy for photolysis (breakdown of water during
photosynthesis.).
 Absence of light causes etiolation (elongation of shoot inter nodes).
 Induces flowering in long-day plants e.g. barley, but inhibits flowering in
short day plants.
 Phototropism, by redistributing auxins on the darker sides of shoots and
roots, with cells on darker side elongating more than those on illuminated
side.
 Germination ; some seeds are positively photoblastic; germination only in
presence of light while other do not require light to germinate.(are
negatively photoblastic)
11 | Ecology Endriyo Phillip.









Stomatal opening and closure; with most plant species opening their
stomata during day (when there is light) and closing during night (in absence
of light/darkness).
Predation ; (hunting and killing of prey by predators require certain levels of
illumination and visibility)
Courtship; with some animals preferring light so as to carry out courtship
while others prefer darkness
Light breaks dormancy of seeds.
Stimulates synthesis of vitamin D in mammals; where lipids(sterols) in the
dermis are converted to vitamin D by uv light
It enables the mechanisms photoreceptions in eyes
Absence of light results in failure of chlorophyll formation in plants i.e.
plant remains yellow, and leaves fail to expand.
Photoperiod affects migratory and reproductive behaviour in various animals
e.g. sunlight polarised by water acts as a compass for migration of salmon
fish.
Necessary for the germination of certain seeds e.g. lettuce
(ii) Topography.;
 Refers to the nature of the landscape, which includes features like
mountains, valleys, lakes etc.
 High altitude is associated with, low atmospheric pressure; low average
temperatures, increased wind speed; decreased partial pressures of oxygen,
thus few organisms live permanently here.
 Slope reduces water logging and there is a lot of soil erosion preventing
proper plant establishment especially at steep slopes
 At low altitudes, average temperatures are high, high atmospheric pressure,
partial pressures of oxygen are high, and in some places there is water
logging.
Assignment. Describe different adaptations of organisms that live in high
altitude.
(iii). Edaphic (soil) factors,
 Soil formed by chemical and physical weathering of rocks, possess both
living components(living organisms like bacteria, fungi, algae and animals
like protozoans, nematodes earthworms, insects, burrowing mammals) and
non-living components (particles of various sizes)
 Also present are; mineral salts, water, organic matter, and grasses.
Soil Ph.
 Influences physical properties of soil and availability of certain minerals to
plants, thus affecting their distribution in soil; i.e. tea and coffee plants
thrive well in acidic soils
 Affects activity of decomposers e.g in acidic medium, the rate of
decomposition is reduced, subsequently recycling of matter in an ecosystem
reduced.
Water content;
 Varies markedly in any well-defined soil,
 Any finely drained soil holding much water as possible is said to be at full
capacity
12 | Ecology Endriyo Phillip.


Addition of more water which cannot be drained away leads to water
logging; and anaerobic conditions, affecting mineral ion uptake by active
transport, subsequently affecting osmotic uptake of water, due to
decreased osmotic potential gradient, causing plants to dry out.
Plants like rice, marshes, and sedges have developed air spaces among root
tissues, allowing some diffusion of oxygen from aerial parts to help supply
the roots.
Biotic content;
 Microorganisms like bacteria and fungi carry out decomposition of dead
organic material, therefore recycling nutrients back to the soil.
 Burrowing organisms e.g. earthworms improve drainage and aeration by
forming air spaces in the soil.
 Earthworms also improve soil fertility by mixing of soil, as they bring
leached minerals from lower layers within reach of plant roots.
 They also improve humus content, by pulling leaves into their burrows
 Also press soil through their bodies making its texture fine.
Air content;
 Spaces between soil particles is filled with air from which plant roots obtain
oxygen by diffusion for aerobic respiration,
 Also essential for aerobic respiration by micro-organisms in the soil that
decompose the humus.
(iv) Salinity;
Is the measure of salt concentration in aquatic bodies and soil water.
 Determines the osmotic pressure of water; therefore the organisms have
developed structural, behavioral, and physiological adaptations to
osmoregulate in the respective salt concentration, ( read adaptations of
fresh water fish, marine water fish and migratory fish to their
osmoregulatory problems).
 Mineral salts in water affect the distribution of plant species, which in turn
affects the animals that depend on plants for food.
 Plants growing in soils deficient of certain salts, e.g insectivorous plants in
nitrogen deficient soils, obtain nitrogen feeding on insects.
Significances of mineral salts to plants
 Mineral salts together with other solutes determine the osmotic pressure of
cells and body fluids
 Determinants in anion and cation balance in cells, e.g Na+ and Cl-, involved
in transmission of nerve impulses
 Constituents of certain pigments like haemoglobin, and chlorophyll
containing iron and magnesium respectively.
 Metabolic activators; some ions activate enzymes, e.g chloride ions activate
salivary amylase, magnesium activate enzymes in phosphate metabolism,
and phosphorus as phosphate is required in activation of sugars during
Glycolysis in tissue respiration.
 Mineral salts like potassium are involved in formation of cell membrane and
opening of stomata;
 Development of stem and root e.g. calcium pectate in formation of plant
cell wall etc.
13 | Ecology Endriyo Phillip.
(v) Fire;
Types of fire
 Natural fires; are set up by natural causes like lightening, volcanic eruptions
etc.
 Artificial fires; are set up by man either intentionally or carelessly
 Wild fires; burn in the direction of wind
 Early fires; set up at beginning of dry season
 Prescribed fires; under ecological management where prevention measures
are taken when setting up the fire.
Properties of fire
 Fire intensity; is the heat content of the fire, Depends on environmental
factors such as wind, temperature as well as the amount and type of
vegetation.
 Fire duration; is the time taken by the fire to destroy a given area.
 Fire severity; is measured in terms of major vegetation destroyed by the
fire.
Ecological effects of fire
Positive effects
 Removes old leaves and stimulates trees and grasses to produce new buds.
 Breaks dormancy (seed dormancy), incase seed coats are hard and
impermeable.
 Causes release of mineral nutrients in form ash; on burning organic matter,
releasing nitrate and phosphate compounds into soil, and subsequently
improving on soil fertility.
 Improves on visibility of organisms such as predators, prey, mates allowing
them easily carry out their activities.
 Improves on food productivity in terms of quality, quantity and productivity,
because after burning new species with high protein content grows.
 Destroys pests
 Controls undesirable plant species and weeds
Negative effects
 Increase soil erosion; leading soil infertility
 Kills slow moving animals e.g snails, earthworms
 Destruction of habitat for most of the animal species may leading migration
or extinction
 Increases fire resistant species.
 Reduction in population density and biodiversity.
 Destroys food for animals like herbivores which may lead to starvation and
eventually death.
 Air pollution by products such as carbon monoxide and carbon dioxide,
increasing on global warming.
Adaptations of plants to fire
 Thick succulent shoot system to reduce the effects of heat.
 Grasses grow in tussocks to protect the young growing buds.
 Some tree stems are succulent i.e. store water in parenchyma cells to
reduce on the effects of fire heat.
14 | Ecology Endriyo Phillip.


Many plants are annuals to avoid fire severity in form of seeds, which may
be underground.
Some trees have heat resistant tissues.
(b). Biotic / living components: these are the plants, animals and decomposers.
Functions of Ecosystem
The functions of the ecosystem are as follows:
1. It regulates the essential ecological processes, supports life systems
and renders stability.
2. It is also responsible for the cycling of nutrients between biotic and
abiotic components.
3. It maintains a balance among the various trophic levels in the
ecosystem.
4. It cycles the minerals through the biosphere.
5. The abiotic components help in the synthesis of organic components
that involve the exchange of energy.
So the functional units of an ecosystem or functional components that work
together in an ecosystem are:




Productivity – It refers to the rate of biomass production.
Energy flow – It is the sequential process through which energy flows from
one trophic level to another. The energy captured from the sun flows from
producers to consumers and then to decomposers and finally back to the
environment.
Decomposition – It is the process of breakdown of dead organic material.
The top-soil is the major site for decomposition.
Nutrient cycling – In an ecosystem nutrients are consumed and recycled
back in various forms for the utilisation by various organisms.
Types of Ecosystem
An ecosystem can be as small as an oasis in a desert, or as big as an ocean,
spanning thousands of miles. There are two types of ecosystem:


Terrestrial Ecosystem
Aquatic Ecosystem
Terrestrial Ecosystem
Terrestrial ecosystems are exclusively land-based ecosystems. There are different
types of terrestrial ecosystems distributed around various geological zones. They
are as follows:
1. Forest Ecosystem
2. Grassland Ecosystem
3. Tundra Ecosystem
15 | Ecology Endriyo Phillip.
4. Desert Ecosystem
Aquatic ecosystems are ecosystems present in a body of water. These can be
further divided into two types, namely:
1. Freshwater Ecosystem
2. Marine Ecosystem
The freshwater ecosystem is an aquatic ecosystem that includes lakes, ponds,
rivers, streams and wetlands. These have no salt content in contrast with the
marine ecosystem.
Freshwater community consists of an array of organisms depending on the physiochemical and biological characteristics of the freshwater environment.
Freshwater habitats are divided into two major categories, lotic (lotus = washed,
or running water), and lentic (lenis = calm, or standing water) habitats.
Lotic habitats are those existing in relatively fast running streams, springs, rivers
and brooks. Lentic habitats are represented by the lakes, ponds, and swamps.
The above classification of the freshwater environments is based on two
conditions: currents and the ratio of the depth to surface area. Since lakes and
ponds often contain currents or at least wave action and since streams often
harbor quiet pools or calm backwaters, the difference between lotic and lentic
waters is not very precise. However, temperature, light, currents, amount of
respiratory gases, and concentration of biogenic salts are important limiting
factors influencing the organisms of all freshwater habitats.
Lentic Community:
Lentic waters are generally divided into three zones or sub-habitats: littoral,
limnetic, and pro-fundal. A small pond may consist entirely of littoral zone.
However, a deep lake with an abruptly sloping basin may possess an extremely
reduced littoral zone.
Lake Zonation:
(a) Littoral zone:
The littoral zone adjoins the shore (and is thus the home of rooted plants) and
extends down to a point called the light compensation level, or the depth at which
the rate of photosynthesis equals the rate of respiration. Within the littoral zone
producers are of two main types: rooted or benthic plants, and phytoplankton
(plant plankton) or floating green plants, which are mostly algae.
The littoral zone is the home of greater variety of consumers than are the other
zones. The zooplankton (animal plankton) of the littoral zone is rather
characteristic and differs from that of the limnetic zone in preponderance of
heavier, less buoyant crustaceans which often cling to plants or rest on the bottom
when not actively moving their appendages. Important groups of littoral
16 | Ecology Endriyo Phillip.
zooplankton are large, weak-swimming species of Daphia and Simocephalus, some
species of copepods, many families of ostracods and some rotifers.
The nekton of littoral zone is often rich in species and numbers. Adult and larval
diving beetles and various adult Hemipetra are conspicuous. Various Diptera larvae
and pupae remain suspended in the water, often near the surface. Pond fish,
frogs, turtles, and water snakes are almost exclusively the members of the littoral
zone community. Tadpoles of the frogs are important primary consumers, feeding
on algae and other plant material.
Periphyton of the littoral zone exhibits a zonation paralleling that of the rooted
plants, but many species occur almost throughout the littoral zone. Among the
periphyton forms, for example, pond snails, damselfly nymphs and climbing
dragonfly nymphs, rotifers, flatworms, bryozoa, hydra, and midge larvae rest on,
or are attached to stems and leaves of the plants.
Another group containing both primary and secondary consumers may be found
resting or moving on the bottom or beneath silt or plant debris— for example,
sprawling odonata nymphs (which have flattened rather than cylindrical bodies),
crayfish, isopods, and certain mayfly nymphs. Descending more deeply into the
bottom mud are burrowing odonata and ephemeroptera, clams, true worms, snails,
chironomids (midges), and other diptera larvae.
(b) Limnetic Zone:
The limnetic zone includes all the waters beyond the littoral zone and down to the
light compensation level. The limnetic zone derives its oxygen content from the
photosynthetic activity of phytoplankton and from the atmosphere immediately
over the lake’s surface. The atmospheric source of oxygen becomes significant
primarily when there is some surface disturbance of water caused by wind action
or human activity. The community of the limnetic zone is composed only of
plankton, nekton, and sometimes neuston (organisms resting or swimming on the
surface).
Phytoplankton producers consist of diatoms, green algae, blue- green algae, and
algae- like green flagellates, chiefly the dinoflagellates. The limnetic zooplankton
consists of few species but the number of individuals may be large. Copepods,
cladocerans, and rotifers are generally of first importance; but their species are
largely different from those found in the littoral zone. The limnetic nekton consists
almost entirely offish. In ponds, the fish of the limnetic zone are the same as those
of the littoral zone, but in large bodies of water a few species may be restricted to
the limnetic zone.
(C) Profundal Zone:
The bottom and deep water area of a lake, which is beyond the depth of effective
light penetration is called the pro-fundal zone. In north-temperate latitudes,
where winters are long and severe, this zone has the warmest water (4°C) in the
lake in winter and coldest water in summer.
The major community consists of bacteria and fungi and three groups of animal
consumers:
17 | Ecology Endriyo Phillip.
(a) Blood worms, or haemoglobin containing chironomid larvae and annelids,
(b) Small clams, and
(c) Phantom larvae, or Chaoborus (corethra).
The first two groups are benthic forms, the last are plankton that regularly move
up into the limnetic zone at night and down to the bottom during the day. All the
animals of the pro-fundal zone are adapted to withstand periods of low oxygen
concentration, whereas many bacteria are anaerobic. Large numbers of bacteria in
the bottom ooze constantly bring about decomposition of the organic matter (plant
debris, animal remains, and excreta) that accumulates on the bottom.
Eventually the organic sediments are mineralized and nitrogen and phosphorus are
put back into circulation in the form of soluble salts. In this way, the pro-fundal
zone provides rejuvenated nutrients, which are carried by currents and swimming
animals to other zones.
Ecological classification of fresh water organisms
Organisms in water can be classified depending on their life form which is based on
their mode of life. The following terms are used:
1. Neuston:
These are organisms resting or swimming on the surface of water. Such organisms
may be supported by the surface film or cling to the surface film from beneath or
swim in the upper waters. Examples include pond skaters, air breathing diving
beetles, water boat men, floating plants like duck weed, bladder work, etc.
2. Plankton (floating):
This is a mass of floating small plants (phytoplankton) and animals (zooplankton)
whose movements and distribution are more or less dependent on currents. Their
powers of locomotion are restricted to small vertical movements or to catching
prey. Examples include arolia, Pistoia, water burg, tadpole, etc.
3. Nekton:
18 | Ecology Endriyo Phillip.
These are free-swimming organisms that can swim against water currents. Some of
them are small e.g. swimming insects while others are large e.g. bony fish,
amphibians, etc.
4. Benthos:
These are organisms attached or resting on the bottom or living in the bottom
sediments. Most of them feed on fresh water organisms in ponds and lakes. They
may also be classified depending on the sub
i) Littoral zone:
This is the shallow-water region with light penetration to the bottom. Such a zone
is typically occupied by plants in natural ponds and lakes.
ii) Limnetic zone:
This is the open water zone to the depth of effective light penetration. The
community in this zone is composed of plankton, nekton and sometimes Neuston.
In shallow ponds, this zone is absent. The total illuminated depth including the
littoral and limnetic zone is referred to as the euphotic zone.
iii) Profundal:
This is the bottom and deep water area which is beyond the depth of effective
light penetration. This zone is often absent in ponds.
Factors affecting productivity of the lake
Temperature
Nutrient availability
Salinity
Water current
Pollution
Warm temperature provide optimum medium for aquatic organisms distribution as
well as enzymes involved in photosynthesis.
Cool temperature of bottom water inactivate enzyme and affect distribution of
phytoplankton thus reduced productivity.
Availability of nutrients in water due to decomposition of organic matter like
sewage, dead organisms and fertilizers washed off from farm and water would lead
to algal blooming or eutrophication of phytoplanktons. This would instead increase
productivity since phytoplanktons are many.
Man’s activities that harm the environment. With the recent increase in the human
population, there has been over exploitation of natural resources.
The marine biome
Marine regions cover about three-fourths of the Earth's surface and include oceans,
coral reefs, and estuaries. Marine algae supply much of the world's oxygen supply
and take in a huge amount of atmospheric carbon dioxide. The evaporation of the
seawater provides rainwater for the land.
Oceans
The largest of all the ecosystems, oceans are very large bodies of water that
dominate the Earth's surface. Like ponds and lakes, the ocean regions are
separated into separate zones: intertidal, pelagic, abyssal, and benthic. All four
zones have a great diversity of species. Some say that the ocean contains the
19 | Ecology Endriyo Phillip.
richest diversity of species even though it contains fewer species than there are on
land.
The intertidal zone is where the ocean meets the land — sometimes it is
submerged and at other times exposed, as waves and tides come in and out.
Because of this, the communities are constantly changing. On rocky coasts, the
zone is stratified vertically. Where only the highest tides reach, there are only a
few species of algae and mollusks. In those areas usually submerged during high
tide, there is a more diverse array of algae and small animals, such as herbivorous
snails, crabs, sea stars, and small fishes. At the bottom of the intertidal zone,
which is only exposed during the lowest tides, many invertebrates, fishes, and
seaweed can be found. The intertidal zone on sandier shores is not as stratified as
in the rocky areas. Waves keep mud and sand constantly moving, thus very few
algae and plants can establish themselves — the fauna include worms, clams,
predatory crustaceans, crabs, and shorebirds.
The pelagic zone includes those waters further from the land, basically the open
ocean. The pelagic zone is generally cold though it is hard to give a general
temperature range since, just like ponds and lakes, there is thermal stratification
with a constant mixing of warm and cold ocean currents. The flora in the pelagic
zone include surface seaweeds. The fauna include many species of fish and some
mammals, such as whales and dolphins. Many feed on the abundant plankton.
The benthic zone is the area below the pelagic zone, but does not include the
very deepest parts of the ocean (see abyssal zone below). The bottom of the zone
consists of sand, slit, and/or dead organisms. Here temperature decreases as
depth increases toward the abyssal zone, since light cannot penetrate through the
deeper water. Flora are represented primarily by seaweed while the fauna, since it
is very nutrient-rich, include all sorts of bacteria, fungi, sponges, sea anemones,
worms, sea stars, and fishes.
The deep ocean is the abyssal zone. The water in this region is very cold (around
3° C), highly pressured, high in oxygen content, but low in nutritional content. The
abyssal zone supports many species of invertebrates and fishes. Mid-ocean ridges
(spreading zones between tectonic plates), often with hydrothermal vents, are
found in the abyssal zones along the ocean floors. Chemosynthetic bacteria thrive
near these vents because of the large amounts of hydrogen sulfide and other
minerals they emit. These bacteria are thus the start of the food web as they are
eaten by invertebrates and fishes.
Coral reefs
Coral reefs are widely distributed in warm shallow waters. They can be found as
barriers along continents (e.g., the Great Barrier Reef off Australia), fringing
islands, and atolls. Naturally, the dominant organisms in coral reefs are corals.
Corals are interesting since they consist of both algae (zooanthellae) and tissues of
animal polyp. Since reef waters tend to be nutritionally poor, corals obtain
nutrients through the algae via photosynthesis and also by extending tentacles to
obtain plankton from the water. Besides corals, the fauna include several species
of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars.
Estuaries
20 | Ecology Endriyo Phillip.
Estuaries are areas where freshwater streams or rivers merge with the ocean. This
mixing of waters with such different salt concentrations creates a very interesting
and unique ecosystem. Microflora like algae, and macroflora, such as seaweeds,
marsh grasses, and mangrove trees (only in the tropics), can be found here.
Estuaries support a diverse fauna, including a variety of worms, oysters, crabs, and
waterfowl.
THE MAJOR BIOTIC / LIVING COMPONENTS OF ECOSYSTEMS
1. Producers,
Are autotrophs capable of synthesizing complex organic food materials from simple
inorganic food raw materials e.g carbon dioxide and water. Examples include;
large green terrestrial plants e.g trees, shrubs, grass. For aquatic ecosystem, the
producers are microscopic algae, blue green bacteria. Others are flagellates like
euglena, chlamydomonas etc. They are collectively called Phytoplanktons
(microscopic marine producers)
NB; Some producers use chemical energy derived from breakdown of chemical
compounds like sulphur to convert carbon dioxide and water into high energy
compounds like carbohydrates e.g sulphur bacteria i.e. they are chemosynthetic.
2. Consumer:
Are organisms that get energy and nutrients by feeding on other organisms or their
remains. They are classified as;
(i) Primary consumers (Herbivore):
A consumer that eats plants. E.g. insects, birds, most mammals (grazers),
In aquatic ecosystem, they include; water fleas, fish, crabs, mollusks, and
protozoans, collectively known as zooplanktons (microscopic marine consumers).
(ii) Secondary consumers (Carnivore):
A consumer that eats other animals. E.g. birds of prey like eagle, kites,
kingfishers; and lions, cheetahs, tigers, hyenas, snakes, big fish.
(iii) Tertiary consumers:
These feed on both primary and secondary consumers. Can be predators that hunt
and kill others for food or scavengers (animals that feed on dead organisms but do
not kill them. E.g. vultures, hyenas, marabou stocks etc.
(iv) Omnivore: A consumer that eats both plants and animals .e.g. man, pigs, etc.
3. Decomposer:
21 | Ecology Endriyo Phillip.
An organism that feeds on dead organic matter. Classified into;
(i) Detrivores/ macro decomposers;
An animal that eats detritus (dead and waste matter not eaten by consumers). E.g
earth worms, rag worms, mites, maggots, wood lice, termites etc.
(ii) Saprophyte:
A microbe (bacterium or fungus) that lives on detritus.
Importance of decomposition:
(1) It enables dead bodies to be disposed off which, if left would accumulate
everywhere.
(2) Recycles nutrients to be used by other organisms e.g. Mineral salts are released
from dead bodies into soil for plant growth.
(3) Unlocks trapped energy in the body of dead organisms.
ENERGY FLOW THROUGH AN ECOSYSTEM
The sun is the primary source of energy in the ecosystem. Light energy is trapped
by photosynthetic organisms (green plants, algae, and some bacteria); converted
into chemical energy by during photosynthesis. It is then transferred from one
feeding level to another through feeding relationships like food chains or food
webs. Most of the energy from sun getting the earth’s surface is reflected by
vegetation, soil, and water or absorbed and radiated to atmosphere; leaving only
between 5%-10% for the producers to make use of. Along the food chain, only a
small proportion of the available energy is transferred from one feeding level to
another; much energy is lost as heat during sweating and evaporation, excretion
, respiration, egestion, and some remains locked up in indigestible parts of the
plant like cellulose, or bones, hooves, hair, skin etc. of animals. The number of
organisms decrease at each successive feeding level because of the great energy
losses, so the energy left in organisms is little to support large numbers of top
consumers; limiting the length of food chain( not exceeding five trophic levels(
feeding level in a food chain containing given amount of energy).
All green plants, and some bacteria, are photoautotrophic – they use sunlight as a
source of energy


This makes light the initial source of energy for almost all communities
In a few ecosystems the producers are chemoautotrophic bacteria, which
use energy derived from chemical processes
Light energy is absorbed by photoautotrophs and is converted into chemical energy
via photosynthesis



This light energy is used to make organic compounds (e.g. sugars) from
inorganic sources (e.g. CO2)
Heterotrophs ingest these organic compounds in order to derive their
chemical energy (ATP)
When organic compounds are broken down via cell respiration, ATP is
produced to fuel metabolic processes
Overview of Photosynthesis
22 | Ecology Endriyo Phillip.
Energy flow in an ecosystem
Energy enters most ecosystems as sunlight, where it is converted into chemical
energy by producers (via photosynthesis)

This chemical energy is stored in carbon compounds (organic molecules) and
is transferred to heterotrophs via feeding
Trophic Levels
The position an organism occupies within a feeding sequence is known as a trophic
level



Producers always occupy the first trophic level in a feeding sequence
Primary consumers feed on producers and hence occupy the second trophic
level
Further consumers (e.g. secondary, tertiary, etc.) may occupy subsequent
trophic levels
The trophic levels in a community are:
Food Chains
A food chain shows the linear feeding relationships between species in a
community


Arrows represent the transfer of energy and matter as one organism is eaten
by another (arrows point in direction of energy flow)
The first organism in a food chain is always a producer, followed by
consumers (primary, secondary, tertiary, etc.)
23 | Ecology Endriyo Phillip.
Examples of Food Chains in Different Habitats
Grassland food chain
Marine food chain
Pond food chain
Food webs
A food web is a diagram that shows how food chains are linked together into more
complex feeding relationships
A food web is more representative of actual feeding pathways within an ecosystem
because:


Organisms can have more than one food source
Organisms can have more than one predator
This means that, unlike a food chain, organisms in a food web can occupy more
than one trophic level

Hint: When constructing food webs, position organisms at their highest
trophic level (keeps all arrows pointing in same direction)
Example of a Food Web (Pond Ecosystem)
24 | Ecology Endriyo Phillip.
Ecological pyramids
Ecological pyramids show the relative amounts of a specific component at the
different trophic levels of an ecosystem. The three main types of ecological
pyramids measure species numbers, biomass and energy
Pyramid of Numbers
A pyramid of numbers shows the relative number of organisms at each stage of a
food chain


These are usually shaped like pyramids, as higher trophic levels cannot be
sustained if there are more predators than prey
However, the shape may be distorted if a food source is disproportionately
large in size / biomass compared to the feeder. For example, a large
number of caterpillars may feed on a single oak tree and many fleas may
feed off a single dog host
Pyramid of Biomass
A pyramid of biomass shows the total mass of organisms at each stage of a food
chain


These pyramids are almost always upright in shape, as biomass diminishes
along food chains as CO2 and waste is released
An exception to this rule is found in marine ecosystems, where zooplankton
have a large total biomass than phytoplankton. This is because
phytoplankton replace their biomass at such a rapid rate and so can support
a larger biomass of zooplankton
Pyramid of Energy
A pyramid of energy shows the amount of energy trapped per area in a given time
period at each stage of a food chain


These pyramids are always upright in shape, as energy is lost along food
chains (either used in respiration or lost as heat)
Each level in the pyramid will be roughly one tenth the size of the
preceding level as energy transformations are 10% efficient
25 | Ecology Endriyo Phillip.
Examples of Ecological Pyramids for a Specific Food Chain
Energy loss
Energy stored in organic molecules (e.g. sugars and lipids) can be released by cell
respiration to produce ATP


This ATP is then used to fuel metabolic reactions required for growth and
homeostasis
A by-product of these chemical reactions is heat (thermal energy), which is
released from the organism
Not all energy stored in organic molecules is transferred via heterotrophic feeding
– some of the chemical energy is lost by:


Being excreted as part of the organism’s faeces
Remaining unconsumed as the uneaten portions of the food
Energy Transformations in Living Organisms
The chemical energy produced by an organism can be converted into a number of
forms, including:



Kinetic energy (e.g. during muscular contractions)
Electrical energy (e.g. during the transmission of nerve impulses)
Light energy (e.g. producing bioluminescence)
All of these reactions are exothermic and release thermal energy (heat) as a byproduct


Living organisms cannot turn this heat into other forms of usable energy
This heat energy is released from the organism and is lost from the
ecosystem (unlike nutrients, which are recycled)
26 | Ecology Endriyo Phillip.

Hence ecosystems require a continuous influx of energy from an external
source (such as the sun)
Energy Transformations in Ecosystems
Energy efficiency
When energy transformations take place in living organisms the process is never
100% efficient



Most of the energy is lost to the organism – either used in respiration,
released as heat, excreted in Feaces or unconsumed
Typically energy transformations are ~10% efficient, with about 90% of
available energy lost between trophic levels
The amount of energy transferred depends on how efficiently organisms can
capture and use energy (usually between 5 – 20%)
As energy is lost between trophic levels, higher trophic levels store less energy as
carbon compounds and so have less biomass



Biomass is the total mass of a group of organisms – consisting of the carbon
compounds contained in the cells and tissues
Because carbon compounds store energy, scientists can measure the amount
of energy added to organisms as biomass
Biomass diminishes along food chains with the loss of carbon dioxide, water
and waste products (e.g. urea) to the environment
Because energy and biomass is lost between each level of a food chain, the
number of potential trophic levels are limited
27 | Ecology Endriyo Phillip.



Higher trophic levels receive less energy / biomass from feeding and so need
to eat larger quantities to obtain sufficient amounts
Because higher trophic levels need to eat more, they expend more energy
(and biomass) hunting for food
If the energy required to hunt food exceeds the energy available from the
food eaten, the trophic level becomes unviable
 Representation of Energy Flow Along a Food Chain

Bio magnification
Because energy transformations are only ~10% efficient, higher trophic levels must
consume more prey to meet energy needs
If a pollutant is ingested by living organisms, it will become concentrated at higher
trophic levels as they eat more exposed prey


The increase of a substance (such as a pollutant) in a particular organisms is
called bioaccumulation
The increase in the concentration of a substance at a particular trophic
level is called bio magnification
Bioaccumulation refers to how pollutants enter a food chain, whereas bio
magnification refers to the tendency of pollutants to concentrate as they move
from one trophic level to the next. Because pollutants become concentrated by bio
magnification, higher trophic levels are more susceptible to their toxic effects


The pesticide DDT caused egg-shell thinning and population declines in
species of birds that fed on exposed insects
Heavy metals (like mercury) released into waterways via industrial
processes may become concentrated in fish
Ecological productivity
In ecology, production (or productivity) refers to the rate of generation of biomass
in an ecosystem
28 | Ecology Endriyo Phillip.

It is usually expressed in units of mass per area per time (e.g. kg m–2 day–1)
Primary Production
Primary production describes the production of chemical energy in organic
compounds by producers
The main source of energy for primary production is sunlight, but a fraction may
be driven by chemosynthesis by lithotrophs
Primary production may be categorised as one of two types:


Gross primary production (GPP) is the amount of chemical energy as
biomass that a producer creates in a given length of time
Net primary production (NPP) is the amount of chemical energy that is not
consumed by respiration (NPP = GPP – respiration)
Secondary Production
Secondary production describes the generation of biomass by heterotrophic
organisms (consumers)


This biomass generation is driven by the transfer of organic compounds
between trophic levels via feeding
Secondary production may also be categorised according to gross (total) and
net (usable) amounts of biomass
Ecological Productivity
Estimating population size
To determine the abundance of different species living in a community. It's
impossible to count every individual living thing in a habitat, so ecologists use
special techniques and formulas to make an educated guess.
The Importance of Population Estimation
29 | Ecology Endriyo Phillip.
Without data, ecologists cannot predict how a community will change over time. A
change in one species population may have a knock-on effect on another
population.
Population dynamics looks at the effect that various factors have on the size of a
population over time.
Populations experience constant change. It can fluctuate either up or down,
depending on several potential causes. Population dynamics can have a major
influence on the stability, development, and growth of a population.
Change Potential Causes
Increase
Decrease




Birth
Immigration
Good environmental conditions
High resource availability






Death
Emigration
Harsh environmental conditions
Competition for resources
Disease
Human activities
Population estimations can detect if a population is experiencing a significant
decline. Such a decline could present an issue for the species because small
populations experience a greater risk of extinction. Why? They tend to have lower
genetic diversity, making them more vulnerable to environmental changes and
inheriting harmful genes.
A change in population dynamics can have a domino effect on the entire
community. All species in a community rely on each other for food, resources,
pollination, shelter, and oxygen. A sudden decline of one species could lead to the
fall of another, which causes the reduction of another, and another…
Methods of Estimating Population Size
Ecologists estimate population size using three different sampling methods.
Quadrats and transects are used for plants or sessile (unmoving) animals, whilst
the mark-recapture method is used for mobile organisms.
THE QUADRAT METHOD
A quadrat is a square frame of a fixed size used to outline a sample area.
Before quadrat sampling, quadrat locations are determined using random
coordinates within the study site. This prevents bias, ensuring an even spread of
quadrats and species. Additionally, it is essential to understand the area of the
study site. For square or rectangular habitats, multiply the length and width.
However, many habitats will require the use of grid references.
30 | Ecology Endriyo Phillip.
Grid references indicate a location on a map using grid lines. These lines are
identified using letters and numbers. For example, on a 4x4 grid, the reference
could be B2, with this representing: two cells in →→ and one down↓.
The quadrat is placed on the ground using random, predetermined coordinates.
The individuals within the quadrat are identified and counted.
A quadrat of 1 m2 was placed in a rock pool. Three barnacles and four limpets
were inside the area of the quadrat.
Sometimes, estimating percentage cover is a more suitable method than counting
individuals. A gridded quadrat is used to calculate percentage cover. This is a
quadrat which is split into smaller squares. The dominant species is determined by
seeing which is more present within each square, and from this, the estimated
percentage cover can be calculated.
A gridded quadrat of 1 m2 was placed in a meadow. It contained 25 smaller
squares, each equivalent to 4% of the quadrat's area (100/25 = 4%). Thirteen
squares were primarily grass, eight were mainly moss, and the remaining four were
bare soil. This translates to an estimated percentage cover of:



13 squares x 4% = 52% grass
8 squares x 4% = 32% moss
4 squares x 4% = 16% bare soil
Multiple quadrat samples are taken to build up a representation of the entire
habitat.
The Transect Method
A transect is a line placed through a habitat. It used to measure vegetation
frequency systematically.


Continuous transects record vegetation along the entire length of the
transect line. As a result, they are best suited for shorter distances.
Interrupted transects are used to record vegetation at regular intervals
along the line.
Transects often measure vegetation changes in successional habitats.
Successional habitats gradually change from one end to the other. The soils,
plants and animals present will vary as you move through the habitat.
Dunes are an example of successional habitats. They change from exposed sandy
slopes to established grasslands and forests.
The species present in this habitat depend on abiotic (non-living) factors:




Proximity to the sea
Salinity
Wind exposure
Soil composition
31 | Ecology Endriyo Phillip.
And biotic (living) factors:

The existing species that are present
Kite diagrams are used to show how vegetation frequency changes along
atransect. The area of the graph shows frequency - the wider the chart, the higher
the frequency. These diagrams give an overall impression of how a successional
habitat changes.
The Mark-Recapture Method
Ecologists capture animals and mark them with tags, paint, markings, or bands.
The marked animals are then released back into their environment, where they
naturally mix with the rest of the population.
Animals with a hard shell are easy to mark. Unsplash
Later, a second animal sample is collected. This will likely include some marked
individuals (known as recaptures) and some unmarked individuals.
How are animals safely captured?





Longworth traps capture small mammals with bait.
Pitfall traps catch arthropods that live on the ground
Beating trays are used to collect arthropods living on plants
Pooters are used to suck insects into a small chamber (don't worry, you
can't suck them into your mouth accidentally!)
Nets are used to sample freshwater organisms of varying sizes.
The ratio of marked to unmarked individuals allows ecologists to estimate the
population size. The mark-recapture method assumes that the larger the
population, the lower the percentage of individuals recaptured.
Estimation Methods: Pros and Cons
Method
Pros
Cons

Quadrats and
Transects
MarkRecapture


Easy to use
Affordable


Low labour intensity
Can rapidly detect
population declines



It can be physically demanding
to use
Inconsistency or incorrect
quadrat size leads to errors
Many assumptions about the
population
Animals may change behaviour
to avoid or permit capture
Estimating Population Size: Formulas
Once data has been collected, it needs to be extrapolated to estimate the
population size for the entire habitat.
32 | Ecology Endriyo Phillip.
The Quadrat Formulae
The formula required for extrapolating quadrat data depends on how the data was
collected.
Counting Individuals
To estimate the population size, the habitat area is divided by the quadrat area
and multiplied by the mean. The following formula can be used:
Suppose an ecologist found a mean of 3 thistles within each 1 m 2 quadrat. The
total habitat size was 12,000 m2.
From this calculation, it can be concluded that there are 36,000 thistles in the
population.
Percentage Cover
To estimate the population size, calculate the mean percentage cover and multiply
this by 100 to obtain a percentage.
Suppose an ecologist measured the percentage of moss cover for ten quadrats in a
moorland habitat.
From this calculation, it can be concluded that the moorland habitat has 68.9%
moss coverage.
The Mark-Recapture Formula
The formula for the mark-recapture method is known as the Lincoln Index.
33 | Ecology Endriyo Phillip.
Suppose an ecologist captured and marked 15 snails during the first sample. They
then caught 21 in the second sample; 3 were already marked as they had been
captured in the first sample.
Using the Lincoln Index formula, the ecologist can conclude that there are 105
snails in the population.
Estimating Population Size: Activity
Estimating population size isn't as difficult as it sounds. All you need is a large
open space (such as a school playing field or local park) and some measuring
apparatus.
Aim: Estimate the population size of a chosen plant species in a habitat using the
quadrat method (counting individuals).
You may need to decide the appropriate estimation method for some activities.
Pay attention to the chosen species and the nature of the habitat.
Equipment:





Quadrat
Two 10 m tape measures
Clipboard
Pen
Paper
Method:
1. Measure the size of your chosen habitat. Select your quadrat locations using
random coordinates within the habitat.
2. At your first coordinates, extend the tape measures to their maximum
length. Lay them on the ground, perpendicular to each other, to form a
right angle. This will create an area of 100 m2.
3. Use a random number generator to obtain two numbers between 0 and 100.
You will use these as coordinates within your 100 m2 area.
4. Place the quadrat at the random coordinates. Count and record the number
of individuals of your chosen species present within the quadrat.
5. Take nine more random samples within the 100 m2 area.
6. Repeat this process at the predetermined quadrat locations within the
habitat.
7. Estimate the total population size.
Control Variables:
34 | Ecology Endriyo Phillip.



Quadrat size
Number of quadrat samples taken
Counting method
Risks:



Cuts or stings
Allergies
Adverse weather conditions
POPULATION GROWTH CURVES
Exponential & logistic growth
How populations grow when they have unlimited resources (and how resource
limits change that pattern).




In exponential growth, a population's per capita (per individual) growth
rate stays the same regardless of population size, making the population
grow faster and faster as it gets larger.
In nature, populations may grow exponentially for some period, but they
will ultimately be limited by resource availability.
In logistic growth, a population's per capita growth rate gets smaller and
smaller as population size approaches a maximum imposed by limited
resources in the environment, known as the carrying capacity (K).
Exponential growth produces a J-shaped curve, while logistic growth
produces an S-shaped curve.
In theory, any kind of organism could take over the Earth just by reproducing. For
instance, imagine that we started with a single pair of male and female rabbits. If
these rabbits and their descendants reproduced at top speed for 7 years, without
any deaths, we would have enough rabbits to cover the entire district. if we used
E. coli bacteria instead, we could start with just one bacterium and have enough
bacteria to cover the Earth with a 1-foot layer in just 36 hours. But this is not
possible. Why, then, don't we see these populations getting as big as they
theoretically could? E. coli, rabbits, and all living organisms need specific
resources, such as nutrients and suitable environments, in order to survive and
reproduce. These resources aren’t unlimited, and a population can only reach a
size that match the availability of resources in its local environment.
Population ecologists use a variety of mathematical methods to model population
dynamics (how populations change in size and composition over time). Some of
these models represent growth without environmental constraints, while others
include "ceilings" determined by limited resources. Mathematical models of
populations can be used to accurately describe changes occurring in a population
and, importantly, to predict future changes.
To understand the different models that are used to represent population
dynamics, let's start by looking at a general equation for the population growth
rate (change in number of individuals in a population over time):
35 | Ecology Endriyo Phillip.
In this equation,
dN/dT is the growth rate of the population in a given instant,
N is population size,
T is time, and
r is the per capita rate of increase –that is, how quickly the population grows per
individual already in the population.
If we assume no movement of individuals into or out of the population, r is just a
function of birth and death rates. You can learn more about the meaning and
derivation of the equation here:
The equation above is very general, and we can make more specific forms of it to
describe two different kinds of growth models: exponential and logistic.


When the per capita rate of increase (r) takes the same positive value
regardless of the population size, then we get exponential growth.
When the per capita rate of increase (r) decreases as the population
increases towards a maximum limit, then we get logistic growth.
Exponential growth
Bacteria grown in the lab provide an excellent example of exponential growth. In
exponential growth, the population’s growth rate increases over time, in
proportion to the size of the population.
Let’s take a look at how this works. Bacteria reproduce by binary fission (splitting
in half), and the time between divisions is about an hour for many bacterial
species. To see how this exponential growth, let's start by placing 1000 bacteria in
a flask with an unlimited supply of nutrients.

After 1 hour: Each bacterium will divide, yielding 2000 bacteria (an increase
of 1000 bacteria).
36 | Ecology Endriyo Phillip.


After 2 hours: Each of the 2000 bacteria will divide, producing 4000 (an
increase of 2000 bacteria).
After 3 hours: Each of the 4000 bacteria will divide, producing 8000 (an
increase of 4000 bacteria).
The key concept of exponential growth is that the population growth rate —the
number of organisms added in each generation—increases as the population gets
larger. And the results can be dramatic: after 1 day (24 cycles of division), our
bacterial population would have grown from 1000 to over 16 billion! When
population size, N, is plotted over time, a J-shaped growth curve is made.
we get exponential growth when r (the per capita rate of increase) for our
population is positive and constant. While any positive, constant r can lead to
exponential growth, you will often see exponential growth represented with an r
of 𝑟𝑚𝑎𝑥
𝒓𝒎𝒂𝒙 is the maximum per capita rate of increase for a particular species under
ideal conditions, and it varies from species to species. For instance, bacteria can
reproduce much faster than humans, and would have a higher maximum per capita
rate of increase. The maximum population growth rate for a species, sometimes
called its biotic potential, is expressed in the following equation:
Logistic growth
Exponential growth is not a very sustainable state of affairs, since it depends on
infinite amounts of resources (which tend not to exist in the real world).
Exponential growth may happen for a while, if there are few individuals and many
resources. But when the number of individuals gets large enough, resources start
to get used up, slowing the growth rate. Eventually, the growth rate will plateau,
or level off, making an S-shaped curve. The population size at which it levels off,
which represents the maximum population size a particular environment can
support, is called the carrying capacity, or K.
37 | Ecology Endriyo Phillip.
We can mathematically model logistic growth by modifying our equation for
exponential growth, using an r (per capita growth rate) that depends on population
size (N) and how close it is to carrying capacity (K). Assuming that the population
has a base growth rate of𝑟𝑚𝑎𝑥 , when it is very small, we can write the following
equation:
At any given point in time during a population's growth, the expression K−N tells us
how many more individuals can be added to the population before it hits carrying
capacity. (K−N)/K is the fraction of the carrying capacity that has not yet been
“used up.” The more carrying capacity that has been used up, the more the
(K−N)/K term will reduce the growth rate.
When the population is tiny, N is very small compared to K. The (K−N)/K term
becomes approximately (K/K) or 1, giving us back the exponential equation. This
fits with our graph above: the population grows near-exponentially at first, but
levels off more and more as it approaches K.
What factors determine carrying capacity?
Basically, any kind of resource important to a species’ survival can act as a limit.
For plants, the water, sunlight, nutrients, and the space to grow are some key
resources. For animals, important resources include food, water, shelter, and
nesting space. Limited quantities of these resources results in competition
between members of the same population, or intraspecific competition (intra- =
within; -specific = species).
Intraspecific competition for resources may not affect populations that are well
below their carrying capacity—resources are plentiful and all individuals can obtain
what they need. However, as population size increases, the competition
intensifies. In addition, the accumulation of waste products can reduce an
environment’s carrying capacity.
38 | Ecology Endriyo Phillip.
Examples of logistic growth
Yeast, a microscopic fungus used to make bread and alcoholic beverages, can
produce a classic S-shaped curve when grown in a test tube. In the graph shown
below, yeast growth levels off as the population hits the limit of the available
nutrients. (If we followed the population for longer, it would likely crash, since the
test tube is a closed system – meaning that fuel sources would eventually run out
and wastes might reach toxic levels).
In the real world, there are variations on the “ideal” logistic curve. We can see
one example in the graph below, which illustrates population growth in harbor
seals in Washington State. In the early part of the 20th century, seals were actively
hunted under a government program that viewed them as harmful predators,
greatly reducing their numbers. Since this program was shut down, seal
populations have rebounded in a roughly logistic pattern.
A shown in the graph above, population size may bounce around a bit when it gets
to carrying capacity, dipping below or jumping above this value. Its common for
real populations to oscillate (bounce back and forth) continually around carrying
capacity, rather than forming a perfectly flat line.
39 | Ecology Endriyo Phillip.
Population size and density
To study the demographics of a population, we'll want to start off with a few
baseline measures. One is simply the number of individuals in the population, or
population size—N. Another is the population density, the number of individuals
per area or volume of habitat.
Size and density are both important in describing the current status of the
population and, potentially, for making predictions about how it could change in
the future:


Larger populations may be more stable than smaller populations because
they’re likely to have greater genetic variability and thus more potential to
adapt to changes in the environment through natural selection.
A member of a low-density population—where organisms are sparsely spread
out—might have more trouble finding a mate to reproduce with than an
individual in a high-density population.
Species distribution
Often, in addition to knowing the number and density of individuals in an area,
ecologists will also want to know their distribution. Species dispersion patterns—
or distribution patterns—refer to how the individuals in a population are
distributed in space at a given time.
The individual organisms that make up a population can be more or less equally
spaced, dispersed randomly with no predictable pattern, or clustered in groups.
These are known as uniform, random, and clumped dispersion patterns,
respectively.



Uniform dispersion. In uniform dispersion, individuals of a population are
spaced more or less evenly. One example of uniform dispersion comes from
plants that secrete toxins to inhibit growth of nearby individuals—a
phenomenon called allelopathy. We can also find uniform dispersion in
animal species where individuals stake out and defend territories.
Random dispersion. In random dispersion, individuals are distributed
randomly, without a predictable pattern. An example of random dispersion
comes from dandelions and other plants that have wind-dispersed seeds.
The seeds spread widely and sprout where they happen to fall, as long as
the environment is favorable—has enough soil, water, nutrients, and light.
Clumped dispersion. In a clumped dispersion, individuals are clustered in
groups. A clumped dispersion may be seen in plants that drop their seeds
straight to the ground—such as oak trees—or animals that live in groups—
40 | Ecology Endriyo Phillip.
schools of fish or herds of elephants. Clumped dispersions also happen in
habitats that are patchy, with only some patches suitable to live in.
As you can see from these examples, dispersion of individuals in a population
provides more information about how they interact with each other—and with their
environment—than a simple density measurement.
Life tables, survivorship, & age-sex structure
These are tools ecologists use to describe the present state of a population and
predict its future growth.




To predict if a population will grow or shrink, ecologists need to know birth
and death rates for organisms at different ages as well as the current age
and sex makeup of the population.
Life tables summarize birth and death rates for organisms at different
stages of their lives.
Survivorship curves are graphs that show what fraction of a population
survives from one age to the next.
An age-sex pyramid is a "snapshot" of a population in time showing how its
members are distributed among age and sex categories.
Governments around the world keep records of human birth and death rates—not
just for the overall population of a country but also for specific groups within it,
broken down by age and sex. Often, this data is arranged in summary tables called
life tables. Enterprising insurance companies make good use of these life tables,
taking the probability of death at a given age and using it to calculate insurance
rates that, statistically, guarantee a tidy profit.
Ecologists often collect similar information for the species they study, but they
don't do it to maximize profits! They do it to gain knowledge and, often, to help
protect species. Take, for example, ecologists concerned about the endangered
white rhinoceros. They might follow a group of rhinoceros from birth to death.
Each year, they would record how many rhinoceros had survived and how many
babies had been born. From this data, they could better understand the life
history, or typical survival and reproduction pattern, of their rhinoceros group.
What's the use of a life history? In some cases, ecologists are just curious about
how organisms live, reproduce, and die. But there is also a practical reason to
collect life history data. By combining birth and death rates with a "snapshot" of
the current population—how many old and young organisms there are and whether
they are male or female—ecologists can predict how a population is likely to grow
or shrink in the future. This is particularly important in the case of an endangered
species, like the rhinoceros in our example.
Life tables
A life table records matters of life and death for a population—literally! It
summarizes the likelihood that organisms in a population will live, die, and/or
reproduce at different stages of their lives. Taking a look at a basic life table that
just shows survival—rather than survival and reproduction. Specifically, we'll focus
on the Dall mountain sheep, a wild sheep of northwestern North America.
41 | Ecology Endriyo Phillip.
This data was collected by an ecologist named Olaus Murie who hiked around
Mount McKinley National Park in Alaska for several years in the 1930s and 1940s.
Every time he came across the skull of a dead Dall mountain sheep, he used the
size of its horns to estimate how old it must have been when it died. From the ages
of the 608 skulls he discovered, he estimated survival and death rates for the
sheep across their lifespans.
The table below is based on Murie's skull collection data. To make it easier to
read, the table is standardized to a population of 1000 sheep. As we look through
the table, we can picture what will happen, on average, to those 1000 sheep—
specifically, how many will survive or die in each age bracket.
In the first row we see that 1000 sheep are born, reach an age of zero. Of those
sheep, 54 will die before they reach 0.5 years of age. That makes for a death, or
mortality, rate of 54/1000, or 0.054, which is recorded in the far-right column.
Number surviving at Number dying Age-specific mortality rate—
Age
beginning of age
in age interval fraction of individuals alive at
interval in
interval out of 1000 out of 1000
beginning of interval that die
years
born
born
during the interval
0–0.5
1000
54
0.054
0.5–1
946
145
0.1533
1–2
801
12
0.015
2–3
789
13
0.0165
3–4
776
12
0.0155
4–5
764
30
0.0393
5–6
734
46
0.0627
6–7
688
48
0.0698
7–8
640
69
0.1078
8–9
571
132
0.2312
9–10
439
187
0.426
10–11
252
156
0.619
11–12
96
90
0.9375
12–13
6
3
0.5
13–14
3
3
1
By looking at the life table, we can see when the sheep have the greatest risk of
death. One high-risk period is between 0.5 and 1 years; this reflects that very
young sheep are easy prey for predators and may die of exposure. The other period
42 | Ecology Endriyo Phillip.
where the death rate is high is late in life, starting around age eight. Here, the
sheep are dying of old age.
This is a relatively bare-bones life table; it only shows survival rates, not
reproduction rates. Many life tables show both survival and reproduction. If we
added reproduction to this table, we would have another column listing the
average number of lambs produced per sheep in each age interval.
Survivorship curves
Life tables are hard to read. Instead survival data as a graph is used, as a
survivorship curve.
A survivorship curve shows what fraction of a starting group is still alive at each
successive age. For example, the survivorship curve for Dall mountain sheep is
shown below:
The graph makes it nice and clear that there's a small dip in sheep survival early
on, but most of the sheep die relatively late in life.
Different species have differently shaped survivorship curves. In general, we can
divide survivorship curves into three types based on their shapes:
43 | Ecology Endriyo Phillip.



Type I. Humans and most primates have a Type I survivorship curve. In a
Type I curve, organisms tend not to die when they are young or middle-aged
but, instead, die when they become elderly. Species with Type I curves
usually have small numbers of offspring and provide lots of parental care to
make sure those offspring survive.
Type II. Many bird species have a Type II survivorship curve. In a Type II
curve, organisms die more or less equally at each age interval. Organisms
with this type of survivorship curve may also have relatively few offspring
and provide significant parental care.
Type III. Trees, marine invertebrates, and most fish have a Type III
survivorship curve. In a Type III curve, very few organisms survive their
younger years. However, the lucky ones that make it through youth are
likely to have pretty long lives after that. Species with this type of curve
usually have lots of offspring at once—such as a tree releasing thousands of
seeds—but don't provide much care for the offspring.
Age-sex structure
How can we use the birth and death rates from a life table to predict if a
population will grow or shrink? To do this effectively, we need to look at a
population in its present state.
For instance, suppose we have two populations of buffalos: one made up mostly of
young, reproductive-aged female buffalos and one made up mostly of male
buffalos past their reproductive years. Even if these populations are the same size
and share a life table—have the same reproduction and survival rates at a given
age—they are likely to follow different paths.


The first population is likely to grow because it has many buffalos that are
in prime position to produce baby buffalos.
The second population is likely to shrink because it has many buffalos that
are close to death and can no longer reproduce.
So, who's currently in a population makes a big difference when we are thinking
about future population growth! Information about the age-sex structure of a
population is often shown as a population pyramid. The x-axis shows the percent
of the population in each category, with males to the left and females to the right.
The y-axis shows age groups from birth to old age.
44 | Ecology Endriyo Phillip.
It's common to see population pyramids used to represent human populations. In
fact, there are specific shapes of pyramids that tend to be associated with
growing, stable, and shrinking human populations, as shown below.




Countries with rapid population growth have a sharp pyramid shape in their
age structure diagrams. That is, they have a large fraction of younger
people, many of whom are of reproductive age or will be soon. This pattern
often shows up for countries that are economically less developed, where
lifespan is limited by access to medical care and other resources.
Areas with slow growth, including more economically developed countries
like the United States, still have age-sex structures with a pyramid shape.
However, the pyramid is not as sharp, meaning that there are fewer young
and reproductive-aged people and more old people relative to rapidly
growing countries.
Other developed countries, such as Italy, have zero population growth. The
age structure of these populations has a dome or silo shape, with an even
greater percentage of middle-aged and old people than in the slow-growing
example.
Finally, some developed countries actually have shrinking populations. This
is the case for Japan33cubed. The population pyramid for these countries
typically pinches inward towards its base, reflecting that young people are a
small fraction of the population.
The basic principles of these human examples hold true for many populations in
nature. Large fractions of young and reproductive individuals mean a population is
likely to grow. Large fractions of individuals past reproductive age mean a
population is likely to shrink.
Life history strategies
How organisms allocate energy to maximize the number of offspring they leave
behind.




The life history of a species is the pattern of survival and reproduction
events typical for a member of the species (essentially, its lifecycle).
Life history patterns evolve by natural selection, and they represent an
"optimization" of tradeoffs between growth, survival, and reproduction.
One tradeoff is between number of offspring produced and the amount of
energy (both physical resources and parental care) put into each offspring.
Timing of first reproduction is another tradeoff. Early reproduction lowers
the chance of dying without offspring, but later reproduction may allow
organisms to have more or healthier offspring or to provide better care.
45 | Ecology Endriyo Phillip.

Members of some species reproduce only once (semelparity), while
members of other species can reproduce multiple times (iteroparity).
What is a "life history"?
What does your life history look like? In the world of ecology, that question doesn't
refer to the many challenges and successes you've experienced, or to the
friendships you've made along the way. Instead, when we're talking about life
history in ecology, we're thinking about basic demographic features of a population
or species – the kind of things that would appear in a life table. That includes when
organisms first reproduce, how many offspring they have in each round of
reproduction, and how many times reproduction occurs. For humans, life history
involves a late start to reproduction, few offspring, and the ability to reproduce
multiple times.
We can define the life history of a species as its lifecycle, and in particular, the
lifecycle features related to survival and reproduction. Life history is shaped by
natural selection and reflects how members of a species distribute their limited
resources among growth, survival, and the production of offspring.
Life history strategies and natural selection
All living things need energy and nutrients to grow, maintain their bodies, and
reproduce. In nature, these resources are in limited supply, and there is often
competition for access to them (e.g., to sunlight and minerals for plants or food
sources for animals). Thus, each organism will have non-infinite resources to divide
among activities like growth, body maintenance, and reproduction.
What does it mean for an organism to allocate its limited resources "well" in this
context? From an evolutionary standpoint, it means that the resources are
distributed among the potential activities (growth, maintenance, reproduction) in
a way that maximizes fitness, or the number of offspring the organism leaves in
the next generation. Organisms with inherited traits that cause them to distribute
their resources in a more effective way will tend to leave more offspring than
organisms lacking these traits, causing the traits to increase in the population over
generations by natural selection.
Over very long periods of time, this process results in species with life history
strategies, or collections of life history traits (number of offspring, timing of
reproduction, amount of parental care, etc.), that are well-adapted for their role
and environment. The optimal life history strategy may be different for each
species, depending on its traits, environment, and other constraints.
Parental care and fecundity
One major tradeoff in life history strategies is between number of offspring and a
parent's investment in the individual offspring. Basically, this is a "quantity versus
quality" question: an organism can have many offspring that each represent a
relatively small energy investment, or few offspring that each represent a
relatively large energy investment.
46 | Ecology Endriyo Phillip.
To put this more formally, we can say that fecundity tends to be inversely related
to the amount of energy invested per offspring. Fecundity is an organism's
reproductive capacity (the number of offspring it's capable of producing). The
higher the fecundity of an organism, the less energy it's likely to invest in each
offspring, both in terms of direct resources – such as fuel reserves placed in an egg
or seed – and in terms of parental care.


Organisms that produce large numbers of offspring tend to make a relatively
small energy investment in each, and don't usually provide much parental
care. The offspring are "on their own," and the idea is that enough are
produced that some will survive (even if the odds for any one are low).
Organisms that make few offspring usually make a large energy investment
in each offspring and often provide lots of parental care. These organisms
are effectively "putting their eggs in one basket" (literally, in some cases!)
and are heavily invested in the survival of each offspring.
As for so many cases in biology, these are general trends and not universal rules.
The main point is just that when organisms have many offspring, they can't invest
as much energy in any single offspring. When they have fewer, they can (and must)
invest more energy to ensure those offspring's survival.
Example 1: Many offspring, low investment/parental care
A typical sea snail produces hundreds of eggs at a pop, and these eggs hatch to
yield baby snails that are pretty self-sufficient from the get-go. In fact, the baby
snails in the first 10% of eggs that hatch will enthusiastically eat their slowerhatching siblings for breakfast.
Cannibalism aside, this example is a good illustration of one common type of
parental investment strategy. Sea snails and many other marine invertebrates
provide little (if any) care to their offspring. Instead, they use most of their energy
budget to make lots of offspring, each of which is relatively small. The sea snail
isn't even that impressive when it comes to numbers—a female sea urchin might
release 100,000,000,000 eggs. In species with this type of strategy, offspring are
often self-sufficient at an early age. Still, since not much energy is invested in
each offspring, they tend to be small and come into the world with low energy
reserves. This makes the offspring vulnerable to predation, so many or most will
not survive—instead, it's their sheer numbers that ensure the survival of the
population.
Example 2: Few offspring, high investment/parental care
To see a strategy at the opposite end of the spectrum, let's consider the giant
panda. Panda females typically have just one cub each time they reproduce, and
the young cub is far from self-sufficient.
Animal species like the elephant, which have few offspring during each
reproductive event, often give extensive parental care. They may also produce
larger, more energetically "expensive" offspring. The newborn elephant may look
tiny, but compared to a hatching sea snail, it's massive! Species with this type of
high-investment strategy use much of their energy budget to care for their
offspring, sometimes at the expense of their own health.
47 | Ecology Endriyo Phillip.
This type of strategy is common in mammals, including humans and kangaroos as
well as pandas. The babies of these species are relatively helpless at birth and
need to develop quite a bit before they become self-sufficient.
Fecundity and investment tradeoffs in plants
The same broad patterns seen in animals also apply to plants. Of course, plants
aren't going to provide parental care in the same way that animals do. However,
they can still produce either large numbers of energetically "cheap" seeds or small
numbers of energetically "expensive" seeds.
For example, plants with low fecundity, such as coconuts and chestnuts, produce
small numbers of energy-rich seeds, each of which has a good chance of
germinating into a new organism. Plants with high fecundity, such as orchids, take
the opposite approach: they usually make many small, energy-poor seeds, each of
which has a relatively low chance of surviving.
Timing of first reproduction (early vs. late)
When a species starts reproducing is another important part of its life history—and
another place where we see trade-offs and lots of variation among species. Some
types of plants and animals start reproducing early, while others delay much
longer. What are the pros and cons of these strategies?
Organisms that reproduce early have less risk of leaving no offspring at all, but this
may be at the expense of their growth or health. For example, small fish like
silverfish use their energy to reproduce early in life, but since they throw all their
energy to reproduction, they don't reach the size that would give them defense
against predators.
Organisms that reproduce at a later age often have greater fecundity or are better
able to provide parental care. On the flip side, they run a greater risk of not
surviving to reproductive age. For example, larger fish, like the shark, use their
energy to grow to a size that gives them more protection. As a consequence, they
delay reproduction, so there's more chance that they will die before reproducing
(or before they've reproduced to their maximum).
In general, age at first reproduction is linked to the lifespan of a species. Shortlived species often start reproducing early, while long-lived species are more likely
to delay reproduction. This is a good reminder that a life history strategy is an
integrated "solution" to the problem of leaving as many offspring as possible, and
that any one part (e.g., age of first reproduction) only makes sense in light of
others (e.g., lifespan).
Single vs. multiple reproductive events
Another important characteristic of life history relates to how many times an
organism reproduces over its lifetime. For some species, reproduction is a onetime, all-out event, and the organism doesn't survive much beyond that one event.
In other species, opportunities for reproduction come around multiple times, or
even many times, throughout the organism's lifetime.
To apply a little ecology vocab, we can split species into two groups:
48 | Ecology Endriyo Phillip.


Those that can reproduce only once (semelparity)
Those that can reproduce multiple times over their lifetime (iteroparity)
Semelparity
In semelparity, a member of a species reproduces only once during its lifetime and
then dies. Species with this pattern use up most of their resource budget in a
single reproductive event, sacrificing their health to the point that they do not
survive.
Examples of species that display semelparity are bamboo, which flowers once and
then dies, and the Chinook salmon, which uses most of its energy reserves to
migrate from the ocean to its freshwater nesting area, where it reproduces and
then dies.
Iteroparity
In iteroparity, individuals of a species reproduce repeatedly during their lives.
Iteroparity can take different forms, depending on the reproductive cycles of the
organisms involved. Species that display iteroparity don't put all of their resources
into a single reproductive event, as there's a fitness benefit (an opportunity to
have more offspring) in surviving to reproduce more times.
Some animals are able to mate only once per year, but can survive through
multiple mating seasons. The pronghorn antelope is an example of an animal that
has a seasonal estrus cycle (“heat”). Estrus is a hormonally induced physiological
condition that prepares the body for successful mating. Females of species with
estrus cycles mate only during the estrus phase of the cycle.
A different pattern is observed in primates, including humans and chimpanzees,
which may attempt reproduction at any time during their reproductive years.
However, the menstrual cycles of the females make pregnancy likely only a few
days per month during ovulation.
Population regulation
What factors limit population sizes?
Key points




In nature, population size and growth are limited by many factors. Some are
density-dependent, while others are density-independent.
Density-dependent limiting factors causes a population's per capita growth
rate to change—typically, to drop—with increasing population density. One
example is competition for limited food among members of a population.
Density-independent factors affect per capita growth rate independent of
population density. Examples include natural disasters like forest fires.
Limiting factors of different kinds can interact in complex ways to produce
various patterns of population growth. Some populations show cyclical
oscillations, in which population size changes predictably in a cycle.
All populations on Earth have limits to their growth. Even populations of bunnies—
that reproduce like bunnies!—don't grow infinitely large. What exactly are these
environmental limiting factors? Broadly speaking, we can split the factors that
49 | Ecology Endriyo Phillip.
regulate population growth into two main groups: density-dependent and densityindependent.
Density-dependent limiting factors
Imagine a population of organisms—let's say, deer—with access to a fixed, constant
amount of food. When the population is small, the limited amount of food will be
plenty for everyone. But, when the population gets large enough, the limited
amount of food may no longer be sufficient, leading to competition among the
deer. Because of the competition, some deer may die of starvation or fail to have
offspring, decreasing the per capita—per individual—growth rate and causing
population size to plateau or shrink.
In this scenario, competition for food is a density-dependent limiting factor. In
general, we define density-dependent limiting factors as factors that affect the
per capita growth rate of a population differently depending on how dense the
population already is. Most density-dependent factors make the per capita growth
rate go down as the population increases. This is an example of negative feedback
that limits population growth.
Density-dependent limiting factors can lead to a logistic pattern of growth, in
which a population's size levels off at an environmentally determined maximum
called the carrying capacity. Sometimes this is a smooth process; in other cases,
though, the population may overshoot carrying capacity and be brought back down
by density-dependent factors.
Density-dependent limiting factors tend to be biotic—living organism-related—as
opposed to physical features of the environment. Some common examples of
density-dependent limiting factors include:




Competition within the population. When a population reaches a high
density, there are more individuals trying to use the same quantity of
resources. This can lead to competition for food, water, shelter, mates,
light, and other resources needed for survival and reproduction.
Predation. Higher-density populations may attract predators who wouldn’t
bother with a sparser population. When these predators eat individuals from
the population, they decrease its numbers but may increase their own.
Disease and parasites. Disease is more likely to break out and result in
deaths when more individuals are living together in the same place.
Parasites are also more likely to spread under these conditions.
Waste accumulation. High population densities can lead to the
accumulation of harmful waste products that kill individuals or impair
reproduction, reducing the population’s growth.
Density-dependent regulation can also take the form of behavioral or physiological
changes in the organisms that make up the population. For example, rodents
called lemmings respond to high population density by emigrating in groups in
search of a new, less crowded place to live. This process has been misinterpreted
as a mass suicide of sorts in popular culture because the lemmings sometimes die
while trying to cross bodies of water.
50 | Ecology Endriyo Phillip.
Density-independent limiting factors
The second group of limiting factors consists of density-independent limiting
factors that affect per capita growth rate independent of how dense the
population is.
As an example, let's consider a wildfire that breaks out in a forest where deer live.
The fire will kill any unlucky deer that are present, regardless of population size.
An individual deer's chance of dying doesn't depend at all on how many other deer
are around. Density-independent limiting factors often take the form of natural
disasters, severe weather, and pollution.
Unlike density-dependent limiting factors, density-independent limiting factors
alone can’t keep a population at constant levels. That’s because their strength
doesn’t depend on the size of the population, so they don’t make a "correction"
when the population size gets too large. Instead, they may lead to erratic, abrupt
shifts in population size. Small populations may be at risk of getting wiped out by
sporadic, density-independent events.
Population fluctuations
In the real world, many density-dependent and density-independent limiting
factors can—and usually do—interact to produce the patterns of change we see in a
population. For example, a population may be kept near carrying capacity by
density-dependent factors for a period then experience an abrupt drop in numbers
due to a density-independent event, such as a storm or fire.
However, even in the absence of catastrophes, populations are not always stably
at carrying capacity. In fact, populations can fluctuate, or vary, in density in many
different patterns. Some undergo irregular spikes and crashes in numbers. For
instance, algae may bloom when an influx of phosphorous leads to unsustainable
growth of the population. Other populations have regular cycles of boom and bust.
Let's take a closer look at these cycles.
Population cycles
Some populations undergo cyclical oscillations in size. Cyclical oscillations are
repeating rises and drops in the size of the population over time. If we graphed
population size over time for a population with cyclical oscillations, it would look
roughly like the wave below—though probably not quite as tidy!
Where do these oscillations come from? In many cases, oscillations are produced by
interactions between populations of at least two different species. For instance,
51 | Ecology Endriyo Phillip.
predation, parasite infection, and fluctuation in food availability have all been
shown to drive oscillations. These density-dependent factors don't always create
oscillations, however. Instead, they only do so under the right conditions, when
populations interact in specific ways.
Interactions in communities
Key points:




An ecological community consists of all the populations of all the different
species that live together in a particular area.
Interactions between different species in a community are called
interspecific interactions—inter- means "between."
Different types of interspecific interactions have different effects on the
two participants, which may be positive (+), negative (-), or neutral (0).
The main types of interspecific interactions include competition (-/-),
predation (+/-), mutualism, (+/+), commensalism (+/0), and parasitism
(+/-).
Introduction
When we took a tour through population ecology, we mostly looked at populations
of individual species in isolation. In reality, though, populations of one species are
rarely—if ever!—isolated from populations of other species.
In most cases, many species share a habitat, and the interactions between them
play a major role in regulating population growth and abundance.
Together, the populations of all the different species that live together in an area
make up what's called an ecological community. For instance, if we wanted to
describe the ecological community of a coral reef, we would include the
populations of every single type of organism we could find, from coral species to
fish species to the single-celled, photosynthetic algae living in the corals. For a
healthy reef, that comes out to a whole lot of different species!
Community ecologists seek to understand what drives the patterns of species
coexistence, diversity, and distribution that we see in nature. A core part of how
they address these questions is by examining how different species in a community
interact with each other. Interactions between two or more species are called
interspecific interactions—inter- means "between."
Name
Description
Effect
Competition
Organisms of two species use the same limited resource
and have a negative impact on each other.
-/-
Predation
A member of one species, predator, eats all or part of the
body of a member of another species, prey.
+/-
52 | Ecology Endriyo Phillip.
Name
Description
Effect
Herbivory
A special case of predation in which the prey species is a
plant
+/-
Mutualism
A long-term, close association between two species in
which both partners benefit
+/+
Commensalism
A long-term, close association between two species in
which one benefits and the other is unaffected
+/0
Parasitism
A long-term, close association between two species in
which one benefits and the other is harmed
+/-
Overview: interspecies interactions
Interspecies interactions can be broken into three main categories: competition,
predation, and symbiosis. Let's take a closer look at each.
Competition
In interspecific competition, members of two different species use the same
limited resource and therefore compete for it. Competition negatively affects both
participants (-/- interaction), as either species would have higher survival and
reproduction if the other was absent.
Species compete when they have overlapping niches. That is, overlapping
ecological roles and requirements for survival and reproduction. Competition can
be minimized if two species with overlapping niches evolve by natural selection to
utilize less similar resources, resulting in resource partitioning.
Predation
In predation, a member of one species—the predator—eats part or all of the
living, or recently living, body of another organism—the prey. This interaction is
beneficial for the predator, but harmful for the prey. Predation may involve two
animal species, but it can also involve an animal or insect consuming part of a
plant, a special case of predation known as herbivory.
Predators and prey regulate each other's population dynamics. Also, many species
in predator-prey relationships have evolved adaptations—beneficial features
arising by natural selection—related to their interaction. On the prey end, these
include mechanical, chemical, and behavioral defenses. Some species also have
warning coloration that alerts potential predators to their defenses; other
harmless species may mimic this warning coloration.
Symbiosis
Symbiosis is a general term for interspecific interactions in which two species live
together in a long-term, intimate association. In everyday life, we sometimes use
the term symbiosis to mean a relationship that benefits both parties. However, in
53 | Ecology Endriyo Phillip.
ecologist-speak, symbiosis is a broader concept and can include close, lasting
relationships with a variety of positive or negative effects on the participants.
Mutualism
In a mutualism, two species have a long-term interaction that is beneficial to both
of them. For example, some types of fungi form mutualistic associations with plant
roots. The plant can photosynthesize, and it provides the fungus with fixed carbon
in the form of sugars and other organic molecules. The fungus has a network of
threadlike structures called hyphae, which allow it to capture water and nutrients
from the soil and provide them to the plant.
Commensalism
In a commensalism, two species have a long-term interaction that is beneficial to
one and has no positive or negative effect on the other. For instance, many of the
bacteria that inhabit our bodies seem to have a commensal relationship with us.
They benefit by getting shelter and nutrients and have no obvious helpful or
harmful effect on us.
It's worth noting that many apparent commensalisms actually turn out to be
slightly mutualistic or slightly parasitic when we look at them more closely. For
instance, biologists are finding more and more evidence that our normal microbial
inhabitants play a key role in health.
Parasitism
In a parasitism, two species have a close, lasting interaction that is beneficial to
one, the parasite, and harmful to the other, the host (+/- interaction).
Some parasites cause familiar human diseases. For instance, if there is a tapeworm
living in your intestine, you are the host and the tapeworm is the parasite—your
presence enhances the tapeworm's quality of life, but not vice versa!
Ecological Succession
Succession as progressive change in an ecological community. Primary vs.
secondary succession. The idea of a climax community.



Succession is a series of progressive changes in the composition of an
ecological community over time.
In primary succession, newly exposed or newly formed rock is colonized by
living things for the first time.
In secondary succession, an area previously occupied by living things is
disturbed—disrupted—then recolonized following the disturbance.
Have you ever looked at a landscape with a complex, diverse community of plants
and animals—such as a forest—and wondered how it came to be? Once upon a time,
that land must have been empty rock, yet today, it supports a rich ecological
community consisting of populations of different species that live together and
interact with one another. Odds are, that didn't happen overnight!
Ecologists have a strong interest in understanding how communities form and
change over time. In fact, they have spent a lot of time observing how complex
communities, like forests, arise from empty land or bare rock. They study, for
54 | Ecology Endriyo Phillip.
example, sites where volcanic eruptions, glacier retreats, or wildfires have taken
place, clearing land or exposing rock.
In studying these sites over time, ecologists have seen gradual processes of change
in ecological communities. In many cases, a community arising in a disturbed area
goes through a series of shifts in composition, often over the course of many years.
This series of changes is called ecological succession.
Succession often involves a progression from communities with lower species
diversity—which may be less stable—to communities with higher species diversity—
which may be more stable though this is not a universal rule.
Primary Succession
Primary succession occurs when new land is formed or bare rock is exposed,
providing a habitat that can be colonized for the first time.
For example, primary succession may take place following the eruption of
volcanoes, such as those on the Big Island of Hawaii. As lava flows into the ocean,
new rock is formed. On the Big Island, approximately 32 acres of land are added
each year. What happens to this land during primary succession?
First, weathering and other natural forces break down the substrate, rock, enough
for the establishment of certain hearty plants and lichens with few soil
requirements, known as pioneer species, see image below. These species help to
further break down the mineral-rich lava into soil where other, less hardy species
can grow and eventually replace the pioneer species. In addition, as these early
species grow and die, they add to an ever-growing layer of decomposing organic
material and contribute to soil formation.
This process repeats multiple times during succession. At each stage, new species
move into an area, often due to changes to the environment made by the
preceding species, and may replace their predecessors. At some point, the
community may reach a relatively stable state and stop changing in composition.
However, it's unclear if there is always—or even usually—a stable endpoint to
succession, as we'll discuss later in the article.
Secondary succession
55 | Ecology Endriyo Phillip.
In secondary succession, a previously occupied area is re-colonized following a
disturbance that kills much or all of its community.
A classic example of secondary succession occurs in oak and hickory forests cleared
by wildfire. Wildfires will burn most vegetation and kill animals unable to flee the
area. Their nutrients, however, are returned to the ground in the form of ash.
Since a disturbed area already has nutrient-rich soil, it can be recolonized much
more quickly than the bare rock of primary succession.
Before a fire, the vegetation of an oak and hickory forest would have been
dominated by tall trees. Their height would have helped them acquire solar
energy, while also shading the ground and other low-lying species. After the fire,
however, these trees do not spring right back up. Instead, the first plants to grow
back are usually annual plants—plants that live a single year—followed within a few
years by quickly growing and spreading grasses. The early colonizers can be
classified as pioneer species, as they are in primary succession.
Over many years, due at least in part to changes in the environment caused by the
growth of grasses and other species, shrubs will emerge, followed by small pine,
oak, and hickory trees. Eventually, barring further disturbances, the oak and
hickory trees will become dominant and form a dense canopy, returning the
community to its original state—its pre-fire composition. This process of succession
takes about 150 years.
The path and endpoint of succession
The early ecologists who first studied succession thought of it as a predictable
process in which a community always went through the same series of stages. They
also thought that the end result of succession was a stable, unchanging final state
called a climax community, largely determined by an area's climate. For instance,
in the example above, the mature oak and hickory forest would be the climax
community.
Today, the idea of a set path for succession and a stable climax community have
been called into question. Rather than taking a predetermined path, it appears
that succession can follow different routes depending on the specifics of the
situation. Also, although stable climax communities can form in some cases, this
may be uncommon in many environments. Ecosystems may experience frequent
disturbances that prevent a community from reaching an equilibrium state—or
knock it quickly out of this state if it manages to get there.
56 | Ecology Endriyo Phillip.
Cyclic Succession
This is only the change in the structure of an ecosystem on a cyclic basis. Some
plants remain dormant for the rest of the year and emerge all at once. This
drastically changes the structure of an ecosystem.
“A seral community is an intermediate stage of ecological succession
advancing towards the climax community.”
Man and the environment
Effects of Population Growth on our Environment
The factors responsible for environment degradation is population growth or
population density. In particular, population density plays the most important role
in shaping the socio-economic environment. Its effects are felt on the natural
environment also.
1. Generation of Waste:
Due to his destructive activities, man has dumped more and more waste in
environment. As the man-made waste is not transformed, it causes degradation
and the capacity of environment to absorb more waste is reduced. Further, waste
leads to air and water pollution.
2. Threat to Biodiversity:
Due to his destructive activities, man has extracted more and more minerals from
the earth. Animals have been hunted and plants have disappeared. There has been
loss of biodiversity. These have led to ecological imbalance.
3. Strain on Forests:
Man has established new housing colonies. National highways and hydropower
projects have been built and forests have been wiped out. These destructive
activities have increased and led to ecological imbalance.
4. Urbanization:
Rapid growth of population has led to urbanization which has adversely affected
environment. Due to population pressure, natural resources in the cities are
depleted at a fast rate due to population pressure.
Moreover, population does not have proper sanitation facilities and pure drinking
water. As a result, the health of the people is adversely affected. No doubt,
urbanization reduces pressure on the rural environment, but it brings with if
environmental damages through industrial growth, emissions and wastes.
5. Industrialization:
57 | Ecology Endriyo Phillip.
Underdeveloped countries are following the policy of heavy industrialization which
is causing environmental degradation. The establishment of such industries as
fertilizers, iron and steel, chemicals and refineries have led to land, air and water
pollution.
6. Land Degradation:
Intensive farming and excessive use of fertilizers and pesticides have led to overexploitation of land and water resources. These have led to land degradation in
the form of soil erosion, water logging and salination.
7. Transport Development:
Environmental degradation is also due to transport development in the different
parts of the world. The automobiles release huge quantities of poisonous gases
such as carbon monoxide, nitrogen oxides and hydrocarbons. The development of
ports and harbours have led to oil spills from ships adversely affecting fisheries,
coral reefs, mangroves and landscapes.
8. Climatic Change:
Climatic changes are irregular due to greenhouse gases. The thin skin of air that
surrounds the planet is being affected by human activities as never before. Urban
people are still being exposed to unaccepted levels of toxic pollutants. Further,
forests are still being degraded by acid deposition generated by faraway industries,
and greenhouse gases continue to accumulate in the atmosphere.
9. Productivity:
Environmental degradation not only harms health but also reduces economic
productivity. Dirty water, inadequate sanitation, air pollution and land degradation
cause serious diseases on an enormous scale in developing countries like India.
These, in turn, reduce the productivity levels in the country. To take specific
instances, water pollution has led to declining fisheries in rivers, ponds and canals
in both urban and rural areas. Water shortages have reduced economic activity in
towns, and cities and villages.
Soil and hazardous wastes have polluted ground water resources which cannot be
used for agricultural and industrial production.
Soil degradation leading to soil erosion, drought, etc. have led to siltation of
reservoirs and blocking of river and canal transport channels. Deforestation has led
to soil erosion and consequent loss of sustainable logging potential.
Loss of bio-diversity has resulted in the loss of genetic resources.
Last but not the least, atmospheric changes have given rise to disruption of marine
food chain, damages to coastal infrastructure due to sea-rise and regional changes
in agriculture productivity due to hurricanes in seas.
Thus, environmental degradation undermines economic productivity of a nation.
58 | Ecology Endriyo Phillip.
10. Technology:
Presently, environmental pollution is caused by old technology which releases
gases and pollutants causing chemical and industrial pressure on environment.
Impact of Environment on Population:
Polluted environment also affects adversely the health of people.
Control/mitigation of the effects of populations on the environment.
Agricultural and industrial development along with urbanization and spread of
infrastructure combined with population growth has led to environmental
degradation. Environmental degradation harms human health, reduces economic
productivity and leads to the loss of amenities. The damaging effects of economic
development on environmental degradation can be reduced by a judicious choice
of economic and environmental policies and environmental investments.
We discuss some policy measures as under:
1. Control of Population Growth:
The rate of population growth should be curtailed through effective family
planning measures. This is essential because the proportion of total population in
the labour force will increase further in the years to come as a result of changes in
the age structure of the population.
The shifting of labour force from the rural to the secondary sector requires
increase in agricultural productivity. Increased agricultural productivity helps in
meeting the demand for raw materials of the expanding manufacturing sector.
With increased productivity, less workers are required to produce raw materials
for industry and food-grains for the population.
It also increases agricultural surplus thereby raising saving and investment for
economic development. So concerted efforts are needed to increase agricultural
productivity through technological advancement. This will ultimately lead to
commercialisation of agriculture and production for exports, thereby earning
foreign exchange for further development.
2. Economic Development:
The aim of population control is not only to bring about a decline in fertility rates
but also to improve the quality of life of the people. These are possible through
rapid economic development. It is not an illusion to believe that a reduction in
population growth will automatically raise living standards. In fact, an effective
family planning policy should be integrated with measures to accelerate economic
development.
3. Improving Health and Nutrition:
The food and nutrition security for the weaker sections in a developing country
should not be considered as issues in the Nutrition Science but should be
59 | Ecology Endriyo Phillip.
considered as part of right to work, right to health, right to education, right to
information and right of the poor. In such a country, there are agricultural, health,
population, nutrition, children and education policies.
On the other hand, there are fiscal and budget revisions, exports, imports,
taxation, price wage, employment policies and policy related to subsidies.
Ultimately, all these policies affect life of the poor, their food and nutritionist
security and health. As a leading nutritionist C. Gopalan notes: “Various types of
food are needed for maximum nutrition and if they are all taken together and in
proper proportions (systematic balanced diet), they can provide necessary
nutrients.
Guarantee of good nutrition and absence of hunger are not the same thing. Our
first effort should be towards removing hunger of the poor, but our long-term goal
should be to provide maximum nutrition to our people which is useful in bringing
out their hereditary talents. Nutrition security is more important than food
security. Nutrition security includes making our food base wider and varietal. ”
Improving health and nutrition levels is an extremely important factor contributing
to the social development of a developing country. Especially the people of the
weaker sections of the society who do not take adequate advantage of health,
family welfare and nutrition services, should be made aware of these facilities so
that their health and nutrition status can be improved.
4. Reducing Poverty:
Such development projects should be started which provide greater employment
opportunities to the poor. The government should expand health and family
planning services and education so as to reach the poor that will help reduce
population growth. Further, making investments in providing civic amenities like
the supply of drinking water, sanitation facilities, alternate habitats in place of
slums, etc. will not only improve welfare but also environment.
5. Removing Subsidies:
To reduce environmental degradation at no financial cost to the government,
subsidies for resource use by the private and public sectors should be removed.
Subsidies on the use of electricity, fertilisers, pesticides, diesel, petrol, gas,
irrigation water, etc. lead to their wasteful use and environmental problems.
Subsidies to capital intensive and highly polluting private and public industries lead
to environmental degradation. Removing or reducing subsidies will bring both
economic and environmental benefits to the country.
6. Clarifying and Extending Property Rights:
Lack of property rights over excessive use of resources leads to degradation of
environment. This leads to overgrazing of common or public lands, deforestation,
and overexploitation of minerals, fish, etc. Clarifying and assigning ownership
titles and tenurial rights to private owners will solve environmental problems.
Places where the use of common lands, forests, irrigation systems, fisheries, etc.
60 | Ecology Endriyo Phillip.
are regulated and rules for their proper use are laid down by the community, the
ownership rights should be clearly specified in the administrative records.
7. Market Based Approaches:
Besides regulator measures, there is urgent need for adopting market based
approaches for the protection of environment. They aim at pointing to consumers
and industries about the cost of using natural resources on environment. These
costs are reflected in the prices paid for goods and services so that industries and
ultimately the consumers are guided by them to reduce air and water pollution.
The Market Based Instruments (MBIs) are in the form of environmental taxes that
include pollution charges (emission tax/pollution taxes), marketable permits,
depositor fund system, input taxes/product charges, differential tax rates and user
administrative charges and subsidies for pollution abatement equipment for air and
water resources.
8. Regulatory Policies:
Regulatory polices also help in reducing environmental degradation. Regulators
have to make decisions regarding prices, quantity and technology. In making
decisions, they have to choose between the quantity or the price of pollution or
resource use of technologies.
The regulating authority has also to decide whether policies should target the
environmental problem directly or indirectly. It lays down technical standards and
regulations and charges on air, water and land pollutants. Regulators should be
impartial in applying environmental standards to both public and private sector
polluters or resources users.
9. Economic Incentives:
Like regulatory policies, economic incentives relate to price, quantity and
technology. Incentives are usually in the form of variable fees to resource users for
the quantity of pollutants in air, water and land use. They are given rebates if less
waste or pollution is generated than the emission standards laid down.
10. Public Participation:
Public awareness and participation are highly effective to improve environmental
conditions. Conducting of formal and informal education programmes relating to
environment management and environmental awareness programmes can go a long
way in controlling environmental degradation and keeping the environment clean.
For instance, the scheme of eco-labelling of products helps consumers to identify
products that are environment friendly.
Public participation can also render costless and useful assistance in Afforestation,
conservation of wildlife, management of parks, improvement of sanitation and
drainage systems and flood control. Use of indigenous institutions, local voluntary
organisations and NGOs can render much help in educating the masses about the
harmful effects of environmental degradation and the benefits of keeping the
environment clean.
61 | Ecology Endriyo Phillip.
EutrophicationEutrophication is the process in which a water body becomes overly enriched with
nutrients, leading to plentiful growth of simple plant life. The excessive growth (or
bloom) of algae and plankton in a water body are indicators of this process.
Eutrophication is considered to be a serious environmental concern since it often
results in the deterioration of water quality and the depletion of dissolved oxygen
in water bodies. Eutrophic waters can eventually become “dead zones” that are
incapable of supporting life.
Eutrophication may be defined as the inorganic nutrient enrichment of natural
waters, leading to an increased production of algae and macrophytes.
The term Eutrophication is more widely known in relation to human activities
where the artificial introduction of plant nutrients has led to community changes
and a deterioration of water quality in many freshwater systems.
Aquatic ecosystems are home to several plant and animal life forms – both simple
and complex. The process of eutrophication destroys the balance in these
ecosystems by favouring the growth of simple plant life. This greatly decreases the
biodiversity of the ecosystem by killing off several desirable species.
Causes of Eutrophication
The availability of nutrients such as nitrogen and phosphorus limits the growth of
plant life in an ecosystem. When water bodies are overly enriched with these
nutrients, the growth of algae, plankton, and other simple plant life is favoured
over the growth of more complex plant life.
How do Water Bodies Become Overly Enriched?
Phosphorus is considered one of the primary limiting factors for the growth of
plant life in freshwater ecosystems. Several sources also claim that the availability
of nitrogen is an important limiting factor for the growth of algae.
62 | Ecology Endriyo Phillip.
Phosphates tend to stick to the soil and are transported along with it. Therefore,
soil erosion is a major contributor to the phosphorus enrichment of water bodies.
Some other phosphorus-rich sources that enrich water bodies with the nutrient
include:




Fertilizers
Untreated sewage
Detergents containing phosphorus
Industrial discharge of waste.
Among these sources, the primary contributors to eutrophication include
agriculture and industrial wastes.
What Happens to the Huge Biomass of Algae in Eutrophic Waters?
The excessive growth of algae in eutrophic waters is accompanied by the
generation of a large biomass of dead algae. These dead algae sink to the bottom
of the water body where they are broken down by bacteria, which consume oxygen
in the process.
Process of Eutrophication
The overconsumption of oxygen leads to hypoxic conditions (conditions in which
the availability of oxygen is low) in the water. The hypoxic conditions at the lower
levels of the water body lead to the suffocation and eventual death of larger life
forms such as fish.
Classification of Eutrophication
The process of eutrophication can be categorized into two types based on its root
cause.
63 | Ecology Endriyo Phillip.
Anthropogenic Eutrophication
Anthropogenic eutrophication is caused by human activity – Agricultural farms, golf
courses, lawns, etc. are supplied with nutrients by humans in the form of
fertilizers. These fertilizers are washed away by rains and eventually find their
way into water bodies such as lakes and rivers.
When introduced to an aqueous ecosystem, the fertilizers supply plentiful
nutrients to algae and plankton, resulting in the eutrophication of the water body.
Overpopulation places a huge demand on industrial and agricultural expansion,
which in turn leads to deforestation. When this occurs, the soil erodes more easily,
resulting in increased soil deposits in water bodies. If the soil is rich in phosphorus,
it can lead to eutrophication and severely damage the ecosystem in and around
the water body.
When sewage pipes and industrial wastes are directed to water bodies, the
nutrients present in the sewage and other wastes increase the rate at which
eutrophication occurs.
Natural Eutrophication
Natural eutrophication refers to the excessive enrichment of water bodies via
natural events. For example, the nutrients from the land can be washed away in a
flood and deposited into a lake or a river. These water bodies become overly
enriched with nutrients, enabling the excessive growth of algae and other simple
plant life.
The process of natural eutrophication is much slower when compared to the
process of anthropogenic eutrophication. This process is also somewhat dependant
on the temperature of the environment. It may even be complemented by the
temperature changes brought on by global warming.
Effects of Eutrophication
Primarily, the adverse effects of eutrophication on aquatic bodies include a
decrease in biodiversity, increase in toxicity of the water body, and change in
species dominance. Some other important effects of this process are listed below.








Phytoplanktons grow much faster in such situations. These phytoplankton
species are toxic and are inedible.
Gelatinous zooplankton blooms fast in these waters.
Increased biomass of epiphytic and benthic algae can be observed in
eutrophic waters.
Significant changes arise in the species composition of macrophytes and the
biomass.
The water loses its transparency and develops a bad smell and colour. The
treatment of this water becomes difficult.
Depletion of dissolved oxygen in the water body.
Frequent fish kill incidents occur and many desirable fish species are
removed from the water body.
The populations of shellfish and harvestable fish are lowered.
64 | Ecology Endriyo Phillip.

The aesthetic value of the water body diminishes significantly.
Ecological Effects of Eutrophication
Natural standing waters range from ultra-oligotrophic to eutrophic with progressive
increase in productivity and related parameters. In addition to such general
changes, eutrophication also affects the vertical structure of lakes with further
implications for the biology of freshwater organisms. The transition from eutrophic
to hypertrophic status is usually the result of human activities, and ultimately
affects the whole ecological balance of the freshwater system.
Decrease in Biodiversity
When an aquatic ecosystem is enriched with nutrients by either natural or artificial
means, the conditions become extremely beneficial to primary producers.
Commonly, algae and other similar species utilize these nutrients and a huge
increase in their population (algal bloom) is observed.
These algal blooms hinder the flow of sunlight to the bottom of the aquatic body
and also cause wide swings in the dissolved oxygen levels in the water.
When the dissolved oxygen in the water reduces to an amount below the hypoxic
level, many marine animals suffocate and die. This reduces the effective
biodiversity of the water body.
Increase in Water Toxicity
A few algae are toxic to many plants and animals. When these algae bloom in
eutrophic waters, they release neurotoxins and hepatotoxins. These toxins can also
move up the food chain via shellfish or other marine animals and lead to the death
of many animals.
65 | Ecology Endriyo Phillip.
Toxic algal blooms can also be harmful to humans and are the root cause of many
cases of neurotoxic, paralytic, and diarrhoetic shellfish poisoning.
Invasion of New Species
A limiting nutrient corresponding to a water body can be made abundant by the
eutrophication process, leading to a shift in the species composition of the aquatic
body and the ecosystem surrounding it.
If a nitrogen deficient water body is suddenly enriched with it, many other
competitive species might relocate to the water body and out-compete the original
inhabitants of the ecosystem. One such example of a new species invading
eutrophic conditions is the common carp, which has adapted to these conditions.
READ AND MAKE NOTES ON POLLUTION AND CONSERVATION.
66 | Ecology Endriyo Phillip.