2007 Ecology III – Environmental factors
P. 1
Factors making up the environment
- Environment:
= sum of all external forces or influences that affect an organism.
-- the number,types, distribution, behaviour, and adaptation shown by the organisms may be
affected by its environment
1. Physical (abiotic / non-living) Factors
i. Temperature
--->- affects the rate of enzyme reactions and thus the metabolic activities and
- at low temperatures ice crystals may form within cells, causing physical disruption,
 hence, affects distribution of organisms (actually the temperature range within which life
exists is relatively small)
The actual temperature of any habitat may differ in time according to season and time of day,
and in space according to latitude, slope, degree of shading or exposure, etc.
-
different biomes have different composition organisms with various tolerance of
temperature:
-- in plants:
temperature affect photosynthetic rate and transpiration rate and hence the
distribution of plants.
-- in animals:
poikilothermic and homoiohermic animals have different adaptation to withstand
cold whether
Tundra
The climate of regions of higher altitude is similar to the regions of larger
latitude, hence the sequence of change in biomes with respect to both latitude
and altitude in northern hemisphere is the same.
The distribution of biomes is controlled by interaction of four variable factors: growing seasons,
annual temperature (the max. and the min.), the availability of minerals and rainfall (average
and the lowest). Temperature and growing seasons are the important factors of coniferous forest
and tundra while rainfall and mineral contents are the important factors of other biomes.
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ii. Light
a. presence of light
- intensity
- rate of photosynthesis, evaporation and transpiration increase with ligh intensity
- the production of chlorophlly only occur in the presence of light
- manufature of vitamine D in human require UV light
- better and colour vision in day
- too high ligh intensity may cause damage on retina, excess water loss, skin
cancer...etc
 - shaded plants may have larger leaves to trap more light
- plants may grow smaller leaves in sunny environment to reduce water loss.
- in the absence of light, plants become yellow. The process is called etiolation.
- positive phototropism to gain more light in plants
- many animals are active in day time (i.e. diurnal animals)
- some animals which active at night (i.e. nocturnal animals) or at twilight (i.e.
Crepuscular animals) may have specific adaptation e.g. bats can detect their
ways with sound waves
- some animals such as earthworm have negative photo-taxis that move away
from light source to reduce water loss.
- light quality
- different wavelength is absorbed by different pigment for metabolism
-> - plants have various pigments to trap different wavelength for photosynthesis
- photosynthesis use mainly red and blue light
- human have melanin to absorbs damaging ultraviolet rays
b.
duration of light
(Photoperiod: = the number of daylight hours in 24 hour cycle)
---> photoperiodism in flowering, fruiting, germination;
bird's migration, hibernation of animals...etc.
iii. Water, Rainfall and Humidity
a. shortage or absence of water supply
- organisms may die from dessication
(as water is the essential constituents of protoplasm)
- loss of buoyancy or turgidity
- loss of medium for transport of substances and transfer of gametes
---> - many organisms are restricted to aquatic, damp or humid habitats
e.g. fish, amphibians and lower plants
- mechanical support is porvided by thick-walled cells in higher terrestrial plants,
skeleton in animals
- water independent / internal fertilization in most higher terrestrial organisms
- according to the among of water supply, plants can be divided into hydrophytes,
mesophytes, xerophytes and halophytes)
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b. low humidity
- high rate of evaporation increase the rate of transpiration in plants, the rate of water
loss from body
---> - sweating aids thermoregulation in mammals
- special features to reduce water loss
iv. Salinity
- major factor in determining the distribution of aquatic organisms because it affect the water
content of organisms' body by osmosis:
- fresh water --- low salinity
- sea water
--- high salinity
- estuary --- high salinity when tide comes in
--- low salinity when tide goes out
---> - osmo-regulation in many organisms
- plant cell with cell wall to prevent burst of cell in hypotonic solution
v.
Gases
- CO2 : ---> photosynthesis
- soil pH (H2CO3)
- bone and shell formation (combined with Calcium)
- O2: ---> aerobic respiration
- in air : stable amount, little effect on distribution of organisms
- in water: -- low oxygen solubility which varied with temperature
-- amount of oxygen dissolved depend on the area of interface
between water bodies and air, speed of water current and the
size of waves.
-- hence have a large effect on aquatic organisms.
vi. pH value
-- pH value will affect the activity of enzymes and hence lower the metabolic rate. Make the
organisms less active or even die.
-- acidic soil may be less fertile due to the washed away of minerals by leaching.
vii. Wind / Water Current /Wave action
- evaporation rate varies with wind speed
 cooling and drying effects
- affect humidity and rainfall
- impact on organisms, soil and objects on environment
 adaptation for anchoragement
- pollination, dispersal of seeds, fruits or even individuals
- amount of dissolved gases in water increases with water current and wave action
- tidal action cause fluctuation in temperature, illumination, exposure to air and salinity of a
microhabitat.
2007 Ecology III – Environmental factors
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viii. Pressure
- altitude: atmospheric pressure and oxygen content
in plants--no effect
in animals – faster breathing rate, more heamoglobin
- water pressure (ocean): aquatic animals distribution.
ix. Shelter
--->
breeding and egg-laying
- hiding place from danger
x.
Edaphic factors (Soil Conditions)
- anchorage, water and minerals for plants
- food, shelter and hiding places of bacteria, fungi, insects, and burrowing animals
xi. Topographic factors
Affect the microclimate of the habitat
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2.
Biotic Factors (living parts)
- existence of living organisms affecting distribution of other living organisms in that area via
interaction directly and / or indirectly.
-
(Ecological) Niche
-- The ecological niche of an organism refers to the position or status or functional role of an
organism (species) within the community.
--
This depends on where organism lives, what it does and what it feeds on in its habitat.
OR
sum total of all ecological requisites activities of a species
e.g. detritivores, herbivores, carnivores, host…etc. (Different stages have different niches)
Interdependence of Organisms (Species Interaction)
- organisms in nature must interact with each other in different ways.
- these interactions can be classified according to their positive or negative results to the species.
Species
A
Species B
*Mutualism
+
+
*Commensalism
+
0
*Parasitism
+
-
Predation
+
-
Competition
-
-
- = harmed,
0 = not affected
Relation
Positive interaction
Negative
interaction
+ = benefited;
*
Symbiosis
It is the association describing two different species （symbionts） living together. Depending on
the nature of association, it can be subdivided into commensalism, mutualism and parasitism.
-
Neutralism
two types of organisms live together in the same habitat without having any effect on one anothers
(i.e. no interaction)
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- Types of interactions:
1. Positive interactions
i. Mutualism (+, +)
- both species benefit from the association
- a type of symbiosis
- associations are usually permanent
because absence of the other will make them unsuccessful for living and may lead to
die.
- resulted from long evolutionary history and becomes a necessary
- e.g.: i lichens
(green alga and fungus)
Photosynthesis organic food  Energy
Algae
Fungi
Anchorage, support, absorb water & minerals from soil
(Environment unsuitable for either one.)
ii. nitrogen-fixing bacteria and leguminous plants in the root nodules
Fix nitrogen gas into amino acids
Nitrogen-fixing
bacteria
Leguminous
plants
Supply carbohydrates and provide
protection
iii. green alga and freshwater green hydra
(Zoochlorella and Chlorohydra)
iv. sea anemones attach permanently onto the shells of hermit- crabs
Crabs are camouflaged to some extent and it's
tentacles with stinging cells provides a sort of
poison shield around the crab. This reduces the
chances of being attacked by enemies
sea anemones attach
permanently onto the shells
of crabs
Hermit-crabs
Obtain food debris from crabs,
Gain movement from place to place
and reach fresh feeding areas and
avoid being stranded in tidal zones or
stagnant water
v. Cellulase-producing bacteria and herbivorous mammals
Digest cellulose of plant tissue into soluble
products and supply nutrients to the herbivore
Cellulase-producing bacteria
Living in the gut of
herbivores
Herbivores
Provide shelter, protection and food
supply
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ii. Commensalism (+, o)
- one species (commensal ) benefits and the other (host) is unaffected. This association is
sometimes necessary for the survival of commensals.
-
a type of symbiosis
commensals usually gain the benefits of feeding arrangement, protection (shelter) and
support (anchorage) from the host
e.g. i. sessile barnacles attach on shells of crabs
ii. Remora (a fish with muscular sucker) on body surface of shark
iii. algae growing on a turtle's shell
iv. Plant growing on the surface of other plant (epiphytes)
They do not take any nourishment from their host and simply benefit from
being better exposed to sunlight
(e.g. algae, mosses, ferns and creeping plants growing on tree trunks)
v. Rock oysters and acorn barnacles (epizoans) on root surfaces of mangrove
plants
2007 Ecology III – Environmental factors
2.
Negative interactions
i. Competitions (-, -)
- both species suffer from their association
P. 8
- two types
a. Resource competition (scramble competition)
--
occurs when a number of organisms utilize common resuouces that are in short supply.
b. Interference competition (Contest competition)
--
occurs when the organisms seeking a resource harm one another in the process, even if the
resource is not in short supply.
--
-
less common in nature
Resources competed:
a. raw materials
-- e.g. - light,
- inorganic nutrients,
- water,
- organic food...etc
b.
space
---> grow,
nest,
shelter...etc
(intersepecific competition Vs intraspecific competition)
-
occurred when two organisms have same or overlapped ecological niche
---> co-exist or either eliminated
(Gause's principle 高斯法則/ Competitive exclusion principle競爭相斥原則/ 4 C
principle:
" Complete Competitors Cannot Coexist")
- not always ture
-- sometimes, the more competitive species force other species to change niche (character
displacement).
-- environments in natural habitats are always heterogeneous
-
in homogeneous environment:
organisms are forced to share simple common resources
---> competition increase
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in heterogeneous environment:
(or greater interspecific differences)
since,
more choice of acceptable resources
---> direct competition of common resources decrease
- character displacement may take place by natural
selection (among variation already exist or futher
mutation) after several generations
-
competition advantage of one species over another depends on specific environmental
conditions.
-
competition can be reduced by:
a. different resources requirement
e.g. Plants take different nutrients from soil
b. need same kind of resources, but at different time
e.g. butterflies: daytime
moth: at night
c. occupy different parts (space) of the same community
e.g. at tree tops / near ground
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ii. Predation / predator-prey interaction (+, -)
- one species (predator) eats another species, and hence one benefits
while the other (prey) loses.
(Natural method of quality control ---> kill out diseased / less fit individuals )
-
Lotka & Volterra model:
-- based on the exponential growth, equation
-- as
prey  --------------------------------------------> predator
more food provided for predator
predator  ----------------------------------------> prey 
larger chance to capture prey
===> stable oscillation with the two populations out of phase
(i.e. The density of predators is slightly out of phase/ there is a time lag behind
with the number of prey)
then
No. of individuals
prey
prey increases when predators
are removed
predator
Time
*
If predators are removed from an area, the number of prey increases.
---
assume that as prey density increases, there is a linear increase
in the rate of predation by each predator.
failure to describe accurately the interaction between prey and
predator is largely due to the complexity of behavior of the
organisms involved.
(e.g. hiding of prey, food preference of predator）
2007 Ecology III – Environmental factors
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P. 14
Factors of predation
-- Food perference depend on -
taste,
energy value
nutritional value
rate of encounter,
handling time...etc
-- Switching of food preference may occur
Interference(干預) of the prey-predator interaction by man (Biological control of population)
Before 1907: about 4000 deer
Population of deer living on Kaibab plateau near Grand Canyon (America)
(No. remains constant by
predators e.g. mountain lions,
wolves.)
From 1907 onwards:
100 000damage to
vegetation
No. of deer
50 000-
by deer
maximum carrying

capacity at 1906
4 0001905
1910
1915
1920
1925
1930
1935
1940 YEAR (A.D.)
Natural predators deliberately
killed by man (by hunting) to
protect the deer. Intensive
grazing cause the carrying
capacity 
1924
Dear population: 100 000
∵ Absence of food
(vegetation)
∴ mass starvation
 death (60% in 2 winters)
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iii. Parasitism (+, -)
- parasite depending upon the host, gains benefits (e.g. food and
protection) at the expense of the host and imposes harm to the host.
-
seldom kills the host but sometimes indirectly causes death of host
-
Obligate parasite Vs Facultative parasite
(e.g. virus)
(e.g. E. coli)
a. Endoparasites
- inside host's body
-e.g. tapeworm, plasmodium (cause malaria)
b. Ectoparasites
- on the host's body surface
- e.g.1: Dodder
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-e.g. 2: body louse of humans
-
Characteristics of parasites:
a. special adaptation to feed, to attach and to reproduce
e.g. gut parasites can resist digestion
b. enormous fertility
e.g. hermaphordite and self-fertilization very common
c. exhibit specificity to some extent
e.g. host of tapeworm Taenia solium: pig
d. exhibit degeneration
e.g. absence of gut in tapeworm
3.
Amensalism (-, o)
- one species population is inhibited, typically by toxin produced by the
other, which is unaffected.
e.g. antibiotic (e.g. penicillin) produced by fungi inhibit growth of certain bacteria.