Unit 2
Ecology
Chapter 3 – The Biosphere
Introduction to Ecology
Ecology - the scientific study of interactions among
organisms and between organisms and their
physical environment.
Ecologist - a scientist who studies organisms as
they interact with other organisms within an
ecosystem
Levels of Organization
 Individual Organism
 Population—a group of individuals that belong to the
same species and live in the same area
 Community—an assemblage of different populations
that live together in a defined area
 Ecosystem—all the organisms that live in a place,
together with their physical environment
 Biome—a group of ecosystems that share similar
climates and typical organisms
 Biosphere—our entire planet, with all its organisms and
physical environments
Types of Ecosystems
Natural Ecosystems
 Self sustaining
 Precipitation
 Sunlight
 All resources to
support life
 Destroyed by
natural disasters
(fires)
Human-Made Ecosystems
 Not self sustaining
 Farms
 Cities
 Flower gardens
 Aquariums
 Zoo
 Huge inputs of
resources and energy
Relationships Within an Ecosystem
•An ecosystem is a group of organisms that live
together and interact with each other and their
environment.
•Organisms respond to their environments and can
change their environments, producing an everchanging biosphere.
Biotic
Factors
 Anything living in
an ecosystem!
 List three
example of
biotic
components in
an ecosystem
and how they
interact?
Abiotic
Factors
• Anything nonliving!
▫ List three
example of
abiotic
components in
an ecosystem
and why they
are important?
Biomes
• A large geographic region
determined by climate, soil
type and plant life.
oWhy is plant life so important
to an ecosystem?
Biomes
Arctic Tundra
Desert
Northern Coniferous
Forest or Taiga
Temperate Deciduous
Forest
Tropical Savanna
Temperate Grasslands
or Prairie
Tropical Rain Forest
Population Studies: factors that affect the
size of a population
1. Carrying
capacity:
The maximum
size of the
population
that an
ecosystem
can hold
2. Limiting factors:
Anything that
prevents the
population size
from increasing
Examples ?
Food Chains and Food
Webs
o How does energy flow through ecosystems?
o Energy flows through an ecosystem in a one-way stream, from primary
o producers to various consumers. Energy moves from the “eaten” to the “eater.”
Where it goes from there depends on who eats whom!
Food Chain
The arrows in a food chain show what
eats what. The arrow replaces the
phrase “is eaten by”.
The arrow must point toward the
“eater”.
Leaf

Grasshopper 
Frog
 Heron
Food Webs
• This is who eats who or what in the
ecosystem. Each organism has a “job title”
that describes their role. Anything that
affects one level will probably affect the
entire ecosystem!
Food Web
A food web shows the many possible food chains that exist in an ecosystem.
Food Webs “Job Titles”
• Producers- Plants. They are the
basis for life in the ecosystem.
• These organisms are also called
autotrophs.
Most Producers get Energy From the Sun
The best-known and most common primary producers harness
solar energy through the process of photosynthesis.
Photosynthesis captures light energy and uses it to power
chemical reactions that convert carbon dioxide and water into
oxygen and energy-rich carbohydrates. This process adds oxygen
to the atmosphere and removes carbon dioxide.
Most photosynthesis occurs in plants on land and algae in water
ecosystems.
Life Without Light
Deep-sea ecosystems depend on primary producers
that harness chemical energy from inorganic
molecules such as hydrogen sulfide.
The use of chemical energy to produce carbohydrates
is called chemosynthesis.
Food Webs “Job Titles”
• Consumers- these organism eat
other organisms. They can not
make their own food, therefore,
they must “order out”!
• Organisms that must acquire
energy from other organisms by
ingesting in some way are also
known as heterotrophs.
Food Webs “Job Titles”
•Consumers may be
herbivores (plant eaters),
carnivores (meat eaters) or
omnivores (both)
•Carnivores are usually
referred to as predators!
Food Webs “Job Titles”
▫ 1st or PRIMARY level consumers are
herbivores
▫ 2nd or SECONDARY level consumers
are carnivores or omnivores and eat
1st order consumers
▫ What are 3rd order (level) consumers?
Food Webs “Job Titles”
• Decomposers- These are the recycling
centers of the ecosystem. They breakdown dead organisms into nutrients in
the soil that plants can use as vitamins.
▫ Bacteria and Fungus
• Detritivores, feed on detritus particles
(what is left from the decomposers,)
often chewing or grinding them into
smaller pieces.
 giant earthworms
Food Webs “Job Titles”
Scavengers- Similar to
decomposers because
they eat already dead
organisms and return
nutrients to the soil.
Animals, birds, insects
Trophic Levels and
Ecological Pyramids
o Each step in a food chain or food web is called a trophic level.
• Primary producers always make up the first trophic level.
• Various consumers occupy every other level. Some examples
are shown.
o Ecological pyramids show the relative amount of energy or matter
contained within each trophic level in a given food chain or food
web.
Advantages and Disadvantages of
the Pyramids
• Pyramids of numbers and biomass can sometimes
be inverted due to certain situations within
ecosystems
• These inverted pyramids then lose their ability to
accurately represent the passage of energy from
one trophic level to the next
Pyramid
of
Numbers
• This
represents
the number
of organisms
that occupy
each trophic
level
http://openlearn.open.ac.uk
Pyramids of Energy
o Pyramids of energy show the relative amount of energy
available at each trophic level.
o On average, about 10 percent of the energy available within
one trophic level is transferred to the next trophic level.
o The more levels that exist between a producer and a
consumer, the smaller the percentage of the original energy
from producers that is available to that consumer.
Pyramid of Biomass
o The total amount of living tissue within a given trophic
level is called its biomass.
o A pyramid of biomass illustrates the relative amount
of living organic matter at each trophic level.
Recycling in the Biosphere
o Unlike the one-way flow of energy, matter is recycled
within and between ecosystems.
o Elements pass from one organism to another and
among parts of the biosphere through closed loops
called biogeochemical cycles, which are powered by
the flow of energy.
• Biogeochemical cycles of matter involve biological
processes, geological processes, and chemical
processes.
Recycling in the Biosphere
o As matter moves through these cycles, it is
never created or destroyed—just changed.
• Biogeochemical cycles of matter pass the
same atoms and molecules around again
and again.
Water Cycle
• Also called the Hydrologic
Cycle
• Movement and storage of
water on the planet
o Total amount of water
doesn’t change – it is
transported around the
earth
o Energy to run the cycle
comes from the sun
• Water re-enters that atmosphere by two processes
o Evaporation changes surface water
(lakes, rivers, oceans) to water vapor
• Water vapor (gaseous state) returns to
the atmosphere
o Transpiration is the loss of water vapor
from the leaves of plants
• Stomata are openings in leaves which
allow the water vapor out of the plant
• Condensation
o As the water vapor rises in the atmosphere, it
looses energy (cools down)
o Water droplets are formed from the water vapor
• Precipitation
o When the water droplets get too heavy it falls
from the sky
o Weather conditions determine the type of
precipitation – rain, snow, sleet
• Some precipitation re-evaporates before it reaches
the ground
• Most precipitation falls into existing bodies of water
o 70% of the earth’s surface is water
• The rest falls on land
o Absorbed into the soil or flows over the surface as
Runoff (back to the oceans/lakes)
o Infiltration is the process of water entering the
ground
The cycle begins again:
o Evaporation and transpiration
o Condensation
o Precipitation
o Runoff and Infiltration
 The amount of precipitation is an important factor in
the type of ecosystem and the population of
organisms it can support
Nutrient Cycles
o The chemical substances that an organism needs to
sustain life are called nutrients.
o Every organism needs nutrients to build tissues and
carry out life functions.
o Nutrients pass through organisms and the environment
through biogeochemical cycles.
The Carbon – Oxygen
Cycle
o Carbon is a major component of all organic
compounds, including carbohydrates, lipids, proteins,
and nucleic acids.
The Carbon – Oxygen
Cycle
• Plants take in carbon dioxide during
photosynthesis and use the carbon to build
carbohydrates.
• Carbohydrates then pass through food webs to
consumers.
• Organisms release carbon in the form of carbon
dioxide gas by respiration.
The Nitrogen Cycle
o All organisms require nitrogen to make amino acids,
which are used to build proteins and nucleic acids,
which combine to form DNA and RNA.
The Nitrogen Cycle
o Nitrogen-containing substances such as ammonia
(NH3), nitrate ions (NO3), and nitrite ions (NO2) are
found in soil, in the wastes produced by many
organisms, and in dead and decaying organic matter.
The Nitrogen Cycle
o Nitrogen gas (N2) makes up 78 percent of Earth’s
atmosphere.
• Although nitrogen gas is the most abundant form
of nitrogen on Earth, only certain types of bacteria
that live in the soil and on the roots of legumes can
use this form directly.
o The bacteria convert nitrogen gas into ammonia, in a
process known as nitrogen fixation.
The Nitrogen Cycle
o Other soil bacteria convert fixed nitrogen into nitrates
and nitrites that primary producers can use to make
proteins and nucleic acids.
o Consumers eat the producers and reuse nitrogen to
make their own nitrogen-containing compounds
The Nitrogen Cycle
o Consumers eat the producers and reuse nitrogen to
make their own nitrogen-containing compounds.
o Decomposers release nitrogen from waste and dead
organisms as ammonia, nitrates, and nitrites that
producers may take up again.
The Nitrogen Cycle
o Other soil bacteria obtain energy by converting
nitrates into nitrogen gas, which is released into the
atmosphere in a process called denitrification.
o A small amount of nitrogen gas is converted to usable
forms by lightning in a process called atmospheric
nitrogen fixation.
o Humans add nitrogen to the biosphere through the
manufacture and use of fertilizers. Excess fertilizer is
often carried into surface water or groundwater by
precipitation.
The Phosphorus Cycle
o Phosphorus forms a part of vital molecules such as
DNA and RNA.
o Although phosphorus is of great biological
importance, it is not abundant in the biosphere.
o Phosphorus in the form of inorganic phosphate
remains mostly on land, in the form of phosphate rock
and soil minerals, and in the ocean, as dissolved
phosphate and phosphate sediments.
The Phosphorus Cycle
o As rocks and sediments wear down, phosphate is
released
o Plants bind phosphate into organic compounds when
they absorb it from soil or water.
o Organic phosphate moves through the food web, from
producers to consumers, and to the rest of the
ecosystem.
Nutrient Limitation
o Ecologists are often interested in an ecosystem’s
primary productivity—the rate at which primary
producers create organic material.
o A nutrient whose supply limits productivity is called the
limiting nutrient.
▫ All nutrient cycles work
together like the gears shown.
▫ If any nutrient is in short
supply—if any wheel “sticks”—
the whole system slows down
or stops altogether.
Nutrient Limitation in Aquatic
Ecosystems
o Sometimes an aquatic ecosystem receives a large
input of a limiting nutrient—for example, runoff from
heavily fertilized fields.
o The result of this runoff can be an algal bloom—a
dramatic increase in the amount of algae and other
primary producers due to the increase in nutrients.
Energy flow in
ecosystems
•
What
is
an
ecosystem?
System = regularly interacting and
interdependent components forming a
unified whole
• Ecosystem = an ecological system;
•
= a community and its physical
environment treated together as a
functional system
OR, MORE SIMPLY
• an ecosystem is composed of the
organisms and physical environment
of a specified area.
• SIZE: micro to MACRO
• Order
•
•
•
•
•
Attributes of Ecosystems
Development
Metabolism (energy flow) 10% RULE
Material cycles
Response to the environment
Porous boundaries
• Emphasis on function, not species
ENERGY FLOW IN ECOSYSTEMS
• All organisms require energy,
for growth, maintenance, reproduction,
locomotion, etc.
• Hence, for all organisms there must be:
A source of energy
•
A loss of usable energy
Types of energy
• heat energy
• mechanical energy (+gravitational energy,
etc.)
• chemical energy = energy stored in
•
molecular bonds
Transformations of energy
• How is solar energy converted to chemical
energy?
An ecosystem has abiotic
and biotic components:
• ABIOTIC components:
• Solar energy provides practically all
the energy for ecosystems.
• Inorganic substances, e.g., sulfur,
boron, tend to cycle through
ecosystems.
• Organic compounds, such as
proteins, carbohydrates, lipids, and
other complex molecules, form a
link between biotic and abiotic
BIOTIC
components:
• The biotic components of an ecosystem can
be classified according to their mode of
energy acquisition.
• In this type of classification, there are:
•
•
•
Autotrophs
and
Heterotrophs
Autotrophs
• Autotrophs (=self-nourishing) are called
primary producers.
• Photoautotrophs fix energy from the sun
and store it in complex organic
compounds
• (= green plants, algae, some bacteria)
light
simple
inorganic
compounds
photoautotrophs
complex
organic
compounds
• Chemoautotrophs (chemosynthesizers)
are bacteria that oxidize reduced
inorganic substances
• (typically sulfur and ammonia compounds)
• and produce complex organic
compounds.
oxygen
reduced
inorganic
compounds
chemoautotrophs
complex
organic
compounds
Chemosynthesis near hydrothermal vents
Other chemoautotrophs:
Nitrifying bacteria in the soil under our feet!
Heterotrophs
• Heterotrophs (=other-nourishing)
cannot produce their own food
directly from sunlight+ inorganic
compounds. They require energy
previously stored in complex
molecules.
complex
organic
compounds
heterotrophs
(this may include several steps, with
several different types of organisms)
heat
simple
inorganic
compounds
• Heterotrophs can be grouped as:
•
•
consumers
•
decomposers
• Consumers feed on organisms or
particulate organic matter.
• Decomposers utilize complex
compounds in dead protoplasm.
• Bacteria and fungi are the main groups
of decomposers.
• Bacteria are the main feeders on
animal material.
• Fungi feed primarily on plants, although
bacteria also are important in some
plant decomposition processes.
Energy flow
• Simplistically:
Producers
heat
Consumers
Decomposers
heat
• This pattern of energy flow among different
organisms is the TROPHIC STRUCTURE of an
• It is useful to distinguish different types
of organisms within these major
groups, particularly within the
consumer group.
Consumers
levels
• We can further separate the TROPHIC
LEVELS, particularly the Consumers:
• Producers (Plants, algae, cyanobacteria;
some chemotrophs)--capture energy,
produce complex organic compounds
• Primary consumers--feed on producers
• Secondary consumers--feed on primary
consumers
• Tertiary consumers--feed on secondary
consumers
More trophic levels:
• Detritivores--invertebrates that feed on
organic wastes and dead organisms
(detritus) from all trophic levels
• Decomposers--bacteria and fungi that
break down dead material into
inorganic materials
Alternate Terminology
• Producers = plants etc. that capture
energy from the sun
• Herbivores = plant-eaters
• Carnivores = animal-eaters
• Omnivores--eat both animals and
plants
• Specialized herbivores:
• Granivores--seed-eaters
• Frugivores--fruit-eaters
• Together, these groups make up a FOOD
CHAIN
• E.g., grass, rabbit, eagle
Producer
Carnivore
Herbivore
Carnivores
• Carnivores can be
further
divided into groups:
• quaternary carnivore
(top)
• tertiary carnivore
• secondary carnivore
• primary carnivore
• The last carnivore in a
chain, which is not
usually eaten by any
other carnivore, is
often referred to as
Food
chains
Problems
• Too simplistic
•
• No detritivores
• Chains too long
• Rarely are things as simple as grass, rabbit, hawk, or
indeed any simple linear sequence of organisms.
• More typically, there are multiple interactions, so
that we end up with a FOOD WEB.
Energy transfers among
trophic levels
• How much energy is passed from one
trophic level to the next?
• How efficient are such transfers?
• Biomass--the dry mass of organic
material in the organism(s).
• (the mass of water is not usually
included, since water content is
variable and contains no usable
energy)
• Standing crop--the amount of
biomass present at any point in
time.
Primary productivity
• Primary productivity is the rate of energy capture by
producers.
• = the amount of new biomass of producers, per unit
time and space
Ecological pyramids
• The standing crop, productivity,
number of organisms, etc. of an
ecosystem can be conveniently
depicted using “pyramids”, where the
size of each compartment represents
the amount of the item in each trophic
level of a food chain.
carnivores
herbivores
producers
• Note that the complexities of the interactions in
a food web are not shown in a pyramid; but,
pyramids are often useful conceptual devices-they give one a sense of the overall form of the
trophic structure of an ecosystem.
•
Pyramid
of
energy
A pyramid of energy depicts the energy
flow, or productivity, of each trophic level.
• Due to the Laws of Thermodynamics,
each higher level must be smaller than
lower levels, due to loss of some energy as
heat (via respiration) within each level.
Energy flow in :
carnivores
herbivores
producers
Pyramid of numbers
• A pyramid of numbers indicates the
number of individuals in each trophic
level.
•
• Since the size of individuals may vary widely
and may not indicate the productivity of that
individual, pyramids of numbers say little or
nothing about the amount of energy moving
through the ecosystem.
# of carnivores
# of herbivores
# of producers
Pyramid of standing crop
• A pyramid of standing crop indicates how much
biomass is present in each trophic level at any one
time.
• As for pyramids of numbers, a pyramid of standing crop may
not well reflect the flow of energy through the system, due to
different sizes and growth rates of organisms.
biomass of carnivores
biomass of herbivores
biomass of producers
(at one point in time)
Inverted pyramids
• A pyramid of standing crop (or of
numbers) may be inverted, i.e., a
higher trophic level may have a larger
standing crop than a lower trophic
level.
• This can occur if the lower trophic level has a
high rate of turnover of small individuals (and
high rate of productivity), such that the First
and Second Laws of Thermodynamics are not
violated.
biomass of carnivores
biomass of herbivores
biomass of producers
(at one point in time)
Pyramid of yearly
biomass production
• If the biomass produced by a trophic level is
summed over a year (or the appropriate complete
cycle period), then the pyramid of total biomass
produced must resemble the pyramid of energy
flow, since biomass can be equated to energy.
Yearly biomass production
(or energy flow) of:
carnivores
herbivores
producers
• Note that pyramids of energy and yearly biomass
production can never be inverted, since this would
violate the laws of thermodynamics.
• Pyramids of standing crop and numbers can be
inverted, since the amount of organisms at any one
time does not indicate the amount of energy
flowing through the system.
• E.g., consider the amount of food you eat in a year
compared to the amount on hand in your pantry.
Ecological Interactions and Interdependence
Population – group of individuals of the same species
living in the same area, potentially interacting
Community – group of populations of different species
living in the same area, potentially interacting
What are some ecological interactions?
Why are ecological interactions important?
Interactions can affect distribution and abundance.
Interactions can influence evolution.
Think about how the following interactions can affect
distribution, abundance, and evolution.
Types of ecological interactions & interdependence
competition
predation
parasitism
mutualism
commensalism
symbiosis
Competition – two species share a requirement for a
limited resource  reduces fitness of one or both species
Predation – one species feeds on another  enhances
fitness of predator but reduces fitness of prey
herbivory is a form of
predation
Parasitism – one species feeds on another  enhances
fitness of parasite but reduces fitness of host
Mutualism – two species provide resources or services
to each other  enhances fitness of both species
Commensalism – one species receives a benefit from
another species  enhances fitness of one species; no
effect on fitness of the other species
Symbiosis – two species live together  can include
parasitism, mutualism, and commensalism
Organizing ecological interactions & interdependence
effect on species 1
+
effect on
species 2
+
mutualism
0
commensalism
-
predation
herbivory
parasitism
0
-
commensalism
predation
herbivory
parasitism
competition
competition
competition