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ECOLOGY
Biology
What you will learn…
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1. Ecology general overview.
 A.
Definition
 B. Levels of Organization
 C. Abiotic vs. Biotic Factors
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2.Populations
3.Communities
4.Ecosystems
1 A. Definition
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Ecology is the study of how organisms interact with
their environment and each other.
This interaction of organisms is a two-way interaction.
Organisms are affected by their environment, but by their
activities they also change the environment.
1 B. Levels of Organization
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Ecology is studied on several levels:
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Organism
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Population
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Consists of all the populations of different species that inhabit a particular area.
Ecosystem
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Group of individuals of the same species living in a particular geographic area.
Community
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Ecologists may examine how one kind of organism meets the challenges of its
environment, either through its physiology or behavior.
Includes all forms of life in a certain area and all the nonliving factors as well.
Biosphere
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The global ecosystem; the sum of all the planet’s ecosystems.
Most complex level in ecology, including the atmosphere to an altitude of several
kilometers, the land down to and including water-bearing rocks under 3,000 m under
Earth’s surface, lakes and streams, caves, and the oceans to a depth of several
kilometers.
It is self contained, or closed, except that its photosynthesizers derive energy from
sunlight, and it loses heat to space.
1 B. Levels of Organization
1 C. Abiotic vs. Biotic Factors
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Abiotic components
 Physical
and chemical factors (abiotic) affecting the
organisms living in a particular ecosystem.
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Biotic components
 Organisms
making up the community
1 C. Examples of Biotic Factors
Anything that has the characteristics of life!
Starfish
Even bacteria!
Polar bears
Trees and grass
1 C. Examples of Abiotic Factors:
 Solar
energy
 Water
 Temperature
 Wind
 Soil composition
 Unpredictable disturbances
2 . What is a population?

Populationa
group of individuals of a single species that occupy
the same general area.
 Rely on the same resources, are influenced by the same
environmental factors, and have a high likelihood of
interacting and breeding with one another.
3. Communities
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A few terms you should know…
Species –
A
group of organisms which can interbreed with each
other and able to produce a fertile offspring.
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Habitat –
 the
environment in which a species normally lives or the
location of a living organism.
3. Communities
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
A biological community is an assemblage of all the
populations of organisms living close enough
together for potential interaction.
Key characteristics of a community:
 a.Species
diversity
 b.Dominant species
 c.Response to disturbances
 d.Trophic structure
 e. Community interactions
3. Response to Disturbances
Communities change drastically following a
severe disturbance that strips away vegetation
and even soil.
 The disturbed area may be colonized by a
variety of species, which are gradually
replaced by a succession of other species, in a
process called ecological succession.

3. Response to Disturbances

Primary succession
 When ecological succession begins in a virtually lifeless area with no
soil.
 Usually takes hundreds or thousands of years.
 For example, new volcanic islands or rubble left by a retreating
glacier. Often the only life-forms initially present are autotrophic
bacteria. Lichens and mosses are commonly the first large
photosynthesizers to colonize the area. Soil develops gradually as
rocks weather and organic matter accumulates from the decomposed
remains of the early colonizers. Lichens and mosses are gradually
overgrown by grasses and shrubs that sprout from seeds blow in from
nearby areas or carried in by animals. Eventually, the area is
colonized by plants that become the community’s prevalent form of
vegetations.
3. Response to Distrurbances
 Secondary
 Occurs
succession
when a disturbance has destroyed an existing
community but left the soil intact.
 For example, forested areas that are cleared for farming,
areas impacted by fire or floods.
3. Response to Disturbances
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Primary Succession
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Example: autotrophic prokaryoteslichens,
mossesgrassesshrubstreesclimax communty
Secondary Succession

Example: herbaceous plants woody shrubs trees climax
community
3. Response to Disturbances
 Early
successional communities are characterized by a
low species diversity, simple structure and broad niches
 The succession proceeds in stages until the formation of
a climax community.
 The
most stable community in the given environment until
some disturbance occurs.
3. Response to Disturbances

Are disturbances always a bad thing? When can
they be beneficial?
3. Response to Disturbances

Small-scale disturbance often have positive effects. 

For example, when a large tree falls in a windstorm, it disturbs the immediate surroundings,
but it also creates new habitats.
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For instance, more light may now reach the forest floor, giving small seedlings the opportunity
to grow; or the depression left by its roots may fill with water and be used as egg-laying
sites by frogs, salamanders, and numerous insects.

Small-scale disturbances may enhance environmental patchiness, which can contribute to
species diversity in a community.
3. Trophic Structure
 The
feeding relationships among the various species
making up the community.
 A community’s trophic structure determines the passage
of energy and nutrients from plants and other
photosynthetic organisms to herbivores and then to
carnivores.
3. Trophic Structure
 The
sequence of food transfer up the trophic levels is
known as a food chain
 Trophic
levels are arranged vertically, and the names of the
levels appear in colored boxes.
 The arrows connecting the organisms point from the food to
consumer. This transfer of food moves chemical nutrients and
energy from the producers up though the trophic levels in a
community.
3. Trophic Structure
 At
the bottom, the trophic level that supports all others
consists of autotrophs, called producers.
 Photosynthetic
producers use light energy to power the
synthesis of organic compounds.
 Plants are the main producers on land.
 In water, the producers are mainly photosynthetic protists
and cyanobacteria, collectively called phytoplankton.
Multicellular algae and aquatic plants are also important
producers in shallow waters.
3. Trophic Structure

All organisms in trophic levels about the producers
are heterotrophs, or consumers, and all consumers
are directly or indirectly dependent on the output
of producers
3. Trophic Structure

Trophic Levels:

Primary producers
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Primary consumers
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Herbivores, which eat plants, algae, or phytoplankton.
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On land include grasshoppers and many insects, snails, and certain vertebrates like grazing
mammals and birds that eat seeds and fruits

aquatic environments include a variety of zooplankton (mainly protists and microscopic animals such
as small shrimp) that eat phytoplankton.
Secondary consumers
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Include many small mammals, such as a mouse, a great variety of small birds, frogs, and spiders, as
well as lions and other large carnivores that eat grazers.

In aquatic ecosystems, mainly small fishes that eat zooplankton
Tertiary consumers
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Mostly photosynthetic plants or algae
Snakes that eat mice and other secondary consumers.
Quaternary consumers
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Include hawks in terrestrial environments and killer whales in marine environment.
3. Trophic Structure

Another trophic level of consumers are called detritivores which derive
their energy from detritus, the dead material produced at all the trophic
levels.
 Detritus includes animal wastes, plant litter, and all sorts of dead
organisms.
 Most organic matter eventually becomes detritus and is consumed
by detritivores.
 A great variety of animals, often called scavengers, eat detritus.
For instance, earthworms, many rodents, and insects eat fallen
leaves and other detritus. Other scavengers include crayfish,
catfish, crows, and vultures.
3. Trophic Structure

A community’s main detritivores are the prokaryotes and fungi, also
called decomposers, or saprotrophs, which secrete enzymes that
digest organic material and then absorb the breakdown products.
 Enormous numbers of microscopic fungi and prokaryotes in the
soil and in mud at the bottom of lakes and oceans convert
(recycle) most of the community’s organic materials to inorganic
compounds that plants or phytoplankton can use.
 The breakdown of organic materials to inorganic ones is called
decomposition.
3. Trophic Structure
3. Trophic Structure
A
more realistic view of the trophic structure of a community
is a food web, a network of interconnecting food chains.
 Food webs, like food chains, do not typically show
detrivores, which consume dead organic material from all
trophic levels.
3. Community Interactions

Consider this…
 You’ve
planted a garden in your backyard. You see
that a squirrel population and a chipmunk population
has begun to inhabit the area. There reproductive
patterns are similar, they eat the same food, and have
similar sleeping patterns.
 What do you expect to happen?
 Is it possible for them to cohabit the area?
3. Community Interactions
 Interspecific
competition:
 If
two different species are competing for the same
resource.
 Causes the growth of one or both populations may be
inhibited.
 May play a major role in structuring a community.
 Examples:
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Weeds growing in a garden compete with garden plants for
nutrients and water.
Lynx and foxes compete for prey such as snowshoe hares in
northern forests.
3. Community Interactions

Intraspecific Competition:
 Intense
competition that exists within individuals of the
same population because they compete for the exact
same habitat and resources
3. Community Interactions
 The
competitive exclusion principle applies to what is
called a species’ niche.
 In
ecology, a niche is a species’ role in its community, or the
sum total of its use of the biotic and abiotic resources of its
habitat.
3. Community Interactions

A niche is the functional position of an organism in
its environment, comprising its habitat, resources and
the periods of time during which it is active.
3. Community Interactions
 Predation
is an interaction between species in which
one species, the predator, kills and eats another, the
prey.
 Because eating and avoiding being eaten are
prerequisites to reproductive success, the adaptations
of both predators and prey tend to be refined through
natural selection.
3. Community Interactions

What are some ways predators can catch prey?
 What
tools can they use?
 What are some essential characteristics?
3. Community Interactions
 Examples
 Most
of prey capturing strategies:
predators have acute senses enable them to locate
prey.
 In addition, adaptations such as claws, teeth, fangs, stingers,
or poisons help catch and subdue prey.
 Predators are generally fast and agile, whereas those that
lie in ambush are often camouflaged in their environments.
 Predators may also use mimicry; some snapping turtles have
a tongue that resembles a wriggling worm, thus luring small
fish.
Camouflage
Chemical Defense
3. Community Interactions

What are some ways prey can avoid predators?
 What
tools can they use?
 What are some essential characteristics?
3. Community Interactions
 Predator
defenses:
 Mechanical
defenses: such as the porcupine’s sharp quills or the
hard shells of clams and oysters.
 Chemical defenses: animals are often bright colored, a warning
to predators; like a poison arrow-frog or a skunk.
 Batesian mimicry: a palatable or harmless species mimics an
unpalatable or harmful one; like the king snake mimics the
poisonous coral snake
 Mullerian mimicry: two unpalatable species that inhabit the same
community mimic each other; like bees and wasps
Batesian Mimicry
Mullerian Mimicry
3. Community Interactions

Herbivory
 Animals that eat plants or algae
 Aquatic herbivores include sea urchins, snails, and some fishes.
 Terrestrial herbivores include cattle, sheep, and deer, and small insects.
 Herbivorous insects may locate food by using chemical sensors on their feet,
and their mouthparts are adapted for shredding tough vegetation or sucking
plant juices.
 Herbivorous vertebrates may have specialized teeth or digestive systems
adapted for processing vegetation. They may also use their sense of smell to
identify food plants.
 Because plants cannot run away from herbivores, chemical toxins, often in
combination with various kinds of anti-predator spines and thorns, are their
main weapons against being eaten.
3. Community Interactions

Herbivory
 Some herbivore-plant interactions illustrate the concept of coevolution, a
series of reciprocal evolutionary adaptations in two species.
 Coevolution
occurs when a change in one species acts as a
new selective force on another species, and
counteradaptation of the second species in turn affects
the selection of individuals in the first species.
3. Community Interactions
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Herbivory Coevolution Example:
 an herbivorous insect (the caterpillar of the
butterfly Heliconius, top left) and a plant (the
passionflower Passiflora, a tropical vine).
3. Community Interactions
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Herbivory Coevolution Explanation:
Passiflora produces toxic chemicals that protect its leaves from
most insects, but Heliconius caterpillars have digestive enzymes
that break down the toxins. As a result, Heliconius gains access to
a food source that few other insects can eat.
The Passiflora plants have evolved defenses against the
Heliconius insect. The leaves of the plant produce yellow sugar
deposits that look like Heliconius eggs. Therefore, female
butterflies avoid laying their eggs on the leaves to ensure that
only a few caterpillars will hatch and feed on any one leaf.
Because of this, the Passiflora species with the yellow deposits
are less likely to be eaten.
3. Community Interactions
 Symbiotic
Relationships are interactions between two
or more species that live together in direct contact.
 Three
main types:
 Parasitism
 Commensalism
 Mutualism
 *Parasitism and mutualism can be key factors in
community structure.
3. Community Interactions
 Parasitism
A
parasite lives on or in its host and obtains its nourishment from
the host.

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For example: A tapeworm is an internal parasite that lives inside the
intestines of a larger animal and absorbs nutrients from its hosts.
Another example: Ticks, which suck blood from animals, and aphids,
which tap into the sap of plants, are examples of external parasites.
 Natural
selection favors the parasites that are best able to find
and feed on hosts, and also favors the evolution of host
defenses.
Tapeworm in Small Intestine
Tick on a dog
3. Community Interactions
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Commensalism
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One partner benefits without significantly affecting the other.
Few cases of absolute commensalism have been documented, because it is
unlikely that one partner will be completely unaffected.
For example: algae that grow on the shells of sea turtles, barnacles that
attach to whales, and birds that feed on insects flushed out of the grass by
grazing cattle.
Algae on Sea Turtle
Barnacles on Whale
3. Community Interactions
 Mutualism
 Benefits
both partners in the relationship.
 For example: the association of legume plants and nitrogenfixing bacteria.

Bacteria turn nitrogen in the air to nitrates that the plants can use
 Another
example: Acacia trees and the predaceous ants they
attract.


Tree provides room and board for ants
Ants benefit the tree by attacking virtually anything that touches it.
Acacia Trees and Ants
4. Ecosystems
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An ecosystem consists of all the organisms in a community as well as the
abiotic environment with which the organisms interact.
Ecosystems can range from a microcosm such as a terrarium to a large area
such as a forest.
4a. Ecosystems- Energy Flow
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Regardless of an ecosystem’s size, its dynamics involve two processesenergy flow and chemical cycling.
Energy flow: the passage of energy through the components of the
ecosystem.
 For most ecosystems, the sun is the energy source, but exceptions include
several unusual kinds of ecosystems powered by chemical energy
obtained from inorganic compounds.
4a. Ecosystems- Energy Flow
4a. Ecosystems- Energy Flow

For example, an a terrarium, energy enters in the form of sunlight.

Plants (producers) convert the light energy to chemical energy.

Animals (consumers) take in some of this chemical energy in the form of organic
compounds when they eat the plants.

Detrivores, such as bacteria and fungi in the soil, obtain chemical energy when they
decompose the dead remains of plants and animals.

Every use of chemical energy by organisms involves a loss of some energy to the
surroundings in the form of heat.

Eventually, therefore, the ecosystem would run out of energy if it were not powered by
a continuous inflow of energy from an outside source.
4a. Ecosystems- Energy Flow

Ecological Pyramids
 Pyramid
of Biomass
 Pyramid of Productivity
 Pyramid of Numbers
4a. Ecosystems- Energy Flow

Pyramid of Biomass:
 shows
the relationship between biomass and trophic
level by quantifying the amount of biomass present at
each trophic level of a community at a particular
moment in time.
4a. Ecosystems- Energy Flow
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Pyramid of Biomass
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Typical units are grams per meter
4a. Ecosystems- Energy Flow
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Pyramid of Production
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Illustrates the cumulative loss of energy with each transfer in a food
chain.
Each tier of the pyramid represents one trophic level, and the width of
each tier indicates how much of the chemical energy of the tier below is
actually incorported into the organic matter of that trophic level.
Note that producers convert only about 1% of the energy in the sunlight
available to them to primary production.
In this idealized pyramid, 10% of the energy available at each trophic
level becomes incorporated into the next higher level.
The efficiencies of energy transfer usually range from 5 to 20%.
In other words, 80 to 95% of the energy at one trophic level never
transfers to the next.
4a. Ecosystems-Energy Flow
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
Pyramid of Production:
Units can be Joules or calories
4a. Ecosystems- Energy Flow

Pyramid of Numbers
 shows
graphically the population of each level in a
food chain.
4b. Ecosystems- Chemical Cycling

Chemical cycling: involves the transfer of materials within the ecosystem.
 An ecosystem is more or less self-contained in terms of matter.
 Chemical elements such as carbon and nitrogen are cycled between
abiotic components (air, water, and soil) and biotic components of the
ecosystem.
 The plants acquire these elements in inorganic form from the air and soil
and fix them into organic molecules, some of which animals consume.
 Detrivores return most of the elements in inorganic form to the soil and
air.
 Some elements are also returned as the by-products of plant and animal
metabolism.
4b. Ecosystems- Chemical Cycling
4b. Ecosystems- Chemical Cycling

Biogeochemical cycles:
 Water
cycle
 Carbon cycle
 Nitrogen cycle
 Phosphorous cycle
4b. Ecosystems- Chemical Cycling
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General Model of Nutrient Cycling:
1. Producers incorporate chemicals from the abiotic reservoir (where a
chemical accumulates or is stockpiled outside of living organisms) into organic
compounds.
2.Consumers feed on the producers, incorporating some of the chemicals into
their own bodies.
3. Both producers and consumers release some chemicals back to the
environment in waste products (CO2 and nitrogen wastes of animals)
4. Detritivores play a central role by decomposing dead organisms and
returning chemicals in inorganic form to the soil, water, and air.
5. The producers gain a renewed supply of raw materials, and the cycle
continues.
4b. Ecosystems- Chemical Cycling
General Model of Nutrient Cycling:
Water Cycle

1.Precipitation
2.Condensation (conversion of gaseous water vapor into liquid water)
3. Rain Clouds
4. and 5. Evaporation (conversion of water to gaseous water vapor) from ocean
6. and 7. precipitation over ocean
8. evaporation from land
9. Transpiration
10. Transpiration
11. evaporation from lakes, rivers
12. surface runof
13. infiltration (movement of water into soil)
14. Water locked in snow
15. Precipitation to land
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**refer to diagrams in handout
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Water Cycle
Carbon Cycle
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1. Carbon in plant and animal tissues
2. fossilization (preserved remains or traces of animals, plants, and other organisms)
3. Death and excretion
4. Decomposers (breakdown organic materials to inorganic ones)
5. coal
6. photosynthesis
7. atmospheric CO2
8. Dissolving
9. combustion (burning of wood and fossil fuels)
10. diatoms (major group of algae, and are one of the most common types of phytoplankton)
11. drilling for oil and gas
12. fossilization
13. oil and gas
14. limestone
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**refer to diagrams in handout
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Carbon Cycle
Nitrogen Cycle
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1. Nitrogen in plant and animal tissue
2. Excretion
3. Ammonia (NH3)
4.Dead organisms
5. decomposers
6. Nitrifying bacteria (convert ammonia to nitrate)
7. nitrogen fixing bacteria (convert N2 to ammonia)
8. nitrate (NO3-)
9. nitrate (NO3-) available to plants
10. swampy ground
11. denitrifying bacteria (return fixed nitrogen to the atmosphere)
12. lightning (atmospheric nitrogen fixation)
13. atmospheric nitrogen (N2 gas)
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**refer to diagrams in handout
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Nitrogen Cycle