Community Interactions and

Ecosystem Changes

Modeling Energy Flow In Ecosystems Revisited…

Ultimate source of energy Sun

Energy Flow in Ecosystems can be modeled in Food Chains & Food Webs

Food ChainsShow 1 feeding relationship from producer consumers

Food WebsInterconnected food chainsThey show all of the feeding relationships in an ecosystem

5

Energy Pyramids and the 10% Rule

•Amount of available energy decreases for higher consumers•Amount of available energy decreases down the food chain•It takes a large number of producers to support a small number of primary consumers•It takes a large number of primary consumers to support a small number of secondary consumers

100%

10%

1%

0.1%

Trophic Levels indicate feeding

position in ecosystems

TL 4

TL 3

TL 2

TL 1

Community Interactions in Ecosystems

Predator Prey Interactions• Predators help control the prey population size

– No natural predators = overpopulation of prey.– Deer in NJ

• Prey can control the size of predators– Few prey = few predators– Many prey = many predators– What would happen to a population of mountain lions if

they were reintroduced to NJ?

• Predators and prey might have no relationship– If the predators rely on many sources of food, one

disappearing may have little effect– Can you think of any examples of this?

Predator Prey Interactions Between Wolves & Moose on Isle Royal

Competition• Interaction between two or more organisms, or

groups of organisms, that use a common limited resource

• May occur within or between populations

The Competitive Exclusion Principle• No two species can occupy the same exact niche• The species with the more rapid growth rate will out

compete the other

The Competitive Exclusion Principle

Population growth of two species of Paramecia alone or in mixed culture over time

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100105110

0 2 4 6 8 10 12 14 16

Time (days)

Num

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of

Para

meci

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(ce

lls/m

L)

P. aurelia grownalone, cells/mL

P. caudatum grownalone, cells/mL

P. aurelia grown in,mixed culturecells /mL

P. caudatum grown,in mixed culturecells /mL

Symbiotic Relationships

Close long-term relationships between two or more organisms

Parasitism +/-One organism benefits, the other is harmed (but not killed… usually)• Mosquitoes• Ticks/Fleas

Mutualism +/+Both organisms benefit• Lichen: Fungi & Algae

• Insects & flowers

Commensalism +/0One organism benefits, the other is unaffected• Birds & Hooved animals

• Fish & Anemone

• A dog becomes infested with fleas. The fleas are thriving by feeding on the dog’s blood. The dog is very uncomfortable but able to survive.

• Is this competition, predation, or symbiosis?

• An insect drinks nectar from a flower. The insect gets a meal, and the flower gets pollinated. The flower can now reproduce.

• What type of symbiosis is this?

• You eat some sushi that contains a tapeworm larvae. It grows and feeds off the nutrients in your intestines, robbing them from you. No matter how much you eat, you become more and more emaciated.

• What type of symbiosis is this?

• Barnacles attach themselves to a whale and feed on particles in the water as the whale moves. The whale is unharmed.

• What type of symbiosis is this?

• A lion hides in the grass waiting for its next meal• Is this competition, predation, or symbiosis?

• Two grizzly bears are fighting over salmon • Is this competition, predation, or symbiosis?

Changes in Terrestrial EcosystemsEcological Succession

Succession• Natural, gradual

changes in the types of species that live in an area; can be primary or secondary

• Gradual changes in community structure over time in response to environmental conditions

Primary Succession• Begins in a place without

any soil – Sides of volcanoes– Landslides– Flooding

• Starts with the arrival of living things such as lichens that do not need soil to survive

• Called PIONEER SPECIES

Primary Succession

• Soil starts to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces

• When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil

Primary Succession

• Simple plants like ferns & mosses can grow in the new soil

http://uisstc.georgetown.edu

http://www.uncw.edu

Primary Succession• The simple plants die, adding

more organic material.• The soil layer thickens, and

grasses, wildflowers, and other plants begin to take over.

• These plants die, and they add more nutrients to the soil.

• Shrubs and tress can survive now

http://www.cwrl.utexas.edu

http://www.rowan.edu

Primary Succession• Insects, small birds, and mammals have begun to move

in• What was once bare rock now supports a variety of life

http://p2-raw.greenpeace.org

Secondary Succession

Occurs in areas that have been disturbed but have not lost their soil; faster and different pioneer species than primary succession

End result of Succession:

• A stable group of plants and animals that is the end result of the succession process

• Does not always mean big trees– Grasses in prairies– Cacti in deserts

Past and Current BeliefsUp to ~1960’s• If undisturbed, ecosystems achieve permanent structure; a

habitat/niche for each organism• If disturbed, returns to the same permanent state “Climax

community” over time

Now• All ecosystems are in continuing state of disturbance/change• Not all species at peak• Called a “mature community”• Moderate, frequent disturbances create communities with

high biodiversity• Each disturbance goes through succession

Not every disturbance is a disaster...

The Intermediate Disturbance Hypothesis

Ecosystems that experience intermediate levels of disturbance are more diverse than those

with high or low disturbance levels.

Not every disturbance is a disaster... • Disturbances may kill some species, but allow others to benefit and

thrive. Therefore, the NPP of the ecosystem may remain unchanged- we can say it is resistant.

• When a disturbance influences populations or communities, but not the overall flow of energy and cycling of matter, we say the ecosystem has high resistance.

• When an ecosystem’s flow of energy and matter are affected by a disturbance, the rate at which recovers to original condition occurs can be measured.

• That rate is called resilience.

• A highly resilient ecosystem would recovery quickly after a disturbance.

Values of Ecosystems

• Provision Services- Goods that humans can use directly.

• Regulating services- The service provided by natural systems that helps regulate environmental conditions.

• Support systems- The support services that natural ecosystems provide such as pollination, natural filters and pest control.

• Cultural services- Ecosystems provide cultural or aesthetic benefits to many people.