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Community Ecology. Remember!. A community includes all organisms that live together in an area. Community Ecology : study of interactions among all populations in a common environment. Ecologists ask - in what ways do the populations interact?. Community Interactions.

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Community Ecology

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Presentation Transcript
  • A community includes all organisms that live together in an area.
  • Community Ecology: study of interactions among all populations in a common environment

Ecologists ask - in what ways do the populations interact?

community interactions
Community Interactions
  • Niche: the role of an organism in an ecosystem
    • Habitat = address vs. niche = job

Bobcat’s Niche: predator, carnivore

Rabbit’s Niche: prey, herbivore

community interactions1
Community Interactions
  • Competition: competing for resources, shelter, space, mates, etc.
    • Interspecific Competition: between members of different species
    • Intraspecific Competition: between members of the same species
niche competition
Niche & Competition
  • Competitive Exclusion: no 2 similar species can occupy the same niche (compete for the same resources) at the same time

The red squirrel is native to Britain, but its population has declined due to competition with the grey squirrel.

The grey squirrel was introduced into Britain & has easily adapted, replacing the red squirrel.

resource partitioning
Resource Partitioning
  • Reduces competition through microhabitats
resource partitioning among dominican republic lizards
Resource Partitioning Among Dominican Republic Lizards

Several species of Anolis Lizards live close in proximity & all feed on insects & other small arthropods.

Competition for food is reduced, because each lizard species occupies a different microhabitat.

interspecific interactions
Interspecific Interactions
  • Predation: an organism hunts & feeds on another organism
interspecific interactions1
Interspecific Interactions
  • Symbiosis: the relationship of organisms from different species living closely together
  • Both species benefit from the relationship

Clownfish live within sea anemones, which normally sting other fish.

The fish gets protection, & the anemone benefits because the clownfish keep it clean of bacteria.


Hummingbirds pollinate flowers. The hummingbirds get food, while helping the flowers reproduce!

  • One organism gains benefits at the other’s expense.

Here, a leech sucks the blood of a human.


A wasp lays its eggs in the larva of another insect (a boll weevil).

When the wasp eggs hatch, they feed on the boll weevil.

  • One species benefits and the other is neither hurt nor helped.

Epiphytes are plants that grow on other plants without harming them. They never set roots in the ground.


Moss growing on a tree


When grazing cows walk around, they disturb the ground, which stirs up insects. Birds follow the cows & eat these insects. The relationship between the bird & the cow is-

  • Mutualism
  • Parasitism
  • Commensalism
  • Competition


Shrimp living in the ocean eat parasites off of larger fish. The shrimp get a meal and the larger fish get rid of a parasite.
  • Mutualism
  • Parasitism
  • Commensalism
  • Competition


a botfly lays maggots inside a man s head providing shelter and nutrition for its young
A botfly lays maggots inside a man’s head, providing shelter and nutrition for its young.
  • Mutualism
  • Parasitism
  • Commensalism
  • Competition


populations in communities
Populations in Communities
  • Population sizes can fluctuate (go up or down).
factors that affect population size
Factors that Affect Population Size
  • # of births
  • # of deaths
  • # of individuals immigrating (entering) & emigrating (leaving)
exponential growth
Exponential Growth
  • If a population has abundant space & food, no disease or predators, it will grow at an exponential rate.
  • It is a J-shaped curve resembling y = ax2 + b
logistic growth
Logistic Growth
  • Population growth slows then stops (stays stable) after a period of exponential growth & resources become less available.
  • The number at which the environment can support this population is known as the carrying capacity.
limiting factors
Limiting Factors
  • Factor that causes a population to decrease in size
  • 2 types:
    • Density Dependent
    • Density Independent
density dependent limiting factors
Density Dependent Limiting Factors
  • Relies on how many organisms in a defined space are in that population; can include:
    • Competition
    • Predation
    • Parasitism
    • Disease

Notice the pattern of population size with predator/prey relationship of hares & lynxes.

density independent limiting factors
Density Independent Limiting Factors
  • Affect all populations in similar ways, regardless of population size
    • Weather
    • Natural Disasters
    • Seasonal Cycles
    • Human Activities
before you leave answer the following question on a sheet of paper share
Before you leave, answer the following question on a sheet of paper (share!)

Is Mycorrhizae an example of mutualism, parasitism, or commensalism? Explain your answer!