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Wize University Biology Textbook > Ecology

Community Ecology

Biogeochemical CyclesPrevious Section
Species InteractionsNext Section
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Community Ecology

Understanding how species compete and coexist. This includes fascinating behaviors that you can observe every day.
  • Niche: combination of a species' physical habitat and ecological role
  • Determined by abiotic and biotic factors
  • Climate
  • Interactions with other species
  • These factors drive evolution and adaptation
  • Specialization allows similar species to coexist
  • Fundamental Niche: the theoretical range in which a species COULD exist
  • Based on climate, food, shelter etc.
  • Species rarely get to occupy all of this theoretical space
  • Realized Niche: the actual range in which a species DOES exists
  • Interactions with other species often excludes animals from parts of their fundamental niche Example: Tree frogs occupy ponds near forests throughout North America – this is their fundamental niche. But they are excluded from ponds that also have larger frogs, because the larger frogs out-compete the tree frogs for food. The tree frog's realized niche is therefore ponds without larger frogs





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  • Competition can shape species niches
  • Competition: when two species compete for the same resource
  • A lose-lose situation, neither benefit
  • Intraspecific Competition: competition between individuals of the SAME species
  • Interspecific Competition: competition between individuals of DIFFERENT species

Photo by Asupernova | CC BY Photo by Summeet Moghe | CC BY
  • Competitive Exclusion: when interspecific competition is so great that one species completely excludes the other
  • Reduces the losers realized niche
  • If the loser tried to stay in the area, it may go extinct due to competition Example: foxes will avoid areas where there are a lot of coyotes because both species waste energy when the two compete with each other for resources.
  • Resource Partitioning: species evolve differences in traits to reduce competition
  • Also called niche differentiation
  • Occurs over time when competition between species is costly
  • Species will diverge in their traits to reduce competition
  • Can lead to new species Examples: Habitat use, feeding strategies, activity times etc...


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Disturbances

Humans are creating unparalleled disturbances in biological communities, understanding how species respond is crucial to conservation
  • Disturbances: events that produce severe physical impacts on a habitat Examples: storms, earthquakes, human activity
  • Can drastically lower species population
  • May disrupt whole ecosystem

Photo by Sam Beebe | CC BY

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  • Pulse disturbances: Short term, immediate disturbances
  • Windstorms
  • Floods
  • Wave activity
  • Fire
  • Sudden increase in the number of herbivores in the habitat Example: locust
  • Disease outbreaks
  • Introduction of invasive species.



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  • Press disturbances: Long term, persistent disturbances
  • Climate changes
  • Geological processes Examples: mountain formation, continental movement, change in river flow
  • Extinction of prey or mutualist


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  • Disturbance Regime: the type, frequency, and the severity of the disturbance
  • Succession: how the community responds to the new habitat created by the disturbance
  • Primary succession: when all life was wiped out Example: glacier melts and exposes bare rock for the first time
  • "Starting from scratch"
  • Secondary succession: when only some life was wiped out Example: Fire burns forest, but leaves the soil and seeds intact

Photo by Joshfn | CC BY
Photo by Katelyn Murphy | CC BY
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  • Pioneer species: first organisms to re-colonize after disturbance
  • Species with high environmental tolerance
  • First - Lichens
  • Second - Annual plants and grasses
  • Third - larger plants, insects, small mammals, birds
  • Climax Community: when the ecosystem reaches equilibrium
  • Not much change in species ("settles")
  • intermediate disturbance hypothesis (IDH): intermediate levels of disturbance supports the greatest diversity
  • At high levels of disturbance all species are at risk of going extinct
  • At intermediate disturbance, species that thrive at both early and late successional stages can both exist
  • At low levels of disturbance, diversity decreases because competitive exclusion increases
Photo by Sciencerelatedusername | CC BY
checklist
Mark Yourself Question
  1. Grab a piece of paper and try this problem yourself.
  2. When you're done, check the "I have answered this question" box below.
  3. View the solution and report whether you got it right or wrong.
Two closely related species of woodpeckers live in Canada. The black variety lives in coniferous forests while the yellow variety in deciduous forests. In the United States however, the black woodpecker is not present and the yellow variety occupies lives both deciduous and coniferous forests. What does this say about the yellow woodpeckers niche in Canada?




checklist
Mark Yourself Question
  1. Grab a piece of paper and try this problem yourself.
  2. When you're done, check the "I have answered this question" box below.
  3. View the solution and report whether you got it right or wrong.
Think of an example of why an animals realized niche may be different from their fundamental niche.
Try to be specific and explain your thinking.
Which type of competition specifically deals with interactions between two different species?
Extra Practice
It was found that guppies (live-bearing fish), when raised in predator free waters, produce larger sized offspring that mature slowly. This is in comparison to guppies raised in the presence of predators whereby the progeny are smaller, mature quicker and reproduce earlier. What phenomena is occurring?
In a forest community three species of rodents exists: mice, rats and voles. All three species eat the same types of nuts although they eat only what is appropriate for their size. A snake species that lives in this forest preys on all three rodents. One year, due to human intervention, the snake population is largely depleted and remains low for several years. Following this low species population there is an increase in the population of the rats while the voles and mice population decreases. What can be said about the snake in this ecosystem?
Two closely related species of woodpeckers live in Canada. The black variety lives in coniferous forests while the yellow variety in deciduous forests. In the United States however, the black woodpecker is not a native species while the yellow variety is and lives in the deciduous and coniferous forests. What does this say about the habitat of this organism?
Which of the following terms describes a group of organisms of a single species that live in the same space, same time and reproduce with one another?
The total range of environmental condition where a species lives and reproduces is commonly referred to as its:
Two closely related species of woodpeckers live in Canada. The black variety lives in coniferous forests while the yellow variety in deciduous forests. In the United States however, the black woodpecker is not a native species while the yellow variety is and lives in the deciduous and coniferous forests.
What does this say about the habitat of this organism?
The population of squirrels in a forest has increased and there are no longer enough Maple trees to nest in.
This is an example of:
State whether the following isolating mechanisms are pre- or post-zygotic mechanisms.
a) Land snakes cannot fertilize water snake eggs
b) Ligers (tiger and lion hybrid) are sterile
Why is fitness relative?
What factors place limits on the logistic model of growth?
In a forest community three species of rodents exists: mice, rats and voles. All three species eat the same types of nuts although they eat only what is appropriate for their size. A snake species that lives in this forest preys on all three rodents. One year, due to human intervention, the snake population is largely depleted and remains low for several years. Following this low species population there is an increase in the population of the rats while the voles and mice population decreases. What can be said about the snake in this ecosystem?
Two closely related species of woodpeckers live in Canada. The black variety lives in coniferous forests while the yellow variety in deciduous forests. In the United States however, the black woodpecker is not a native species while the yellow variety is and lives in the deciduous and coniferous forests. What does this say about the habitat of this organism?
Ecology Practice Problem 4
It was found that guppies (live-bearing fish), when raised in predator free waters, produce larger sized offspring that mature slowly. This is in comparison to guppies raised in the presence of predators whereby the progeny are smaller, mature quicker and reproduce earlier. What phenomena is occurring?
Ecology Practice Problem 3
In a forest community three species of rodents exists: mice, rats and voles. All three species eat the same types of nuts although they eat only what is appropriate for their size. A snake species that lives in this forest preys on all three rodents. One year, due to human intervention, the snake population is largely depleted and remains low for several years. Following this low species population there is an increase in the population of the rats while the voles and mice population decreases. What can be said about the snake in this ecosystem?
Ecology Practice Problem 2
Two closely related species of woodpeckers live in Canada. The black variety lives in coniferous forests while the yellow variety in deciduous forests. In the United States however, the black woodpecker is not a native species while the yellow variety is and lives in the deciduous and coniferous forests. What does this say about the habitat of this organism?
Which of the following is an example of intersexual selection?
Which of the following scenarios represents intrasexual competition?
What metabolic pathways generate ATP to be used during cruising activity versus burst activity?
The total range of environmental condition where a species lives and reproduces is commonly referred to as its:
Levels of Diversity
What is the difference between the following levels of organization?
Community and Ecosystem
Which of the following is not correct:
Which organism could be found in an area soon after primary ecological succession?
The population of squirrels in a forest has increased and there are no longer enough Maple trees to nest in. This is an example of:
The total range of environmental condition where a species lives and reproduces is commonly referred to as its: