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AP Biology 8.5: Community Interactions

Practice AP Biology 8.5 questions on how competition, predation, cooperation, symbiosis, and niche partitioning influence populations, energy flow, and community structure.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • classify and explain how competition, predation, cooperation and symbioses—including parasitism, mutualism and commensalism—affect interacting populations
  • use food webs, population data and experimental results to model how interactions alter access to energy and matter and change community structure
  • explain how trophic cascades and niche partitioning can redistribute resources, reduce competition or change population abundance

Covered syllabus points

8.5.A—Describe the structure of a community according to its species composition and diversity8.5.B—Explain how interactions within and among populations influence community structure

8.5 Community Ecology question 1

[Maximum number: 1]

Biological communities containing a large number of species that are evenly distributed exhibit high species diversity-a concept that encompasses both species richness (the number of different species present) and relative abundance (the number of individuals of each species). One measure of species diversity is Simpson's index of diversity, which is represented by the following mathematical equation.

Ds=1−∑ni(ni−1)N(N−1)D_{s}=1-\frac{\sum n_{i}\left(n_{i}-1\right)}{N(N-1)}

Where Ds=D_{s}= index of diversity for a community
N= total number of individuals of all species
ni=n_{i}= number of individuals in each individual species
The following data were collected from a community of trees.

Species

Number of
Individuals

1

20

2

34

3

4

4

10

Calculate the Simpson's index of diversity for the community of trees. Enter your answer as a value between 0 and 1 to the nearest hundredth.

8.5 Community Ecology question 2

[Maximum number: 2]

Twenty million years ago the Caribbean Sea and Pacific Ocean were connected, and water

flowed freely between the two bodies of water. Many of the same marine species were found

in both areas. Over millions of years, the land referred to as the Isthmus of Panama formed,

eventually closing off the connection between the Caribbean Sea and Pacific Ocean and creating

two separate bodies of water. The ecology of these two marine habitats was dramatically altered

by this land formation. The warmer Caribbean water could no longer flow west, so the Pacific

water cooled and became more nutrient-rich, while the Caribbean water became warmer.

Question (a)

(a)

Predict the effect the formation of the isthmus had on resource availability for South

American species.

[ 1 ]

Question (b)

(b)

Justify your prediction in part C.

[ 1 ]
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