8.5: Community Ecology

What is a community?

a group of different species living together in the same location and interacting with one another

How do we describe communities?

based on species diversity and composition

What is species diversity?

the variety of species and quantity of individuals included in each species within a given community

ex: ocean community of one shark and sea turtle species but there are 15 sharks and 62 sea turtles

What is species composition?

the identity of each species in the community

ex: an ocean community consisting of Pomacanthus paru and Pomacanthus xanthometopon: two species of angelfish

What is the Simpson’s Diversity Index?

an equation used to measure species diversity and biodiversity of a habitat; higher values mean the community is more diverse

How can competition occur?

within or between species

How can interactions between organisms be?

positive, negative, or neutral

What is mutualism?

when both species benefit from an interaction

What is commensalism?

when one species benefits but the other is not harmed or helped by an interaction

What is predator-prey relationship?

one species uses another for a food source

What is parasitism?

one species benefits at the harm of another

What are two examples of positive interactions between species?

1) mutualism

2) commensalism

What are two examples of negative interactions between species?

1) predator-prey

2) parasitism

What is an example of a neutral interaction between species?

deer & rabbits living in the same forest together

Why is the interaction between shelf fungi and trees considered negative?

The shelf fungi are parasites that produce fruit that absorb nutrients from the outer bark of the tree which weakens it’s external structure and reduces its canopy and foliage density. It also can infect the interior of the tree.

What positive effects could the interaction between shelf fungi and trees have its the community?

1) If the tree rots and falls, it can provide niches and microhabitats for insects and other organisms.

2) It can also provide food sources for insects and other organisms that eat the fungi

How are increases in prey and predator populations related?

1) an increase in predator populations occurs slightly after an increase in prey populations

2) an increase in predator populations will eventually cause a decrease in prey populations

What is a trophic cascade?

the negative effect the removal of or decrease in a key species has on other trophic levels; can result in exponential growth/decay and interruption of the flow of energy through the ecosystem and resource availability

What is niche partitioning?

a decrease in competition over limited resources between two similar species because each species is accessing the resource in different ways