Question

20.1. explain the concept of an ecological community and how it relates to ecological diversity.
the sea star pisaster ochraceus is an example of a keystone species. in a classic experiment
conducted along the pacific coast of washington state in 1963, sea stars were removed from one
site while an adjacent site was left undisturbed. although relative species abundance is not shown
in these data, you can make some inferences/deductions from the species numbers that are
shown. based on this graph, which experiment contained the highest relative species abundance
at the end of the experiment (1973)?
loss of a keystone species reduces diversity
sea stars completely
eliminated mussels in
submerged areas of this
marine community,
enabling other intertidal
species to thrive there.
when the sea star pisaster
was removed from a
community experimentally,
the number of species
dropped from 18 to 1, a
mussel.

Explanation:

The graph shows two lines: one for the site where the sea star (a keystone species) was removed (red line) and one for the site where it was not removed (blue line). Relative species abundance is related to the number of species. At the end of the experiment (1973), we look at the number of species for each site. The site with the sea star not removed (blue - line) has a higher number of species. Since relative species abundance is higher when there are more species (assuming evenness, but since the problem only gives species number data), the site where the sea star was not removed has higher relative species abundance.

Answer:

The experiment where the sea star was not removed (the site represented by the blue - line in the graph) contained the highest relative species abundance at the end of the experiment (1973).