Lecture 9

Topics

• Species packing

• Charles Elton's work on Bear Island

The Main Points

• Part of the theory presented in Island Biogeography has to do with McArthur's and Wilson's thinking on what happens to species that come to live on an island.
  1. The problem is that as more and more species arrive, space and resources become limiting.

  2. Some species do not find enough resources to maintain a population and they become extinct. Others, however, remain but are limited in both habitat choice and resource variety. In the long term, selection favors those individuals in the populations that find unique combinations of habitat and resources (we will be talking about this a lot more in the coming weeks).

  3. The result of selection is a "packing" of species on the island into increasingly specialized conditions.

• By the time McArthur and Wilson wrote Island Biogeography, we already had a good sense about what life on islands looked like and knew much about how species were connected with one another.
  1. In the 1920s, Charles Elton was describing, in many kinds of communities, dynamical qualities that emphasized the interactions among the plants and animals. He thought of the "community" as a group of species related through "food-chains". His classic work with fellow worker, Summerhayes, is presented by Ricklefs in Fig. 9-1. (I presented this in class).

  2. Bear Island is off the northcoast of Norway. It is rocky and cold place supports a relatively simple community. The pond communities and the plants associated with the wet places serve as the major places where food is obtained by the birds. In turn, the birds are the major sources of food for the mammals on the island. Follow the arrows around the figure and notice how intertwined the "food chain" become. Elton refered to this complex set of food chains as the "food cycle". We would now call this complex the "food web."

• Read this section (175-176), in which Ricklefs quotes some of Elton's writing.

• Also look at Fig. 9-2. In 1925, A.J. Lotka visualized the "community" as a network of multi-directional paths through which energy was moved and transformed. Here was a thermodynamic view that we really didn't see again until Lindeman's work was published 15 years later.