Why Do More Productive Habitats Have Fewer Species? An Experimental Field Investigation

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In many environments, the richer the environment, the fewer species it can support. This is true at least in lakes, tropical forest, semi-arid plains and mountainsides, and oceans. It is true of trees and other vegetation, terrestrial mammals, and various kinds of aquatic invertebrates. No general explanation for it has yet been proved. However, preservation of the world's species requires an understanding of the mechanisms which regulates the number of species in natural environments. This research will test two hypotheses in the field. 1) Do other forms of life usurp the resources of a given form as production rises? For example, does the number of mammal species decline because birds and ants take their food? 2) Does the habitat become simpler, costing some specialists their livelihood as production rises? For example, does the variety of architectural forms found among plants diminish, causing the loss of some mammal species? In one set of experiments, the rate at which seeds become available to mammals (but not birds or ants) will be doubled. In another set, in a fairly uniform grassland, the patchiness will be increased by removing small areas of grass. Small mammals will be censused and the natural rate at which they remove seeds from the environment will be measured. Results for this 4-year project will be of immediate interest to basic ecologists as a test of general theory. Findings will also be valuable to scientists developing strategies of bioconservation.