Species packing and the competition function with illustrations from coral reef fish |
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Authors: | J Roughgarden |
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Institution: | Department of Biological Sciences, Stanford University, Stanford, California 94305 U.S.A. |
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Abstract: | This paper concerns the contrast between guilds whose species show resource partitioning and those that show extensive overlap. Using a Lotka-Volterra model, the ease of invasion by a third species into a guild already containing two species is examined for various shapes of resource utilization curves. I show that (a) a guild is more easily invasible and allows tighter packing if its member species have leptokurtic (thick-tailed) resource utilization curves than if they have platykurtic (thin-tailed) curves; (b) the distribution of niche separation distances is bimodal in a “thin-tailed” guild and is unimodal in a “thick-tailed” guild; (c) there are three-species guilds such that removal of one particular species leaves a two-species system in which one of the remaining species excludes the other. In this context, competition pressure is a force maintaining species diversity.Groupers (Serranidae) appear to be a thin-tailed guild, and Parrotfish (Scaridae) and Surgeonfish (Acanthuridae) together appear to be a thick-tailed guild, and these guilds show many properties predicted by the model. I conjecture that thick-tailed guilds form when the constituent species are selected to be generalists and apply this idea to tropical fruit- and flower-feeding birds. |
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