Evolutionary divergence in competition strength

Competition is an important mechanism for understanding how species compete for resources and coexist, and is also an important process to understand biodiversity in nature. However, the traits that determine the outcome of interspecific competition are often assumed to be constant for each species. Many studies have shown rapid evolution in traits that can influence competition, but no study to date has quantified whether the strength of competition between two species is a heritable trait. My proposed summer research project will measure the strength of competition between two freshwater zooplankton species and quantify how much of this trait is heritable from one generation to the next. I plan to extend the results of the summer research project to a broader honors thesis project, which will determine how the spatial proximity of rock pools on the James River (Richmond, VA) influences (i) competition between zooplankton species and (ii) regional coexistence and biodiversity patterns in this natural system.

This summer I will study two species that compete for algal resources, the small freshwater crustacean  and the rotifer Brachionus calyciflorus. Both of these species inhabit rock pools adjacent to the James River (Richmond, VA). Rock pools are small depressions that are transiently filled with rain water. It is an ideal system to study community ecology. The experiment comprises two parts. The goal of the first experiment is to purge any effects of experimental organisms’ natal environment (the rock pools they were collected from), so that subsequent measurements of traits will be measurements of the heritable genetic component of that trait. The goal of the second experiment is a response surface experiment (Inouye 2001) to measure competition strength between two species. Response surface experiments quantify competitive strength by measuring the change in density (number of individuals per unit volume) of Species X when Species Y is present, and vice-versa.  For Species X, we can estimate αXY (the per-capita influence of Species Y on Species X) using the formula:

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where X is the density of Species X, t is the generation, λ is the maximum population growth rate of Species X, K is the carrying capacity of Species X, and Y is the density of Species Y.

We expect that clones will vary in their competition strength with other species, which indicates there is genetic variation in competition. Moreover, a population’s initial density will also influence the competition strength. Our experimental quantification of competition strength will be useful for my planned future experiment to match the competition strength measured in the laboratory to observed coexistence patterns in James River rock pool communities.

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Cited Literature: Inouye, B. (2001). Response Surface Experimental Designs for Investigating Interspecific Competition. Ecology, 82(10), 2696-2706.


  1. Hi Zeyi, the topic is really intriguing. The examination of the strength of competition between two species and the traits’ heritability is of importance both in biological sense and mathematical sense. The competition exists between two species and the mechanism behind it are systems that people want to understand. It reminds me of the system of Ordinary Differential Equation. Your equation measuring the relation between density of species X and species Y also make mathematical sense to me. It is certainly an attractive research.