Comparing Methods of Quantifying Coexistence Using Protist Microcosms

Abstract

Species in a community must be able to increase from rarity for coexistence to be possible. It is possible to quantify this ability, and thus the strength of coexistence, by estimating invasion growth rates. This is typically done by fitting a mathematical model to the community. However, modeling is far from a simple task, and resulting estimates can depend upon model choice. A more direct method, one that bypasses the need to fit a model, could be a better option. Using protist microcosms, I conducted numerous small-scale invasion assays to estimate invasion growth rates directly. I compared these direct estimates with those I obtained by fitting a model. I obtained quantitatively different results depending on the method used. This may be due to differences in spatial environment as the culture vessels used for invasions were much smaller than those used for the long-term competition experiment. Modifications to this method of direct invasion could be made to obtain more comparable estimates and to further investigate the importance of spatial variables in protist microcosms.