Same same but different - quantifying the importance of intra-specific variability to plankton biodiversity

Planktonic microbes are vastly more diverse than theoretically explicable (Hutchinson 1961). We recently suggested that intra-specific variability was the key characteristic that allowed co-existence of dozens of planktonic species because the outcome of competitions between individuals with variable competitive abilities was unpredictable (Menden-Deuer and Rowlett 2014). Building on this game-theoretic model, here we examine the quantitative consequences of different degrees of intra-specific variability on species survival and co-existence probability. Frequency distributions of species competitive abilities (i.e. species behavior distributions SBD) vary, including invariant distributions with each individual’s competitive ability identical to the mean to entirely bimodal distributions, consisting only of individuals with the highest and lowest competitive ability. In total, we explore the effect of 14 different SBDs on species survival probability in individual-based competition model simulations across varying durations and population sizes. We find that particularly at small population sizes intra-specific diversity enhances survival probability and for some SBDs extinctions are not observed. These results have implications for anticipating species ability to withstand changing environmental conditions and understand diverse planktonic communities in a seemingly uniform ocean.