A mechanistic approach to modeling ant communities under warming regimes

Background/Question/Methods Dominance-discovery trade-offs might promote coexistence in ant assemblages, and this has been studied mathematically using a differential equation model developed by Adler and colleagues. While dominance-discovery trade-offs appear to be common in many systems, when predicting the sensitivity of ant assemblages to climatic change, it may be more important to consider alternative trade-offs.  In particular, differences in thermal tolerance likely play a key role in determining ant community composition under climatic warming, and a dominance thermal-tolerance relationship has been proposed in several systems.  In order to mathematically interpret and predict shifts in ant species abundance that occur as a result of climatic warming, we take the basic assumption of linear transitive dominance hierarchies from the dominance-discovery model, and then extend the model by including terms to describe species specific seasonal foraging patterns, which we use as a proxy for species specific thermal tolerances.

Results/Conclusions

We apply our ‘dominance-thermal tolerance model’ to a system of three sympatric ant species (Paratrechina terricola, Aphaenogaster rudis and Prenolepis imparis) in an eastern hardwood forest.  Our model predicts coexistence assuming parameter estimates made from data collected under current climatic conditions.  We then consider potential changes in these parameters that might occur as a result of climatic warming.  In particular, we focus on altered ant behavior, food availability and competitor abundance, and use our model to predict the effects that these changes will have on ant community composition.  As an example, we that expect that climatic warming will alter the phenology of many species that ants rely on for food. We thus consider the effects of increasing/decreasing food supply at different times of the year.  Our analysis suggests that increased food availability in early spring will increase the P. imparis population, decrease the P. terricola population, and have a relatively small impact on the A. rudis population.  In contrast, increased food availability in mid-summer will decrease the P. imparis population, and increase both the P. terricola and A. rudis populations.  Finally, increased food availability in late fall will increase both the P. terricola and P. imparis populations, but will, once again, have a limited effect on the A. rudis population.  To our knowledge, this is the first attempt to model how coexistence among ant species might be altered by climatic warming. Further work is necessary to predict coexistence in more species-rich systems and those that are likely to be most susceptible to climatic change.