A critically important challenge in theoretical ecology is to better predict responses of ecological networks to global change, especially responses to increasing rates of species invasions. Invaders have been widely observed to trigger changes in species’ interactions and abundances and even cause catastrophic extinction cascades of native species. Classical food web models have focused on explaining and predicting such ecological responses on relatively short time scales. However, these models typically neglect changes in selection pressure on native species caused by the invaders and their subsequent effects on the structure and stability of food webs on longer time scales. We evaluate these effects using an eco-evolutionary approach that synthesizes population dynamics, classical assembly and evolutionary food web models. Our integrative model uses body masses and diets as the key traits that determine metabolic rates and species interactions. We vary the frequency of invasion events in relation to speciation events and the relatedness between native species and invaders. As outputs of our model, we analyze the size of the emerging network (in terms of total biomass and number of morphs or ‘species’), its ecological and evolutionary stability, and its species turnover pattern.
Results/Conclusions
Our results show that food webs evolve most diverse and accumulate the most biomass when being exposed to frequent invasions of species similar to native species. The system is also most stable in such invasion context, both evolutionary (i.e., lower variability in the number of morphs/species over time) and ecologically (i.e., lower variability in total biomass over time). We also found that food webs with higher fractions of generalized consumers achieved the highest ecological stability but also the lowest evolutionary stability. This is because our model assumes that more generalized consumers have in average lower attack rates per-prey than specialized consumers, which results in stabilizing weak interactions and wider diet breadths that allow fewer morphs to coexist. By contrast, high degree of specialization and high attack rates produce strong biomass flows into higher trophic levels leading to oscillations (low ecological stability), but also narrow diet breadths that allow more different morphs to coexist. Our work illuminates possible mechanisms by which invasion and mutation processes may shape the structure and dynamics of food webs in longer time scales.