Assessing the impacts of trait evolution in ecological food webs
Understanding the ecological dynamics in food webs is a classic problem in community ecology. More recently, there has been a focus on how rapid evolutionary changes and ecological dynamics feedback on each other. Applying this framework to food webs will provide insights into the importance of eco-evolutionary feedbacks in a ubiquitous form of ecological community. Quantitative genetic models of trait evolution in food webs have primarily focused on how evolution leads to the emergence of food web structures on long evolutionary time scales. By contrast, we are interested in understanding how concurrent evolutionary and ecological changes impact intraspecific trait distributions and species abundances. In particular, we seek to understand the impacts of trait evolution on the diversity-stability relationship in food webs. Here, we present a stochastic, individual-based quantitative genetic simulation of trait evolution in food webs. Following previous models, we model interaction strengths, as well as demographic parameters, as functions of trait values (e.g., body size).
Our simulation approach allows us to model a variety of food web structures (e.g., random, cascade, niche models). We directly compared ecological dynamics of communities with and without trait evolution, allowing us to isolate the role of evolution on the maintenance of diversity and the stability of the communities. We found that, in the absence of external immigration, simulations with trait evolution led to higher levels of trophic diversity than those with no intraspecific variation. This is because consumer species were able to evolve towards body sizes that increased their probability of successful predation. In simulations with higher initial diversity, we also found that trait evolution facilitated higher trophic diversity. However, these communities tend to be less stable over time and prone to extinction. These transient fluctuations are functions of trait-dependent demographic parameters in our model as well as heritability. While we find that trait evolution can alter coexistence and diversity, we also find that it significantly alters transient dynamics of species abundances within the community, which may not impact local diversity, but could have strong regional effects in a metacommunity context. Our results point to a need for further investigation of trait evolution within community contexts.