Our world is changing. Increases in temperature, relocation of species, and shifts in predation risk are altering the ecology of communities around the globe. A significant part of these shifts is linked to changes in body size. Despite a long appreciation for the relevance of body size in ecology, we have not developed the understanding needed to explain past changes or predict future changes in size, nor can we predict the consequences of body size evolution on ecological communities and the services these communities provide.
My current research program has focused on developing three approaches that together can foster a holistic understanding of body size evolution and its effect on ecological communities. These approaches include: 1) building exhaustive databases on body size-dependent processes that are central to ecological interactions, 2) deriving a mechanistic optimality model for the evolution of body size (i.e., the Supply-Demand [SD] model), and 3) developing a new class of eco-evolutionary model that enables rapid evolution to arise naturally from the fitness landscape generated by ecological processes. The models from the third approach, called Gillespie eco-evolutionary models (GEMs), can connect traits such as body size to any ecological process, allowing us to predict the direction of trait evolution and the feedback of that evolution on ecological dynamics.
In this essay, I describe my goal of bringing these three approaches together to build SD-GEMs. These models will allow us to resolve the problem of how body size evolution may mediate the effects of environmental change on ecological communities. Importantly, SD-GEMs contribute to complex systems science by 1) linking individual-level processes (fitness, traits) to species interactions (predation, competition) and community-level patterns (dynamics, species persistence, diversity) and 2) enabling many (or all) ecological interactions to simultaneously influence the evolution of traits. With this new complex systems approach, we can attempt to understand how and when body size should evolve and what happens to the parts and the whole ecological system as a result.
Two examples illustrate the broad applicability of the SD-GEM approach. First, invasive predators – many of which are getting larger as time progresses – are disrupting food webs around the world. SD-GEMs can help us understand how invaded systems may change and predict the course of body size evolution for the invader or the surviving native prey. Second, the practice of biocontrol uses predators to control insect pests, and such predators have size-dependent links with their prey. SD-GEMs will help us understand how the introduction of natural enemies influences body size evolution of the predator or the target pest and help us predict how well the biocontrol approach should work through time.
In both of the above scenarios, not accounting for both the size-dependence of processes and the evolution of body size will severely limit our ability to forecast ecological change. SD-GEMs are uniquely positioned to predict the ecological changes that may unfold as body size evolves in response to environmental change.