An Agent-Based Approach to Modeling mammalian Evolution: How Resource Distribution and predation Affect Body Size

Macro-evolutionary investigations into cross-scale patterns of body size variation have put many of the pieces of the evolutionary body size puzzle in place. To further tackle micro- and meso-scale process-based reasons underlying changes in body size, researchers compare natural populations across different habitat structures, assessing which habitat structures correspond to which changes in body size variation. The complex multi-scale dynamics underlying the effect of the external environment on body size evolution, however, inherently limits empirical interpretations with regard to the differential contribution of particular aspects of habitat architecture on body size variation, leaving open many questions as to the how and why of changes in body size variation across different habitats. We develop an agent-based simulation approach with the principal aim of investigating the differential effects of particular habitat conditions on the evolution of body size and other life history traits. Our approach simulates animals' individual decisions with regard to growth and reproduction, and records their effect on population-level variation across different habitat structures. This approach has the potential to include numerous different habitat conditions and/or growth laws and allows detailed controlled comparisons of the isolated effects of particular habitat conditions and/or perturbations. In the current study, we assess the usefulness of our approach in a pilot exploration of the effects of predation and resource distribution on body size variation in mammals. We find independent effects of predation, resource availability and resource predictability on changes in body size and quantify the relation between body size and population size across different habitat conditions.