Biological Communities as Complex Systems:
Key to understanding the processes generating variation in body size and biodiversity I the separation of biological mechanisms from those inherent to all complex systems, whether biological or not. Discerning the processes influencing geographical patterns of species richness remains one of the central goals of modern ecology. Traditional approaches to exploring these patterns focus on environmental and ecological correlates of observed species richness; however some suggest these gradients may reflect simply species ranges being constrained to occur within a bounded domain, an idea that has generated substantial debate. My past work demonstrates the major challenges in the application of these null models and their inability to explain patterns of richness. With regard to community structure and the morphological disparity, I have developed models to test whether communities are built through random, stochastic processes or constructed upon assembly rules.
With respect to body size, it has become increasingly important to understand the evolutionary backdrop of passive verses directed mechanisms on which body size occurs. Recently, collaborators and I proposed that examination of body size variability, reminiscent of Taylor’ Power Law scaling, can determine whether passive processes govern body size evolution. Comparing passive models of body-size evolution with a global body-size dataset, we find that mean and variance of body sizes across the animal kingdom exhibit a power-law scaling relationship with an exponent near 2, a value consistent with a random multiplicative process of body size change. We suggest this provides a canonical expectation with respect to phylogenetic, morphological and selection constraints, and that meaningful differences between groups can be measured relative to this prediction. Our current work, suggests that the multiplicative, diffusive evolution can also be used to explain the perplexing relationship between richness and body size range across modern invertebrate phyla.