Evolution of body size, range size, and food composition in a predator-prey metapopulation

Relationships among body size, range size, and food composition are central to community ecology. Utilizing a simple framework of allopatric speciation, a stochastic, cellular automaton model of predator-prey metapopulations in one- and two-dimensional patchy networks are constructed. In the model, ecological processes, such as local extinction, recolonization, and predation, and evolutionary processes, such as mutation, influence the average body size or morphological value of a local population in a patch. Accumulating morphological divergence between local populations incurs allopatric speciation. Results of the model, highly correlated with some experimental data (795 species totally in China: Tetrigoidea 139 species, Fringillidae 453 species, and Serpentes 203 species), show that distribution of body size is right-skewed and multimodal. The right-skewed distribution arises from the proportionality assumption and multimodality is a result of adjacent colonization. Predation (the increase of tropic level) can decrease the skewness and increase the number of modes in the distribution. Distributions of range size and food composition are also right-skewed. Species with small range size like to aggregate in space surrounding by widespread species, forming a fountain of allopatric speciation. Furthermore, two rough rules from these distributions about the proportion of prey numbers to predator numbers and food composition are represented, showing that the proportion is about 2.3 and the number of prey species in food is 4.3 with about 47% similar between neighboring predator species. Additionally, the relationship between range size and body size is triangular, implying that widespread species has medium body size and large or small species is always spatially restricted. Relationship between body size and food composition is also triangular and indicates that extreme body size, largest or smallest, is always accompanied with stenophagic, while species with medium body size can be either euryphagic or stenophagic.