Individual-Based Modeling in Comparing Marine Ecosystems

A goal of community ecology is to understand and predict the characteristics of communities that  develop under different environmental conditions. We address that goal for fish communities by using an individual-based community assembly model for fish life histories and trophic interactions. It integrates theories for individual physiology, growth, reproduction, and feeding in the same dynamical framework. Communities are formed by a sequential assembly process which selects for species best adjusted to local conditions. Simulation experiments were carried out to evaluate the distribution of diversity and selective response of 10 bionomic features along gradients of resource productivity, predators maximum attack rates, skewness of body size distribution in species pool, and the presence/absence of asymmetries in both the abilities of fish to consume prey and to avoid being consumed. This last factor includes tradeoffs concerning capture efficiency versus diet generality and foraging intensity (associated to growth rate) versus defense against predators. The resulting communities were strongly affected by the gradients. Richness peaks are localized at moderately low productivities associated to low maximum attack rates, which might be related to the stabilizing effect of less saturated functional responses and to the emergent features of selected species. At low resource availability (i.e. low productivity and low attack rate), only very small, slow growing, early reproducing, less fecund, and less piscivorous species were able to persist. On the other hand, at high resource availability fast growing species with much more variable sizes dominated, promoting fast resource depletion early during assembly and leading to strong priority effects, which prevent the establishment of later arrivals. Less skewed (more uniform) body size distributions diminish the availability of smaller species, which resulted in lower overall richness, but mainly at the gradient points where such species are dominant. This work emphasizes that studying gradients and properly including the multiple tradeoffs faced by organisms like fish is of great importance to understand the mechanisms determining the distribution of biological diversity under different conditions.