Resource seasonality explains latitudinal size and clutch size patterns in a Dynamic Energy Budget model

Animals show a vast array of geographical variation in phenotypic traits. The most common patterns are the tendency of size and clutch size to increase with latitude among related species. Nevertheless, the precise mechanisms behind these patterns remain controversial. Here, we show how resource seasonality can drive latitudinal trait variation. We conducted numerical simulations of a dynamic energy budget model, quantifying individual biomass and reproductive output, both under constant and seasonal resource conditions. We evaluated 48 different genetically-determined physiological characters (equivalent to different species and represented by the model parameters for assimilation, mobilization, and energy allocation). In both scenarios, we found that resource availability determines interspecific trait differences in the DEB model. Our findings show that individuals can reach greater biomass and reproductive output in a seasonal environment than in a constant environment of equal average resource due to the peaks of food surplus. Our results agree with the classical patterns of interspecific trait variation and provide a mechanistic understanding supporting recent explanatory hypotheses: the resource and the eNPP (net primary production during the growing season) rules. The current alterations to ecosystems and communities make disentangling trait variation increasingly important to understand and predict biodiversity dynamics under environmental change.