Intraspecific variation in the ontogenetic niche shift of <i>Caiman crocodilus</i> in Colombia, South America

Abstract When differences in traits within a species entail distinct ecological outcomes, this can provide unique insight into the selective forces driving macroevolutionary diversification. In crocodylomorphs, selection to consume different prey has been proposed as a hypothesis to explain the remarkable variation in cranial shape found within the group. However, such interspecific differentiation must ultimately arise from intraspecific variation, because different populations can face different ecological and selective conditions promoting diversification. Here, we test whether differences in prey consumption are associated with variation in cranial shape within the widely distributed Western Hemisphere crocodylian Caiman crocodilus. We find the ontogenetic niche shift (i.e. the shift from consuming one prey type to another as individuals develop) varies within this species as the macroevolutionary hypothesis predicts: subpopulations known to have relatively long- and narrow-snouted C. crocodilus grow to consume fish, whereas subpopulations characterized by relatively short- and broad-snouted C. crocodilus grow to consume a wider variety of prey (e.g. terrestrial vertebrates). Our results provide intraspecific insight on how selection to consume different prey might drive cranial morphological diversification in crocodylomorphs.