From the ground to the skies: Ecomorphological predictors of diet and trophic diversification in small Neotropical mammals

Abstract

During the evolution and dietary diversification of vertebrates, astounding morphological, physiological and behavioral adaptations evolved to procure and efficiently process their preferred food resources. These adaptations affect how well each species obtains energy, survives and reproduces in their environment, and are directly related to resource partitioning and diversification patterns. This dissertation seeks to elucidate patterns of morphological and functional adaptations on small Neotropical mammals related to selective pressures exerted by their dietary ecology. I used myomorph rodents and bats as model taxa to develop my research, as these animals show exceptionally high taxonomic and ecological diversity, which makes them ideal for understanding ecomorphological trends in the evolution of feeding structures. Through my three chapters, I tested the hypothesis that evolved differences in size and shape of morphological structures are directly associated with differences in the feeding ecology of the species. Moreover, by linking these adaptations to variations in performance among tasks of vital importance for energy acquisition during feeding (e.g., biting, chewing), I also explored how functional adaptations might have allowed subsequent functional dietary specialization on some taxa and, ultimately, trophic segregation among Neotropical mammal communities. In chapter 1, I coupled data on functional mandibular measurements and dental topography metrics with dietary information under a phylogenetic framework to investigate the functional correlates of mandibular and molar diversity among Akodontine rodents. Here, both mandibular and dental morphologies seem to have evolved to facilitate the efficient processing of specific food items with unique mechanical properties (e.g., arthropod exoskeleton vs plant materials). Both mandibular and dental traits show strong dietary signals towards processing specific food resources, with herbivory and insectivory dietary regimes shaping the most extreme morphologies. Altogether, our study gives insight into the strong relationship between rodent’s feeding structures and dietary ecology, highlighting the traits that are, potentially, under stronger selective forces and that might have facilitated the trophic diversification and specialization in the Akodontine tribe. In chapter 2, I used morphological and performance traits to investigate the influence of feeding ecology on the form-function relationships of feeding structures in rodents, and explored the potential implications of these differences on morphological specialization and resource partitioning among sympatric members of a community in Costa Rica. I found a strong dietary signal on multiple external, mandibular and dental traits, with shape differences being more extreme in specialized feeding ecologies. I also found multiple trade-offs between the morphology and performance of the feeding apparatus of these rodents, highlighting the compromise that usually is detected when extreme morphologies evolve. Our data give insight into form-function-performance relationships of rodent feeding structures and provide clues on potential mechanisms that have allowed trophic diversification among sympatric species. In chapter 3, I investigated the functional relationship among size, shape and feeding performance in a community of Neotropical Free-tailed bats in Costa Rica. Specifically, we evaluated how the size of cranial structures and the shape of molar teeth correlate and influence food processing. We found strong connections of morphological and functional specialization with performance outcomes, highlighting mechanisms of trophic resource partitioning among members of the community. These, in turn, might be influenced by adaptations to the mechanical properties of different food resources. Altogether, our study successfully connected morphology and performance with dietary ecology, setting an example on how to couple these data to better understand ecological patterns and trade-offs of trophic specialization.