Chiroptera (bats) forms the second most diverse branch of mammals, with over 1,300 species documented. Bats play important roles within the environment because they feed on a wide range of prey items, ranging from fruit, nectar, to insects and blood. One of the main drivers of species diversification in bats is the structural specialization of the cranium and jaw muscles, which allow bats to produce adequate bite forces to exploit and process different types of food. This study investigated differences in bite force and prey hardness among insectivorous free-tailed bats (Family Molossidae), and the factors explaining the breakdown and processing of their meals through physical digestion. The bite forces of seven Costa Rican molossid species were measured and compared with the degree to which insect exoskeleton was broken down in their feces. The size of the exoskeleton particles in the fecal samples gave clues as to how much bats chewed and broke down their meal, whereas the thickness of these particles was a proxy for insect hardness. We anticipate to find a clear correlation between exoskeleton particle thickness and size across species, which would support the prediction that the size and morphology of the skull and teeth have an effect on the food these bats can consume. A relationship between the thickness of the insect exoskeleton particles and bite force would indicate that each bath species is specialized to feed on certain types of insects with varying level of exoskeleton hardness. Our results will provide clues to understanding feeding behavior of free-tailed bats and the role of morphology on species ecology.

Intraspecific studies of morphology and performance are essential for understanding the factors that enable resource partitioning within ecological communities, yet these have received little attention in mammal ecomorphology. Sea otters (Enhydra lutris) is one of the few marine mammal species in which individual-level dietary specialization has been quantified and linked to competition and prey abundance, making them an ideal system to investigate the morphological basis of food resource partitioning. Here, we assess whether differences in cranial morphology and bite force predict dietary variation among sea otter populations. We use geometric morphometric analyses and two-dimensional bite force models to (1) estimate differences in cranial shape and bite force among the three sea otter subspecies groups, E. l. kenyoni, E. l. lutris and E. l. nereis, (2) evaluate the extent of sexual dimorphism in cranial morphology and bite force within subspecies, and (3) relate the variation in cranial morphology and bite force to available dietary information. Although some sexual dimorphism in cranial features exists, preliminary results do not show significant differences in bite force between subspecies or between male and female sea otters. These results suggest that resource-use variation may be linked to individual foraging behavior and not to differences in morphology in sea otters. However, unique cranial features leading to high bite forces may enable this species to have higher diet plasticity; higher bite force in sea otters allows for the consumption of a variety of hard-bodied prey items and allows for either generalized or specialized diets, depending on prey availability and competition.