Ecological morphology and nectar-feeding performance in flower-visiting bats

Many species of New World leaf-nosed bats (family Phyllostomidae) feed on nectar from flowers, and consequently serve as pollinators of hundreds of different species of plants in environments from tropical rainforests to arid deserts. The phyllostomids that visit flowers range from opportunistic visitors to bats highly specialized for feeding on nectar. This dissertation explores morphological variation in the skulls and jaws of flower-visiting phyllostomids and examines nectar-feeding performance in live animals. Morphometric analysis of skull shape revealed that specialized nectarivores (collectively "glossophagines") are generally smaller and possess relatively lengthened snouts and jaws compared to other phyllostomids. Bone densitometry (micro-CT analysis) examined cross-sectional geometric properties of the mandibular symphysis and corpus. These studies indicate that glossophagines have lightly-built jaws compared to other phyllostomids, presumably reflecting decreased emphasis on mastication in favor of feeding with the tongue. The mandibular symphysis of glossophagines is different than other phyllostomids, being fused and aligned relatively horizontal to the toothrow. Symphyseal fusion also characterizes the subfamily Stenodermatinae and occurs in one species of vampire bat and at least one species within Phyllostominae. Nectar-feeding performance was measured in feeding experiments using artificial flowers of different dimensions for six species (three glossophagines: Choeronycteris mexicana, Leptonycteris curasoae, Glossophaga soricina, and three other phyllostomids: Carollia perspicillata, Phyllostomus discolor and Artibeus jamaicensis). Two measures of performance were examined, feeding rate and maximum tongue extension. Glossophagines hovered while feeding, visited quickly, and took less nectar per visit than the other phyllostomids, who landed or anchored on the flowers and took more nectar during longer visits. Increasing flower length negatively affected feeding rate in all species. Size-adjusted feeding rate was not highly correlated with morphological specialization for nectarivory. Leptonycteris had the highest feeding rate of all species. Phyllostomus had feeding rates comparable to the glossophagines and much greater tongue extension than the other non-glossophagines. Morphological specialization is more closely associated with maximum tongue extension and the amount of nectar taken per lick, suggesting specialization in glossophagines may reflect increased ability to reach and extract nectar, but does not necessarily reflect increased feeding rate.