Resource partitioning and community structure of bats (Chiroptera) in a neotropical savanna.

摘要

In this thesis I want to explore how bats exploit and partition resources within a neotropical savanna community and the way these factors shape the community of bats in this naturally fragmented landscape.; To know how some temporal and spatial patterns affect the assembly of bat species and trophic guilds in the savanna, I firstly describe the community structure of bats in Espiritu (Bolivia). This savanna is inhabited by at least 37 species of bats. Although I found almost all trophic guilds known to occur in the New World, small- to medium-size low-flying insectivorous species and medium to large fruit eating bats predominate. Secondly, I test if turnover rates differ between trophic guilds and examine the consequences of species dynamics on shaping the community in two forest islands. Species relying on fluctuating food resources were more likely to be absent in particular years, whereas species relying on more predictable food supplies were present in all years.; With respect to resource partitioning within savanna bat communities, I examined roosting patterns of 10 bat species in Espiritu, in order to see if roosts could be a limiting factor in shaping the community. Roosts were more common in open woodlands than in forest islands and human settlements. In open woodlands, Tabebuia heptaphylla comprised the largest portion of roosting trees, whereas in forest islands, Gallesia integrifolia was the most important roosting tree for phyllostomid bats. Roosts appear to be a crucial resource affecting the community of bats and any disturbance at a minor (direct roost destruction) or major (forestry practices) scale will directly affect the presence of several species of bats.; I investigate patterns of food resource partitioning in a savanna bat community and by assessing food hardness experimentally I test whether food items consumed by the species, at the community and guild levels, show marked differences in physical properties such as size and hardness. Our results show that food hardness increases with the size of the food item, and that distinct differences exist in the amount of force needed to crush different food items (beetles vs. other insects vs. fruits). Based on these data, differences in food hardness may play an important role in structuring this bat community, and may have important consequences for the potential dietary scope of some feeding specialists. Finally, by studying differences in organismal performance I explain patterns in resource utilisation, and identify key evolutionary innovations that allowed the explosive, adaptive radiation within phyllostomid bats. I examine the evolutionary relationships between bite force and head shape and the results show that bite force increases exponentially with body size across all species examined. Despite the significant differences between large dietary groups using non-phylogenetic analysis and the strong evolutionary correlations between body mass and bite force, phylogenetic analyses indicated no differences in bite performance between insectivorous, omnivorous and frugivorous bats. Specialisation in trophic niches comes at the expense of bite performance and, hence, may result in a reduction of the trophic niche breadth. Bite force appears to be an ecologically relevant performance variable explaining the evolution, and thus resource partitioning within this bat community.