Understanding the dietary needs of syntopic species is essential for examining species coexistence and resource partitioning. We analysed stable isotopes of carbon (δ13C) and nitrogen (δ15N) to estimate the diet of two putative nectarivorous bats on Puerto Rico, the brown flower bat (Erophylla bombifrons) and the Greater Antillean long-tongued bat (Monophyllus redmani). Isotopic ratios of δ13C and δ15N were obtained from whole blood of both species of bat and tissues of available plant foods and insect prey over 15 wk at the same locality. We used a concentration-dependent Bayesian mixing model to determine probability distributions of feasible dietary contributions for major potential foods used by each species of bat. Additionally, separate dietary estimates were conducted for males and non-reproductive, pregnant and lactating females to determine differences due to reproductive condition. Insects were an important source of protein for M. redmani, whereas E. bombifrons obtained most of its protein from plants. In both species of bat, lactating females had lower assimilated nitrogen than males, suggesting more reliance on plants for protein. We observed no intraspecific differences in assimilated carbon among reproductive conditions. Flight and lactation are energetically expensive and may explain the increased consumption of high-energy foods, such as fruit or nectar, in lactating female bats. Comparison of isotopes between E. bombifrons and M. redmani illustrate the differential use of food resources by these insular syntopic species of bat.

Insectivorous birds and bats often protect plants through density- and trait-mediated cascades, but the degree to which insectivores reduce herbivorous arthropods and leaf damage varies among systems. Top-down interaction strength may be influenced by the biotic and abiotic context, including the presence of vegetation-disturbing animals. We tested two hypotheses: (1) insectivorous birds and bats initiate trophic cascades in tropical rain-forest understorey; and (2) the native, omnivorous collared peccary (Pecari tajacu) negates these cascades via non-trophic effects. We studied the top-down effects of birds and bats on understorey plants in north-eastern Costa Rica using 60 netted exclosures within and outside existing peccary exclosures. Excluding birds and bats increased total arthropod densities by half, both with and without peccaries. Bird/bat exclosures increased Diptera density by 28% and leaf damage by 24% without peccaries, consistent with a trophic cascade. However, bird/bat exclosures decreased Diptera density by 32% and leaf damage by 34% with peccaries, a negation of the trophic cascade. Excluding peccaries increased leaf damage by 43% on plants without birds and bats. This is the first study, to our knowledge, to demonstrate that the non-trophic activity of an omnivorous ungulate can reverse a trophic cascade.

In the Neotropics, crops that are grown in agroforestry systems with shade trees support high levels of bird diversity compared with crops grown without shade (Estrada & Coates-Estrada 2005, Faria et al. 2006). Several experiments in shaded coffee farms have explored how insectivorous birds reduce herbivore numbers and their damage to plants and have simultaneously approached ecological questions that are applied (e.g. biological control) and basic (e.g. tri-trophic interactions) (Borkhataria et al. 2006, Greenberg et al., Perfecto et al. 2004). Here we used exclosures to test whether birds lower the densities of herbivorous insects and reduce insect damage to cocoa (Theobroma cacao L., Sterculiaceae) foliage in shaded farms of western Panama. Although bird predation has been shown to reduce insect damage to crops in other systems (Mols & Visser 2002), we provide the first test for shade-grown cocoa.

Predators of herbivorous insects play important roles in tropical ecosystems as herbivory may affect structure and diversity of plant populations. Although insectivorous bats are particularly abundant and diverse in the tropics, their impact on herbivorous insects is little understood. To assess prey consumption, we observed the gleaning bat Micronycteris microtis (Phyllostomidae) continuously for 3 mo including 16 full nights at a nightly feeding roost on Barro Colorado Island in Panama using infrared videotaping combined with collection of prey remains. Individual bats consumed about 61–84% of their body mass in arthropods per night. Diet analysis revealed a high percentage of herbivorous insects, constituting more than half (51%) of all prey and over 70% of prey biomass. Dominant prey were caterpillars (33% of prey biomass), and other herbivores including crickets, katydids, scarab beetles and phasmids. Furthermore, a novel feeding behaviour was observed as M. microtis selectively discarded parts of intestines of phytophagous insects before consumption, probably to avoid intake of plant material either for ballast reduction and/or for protection from secondary plant compounds. Combined with estimated feeding rates of insects in sympatric bat species, our data suggest that gleaning bats are important predators of herbivorous insects and might be under-estimated reducers of herbivory in the tropics.

This study investigates the effect of tooth sharpness on the force and energy necessary for a tooth to divide foods of differing physical properties. The material properties of foods are likely to affect the shape that is best to divide them. In order to test the effect of sharpness on a tooth's proficiency in dividing insect prey, experiments involving penetrating and driving through insect prey of differing physical properties were carried out using specially designed punches that varied in tip- and cusp-sharpness. A refinement of tooth measurements which are relevant to their effectiveness in penetrating and driving through food is expounded. ‘Tip-sharpness’ is defined as the radius of curvature at the tip of a cusp. ‘Cusp-sharpness’ is defined as the volume or surface area of the tooth per unit distance from the tip of a cusp. The experiments show that tooth shape is important in the force and energy needed for teeth to penetrate and drive through insects. Also, the scale of teeth is important – teeth of the same shape but different size vary in their effectiveness to divide foods.