Rodrigo García-Morales

Response of Neotropical bat assemblages to human land use

Neotropical bats are sensitive to human-induced habitat changes, and some authors believe bats can be used as bioindicators. In the literature, however, the results are disparate. Some results show bat diversity deceases as disturbance increases, whereas others indicate no effect. Determining the general response patterns of bats when they encounter different degrees of human-induced disturbance across the Neotropics would help to determine their usefulness as bioindicators. In a series of meta-analyses, we compared the occurrence frequency of bat species between well-preserved forests and human-use areas. We obtained data through an extensive review of published peer-reviewed articles, theses, and reports. The overall effect size indicated that human-use areas harbored more bat species than well-preserved forests. Different response patterns emerged when meta-analyses were conducted separately by family, feeding habit, vegetation stratum, and conservation status. Our results suggest that bat assemblages display strong responses to forest loss and land-use change and that the direction and magnitude of these responses depends on the bat group under study and the type of disturbance. Our results are consistent with the idea that bats are useful for assessing the effects of habitat changes in the Neotropics. However, with our meta-analyses we could not detect fine differences in bat feeding habits, especially within Phyllostomidae, or elucidate the effect of landscape configuration.

Seed Dispersal Among Three Different Vegetation Communities in the Huasteca Region, Mexico, Analyzed from Bat Feces

Seed dispersal is a key process for plant colonization and for the establishment of many plant populations in tropical environments. A large proportion of all tropical woody plants with fruits and seeds depend on frugivorous vertebrates for their dispersal, and frugivorous bats are essential for the dispersal of seeds from many tropical plants. Many of these plants are important for vegetative regeneration after disturbances. Our main goal was to document the process of seed dispersal through feces-seed analysis by the bat community among semi-deciduous, evergreen, and secondary forests in the ‘Huasteca’ region of San Luis Potosí, Mexico. We hypothesized that bats would disperse seeds among all three forest types, and thus predicted that we would find seeds from both early and late successional stages in bat feces in all three forest types. In each of three replicate sites representative of each of these forest types, we trapped bats with mist-nets and collected their feces with seeds. A total of 558 individuals from eight frugivorous bat species were captured. The most abundant species were Sturnira ludovici, Glossophaga soricina and Artibeus jamaicensis. We documented seeds in bat feces from 16 plant species belonging to four families: Moraceae, Piperaceae, Solanaceae, and Myrtaceae; 43% were pioneer species, and thus important for the initial stages of regeneration, and 37% were species of late successional stages. Seeds in bat feces were found in similar proportions in all forest types, thus contributing to the regeneration of highly deforested habitats in the Huasteca region. To maintain the entire mutualistic network between bats and plant species, diverse bat communities are important.

Deforestation Impacts on Bat Functional Diversity in Tropical Landscapes

Functional diversity is the variability in the functional roles carried out by species within ecosystems. Changes in the environment can affect this component of biodiversity and can, in turn, affect different processes, including some ecosystem services. This study aimed to determine the effect of forest loss on species richness, abundance and functional diversity of Neotropical bats. To this end, we identified six landscapes with increasing loss of forest cover in the Huasteca region of the state of Hidalgo, Mexico. We captured bats in each landscape using mist nets, and calculated functional diversity indices (functional richness and functional evenness) along with species richness and abundance. We analyzed these measures in terms of percent forest cover. We captured 906 bats (Phyllostomidae and Mormoopidae), including 10 genera and 12 species. Species richness, abundance and functional richness per night are positively related with forest cover. Generalized linear models show that species richness, abundance and functional richness per night are significantly related with forest cover, while seasonality had an effect on abundance and functional richness. Neither forest cover nor season had a significant effect on functional evenness. All these findings were consistent across three spatial scales (1, 3 and 5 km radius around sampling sites). The decrease in species, abundance and functional richness of bats with forest loss may have implications for the ecological processes they carry out such as seed dispersal, pollination and insect predation, among others.

Deforestation Thresholds for Phyllostomid Bat Populations in Tropical Landscapes in the Huasteca Region, Mexico

The loss and degradation of forests in tropical regions have modified tree cover, creating deforested landscapes. It has been suggested that there are thresholds in these landscapes beyond which the diversity, distribution, abundance, and fitness of different biological groups can be affected. In this study, the ecological habitat thresholds were detected for eight populations of phyllostomid bats along an environmental gradient of forest loss in the Huasteca region, Mexico. At a local scale, we analyzed canopy loss, and we also detected these thresholds at the landscape level, as a function of forest remnant area at three scales with radii of 1, 3 and 5 km. The data were analyzed using the Threshold Indicator Taxa ANalysis (TITAN) method for detecting indicator species along gradients. The bats exhibited three different types of response to habitat loss: 1) Leptonycteris yerbabuenae, Chiroderma salvini, Sturnira hondurensis, and Artibeus lituratus were more abundant where canopy cover was present at the local site, even though the landscape had been deforested; 2) Sturnira parvidens and Artibeus jamaicensis required tree cover at all spatial scales; and 3) Glossophaga soricina and Desmodus rotundus are species that might be locally abundant in habitats with little canopy, but both species need landscapes that have not been deforested. In conclusion, these populations of phyllostomid bats were sensitive to deforestation in different ways, their response to the habitat loss gradient varying among species and with spatial scale.