Local and Landscape Factors Determining Occurrence of Phyllostomid Bats in Tropical Secondary Forests

Neotropical forests are being increasingly replaced by a mosaic of patches of different successional stages, agricultural fields and pasture lands. Consequently, the identification of factors shaping the performance of taxa in anthropogenic landscapes is gaining importance, especially for taxa playing critical roles in ecosystem functioning. As phyllostomid bats provide important ecological services through seed dispersal, pollination and control of animal populations, in this study we assessed the relationships between phyllostomid occurrence and the variation in local and landscape level habitat attributes caused by disturbance. We mist-netted phyllostomids in 12 sites representing 4 successional stages of a tropical dry forest (initial, early, intermediate and late). We also quantitatively characterized the habitat attributes at the local (vegetation structure complexity) and the landscape level (forest cover, area and diversity of patches). Two focal scales were considered for landscape characterization: 500 and 1000 m. During 142 sampling nights, we captured 606 individuals representing 15 species and 4 broad guilds. Variation in phyllostomid assemblages, ensembles and populations was associated with variation in local and landscape habitat attributes, and this association was scale-dependent. Specifically, we found a marked guild-specific response, where the abundance of nectarivores tended to be negatively associated with the mean area of dry forest patches, while the abundance of frugivores was positively associated with the percentage of riparian forest. These results are explained by the prevalence of chiropterophilic species in the dry forest and of chiropterochorous species in the riparian forest. Our results indicate that different vegetation classes, as well as a multi-spatial scale approach must be considered for evaluating bat response to variation in landscape attributes. Moreover, for the long-term conservation of phyllostomids in anthropogenic landscapes, we must realize that the management of the habitat at the landscape level is as important as the conservation of particular forest fragments

Composition, structure and diversity of phyllostomid bat assemblages in different successional stages of a tropical dry forest

International audienceStudies on successional dynamics in tropical systems have mostly focused on plant communities and mainly have been conducted in tropical humid areas. Here, we document changes in the structure of batassemblages among secondary successional stages of a neotropical dry forest. We specifically focused on the speciose phyllostomid bat family, comprising most of the foraging guilds found among neotropicalbats, including nectarivores and frugivores that play important roles in processes of plant reproduction and forest regeneration. To investigate bat species richness, diversity and abundance during successionnal processes, we mist-netted bat assemblages in 12 sites belonging to 4 different successional stages, namely pastures (0 yrs), early (3–5 yrs), intermediate (8–12 yrs) and late successional stage (>50 yrs). A capture effort of 142 nights using five mist-nets per night yielded 606 phyllostomid bats belonging to 16 species. Late stage was the most speciose sustaining all species found in the study (16 species against 9 for early and intermediate stages and 4 in pastures), and was the only environment where rare species occurred. Species found within any one successional stage were a combination of species found at the previous stage plus additional ones. This additive pattern appeared to be driven by the natural abundance of species, as the abundant species were found across more succesisonal stages than rarer species. Bats were significantly less speciose and less abundant in pastures, regardless of the foraging guild. Bat diversity and abundance did not differ significantly among early, intermediate and late stages. However, nectarivores were more abundant in early compared to late stage, probably as a consequence of differences in patterns of food availability. We conclude that areas of forest, recognized as late stage in our study, are the most important reservoirs of species richness. Secondary vegetation also contains diverse bat assemblages, while pastures only harbour a few abundant and vagile species occasionally crossing this habitat. We suggest that land-use regulations in this region focus on maintaining connectivity of a mosaic of areas of secondary and mature vegetation to insure the conservation of bat diversity as well as their important ecological interactions

Summary statistics of parameters at population, ensemble and assemblage-level.

<p>Parameters at population-level: capture rate (individuals/night) as indicator of species local abundance. Parameters at ensemble-level: rarified number of nectarivorous (S₈N) and frugivorous species (S₈F), capture rate of nectarivores (AbN) and frugivores (AbF). Parameters at assemblage-level: scores of the first (SC₁) and second (SC₂) ordination axis reflecting assemblage's dissimilarities in species composition and structure, rarified number of phyllostomid species (S₈P) and capture rate of phyllostomids (AbP). Mean: mean per site of the parameters at population, ensemble and assemblage-level. SD: standard deviation. Species in bold are those analyzed at the population-level. Species ensemble assignations are shown between parentheses: gleaning insectivores (GI), nectarivores (N), frugivores (F) and sanguivores (S). The number of sites sampled was 12 for all parameters except for three, which are marked with an asterisk. In these three parameters the site P1 was excluded from the analyses due to its low number of sampling nights.</p

The Assembly of Tropical Dry Forest Tree Communities in Anthropogenic Landscapes: The Role of Chemical Defenses

The effect of anthropogenic disturbance on plant community traits and tradeoffs remains poorly explored in tropical forests. In this study, we aimed to identify tradeoffs between defense and other plant functions related to growth processes in order to detect potential aboveground and edaphic environmental conditions modulating traits variation on plant communities, and to find potential assembly rules underlying species coexistence in secondary (SEF) and old-growth forests (OGF). We measured the foliar content of defense phytochemicals and leaf traits related to fundamental functions on 77 species found in SEF and OGF sites in the Jalisco dry forest ecoregion, Mexico, and we explored (1) the trait-trait and trait-habitat associations, (2) the intra and interspecies trait variation, and (3) the traits-environment associations. We found that phytochemical content was associated with high leaf density and leaf fresh mass, resulting in leaves resistant to drought and high radiation, with chemical and physical defenses against herbivore/pathogen attack. The phytochemicals and chlorophyll concentrations were negatively related, matching the predictions of the Protein Competition Model. The phylogenetic signal in functional traits, suggests that abundant clades share the ability to resist the harsh biotic and abiotic conditions and face similar tradeoffs between productive and defensive functions. Environmental filters could modulate the enhanced expression of defensive phytochemicals in SEF, while, in OGFs, we found a stronger filtering effect driving community assembly. This could allow for the coexistence of different defensive strategies in OGFs, where a greater species richness could dilute the prevalence of pathogens/herbivores. Consequently, anthropogenic disturbance could alter TDF ecosystem properties/services and functioning

Relationships between population, ensemble and assemblage-level parameters and the habitat attributes.

<p>Parameter at population-level: species abundance. Parameters at ensemble-level: rarified number of nectarivorous (S₈N) and frugivorous species (S₈F), abundance of nectarivores (AbN) and frugivores (AbF). Parameters at assemblage-level: scores of the first (SC₁) and second ordination axis (SC₂) reflecting assemblage dissimilarities in species composition and structure, rarified number of phyllostomid species (S₈P) and abundance of phyllostomids (AbP). Habitat attributes: vegetation structural complexity (V_struct), mean area of dry (DF_area) and riparian forest patches (RF_area), percentage of riparian forest cover (RF_%) and diversity of patch types (Div). Negative relationships are shown in parentheses.</p

Classified image showing sampling sites and concentric focal scales.

<p>Circles around sampling sites represent the focal scales of 500 and 1000 m radii. Successional stages: pasture (P), early (E), intermediate (I) and late (L). Dry forest is colored light gray, whereas small areas of riparian forest are colored dark gray. The polygon encloses the area of the Chamela-Cuixmala Biosphere Reserve.</p

Number of chiropterophylic and chiropterochoric species per plant family occurring in dry and riparian forest.

<p>A: chiropterophylic species, B: chiropterochoric species. Dry and riparian forests arerepresented by white and black bars respectively. The entire species' checklist of the Chamela-Cuixmala region, as well as detailed information on how it was generated, appear in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035228#pone.0035228.s004" target="_blank">Table S3</a>.</p

Taxonomic and Functional Diversity and Composition of Bats in a Regenerating Neotropical Dry Forest

This study evaluated the response of bat communities, from a taxonomic and functional perspective, to variation in the vegetation and landscape attributes produced by anthropogenic activities. We characterized the following: (1) the community of phyllostomid and mormoopid bats associated with the initial successional stages of a tropical dry forest, (2) the response of these communities to the variation in the attributes of the vegetation and the landscape, and (3) how the seasonality modulates such response. This allowed us to identify potential mechanisms underlying the response of bat communities to human disturbance. Our results showed that the species negatively affected by the anthropoghenic disturbance are those with greater body mass, larger nose-leaves, or a lower wing aspect ratio and relative wing loading, which perform low-speed flights and have high maneuverability and, potentially, a high directionality in their emissions. We also detected a greater sensitivity of bats to changes in the landscape attributes regarding the riparian than the dry forest, and that the effect of anthropic transformation on bats was intensified during the dry season. Then, the continued loss of the original vegetation can lead to a loss of certain groups of bat species in neotropical landscapes, reducing the resilience of the system

Phyllostomid bat occurence in successional stages of neotropical dry forests

Tropical dry forests (TDFs) are highly endangered tropical ecosystems being replaced by a complex mosaic of patches of different successional stages, agricultural fields and pasturelands. In this context, it is urgent to understand how taxa playing critical ecosystem roles respond to habitat modification. Because Phyllostomid bats provide important ecosystem services (e.g. facilitate gene flow among plant populations and promote forest regeneration), in this study we aimed to identify potential patterns on their response to TDF transformation in sites representing four different successional stages (initial, early, intermediate and late) in three Neotropical regions: México, Venezuela and Brazil. We evaluated bat occurrence at the species, ensemble (abundance) and assemblage level (species richness and composition, guild composition). We also evaluated how bat occurrence was modulated by the marked seasonality of TDFs. In general, we found high seasonal and regional specificities in phyllostomid occurrence, driven by specificities at species and guild levels. For example, highest frugivore abundance occurred in the early stage of the moistest TDF, while highest nectarivore abundance occurred in the same stage of the driest TDF. The high regional specificity of phyllostomid responses could arise from: (1) the distinctive environmental conditions of each region, (2) the specific behavior and ecological requirements of the regional bat species, (3) the composition, structure and phenological patterns of plant assemblages in the different stages, and (4) the regional landscape composition and configuration. We conclude that, in tropical seasonal environments, it is imperative to perform long-term studies considering seasonal variations in environmental conditions and plant phenology, as well as the role of landscape attributes. This approach will allow us to identify potential patterns in bat responses to habitat modification, which constitute an invaluable tool for not only bat biodiversity conservation but also for the conservation of the key ecological processes they provide

Species richness estimated with the first-order jackknife estimator, per site and per season.

<p>Study regions: Chamela Cuixmala Biosphere Reserve in Mexico (A), Unidad de Producción Socialista Agropecuaria Piñero in Venezuela (B), and Mata Seca State Park in Brazil (C). Sampling sites representing different successional stages are: pastures (from P1 to P3), early (from E1 to E3), intermediate (from I1 to I3) and late stage (from L1 to L3). Seasons: rainy season (triangles) and dry season (circles). Error bars represent the ±95% confidence intervals.</p