Laura M. Cisneros

Multiple dimensions of bat biodiversity along an extensive tropical elevational gradient

Research concerning spatial dynamics of biodiversity generally has been limited to considerations of the taxonomic dimension, which is insensitive to interspecific variation in ecological or evolutionary characteristics that play important roles in species assembly and provide linkages to ecosystem services. Consequently, the assumption that the taxonomic dimension is a good surrogate for other dimensions remains unconfirmed. We assessed variation in taxonomic (species richness) as well as phylogenetic and functional (Raos quadratic entropy, a measurement of dispersion) dimensions of bat biodiversity along an elevational gradient in the Manu Biosphere Reserve of Peru. Phylogenetic dispersion was based on relatedness of species derived from a mammalian supertree. Functional dispersion was estimated separately for each of six functional components that reflect particular niche axes (e.g. diet, foraging strategy, body size) and for all functional components combined. Species richness declined nonlinearly with elevation, whereas phylogenetic dispersion and functional dispersion based on all functional components were not significantly associated with elevation (orthogonal polynomial regression). Moreover, considerable heterogeneity in the form of elevational relationships existed among functional components. After accounting for variation in species richness, dispersion of phylogenetic, diet and foraging strategy attributes were significantly greater than expected at high elevations, whereas dispersion of body size was significantly less than expected at high elevations. Species richness was a poor surrogate for phylogenetic or functional dispersion. Functional dispersion based on multiple components obscured patterns detected by particular components and hindered identification of mechanistic explanations for elevational variation in biodiversity. Variation in phylogenetic dispersion effectively captured the composite variation represented by all functional components, suggesting a phylogenetic signal in functional attributes. Mechanisms that give rise to variation in richness do not fully account for variation in phylogenetic or functional characteristics of assemblages. Greater than expected phylogenetic, diet and foraging strategy dispersion at high elevations were associated with the loss of phylogenetically or functionally redundant species, suggesting that increasing interspecific competition with decreasing productivity resulted in competitive exclusion. In contrast, low dispersion of size attributes at high elevations suggests the importance of abiotic filtering that favours small-sized species that can more easily enter torpor.

Creation of forest edges has a global impact on forest vertebrates

Forest edges influence more than half of the world’s forests and contribute to worldwide declines in biodiversity and ecosystem functions. However, predicting these declines is challenging in heterogeneous fragmented landscapes. Here we assembled a global dataset on species responses to fragmentation and developed a statistical approach for quantifying edge impacts in heterogeneous landscapes to quantify edge-determined changes in abundance of 1,673 vertebrate species. We show that the abundances of 85% of species are affected, either positively or negatively, by forest edges. Species that live in the centre of the forest (forest core), that were more likely to be listed as threatened by the International Union for Conservation of Nature (IUCN), reached peak abundances only at sites farther than 200–400 m from sharp high-contrast forest edges. Smaller-bodied amphibians, larger reptiles and medium-sized non-volant mammals experienced a larger reduction in suitable habitat than other forest-core species. Our results highlight the pervasive ability of forest edges to restructure ecological communities on a global scale.

Season‐specific and guild‐specific effects of anthropogenic landscape modification on metacommunity structure of tropical bats

Fragmentation per se due to human land conversion is a landscape-scale phenomenon. Accordingly, assessment of distributional patterns across a suite of potentially connected communities (i.e. metacommunity structure) is an appropriate approach for understanding the effects of landscape modification and complements the plethora of fragmentation studies that have focused on local community structure. To date, metacommunity structure within human-modified landscapes has been assessed with regard to nestedness along species richness gradients. This is problematic because there is little support that species richness gradients are associated with the factors moulding species distributions. More importantly, many alternative patterns are possible, and different patterns may manifest during different seasons and for different guilds because of variation in resource availability and resource requirements of taxa. We determined the best-fit metacommunity structure of a phyllostomid bat assemblage, frugivore ensemble, and gleaning animalivore ensemble within a human-modified landscape in the Caribbean lowlands of Costa Rica during the dry and wet seasons to elucidate important structuring mechanisms. Furthermore, we identified the landscape characteristics associated with the latent gradient underlying metacommunity structure. We discriminated among multiple metacommunity structures by assessing coherence, range turnover, and boundary clumping of an ordinated site-by-species matrix. We identified the landscape characteristics associated with the latent gradient underlying metacommunity structure via hierarchical partitioning. Metacommunity structure was never nested nor structured along a richness gradient. The phyllostomid assemblage and frugivore ensemble exhibited Gleasonian structure (range turnover along a common gradient) during the dry season and Clementsian structure (range turnover and shared boundaries along a common gradient) during the wet season. Distance between forest patches and forest edge density structured the phyllostomid metacommunity during the dry and wet seasons, respectively. Proportion of pasture and forest patch density structured the frugivore metacommunity during the dry season. Gleaning animalivores exhibited chequerboard structure (mutually exclusive species pairs) during the dry season and random structure during the wet season. Metacommunity structure was likely mediated by differential resource use or interspecific relationships. Furthermore, the interaction between landscape characteristics and seasonal variation in resources resulted in season-specific and guild-specific distributional patterns.

BIOFRAG - a new database for analyzing BIOdiversity responses to forest FRAGmentation

Habitat fragmentation studies have produced complex results that are challenging to synthesize. Inconsistencies among studies may result from variation in the choice of landscape metrics and response variables, which is often compounded by a lack of key statistical or methodological information. Collating primary datasets on biodiversity responses to fragmentation in a consistent and flexible database permits simple data retrieval for subsequent analyses. We present a relational database that links such field data to taxonomic nomenclature, spatial and temporal plot attributes, and environmental characteristics. Field assessments include measurements of the response(s) (e.g., presence, abundance, ground cover) of one or more species linked to plots in fragments within a partially forested landscape. The database currently holds 9830 unique species recorded in plots of 58 unique landscapes in six of eight realms: mammals 315, birds 1286, herptiles 460, insects 4521, spiders 204, other arthropods 85, gastropods 70, annelids 8, platyhelminthes 4, Onychophora 2, vascular plants 2112, nonvascular plants and lichens 320, and fungi 449. Three landscapes were sampled as long-term time series (>10 years). Seven hundred and eleven species are found in two or more landscapes. Consolidating the substantial amount of primary data available on biodiversity responses to fragmentation in the context of land-use change and natural disturbances is an essential part of understanding the effects of increasing anthropogenic pressures on land. The consistent format of this database facilitates testing of generalizations concerning biologic responses to fragmentation across diverse systems and taxa. It also allows the re-examination of existing datasets with alternative landscape metrics and robust statistical methods, for example, helping to address pseudo-replication problems. The database can thus help researchers in producing broad syntheses of the effects of land use. The database is dynamic and inclusive, and contributions from individual and large-scale data-collection efforts are welcome.

Reproductive phenologies of phyllostomid bats in Costa Rica

Abstract Reproductive phenologies of populations are strongly molded by environmental variation because natural selection favors individuals that time energetically demanding portions of their life cycle to correspond with periods of high resource availability. To evaluate how seasonal variation in abiotic characteristics and resources affects reproductive strategies, comparison among reproductive phenologies of species that use different resources and across geographic locations is crucial. To facilitate comparisons, it is essential to employ a rigorous and consistent classification scheme. Yet, few studies on the reproductive phenologies of bats, important seed dispersal and pollination agents in the tropics, have employed a clear or consistent classification scheme. We employed concise criteria to classify reproductive phenologies of frugivorous (Artibeus jamaicensis, A. watsoni, Carollia castanea, C. perspicillata, and C. sowelli) and nectarivorous (Glossophaga soricina) bat species, as well as 3 feeding ensembles of phyllostomids in northeastern Costa Rica. All 6 species exhibited bimodal phenologies (2 peaks). Each of the 3 ensembles exhibited different phenologies (i.e., frugivores: bimodal; nectarivores: polymodal [3 peaks]; and gleaning animalivores: unimodal [1 peak]). Bat species that consume plant material evinced pregnancy peaks in the late dry season and middle wet season, whereas gleaning animalivores exhibited a single peak in the middle to late dry season. Examination of geographic and temporal variation in phenologies revealed that strategies of frugivorous and nectarivorous species were geographically and temporally invariant, whereas strategies of gleaning animalivores differed among geographic locations. Resumen Los patrones reproductivos de las poblaciones se ven afectados por la variabilidad en el ambiente. La selección natural favorece a los individuos que sincronizan las fases de su ciclo de vida que son energéticamente costosas con los periodos de alta disponibilidad de recursos. Para evaluar como la variación estacional en factores abióticos y recursos afecta las estrategias reproductivas, es vital realizar comparaciones entre los patrones reproductivos de especies que usan diferentes recursos y diferentes ubicaciones geográficas. Para facilitar comparaciones, es esencial emplear un esquema de clasificación riguroso y constante. Sin embargo, muy pocos estudios sobre fenologías reproductivas de murciélagos, los cuales son agentes importantes de polinización y dispersión de semillas en los bosques tropicales, han empleado esquemas de clasificación claros o consistentes. En el presente estudio, empleamos criterios concisos para clasificar las fenologías reproductivas de 5 especies de murciélagos frugívoros (Artibeus jamaicensis, A. watsoni, Carollia castanea, C. perspicillata, y C. sowelli), un murciélago nectarívoro (Glossophaga soricina), y 3 ensamblajes de phyllostomidos en el noreste de Costa Rica. Las 6 especies exhibieron patrones bimodales (2 picos). Cada uno de los ensamblajes mostro diferentes patrones reproductivos (i.e., frugívoros: bimodal; nectarívoros: polimodal [3 picos]; y insectívoros de follaje: unimodal [1 pico]). Las especies de murciélagos que se alimentan de material vegetal, mostraron picos de gestación al final de la estación seca y a mediados de la estación lluviosa, mientras que los insectívoros de follaje muestran solamente un pico de gestación a mediados de la estación seca. Los patrones reproductivos de las especies de murciélagos frugívoros y nectarívoros no se ven afectados por la variación geográfica y temporal, mientras que las estrategias usadas por los murciélagos insectívoros de follaje muestran diferencias entre distintas ubicaciones geográficas.