Steven J. Presley

Effects of Habitat Conversion on Temporal Activity Patterns of Phyllostomid Bats in Lowland Amazonian Rain Forest

Abstract Ecological assessments of the effects of anthropogenic change often focus on species richness or species abundances. Nonetheless, changes in behavior (e.g., activity patterns) may provide equally important insights into responses to disturbance that have conservation or management implications. Because many neotropical bats provide critical ecosystem services, their responses may be of particular conservation concern. We evaluated the effects of season and habitat conversion on temporal activity patterns of 8 abundant species of frugivorous bats in lowland tropical rain forest of Iquitos, Perú. Season had little effect on activity patterns of any species of bat. Five species exhibited different activity patterns in primary or secondary forest compared to agricultural habitats. No interspecific differences in activity patterns occurred in primary forest. In agricultural areas, the patterns of activity of Carollia benkeithi and Rhinophylla pumilio were distinct from those of other species. In secondary forest, activity patterns of Artibeus lituratus and R. pumilio were distinct from those of other species. Temporal activity patterns of common frugivores overlapped more than expected by chance, regardless of season or habitat. Neotropical frugivores avoid open areas during twilight to reduce risk of predation. Nonetheless, to meet their considerable minimum daily caloric intake requirements, frugivores forage throughout most of the night. Increased habitat fragmentation may effectively reduce foraging times and subject bats to increased risk from predators during twilight and periods of great lunar illumination, when bats avoid open areas.

COMPOSITION AND STRUCTURE OF BAT ASSEMBLAGES IN PARAGUAY: A SUBTROPICAL–TEMPERATE INTERFACE

Abstract Little is known about geographic variation in the local composition of South American assemblages of mammals or the factors that may produce such variation. This is particularly unfortunate in Paraguay because it occurs at the interface of a number of phytogeographic regions (e.g., Cerrado, Chaco, Interior Atlantic Rainforest, and Pantanal) and is the point at which many temperate species reach their northern limits or at which tropical species reach their southern limits. Based on 2 years of intensive fieldwork, we documented the species and familial composition of bat assemblages at 25 sites throughout the country. We also estimated similarity among sites based on indices sensitive to presence or absence of species (Ochiais index), to rank abundance of species (rank correlation index), or to relative abundance of species (Euclidean index). Geographic distance between sites accounted for little variation in composition based on presence–absence or rank abundances of species but accounted significantly for variation related to both identity and relative frequency of species. Distinct assemblages of species do not correspond to the 7 distinct biomes of the country; rather, strong differences exist between sites east (mesic) and west (xeric) of the Río Paraguay. For the most part, these differences are related to dominance by molossids (e.g., Eumops patagonicus, Molossops temminckii, and Molossus molossus) and vespertilionids (e.g., Lasiurus ega, Myotis albescens, and M. nigricans) in dry regions versus phyllostomids (e.g., Artibeus fimbriatus, A. lituratus, and Sturnira lilium) in mesic regions. As a consequence, classification of sites into 2 broad biogeographic regions based on bat familial composition generally is concordant with that based on plants.

Elements of metacommunity structure of Paraguayan bats: multiple gradients require analysis of multiple ordination axes

Techniques to evaluate elements of metacommunity structure (EMS; coherence, species turnover and range boundary clumping) have been available for several years. Such approaches are capable of determining which idealized pattern of species distribution best describes distributions in a metacommunity. Nonetheless, this approach rarely is employed and such aspects of metacommunity structure remain poorly understood. We expanded an extant method to better investigate metacommunity structure for systems that respond to multiple environmental gradients. We used data obtained from 26 sites throughout Paraguay as a model system to demonstrate application of this methodology. Using presence–absence data for bats, we evaluated coherence, species turnover and boundary clumping to distinguish among six idealized patterns of species distribution. Analyses were conducted for all bats as well as for each of three feeding ensembles (aerial insectivores, frugivores and molossid insectivores). For each group of bats, analyses were conducted separately for primary and secondary axes of ordination as defined by reciprocal averaging. The Paraguayan bat metacommunity evinced Clementsian distributions for primary and secondary ordination axes. Patterns of species distribution for aerial insectivores were dependent on ordination axis, showing Gleasonian distributions when ordinated according to the primary axis and Clementsian distributions when ordinated according to the secondary axis. Distribution patterns for frugivores and molossid insectivores were best described as random. Analysis of metacommunities using multiple ordination axes can provide a more complete picture of environmental variables that mold patterns of species distribution. Moreover, analysis of EMS along defined gradients (e.g., latitude, elevation and depth) or based on alternative ordination techniques may complement insights based on reciprocal averaging because the fundamental questions addressed in analyses are contingent on the ordination technique that is employed.

TAXONOMIC STATUS OF MYOTIS (CHIROPTERA: VESPERTILIONIDAE) IN PARAGUAY

Abstract Qualitative and quantitative variation in morphology was assessed for 6 species of Myotis from South America to determine which taxa occur in Paraguay, characteristics that allow for their discrimination, and the degree of geographic and secondary sexual variation that occurs in Paraguayan forms. Secondary sexual dimorphism and geographic variation were evaluated from univariate and multivariate perspectives. Multivariate morphometric differences in cranial morphology among taxa, independent of size, and mensural characters that best separate species were determined using principal components analysis followed by size-adjusted discriminant function analysis. Five species, M. albescens, M. nigricans, M. riparius, M. ruber, and M. simus, occur in Paraguay and can be distinguished using combinations of cranial and external characteristics. No significant sexual dimorphism or geographic variation was detected in these taxa of Myotis in Paraguay. M. levis has not been recorded for Paraguay as previously reported, but it may occur in the country. M. simus, a species previously considered to be restricted to the Amazon Basin, occurs as far south as Paraguay and northern Argentina. Although M. simus varies significantly in size across its range, highly differentiated cranial and external morphology allows for recognition of this species across its range.

LATITUDINAL GRADIENTS OF BIODIVERSITY

The gradient of increasing species richness with decreasing latitude is one of the most well-established patterns in macroecology. The gradient is pervasive in time and space, and pertains to all major taxa. Many ecological and evolutionary mechanisms have been hypothesized to cause the gradient, but it is unlikely that a single mechanism dominates. Recent research suggests that other components of taxonomic biodiversity (e.g., species evenness and dominance) do not evince a latitudinal gradient. Latitudinal gradients in functional, phenetic, and phylogenetic biodiversity are strong, but are not wholly a product of variation in species richness.

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.

Biodiversity and Disturbance

As patch-generating and patch-modifying phenomena, disturbances have profound effects on the temporal and spatial dynamics of biodiversity, including aspects such as species composition, species richness, and species diversity. Less well documented are the effects of disturbance on phylogenetic or functional dimensions of biodiversity. The temporal dynamics of biodiversity in response to disturbance are captured in studies of ecological succession. If trade-offs exist between species dispersal and density-dependent competitive abilities, dominance-controlled dynamics stimulate ecological succession in which species composition changes over time in a predictable manner, with richness and diversity peaking at intermediate times after the impact of a disturbance, and terminal “climax communities” remaining relatively invariant over time in the absence of additional disturbances. Alternatively, if all species in the regional pool have equivalent dispersal abilities and equivalent density-dependent competitive abilities (i.e., no trade-offs), the temporal dynamics in species composition are more or less random; species richness and diversity increase over time until space becomes limiting, at which time they remain invariant (although species composition is in flux). The spatial dynamics of the effects of disturbance on biodiversity are complex and captured in studies of landscape ecology. To the extent that disturbances create heterogeneous patches of various compositions and configurations, they are expected to enhance landscape-level (γ-component) biodiversity, primarily by increasing between-patch differences in species composition (β-component). The intermediate disturbance hypothesis (IDH) posits that biodiversity should be highest at intermediate time periods after a disturbance, at intermediate frequencies of disturbance, and at intermediate extents of disturbance. Nonetheless, empirical studies suggest that the humped-shape pattern is neither common nor strong. Moreover, theoretical studies suggest that foundational assumptions of the IDH are logically flawed and should be replaced by models in which species have negative frequency-dependent growth rates or by models in which both the frequency and intensity of disturbance can interact to affect species-specific growth rates.

Intraspecific patterns of ectoparasite abundances on Paraguayan bats : effects of host sex and body size

Although levels of parasitism can vary greatly among individual bats of the same species, little is known about the characteristics of hosts that affect such variation. Bats were captured via mist nets from June 1995 to July 1997 from 28 localities throughout Paraguay. Over 17500 ectoparasites were collected from 2909 bats; however, analyses of ectoparasite abundance were restricted to more abundant taxa of host and ectoparasite. We quantified the abundancesof29taxaofectoparasiteon19speciesofbathost,aswellastotalabundanceofectoparasitesregardlessof taxonomicaffiliationfor22speciesofbatfromParaguay.Theeffectsofhostsexandhostbodysizeontheseestimatesof ectoparasiteabundancewereevaluatedseparatelyforeachspeciesofhost.Ectoparasitesdidnotrespondconsistentlyto hostbodysize:ectoparasiteabundanceincreasedwithhostbodysizein12instancesanddecreasedwithhostbodysize in 11 instances. Regardless of the existence or direction of effects of host body size on ectoparasite abundance, female hosts generally harboured more ectoparasites than did male hosts. Differences in host quality associated with the sex of bats, especially those related to behaviour, may be a more important determinant of ectoparasite abundance than are differences in size. Opportunities for host transfer are critical for species persistence of ectoparasites; consequently, ectoparasitepopulationsonhostindividualsthatformsocialgroupsorcoloniesshouldbelarger,lesspronetostochastic extinction, and have greater opportunity for speciation.

Streblid bat fly assemblage structure on Paraguayan Noctilio leporinus (Chiroptera: Noctilionidae) : nestedness and species co-occurrence

Evaluation of proximate mechanisms (e.g. dispersal, immigration, competition, facilitation) that determine patterns of assemblage or community structure is an important step in the development of paradigms in ecology. Host–parasite systems are useful for such studies because host-parasite assemblages are easily defined units of study, each host individual harbours a sample from a community or assemblage, and many host species are common, providing replicate samples. I used ectoparasite assemblages from Noctilio leporinus collected from Paraguay to evaluate effects of host sex and body size on ectoparasite abundance and to determine if these assemblages exhibit a nested pattern of species co-occurrence. A total of 533 ectoparasites representing seven species and four families were collected from 28 hosts. Abundances of Paradyschiria fusca and Noctiliostrebla aitkeni responded positively to host body size. Host sex had no affect on ectoparasite abundances. Streblid bat fly assemblages from Noctilio leporinus were strongly and significantly nested. Abundances of all species of streblid were positively correlated with one another with Pearson product moment correlation coefficients between 0.424 and 0.646. Competition does not appear to affect community structure of streblids from Paraguayan Noctilio leporinus . Independent responses of species of streblid to host characteristics appear to mould assemblage structure in this system.

The seasonal dynamic of ant-flower networks in a semi-arid tropical environment

1. Several studies have recently focused on the structure of ecological networks involving ants and plants with extrafloral nectaries; however, little is known about the effects of temporal variation in resource abundance on the structure of ant–plant networks mediated by floral nectar.