[Show abstract][Hide abstract] ABSTRACT: Landscape complexity influences patterns of animal dispersal, which in turn may affect both gene flow and the spread of pathogens. White-nose syndrome (WNS) is an introduced fungal disease that has spread rapidly throughout eastern North America, causing massive mortality in bat populations. We tested for a relationship between the population genetic structure of the most common host, the little brown myotis (Myotis lucifugus), and the geographic spread of WNS to date by evaluating logistic regression models of WNS risk among hibernating colonies in eastern North America. We hypothesized that risk of WNS to susceptible host colonies should increase with both geographic proximity and genetic similarity, reflecting historical connectivity, to infected colonies. Consistent with this hypothesis, inclusion of genetic distance between infected and susceptible colonies significantly improved models of disease spread, capturing heterogeneity in the spatial expansion of WNS despite low levels of genetic differentiation among eastern populations. Expanding our genetic analysis to the continental range of little brown myotis reveals strongly contrasting patterns of population structure between eastern and western North America. Genetic structure increases markedly moving westward into the northern Great Plains, beyond the current distribution of WNS. In western North America, genetic differentiation of geographically proximate populations often exceeds levels observed across the entire eastern region, suggesting infrequent and/or locally restricted dispersal, and thus relatively limited opportunities for pathogen introduction in western North America. Taken together, our analyses suggest a possibly slower future rate of spread of the WNS pathogen, at least as mediated by little brown myotis. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Undersampling is commonplace in biodiversity surveys of species-rich tropical assemblages in which rare taxa abound, with possible repercussions for our ability to implement surveys and monitoring programmes in a cost-effective way. We investigated the consequences of information loss due to species undersampling (missing subsets of species from the full species pool) in tropical bat surveys for the emerging patterns of species richness (SR) and compositional variation across sites. For 27 bat assemblage data sets from across the tropics, we used correlations between original data sets and subsets with different numbers of species deleted either at random, or according to their rarity in the assemblage, to assess to what extent patterns in SR and composition in data subsets are congruent with those in the initial data set. We then examined to what degree high sample representativeness (r ≥ 0·8) was influenced by biogeographic region, sampling method, sampling effort or structural assemblage characteristics.
Full-text · Article · Jan 2015 · Journal of Animal Ecology
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Disease can play important roles in structuring species communities, driving some species toward extinction, while other species suffer relatively little impact. White-nose syndrome, caused by the fungal pathogen Pseudogymnoascus destructans, has heavily impacted several species of bats, resulting in extirpation of one species from most sites. Intensity of fungal infection on hosts (fungal loads) may enhance transmission, and potentially drive mortality from disease. Differences in host species behavior and habitat use may in turn affect fungal growth, causing variation in mortality among species. We measured transmission of P. destructansby collecting swabs from exposed wing and muzzle tissue of bats and quantified fungal loads using real-time quantitative PCR.
Intense transmission occurred during winter, and by late winter all bat species were infected with prevalence reaching 70%-100% in six species. In contrast, P. destructans loads at the end of winter were more variable among species, and were highly positively correlated with disease impacts. Impacts varied from 7% to 80% declines in the initial year following white-nose syndrome detection, resulting in changes to bat species community composition. Loads were correlated with the roosting temperature of bats, with bats roosting at warmer temperatures having higher P. destructans loads. Differential mortality among species, driven by differences in loads, has resulted in changes to bat species community composition pre- to post- disease arrival. These results also suggest that habitat selection by bats during hibernation influences pathogen growth, which determines mortality. This illustrates how behavioral patterns that may have been beneficial in the absence of disease can be detrimental once the pathogen is present.
[Show abstract][Hide abstract] ABSTRACT: The nature of forest structure plays an important role in the study of foraging behaviors of bats. In this study, we demonstrate a new combined methodology that uses both thermal imaging technology and a ground-based LiDAR system to record and reconstruct Eptesicus fuscus (big brown bats) flight trajectories in three-dimensional (3-D) space. The combination of the two 3-D datasets provided a fine-scale reconstruction of the flight characteristics adjacent to and within the forests. A 3-D forest reconstruction, assembled from nine Echidna Validation Instrument LiDAR scans over the 1 ha site area, provided the essential environmental variables for the study of bat foraging behaviors, such as the canopy height, terrain, location of the obstacles, and canopy openness at a bat roosting and maternity site in Petersham, Massachusetts. Flight trajectories of 24 bats were recorded over the 25 m × 37.5 m region within the LiDAR forest reconstruction area. The trajectories were reconstructed using imaging data from multiple FLIR ThermoVision SC8000 cameras and were co-registered to the 3-D forest reconstruction. Twenty-four of these flight trajectories were categorized into four different behavior groups according to velocity and altitude analysis of the flight trajectories. Initial results showed that although all bats were guided by echolocation and avoided hitting a tree that was in all of their flight paths, different bats chose different flight routes. This study is an initial demonstration of the power of coupling thermal image analysis and LiDAR forest reconstructions. Our goal was to break ground for future ecological studies, where more extensive flight trajectories of bats can be coupled with the canopy reconstructions to better establish responses of bats to different habitat characteristics and clutter, which includes both static (trees) and dynamic (other bats) obstacles.
Full-text · Article · Dec 2013 · Canadian journal of remote sensing
[Show abstract][Hide abstract] ABSTRACT: This study examines mercury exposure in bats across the northeast U.S. from 2005 to 2009. We collected 1,481 fur and 681 blood samples from 8 states and analyzed them for total Hg. A subset (n = 20) are also analyzed for methylmercury (MeHg). Ten species of bats from the northeast U.S. are represented in this study of which two are protected by the Endangered Species Act (ESA 1973) and two other species are pending review. There are four objectives in this paper: (1) to examine correlates to differences in fur-Hg levels among all of the sampling sites, including age, sex, species, and presence of a Hg point source; (2) define the relationship between blood and fur-Hg levels and the factors that influence that relationship including age, sex, species, reproductive status, and energetic condition; (3) determine the relationships between total Hg and MeHg in five common eastern bat species; and (4) assess the distribution of Hg across bat populations in the northeast. We found total blood and fur mercury was eight times higher in bats captured near point sources compared to nonpoint sources. Blood-Hg and fur-Hg were well correlated with females on average accumulating two times more Hg in fur than males. On average fur MeHg accounted for 86 % (range 71-95 %) of the total Hg in bat fur. Considering that females had high Hg concentrations, beyond that of established levels of concern, suggests there could be negative implications for bat populations from high Hg exposure since Hg is readily transferred to pups via breast milk. Bats provide an integral part of the ecosystem and their protection is considered to be of high priority. More research is needed to determine if Hg is a stressor that is negatively impacting bat populations.
[Show abstract][Hide abstract] ABSTRACT: White-nose syndrome (WNS) is an emerging infectious disease devastating hibernating North American bat populations that is caused by the psychrophilic fungus Geomyces destructans. Previous histopathological analysis demonstrated little evidence of inflammatory responses in infected bats, however few studies have compared other aspects of immune function between WNS-affected and unaffected bats. We collected bats from confirmed WNS-affected and unaffected sites during the winter of 2008-2009 and compared estimates of their circulating levels of total leukocytes, total immunoglobulins, cytokines and total antioxidants. Bats from affected and unaffected sites did not differ in their total circulating immunoglobulin levels, but significantly higher leukocyte counts were observed in bats from affected sites and particularly in affected bats with elevated body temperatures (above 20°C). Bats from WNS-affected sites exhibited significantly lower antioxidant activity and levels of interleukin-4 (IL-4), a cytokine that induces T cell differentiation. Within affected sites only, bats exhibiting visible fungal infections had significantly lower antioxidant activity and levels of IL-4 compared to bats without visible fungal infections. Overall, bats hibernating in WNS-affected sites showed immunological changes that may be evident of attempted defense against G. destructans. Observed changes, specifically elevated circulating leukocytes, may also be related to the documented changes in thermoregulatory behaviors of affected bats (i.e. increased frequencies in arousal from torpor). Alterations in immune function may reflect expensive energetic costs associated with these processes and intrinsic qualities of the immunocapability of hibernating bats to clear fungal infections. Additionally, lowered antioxidant activity indicates a possible imbalance in the pro- versus antioxidant system, may reflect oxidative tissue damage, and should be investigated as a contributor to WNS-associated morbidity and mortality.
[Show abstract][Hide abstract] ABSTRACT: 1. Frugivory among bats (Chiroptera) has evolved independently in the New and Old World tropics: within the families Phyllostomidae and Pteropodidae, respectively. Bats from both families rely primarily on olfaction for the location of fruits. However, the influence of bats on the evolution of fruit scent is almost completely unknown. 2. Using the genus Ficus as a model, the aims of this study were to explore the chemical composition of fruit scent in relation to two contrasting seed dispersal syndromes in Panama and Malaysia and to assess the influence of fruit scent on the foraging behaviour of neo- and palaeotropical fruit-eating bats (Artibeus jamaicensis and Cynopterus brachyotis, respectively). Two hypotheses were tested: (i) variation in fruit scent, between bat- and bird-dispersed figs, is independent of phylogeny and (ii) Old and New World fruit bats, which have evolved independently in each hemisphere, share the same olfactory preferences with respect to fruit scent. 3. The fruit scents of bat- and bird-dispersed fig species were sampled in the field, using dynamic headspace adsorption techniques. New and Old World fruit bats were then captured and tested on natural fig fruit scents from both hemispheres. 4. Chemical analyses, using gas chromatography (GC) and GC/mass spectrometry (MS), revealed a broad overlap in scent compounds between bat-dispersed fig species from both hemispheres. Their fruit scents were dominated by monoterpenes, which contrary to phylogenetic predictions, were completely absent from bird-dispersed species from both regions. 5. The fruit scents of bat-dispersed figs were highly attractive to neotropical bats (A. jamaicensis) in behavioural experiments, whereas those of bird-dispersed figs were completely rejected. Neotropical bats (A. jamaicensis) exhibited a significant preference for fig fruit scents dominated by monoterpenes, independent of the geographical origin of the scent. Palaeotropical bats (C. brachyotis), by contrast, rejected monoterpene-rich fruit scents from the Neotropics. 6. In a cluster analysis (which included additional, published data from the literature), the fruit scents of bat-dispersed figs were clumped by subgenus, with the exception of palaeotropical figs of the subgenus Sycomorus. C. brachyotis, from Malaysia, was the only fruit bat species that significantly preferred the fruit scents of Sycomorus figs that contained no monoterpenes.
No preview · Article · Aug 2013 · Functional Ecology
[Show abstract][Hide abstract] ABSTRACT: Acoustic signals are important in maintaining group cohesion, particularly in highly mobile species. For these signals to
facilitate group cohesion, individuals must be able to recognize, and respond to, calls emitted by group members. In this
study, we document the use and recognition of complementary contact calls in Spix’s disc-winged bat (Thyroptera tricolor), a species known to form very stable social groups despite using an extremely ephemeral roosting resource. This bat uses
2 sets of calls: “inquiry,” which are emitted by flying bats that are seeking roosts or group mates, and “response,” which
are produced in reply to an inquiry call by individuals that have already located a roost. Here, we test if bats are capable
of discriminating between the inquiry and response calls of group and nongroup mates using playback experiments. Results show
that flying bats can discriminate between the inquiry and response calls emitted by group and nongroup members and can maintain
contact preferentially with the former. Roosting bats, however, exhibited no preference for group over nongroup members and
thus responded indiscriminately. We argue that differences in how individuals respond to calls from group and nongroup members
may be partly attributed to the costs associated with flight and the potential benefits of recruiting roost mates.
Full-text · Article · Mar 2013 · Behavioral Ecology
[Show abstract][Hide abstract] ABSTRACT: The movements of birds, bats, and other flying species are governed by
complex sensorimotor systems that allow the animals to react to
stationary environmental features as well as to wind disturbances, other
animals in nearby airspace, and a wide variety of unexpected challenges.
The paper and talk will describe research that analyzes the
three-dimensional trajectories of bats flying in a habitat in Texas. The
trajectories are computed with stereoscopic methods using data from
synchronous thermal videos that were recorded with high temporal and
spatial resolution from three viewpoints. Following our previously
reported work, we examine the possibility that bat trajectories in this
habitat are governed by optical flow sensing that interpolates periodic
distance measurements from echolocation. Using an idealized geometry of
bat eyes, we introduce the concept of time-to-transit, and recall some
research that suggests that this quantity is computed by the animals'
visual cortex. Several steering control laws based on time-to-transit
are proposed for an idealized flight model, and it is shown that these
can be used to replicate the observed flight of what we identify as
typical bats. Although the vision-based motion control laws we propose
and the protocols for switching between them are quite simple, some of
the trajectories that have been synthesized are qualitatively bat-like.
Examination of the control protocols that generate these trajectories
suggests that bat motions are governed both by their reactions to a
subset of key feature points as well by their memories of where these
feature points are located.
Full-text · Article · Mar 2013 · Proceedings of the IEEE Conference on Decision and Control
[Show abstract][Hide abstract] ABSTRACT: In Central Amazonia, large mammals create water-filled puddles when consuming soil. These mineral licks are visited by pregnant and lactating frugivorous bats; possibly for two reasons. Frugivorous bats could supplement their mineral-depleted fruit diet by drinking salty water, or they could buffer dietary plant secondary compounds by consuming soil. We analysed bat fruits from Ecuador and showed that they are depleted in elemental concentrations (Na, K, P) compared with similar fruits collected from Costa Rica, where no mineral licks occur (n = 32). Analyses of water from Ecuador revealed that water samples from six mineral licks contained more physiologically relevant elements (Na, K, Mg, Ca) than four samples from river and stream water control sites (Mann–Whitney U-test). In support of the nutrient supplement hypothesis, we observed bats drinking mineral-enriched water at these licks (video observation). Furthermore, blood collected from 68 bats differed in composition with respect to physiologically relevant minerals (Na, K, Mg, Fe) from that of frugivorous bats captured at control sites. To test whether frugivorous bats also consumed clay for detoxification, we checked for soil tracer elements in 31 faecal samples. Soil tracers are insoluble in water and, thus, are not included in a strict fruit diet. Bats from mineral licks showed higher aluminium soil tracer concentrations in their faeces than bat species that never visit licks, suggesting that frugivorous bats take up clay material at mineral licks. Our results provide evidence that frugivorous bats ingest soluble mineral nutrients and insoluble soil by consuming soil-enriched water at mineral licks, thus supporting the hypothesis that frugivorous bats of western Amazonia may derive a dual benefit from drinking water from mineral licks.
Full-text · Article · Jan 2013 · Journal of Tropical Ecology
[Show abstract][Hide abstract] ABSTRACT: Acoustic signals are important in maintaining group cohesion, particularly in highly mobile species. For these signals to facilitate group cohesion, individuals must be able to recognize, and respond to, calls emitted by group members. In this study, we document the use and recognition of complementary contact calls in Spix's disc-winged bat (Thyroptera tricolor), a species known to form very stable social groups despite using an extremely ephemeral roosting resource. This bat uses 2 sets of calls: "inquiry," which are emitted by flying bats that are seeking roosts or group mates, and "response," which are produced in reply to an inquiry call by individuals that have already located a roost. Here, we test if bats are capable of discriminating between the inquiry and response calls of group and nongroup mates using playback experiments. Results show that flying bats can discriminate between the inquiry and response calls emitted by group and nongroup members and can maintain contact preferentially with the former. Roosting bats, however, exhibited no preference for group over nongroup members and thus responded indiscriminately. We argue that differences in how individuals respond to calls from group and nongroup members may be partly attributed to the costs associated with flight and the potential benefits of recruiting roost mates.
[Show abstract][Hide abstract] ABSTRACT: It has long been accepted that most vertebrate animals meet their vitamin D requirements from exposure of skin to UV-B (UV-B) radiation. Many factors affect this endogenous synthesis of vitamin D, including season, latitude, time of day, age, presence of hair, and degree of skin pigmentation. Most bats roost in dark places by day and forage at night, and thus have little or no potential for sunlight exposure. Notwithstanding, some tropical species are diurnal and are known to roost in the canopy of trees where they may be exposed to sunlight for up to 12 h each day. In this study, two species of captive tropical bats (both species are active at night but one, Rousettus aegyptiacus, roosts in caves, tombs, and buildings, whereas the other, Pteropus hypomelanus, roosts in trees) were evaluated for their ability to endogenously synthesize vitamin D. Following timed periods of sunlight exposure, blood plasma was analyzed using a competitive protein binding assay (CPBA) to determine concentrations of 25-hydroxyvitamin D [25(OH)D], the major circulating vitamin D metabolite. The ability to photoconvert provitamin D (7-dehydrocholesterol, 7-DHC) in the sub-tropical winter was determined using sunlight exposed borosilicate samples of 7-DHC in hourly increments. Finally, both species were evaluated in their preference for a roost site by the release of individuals into sunlight or shade in timed trials.
(1) when exposed to natural sunlight, both species exhibited an ability to endogenously synthesize vitamin D, although significant differences were found between the two, (2) photoconversion of 7-DHC to previtamin D3 is possible during the mid-day hours of a sub-tropical winter day and (3) captive, cave roosting R. aegyptiacus will choose shaded roost sites while captive P. hypomelanus will show no preference for either shade or sun.
Full-text · Article · Jan 2013 · Dermato-Endocrinology
[Show abstract][Hide abstract] ABSTRACT: The role of bats or any generalist predator in suppressing prey populations depends on the predator's ability to track and exploit available prey. Using a qPCR fecal DNA assay, we document significant association between numbers of Brazilian free-tailed bats (Tadarida brasiliensis) consuming corn earworm (CEW) moths (Helicoverpa zea) and seasonal fluctuations in CEW populations. This result is consistent with earlier research linking the bats' diet to patterns of migration, abundance, and crop infestation by important insect pests. Here we confirm opportunistic feeding on one of the world's most destructive insects and support model estimates of the bats' ecosystem services. Regression analysis of CEW consumption versus the moth's abundance at four insect trapping sites further indicates that bats track local abundance of CEW within the regional landscape. Estimates of CEW gene copies in the feces of bats are not associated with seasonal or local patterns of CEW abundance, and results of captive feeding experiments indicate that our qPCR assay does not provide a direct measure of numbers or biomass of prey consumed. Our results support growing evidence for the role of generalist predators, and bats specifically, as agents for biological control and speak to the value of conserving indigenous generalist predators.
[Show abstract][Hide abstract] ABSTRACT: Weather radars provide near-continuous recording and extensive spatial coverage, which is a valuable resource for biologists, who wish to observe and study animal movements in the aerosphere over a wide range of temporal and spatial scales. Powerful biological inferences can be garnered from radar data that have been processed primarily with the intention of understanding meteorology. However, when seeking to answer certain quantitative biological questions, e.g., those related to density of animals, assumptions made in processing radar data for meteorological purposes interfere with biological inference. In particular, values of the radar reflectivity factor (Z ) reported by weather radars are not well suited for biological interpretation. The mathematical framework we present here allows researchers to interpret weather radar data originating from biological scatterers (bioscatterers) without relying on assumptions developed specifically for meteorological phenomena. The mathematical principles discussed are used to interpret received echo power as it relates to bioscatterers. We examine the relationships among measurement error and these bioscatter signals using a radar simulator. Our simulation results demonstrate that within 30–90 km from a radar, distances typical for observing aerial vertebrates such as birds and bats, measurement error associated with number densities of animals within the radar sampling volume are low enough to allow reasonable estimates of aerial densities for population monitoring. The framework presented for using radar echoes for quantifying biological populations observed by radar in their aerosphere habitats enhances use of radar remote-sensing for long-term population monitoring as well as a host of other ecological applications, such as studies on phenology, movement, and aerial behaviors.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Disease has caused striking declines in wildlife on several continents and threatens numerous species with extinction. Theory suggests that ecology of transmission dynamics can determine the probability of disease-caused extinction, but few empirical studies have examined factors that influence impacts of disease on populations.
We show that differences sociality of hibernating bats can influence the scaling of disease impact with population size and thus the risk of extinction from a recently emerged fungal pathogen. In socially gregarious species, declines were equally severe in populations spanning four orders of magnitude, whereas in more solitary species, declines were less severe in smaller populations. Changes in sociality in declining populations may reduce the likelihood of extinction. For some species, roost microclimates (temperature and humidity) also affected severity of declines. These results provide an empirical basis for determining which host species are likely to be driven extinct while management action is still possible.