Land-cover and climate change are both expected to alter species distributions and contribute to future biodiversity loss. However, the combined effects of land-cover and climate change on ...assemblages, especially at the landscape scale, remain understudied. Lowland tropical amphibians may be particularly susceptible to changes in land cover and climate warming because many species have narrow thermal safely margins resulting from air and body temperatures that are close to their critical thermal maxima (CTmax). We examined how changing thermal landscapes may alter the area of thermally suitable habitat (TSH) for tropical amphibians. We measured microclimates in 6 land-cover types and CTmax of 16 frog species in lowland northeastern Costa Rica. We used a biophysical model to estimate core body temperatures of frogs exposed to habitat-specific microclimates while accounting for evaporative cooling and behavior. Thermally suitable habitat area was estimated as the portion of the landscape where species CTmax exceeded their habitat-specific maximum body temperatures. We projected changes in TSH area 80 years into the future as a function of land-cover change only, climate change only, and combinations of land-cover and climate-change scenarios representing low and moderate rates of change. Projected decreases in TSH area ranged from 16% under low emissions and reduced forest loss to 30% under moderate emissions and business-as-usual land-cover change. Under a moderate emissions scenario (A1B), climate change alone contributed to 1.7- to 4.5-fold greater losses in TSH area than land-cover change only, suggesting that future decreases in TSH from climate change may outpace structural habitat loss. Forest-restricted species had lower mean CTmax than species that occurred in altered habitats, indicating that thermal tolerances will likely shape assemblages in changing thermal landscapes. In the face of ongoing land-cover and climate change, it will be critical to consider changing thermal landscapes in strategies to conserve ectotherm species. Se espera que el cambio climático y el uso del suelo alteren la distribución de las especies y que contribuyan a la futura pérdida de biodiversidad. Sin embargo, los efectos combinados del cambio climático y del cambio de uso de suelo sobre los ensamblajes, especialmente a escala de paisaje, siguen estando subestudiados. Los anfibios de zonas tropicales bajas pueden ser particularmente susceptibles a los cambios en la cobertura del suelo y al calentamiento climático porque muchas especies tienen márgenes estrechos de seguridad termal, resultantes de la temperatura corporal y la temperatura del aire que están cerca de su temperatura crítica máxima (TCmax). Examinamos cómo los paisajes térmicos cambiantes pueden alterar el área del habitat térmico apto para los anfibios tropicales. Medimos los microclimas en seis tipos de cobertura de suelo y la TCmax de 16 especies de ranas en las zonas bajas del noreste de Costa Rica. Utilizamos un modelo biofísico para estimar las temperaturas nucleares del cuerpo de las ranas expuestas a los microclimas específicos de hábitat mientras tomábamos en cuenta el enfriamiento por evaporación y el comportamiento. El área de habitat térmico apto (HTA) se estimó como la porción de paisaje en el que la TCmax de las especies excedió las temperaturas corporales máximas específicas al hábitat. Proyectamos los cambios en el área de HTA a 80 años en el futuro como consecuencia unicamente del cambio en la cobertura de suelo, unicamente del cambio climático y como consecuencia de escenarios combinados del cambio en la cobertura de suelo y del cambio climático representando tasas bajas y moderadas de cambio. Las disminuciones proyectadas en el área de HTA variaron desde 16 % en condiciones de emisiones bajas y pérdida reducida de bosque a 30 % en condiciones de emisiones moderadas y el cambio usual actual de cobertura de suelo. Bajo un escenario de emisiones moderadas (A1B), el cambio climático por sí solo contribuyó a pérdidas 1.7 y hasta 4.5 veces mayores en el área de HTA que la cobertura de suelo por sí sola, lo que sugiere que las futuras disminuciones en el HTA causadas por el cambio climático podrían superar a la pérdida de hábitat estructural. Las especies restringidas a los bosques tuvieron una media más baja de TCmax que las especies que se encuentran en hábitats alterados, lo que indica que las tolerancias térmicas probablemente moldeen los ensamblajes en los paisajes térmicos cambiantes. Ante el al cambio continuo del uso de suelo y el cambio climático, será crítico considerar los paisajes térmicos cambiantes en las estrategias para conservar a las especies ectotermas.
Human activities often replace native forests with warmer, modified habitats that represent novel thermal environments for biodiversity. Reducing biodiversity loss hinges upon identifying which ...species are most sensitive to the environmental conditions that result from habitat modification. Drawing on case studies and a meta‐analysis, we examined whether observed and modelled thermal traits, including heat tolerances, variation in body temperatures, and evaporative water loss, explained variation in sensitivity of ectotherms to habitat modification. Low heat tolerances of lizards and amphibians and high evaporative water loss of amphibians were associated with increased sensitivity to habitat modification, often explaining more variation than non‐thermal traits. Heat tolerances alone explained 24–66% (mean = 38%) of the variation in species responses, and these trends were largely consistent across geographic locations and spatial scales. As habitat modification alters local microclimates, the thermal biology of species will likely play a key role in the reassembly of terrestrial communities.
Scientific interest in the impact of habitat fragmentation on biodiversity is increasing, but our understanding of fragmentation is clouded by a lack of appreciation for fundamental similarities and ...differences across studies representing a wide range of taxa and landscape types. In an effort to synthesize data describing ecological responses of animals to fragmentation across two classes of independent variables (taxonomic group and landscape), we sampled 148 studies of five major faunal groups from the primary literature and analyzed data on 13 variables extracted from those studies. We focused our analyses on three classes of dependent variables (effects of area and isolation on species richness, z values, and nestedness and species composition). Area ranged over more orders of magnitude than isolation and tended to explain more variation in species richness than isolation. There were few matrix or taxon effects on the patterns we investigated, although we did find that sky islands tended to manifest isolation effects on both species richness and nestedness more frequently than other patch types. Sky islands may offer insight into the future of habitat patches fragmented by contemporary habitat loss, and because they show a stronger effect of isolation than other patch types, we suggest that isolation will play an increasing role in the biology of habitat fragments. We use multiple lines of evidence to suggest that our understanding of the role of isolation on community assembly in fragmented landscapes is inadequate. Finally, our observation that consistent taxonomic differences in community patterns were minimal suggests that conservation actions intended to mitigate the negative effects of extinction may have far-reaching effects across taxonomic groups.
Aim: Connectivity is a key determinant of the distribution and abundance of organisms and is greatly influenced by anthropogenic landscape modification, yet we lack a synthetic perspective on the ...magnitude and extent of matrix effects on connectivity. We synthesize results from published studies to understand the importance of matrix effects on fragmented animal populations. Location: Global. Methods: We conduct a meta-analysis of 283 fragmented populations representing 184 terrestrial animal taxa to determine the strength of matrix composition effects on the occurrence and abundance of animals in fragmented habitat. Results: Studies that use data on matrix composition report greater effects on abundance and occupancy of fragmented populations than studies that define connectivity without regard to the surrounding matrix (i. e. 'binary' studies that describe only characteristics of patch habitat). Main conclusions: Our findings underscore that conservation strategies must consider the importance of matrix habitat, have important implications for metapopulation and metacommunity paradigms, and provide direct large-scale, multi-taxa evidence that matrix habitat is an important driver of ecological dynamics in heterogeneous landscapes.
The extensive clearing and modification of forests by anthropogenic activities is a major driver of biodiversity loss. Declines of common species are especially concerning because of the potentially ...large cascading effects they might have on ecosystems. Regrowth of secondary forests may help reverse population declines by restoring habitats to similar conditions prior to land conversion but the value of these secondary forests to fauna is not well understood. We compared the abundance of a direct-developing terrestrial frog, Craugastor stejnegerianus, in riparian and upland habitats of pasture, secondary forest, and mature forest sites. Mean abundance per transect was lower in upland pasture compared to mature forest. Secondary forest had similar abundance to mature forest regardless of age. We show that conversion of forest habitat to pasture represents a conservation threat to this species. However, riparian buffers help mitigate the negative effect of conversion of forest to pasture, and regrowth of secondary forest is an effective management strategy for restoring the abundance of this common leaf-litter species.
Habitat loss and degradation are primary threats to amphibians and reptiles, but the relative effects of common land uses on assemblages and the mechanisms that underlie faunal responses are poorly ...studied. We reviewed the effects of four prevalent types of habitat alteration (urbanization, agriculture, livestock grazing, and silviculture) on amphibian and reptile species richness and abundance by summarizing reported responses in the literature and by estimating effect sizes across studies for species richness in each land‐use type. We then used a multinomial model to classify species as natural habitat specialists, generalists, and disturbed habitat specialists and examined variation in effect sizes for each land‐use type according to habitat specialization categories. There were mixed conclusions from individual studies, some reporting negative, neutral, or positive effects of land use on species richness and total abundance. A large proportion of studies reported species‐specific effects of individual species abundance. However, in our analysis of effect sizes, we found a general trend of negative effects of land use on species richness. We also demonstrate that habitat associations of common species and species turnover can explain variation in the effect of land use on herpetofauna. Our review highlights the pervasive negative effects of common land uses on amphibians and reptiles, the importance of identifying groups vulnerable to land‐use change (e.g., forest‐associated species) in conservation studies, and the potential influence of disturbance‐associated species on whole assemblage analyses.
Aim: Habitat modification is causing widespread declines in biodiversity and the homogenization of biotas. Amphibians are especially threatened by habitat modification, yet we know little about why ...some species persist or thrive in the face of this threat whereas others decline. Our aim was to identify intrinsic factors that explain variation among amphibians in their sensitivity to habitat modification (SHM), factors that could help target groups of species for conservation. Location: Global. Time period: 1986-2015 Major taxon studied: Amphibians. Methods: We quantified SHM using species abundances in natural and altered habitats as reported in published field surveys. We first examined associations between local SHM and range-wide threatened status, population trends and invasiveness. We then evaluated the importance of intrinsic and extrinsic variables in explaining species SHM using multiple comparative methods. Our analyses included over 200 species that could be ranked with confidence from 47 studies across five continents. Results: Amphibians species varied considerably in local SHM. High SHM was associated with elevated range-wide extinction risk and declining population trends. Species that were tolerant of habitat modification were most likely to be invasive outside their native range. Geographical range size was the most important intrinsic predictor and was negatively associated with SHM. Larval habitat was also an important predictor, but was tightly coupled with phylogenetic position. Main conclusions: Narrowly distributed species whose larvae develop on land or in lotic habitats are most sensitive to habitat modification. However, other unmeasured, phylogenetically constrained traits could underlie the effect of larval habitat. Species range size is frequently correlated with global extinction risk in vertebrates, and our analysis extends this macroecological pattern to the sensitivity of amphibians to local habitat loss, a proximate driver of extinction. These general patterns of SHM should help identify those groups of amphibians most at risk in an era of rapid habitat loss and scarce conservation resources.
Herein we review what is known about the chemical ecology of poison frogs with a focus on dendrobatid poison frogs. While five anuran families are known to have an alkaloid-derived chemical defense, ...the dendrobatids have been studied in greatest detail and provides chemical ecologists with a complex model system for understanding how chemical defenses operate in real time and may have evolved through evolutionary time. We describe the diversity of alkaloid defenses known from frogs, alkaloid sequestration, biosynthesis and modification, and we review what is known concerning arthropod sources for alkaloids. There is variation in nearly every attribute of the system and we try to describe some of the challenges associated with unraveling the complexities of this model system.
Amphibians stand at the forefront of a global biodiversity crisis. More than one-third of amphibian species are globally threatened, and over 120 species have likely suffered global extinction since ...1980. Most alarmingly, many rapid declines and extinctions are occurring in pristine sites lacking obvious adverse effects of human activities. The causes of these "enigmatic" declines remain highly contested. Still, lack of long-term data on amphibian populations severely limits our understanding of the distribution of amphibian declines, and therefore the ultimate causes of these declines. Here, we identify a systematic community-wide decline in populations of terrestrial amphibians at La Selva Biological Station, a protected old-growth lowland rainforest in lower Central America. We use data collected over 35 years to show that population density of all species of terrestrial amphibians has declined by almost equal to75% since 1970, and we show identical trends for all species of common reptiles. The trends we identify are neither consistent with recent emergence of chytridiomycosis nor the climate-linked epidemic hypothesis, two leading putative causes of enigmatic amphibian declines. Instead, our data suggest that declines are due to climate-driven reductions in the quantity of standing leaf litter, a critical microhabitat for amphibians and reptiles in this assemblage. Our results raise further concerns about the global persistence of amphibian populations by identifying widespread declines in species and habitats that are not currently recognized as susceptible to such risks.
Context
Habitat destruction is the leading threat to terrestrial biodiversity, isolating remnant habitat in a matrix of modified vegetation.
Objectives
Our goal was to determine how species richness ...in several broad taxonomic groups from remnant forest was influenced by matrix quality, which we characterized by comparing plant biomass in forest and the surrounding matrix.
Methods
We coupled data on species-area relationships (SARs) in forest remnants from 45 previously published studies with an index of matrix quality calculated using new estimates of plant biomass derived from satellite imagery.
Results
The effect size of SARs was greatest in landscapes with low matrix quality and little forest cover. SARs were generally stronger for volant than for non-volant species. For the terrestrial taxa included in our analysis, matrix quality decreased as the proportion of water, ice, or urbanization in a landscape increased.
Conclusions
We clearly demonstrate that matrix quality plays a major role in determining patterns of species richness in remnant forest. A key implication of our work is that activities that increase matrix quality, such as active and passive habitat restoration, may be important conservation measure for maintaining and restoring biodiversity in modified landscapes.
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