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The outcome of competitive interactions is likely to be influenced by both competitive dominance (i.e. niche-based dynamics) and ecological drift (i.e. neutral dynamics governed by demographic stochasticity). However, spatial models of competition rarely consider the joint operation of these two processes. We develop a model based on the original competition-colonization trade-off model that incorporates niche and neutral processes and several realistic facets of ecological dynamics: it allows local competition (i.e. competition within a patch) to occur within communities of a finite size, it allows competitors to vary in the degree of competitive asymmetry, and it includes the role of local migration (i.e. propagule pressure). The model highlights the role of community size, i.e. the number of competitors in the local community, in mediating the relative importance of stochastic and deterministic forces. In metacommunities where local communities are small, ecological drift is substantial enough that strong competitors become effectively neutral, creating abrupt changes in the outcome of competition not predicted by the standard competition-colonization trade-off. Importantly, the model illustrates that, even when other aspects of species interactions (e.g. migration ability, competitive ability) are unchanged, local community size can alter the dynamics of metacommunity persistence. Our work demonstrates that activities which reduce the size of local communities, such as habitat destruction and degradation, effectively compound the extinction debt.

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 use of oceans has dramatically increased in the 21st century. Sea turtles are vulnerable to anthropogenic stressors in the marine environment because of lengthy migrations between foraging and breeding sites, often along coastal migration corridors. Little is known about how movement and threat interact specifically for male sea turtles. To better understand male sea turtle movement and the threats they encounter, we satellite-tagged 40 adult male sea turtles of four different species. We calculated movement patterns using state-space modeling (SSM), and quantified threats in seven unique categories; shipping, fishing, light pollution, oil rigs, proximity to coast, marine protected area (MPA) status, and location within or outside of the U.S. Exclusive Economic Zone (EEZ). We found significantly higher threat severity in northern and southern latitudes for green turtles (Chelonia mydas) and Kemp’s ridleys (Lepidochelys kempii) in our study area. Those threats were pervasive, with only 35.9% of SSM points encountering no high threat exposure, of which 47% belong to just two individuals. Kemp’s ridleys were most exposed to high threats among tested species. Lastly, turtles within MPA boundaries face significantly lower threat exposure, indicating MPAs could be a useful conservation tool.

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.

Climate envelope models are a potentially important conservation tool, but their ability to accurately forecast species' distributional shifts using independent survey data has not been fully evaluated. We created climate envelope models for 12 species of North American breeding birds previously shown to have experienced poleward range shifts. For each species, we evaluated three different approaches to climate envelope modeling that differed in the way they treated climate-induced range expansion and contraction, using random forests and maximum entropy modeling algorithms. All models were calibrated using occurrence data from 1967-1971 (t1 ) and evaluated using occurrence data from 1998-2002 (t2). Model sensitivity (the ability to correctly classify species presences) was greater using the maximum entropy algorithm than the random forest algorithm. Although sensitivity did not differ significantly among approaches, for many species, sensitivity was maximized using a hybrid approach that assumed range expansion, but not contraction, in t2. Species for which the hybrid approach resulted in the greatest improvement in sensitivity have been reported from more land cover types than species for which there was little difference in sensitivity between hybrid and dynamic approaches, suggesting that habitat generalists may be buffered somewhat against climate-induced range contractions. Specificity (the ability to correctly classify species absences) was maximized using the random forest algorithm and was lowest using the hybrid approach. Overall, our results suggest cautious optimism for the use of climate envelope models to forecast range shifts, but also underscore the importance of considering non-climate drivers of species range limits. The use of alternative climate envelope models that make different assumptions about range expansion and contraction is a new and potentially useful way to help inform our understanding of climate change effects on species.

CONTEXT: Although amphibian distributions are associated with environmental moisture at global and local scales, less is known about how desiccation tolerance influences landscape distributions of amphibians. OBJECTIVES: We evaluated two hypotheses linking amphibian distributions in a fragmented tropical forest landscape to desiccation risk. The patch quality hypothesis predicts that desiccation-prone species are absent on small forest patches, which are generally warmer and drier than large patches. Alternatively, the matrix effects hypothesis suggests that desiccation-prone species are absent on isolated forest patches surrounded by open savanna because they will be unable to traverse the matrix in which patches occur. METHODS: We quantified interspecific variation in desiccation proneness using field-based desiccation trials, and tested for associations between desiccation proneness and distributions of amphibians in fragmented forest in northeastern Bolivia. RESULTS: Rates of evaporative water loss were negatively associated with an index of dispersal limitation, but unrelated to species’ area requirements. CONCLUSIONS: By demonstrating that desiccation-prone species do not occur on isolated forest patches, we provide clear support for the matrix effects hypothesis. We suggest that desiccation proneness is a key trait that may determine amphibian responses to a range of global change drivers, including habitat loss and fragmentation, invasive species, and climate change.

The presence of multiple interacting threats to biodiversity and the increasing rate of species extinction make it critical to prioritize management efforts on species and communities that maximize conservation success. We implemented a multi-step approach that coupled vulnerability assessments evaluating threats to Florida taxa such as climate change, sea-level rise, and habitat fragmentation with in-depth literature surveys of taxon-specific ecological traits. The vulnerability, adaptive capacity, and ecological traits of 12 threatened and endangered subspecies were compared to non-listed subspecies of the same parent species. Overall, the threatened and endangered subspecies showed high vulnerability and low adaptive capacity, in particular to sea level rise and habitat fragmentation. They also exhibited larger home ranges and greater dispersal limitation compared to non-endangered subspecies, which may inhibit their ability to track changing climate in fragmented landscapes. There was evidence for lower reproductive capacity in some of the threatened or endangered taxa, but not for most. Taxa located in the Florida Keys or in other low coastal areas were most vulnerable to sea level rise, and also showed low levels of adaptive capacity, indicating they may have a lower probability of conservation success. Our analysis of at-risk subspecies and closely related non-endangered subspecies demonstrates that ecological traits help to explain observed differences in vulnerability and adaptive capacity. This study points to the importance of assessing the relative contributions of multiple threats and evaluating conservation value at the species (or subspecies) level when resources are limited and several factors affect conservation success.

Protected areas (PAs) are the primary strategy for slowing terrestrial biodiversity loss. Although expansion of PA coverage is prioritized under the Convention on Biological Diversity, it remains unknown whether PAs mitigate declines across the tetrapod tree of life and to what extent land cover and climate change modify PA effectiveness 1 , 2 . Here we analysed rates of change in abundance of 2,239 terrestrial vertebrate populations across the globe. On average, vertebrate populations declined five times more slowly within PAs (−0.4% per year) than at similar sites lacking protection (−1.8% per year). The mitigating effects of PAs varied both within and across vertebrate classes, with amphibians and birds experiencing the greatest benefits. The benefits of PAs were lower for amphibians in areas with converted land cover and lower for reptiles in areas with rapid climate warming. By contrast, the mitigating impacts of PAs were consistently augmented by effective national governance. This study provides evidence for the effectiveness of PAs as a strategy for slowing tetrapod declines. However, optimizing the growing PA network requires targeted protection of sensitive clades and mitigation of threats beyond PA boundaries. Provided the conditions of targeted protection, adequate governance and well-managed landscapes are met, PAs can serve a critical role in safeguarding tetrapod biodiversity. An analysis of 2,239 terrestrial vertebrate populations shows that they decline more slowly in protected areas than outside protected areas, but the benefits vary across vertebrate classes and depend on the regional context of the protected area.

ContextHabitat destruction is the leading threat to terrestrial biodiversity, isolating remnant habitat in a matrix of modified vegetation.ObjectivesOur 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.MethodsWe 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.ResultsThe 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.ConclusionsWe 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.