James I. Watling

Extracts of the invasive shrub Lonicera maackii increase mortality and alter behavior of amphibian larvae

Water-soluble phytochemicals produced by invasive plants may represent novel elements of invaded ecosystems that can precipitate a variety of direct and indirect effects on native organisms. Phenolic compounds in particular are a common plant defense, and these compounds may have disproportionate impacts on amphibians compared to other taxa. We coupled an exploration of invasive plant extract effects on larvae of four amphibian species (the salamander Ambystoma maculatum, the toad Anaxyrus americanus, and the frogs Hyla sp. and Lithobates blairi) with behavioral observations designed to determine whether behavior can ameliorate the negative effects of exposure to invasive plant extracts. Larvae were reared in extracts of the widespread invasive Amur honeysuckle (Lonicera maackii), mixed native leaf litter, and a water control. Anaxyrus americanus tadpoles reared in L. maackii extracts were more likely to die than tadpoles reared in native extracts, but differences in mortality following rearing in native and exotic extracts were not significant for the other three species. Anaxyrus americanus and L. blairi tadpoles made more trips to the surface in L. maackii extracts than in native extracts, consistent with the hypothesis that exotic extracts may interfere with respiratory physiology and suggesting that L. blairi can behaviorally ameliorate the negative effects of L. maackii extracts. Our study highlights both a direct and indirect pathway by which invasive plant extracts may alter the ecological dynamics of native fauna.

Measuring edge contrast using biotic criteria helps define edge effects on the density of an invasive plant

Habitat edges can alter population dynamics, influence community structure, determine the success of conservation efforts, and facilitate the spread of invasive species. Despite recognition that edges influence the nature and strength of ecological interactions, edges are generally characterized using abiotic measures that likely capture habitat quality for only the focal taxa, and ignore the potential for biotic interactions to explain edge effects. Here we describe the association between edges and the density of an invasive shrub, Lonicera maackii, and infer the functional role of edges by using multiple criteria to weight edge contrast. We define edge contrast using both an abiotic criterion in which contrast is weighted by differences in light availability, and a biotic criterion in which edge contrast is weighted by the association between edges and the abundance of the American Robin (Turdus migratorius), an important avian seed disperser. Biotically defining edge contrast significantly improved model fit in all cases, demonstrating that the large-scale distribution of an invasive shrub is best predicted using both abiotic and biotic edge characterization. More generally, our work suggests that weighting edge contrast using key biological interactions in addition to abiotic criteria may be a promising way to understand the multiple pathways by which edges influence the distribution and abundance of organisms.

Validating Predictions from Climate Envelope Models

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.

Invasive plant alters ability to predict disease vector distribution

Risk models for vector-borne diseases rely on accurate quantification of the relationship between vector abundance and habitat, but this relationship can be obscured if habitats are modified by invasive species in ways that alter vector behavior but are undetectable in remotely sensed data. At a forest in eastern Missouri we assessed whether the presence of an invasive shrub, Amur honeysuckle, Lonicera maackii, affects oviposition by treehole mosquitoes, Aedes triseriatus, a primary vector of La Crosse virus in the United States. Oviposition significantly decreased with increasing density of L. maackii. Moreover, our results indicate that L. maackii may hinder the efficacy of models that use remotely sensed data to predict vector abundance: there was a strong relationship between landscape composition around plots and oviposition, but only in plots not invaded by L. maackii. Overlooking potentially important but cryptic effects of invasive plants on habitat selection by vectors may undermine accurate forecasting of disease risk.

Climate downscaling effects on predictive ecological models: a case study for threatened and endangered vertebrates in the southeastern United States

High-resolution (downscaled) projections of future climate conditions are critical inputs to a wide variety of ecological and socioeconomic models and are created using numerous different approaches. Here, we conduct a sensitivity analysis of spatial predictions from climate envelope models for threatened and endangered vertebrates in the southeastern United States to determine whether two different downscaling approaches (with and without the use of a regional climate model) affect climate envelope model predictions when all other sources of variation are held constant. We found that prediction maps differed spatially between downscaling approaches and that the variation attributable to downscaling technique was comparable to variation between maps generated using different general circulation models (GCMs). Precipitation variables tended to show greater discrepancies between downscaling techniques than temperature variables, and for one GCM, there was evidence that more poorly resolved precipitation variables contributed relatively more to model uncertainty than more well-resolved variables. Our work suggests that ecological modelers requiring high-resolution climate projections should carefully consider the type of downscaling applied to the climate projections prior to their use in predictive ecological modeling. The uncertainty associated with alternative downscaling methods may rival that of other, more widely appreciated sources of variation, such as the general circulation model or emissions scenario with which future climate projections are created.

Rodent Granivores Generate Context-specific Seed Removal in Invaded and Uninvaded Habitats

Abstract Invasive plants threaten biodiversity and impact natural ecosystems through both well-studied direct effects and lesser known indirect effects. We examined one indirect effect: whether the presence of an invasive exotic shrub, Lonicera maackii, changes seed predation of native shrub species by providing dense cover that might harbor shared seed predators (i.e., apparent competition). Our study quantified removal of seeds of exotic L. maackii and native plant species by granivores in invaded and uninvaded plots during winter and spring trials. We found that the presence of L. maackii did not change removal of native seeds in either season and that rodent granivores contributed significantly to seed removal compared to arthropods. Removal of L. maackii seeds by rodent seed predators was significantly greater than the native species studied in the spring (Cornus drummondii), suggesting that rodents may have negative effects on L. maackii in some ecological contexts by consuming seeds. Our findings h...

Reproductive Phenology of Three Lizard Species in Costa Rica, with Comments on Seasonal Reproduction of Neotropical Lizards

Abstract We quantified reproductive phenology for three lizard species collected in northeastern Costa Rica over a 14-month sampling period from November 1973 to December 1974. Two species, a gecko (Lepidoblepharis xanthostigma) and a skink (Sphenomorphus cherriei), reproduced continuously at this site, whereas an anole (Norops limifrons) showed a slight decline in reproduction during the dry season. The decrease in reproduction of N. limifrons may reflect a response to moisture stress during the driest part of the year. When seasonal patterns of reproduction among 32 populations of Neotropical lizards with small clutch sizes were analyzed with the effect of phylogenetic relatedness removed, we found that seasonality of reproduction was strongly related to mean annual rainfall but not to number of dry season months.

Desiccation resistance explains amphibian distributions in a fragmented tropical forest landscape

AbstractContextAlthough amphibian distributions are associated with environmental moisture at global and local scales, less is known about how desiccation tolerance influences landscape distributions of amphibians. ObjectivesWe 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.MethodsWe 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.ResultsRates of evaporative water loss were negatively associated with an index of dispersal limitation, but unrelated to species’ area requirements.ConclusionsBy 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.

Threatened and endangered subspecies with vulnerable ecological traits also have high susceptibility to sea level rise and habitat fragmentation.

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.

Assessing effects of variation in global climate data sets on spatial predictions from climate envelope models

Abstract Climate change poses new challenges for natural resource managers. Predictive modeling of species–environment relationships using climate envelope models can enhance our understanding of climate change effects on biodiversity, assist in assessment of invasion risk by exotic organisms, and inform life-history understanding of individual species. While increasing interest has focused on the role of uncertainty in future conditions on model predictions, models also may be sensitive to the initial conditions on which they are trained. Although climate envelope models are usually trained using data on contemporary climate, we lack systematic comparisons of model performance and predictions across alternative climate data sets available for model training. Here, we seek to fill that gap by comparing variability in predictions between two contemporary climate data sets to variability in spatial predictions among three alternative projections of future climate. Overall, correlations between monthly tempe...