Optimizing conservation in species-specific agricultural landscapes.

Recovery of grassland birds in agricultural landscapes is a global imperative. Agricultural landscapes are complex, and the value of resource patches may vary substantially among species. The spatial extent at which landscape features affect populations (i.e., scale of effect) may also differ among species. There is a need for regional-scale conservation planning that considers landscape-scale and species-specific responses of grassland birds to environmental change. We developed a spatially explicit approach to optimizing grassland conservation in the context of species-specific landscapes and prioritization of species recovery and applied it to a conservation program in Kentucky (USA). We used a hierarchical distance-sampling model with an embedded scale of effect predictor to estimate the relationship between landscape structure and abundance of eastern meadowlarks (Sturnella magna), field sparrows (Spizella pusilla), and northern bobwhites (Colinus virginianus). We used a novel spatially explicit optimization procedure rooted in multi-attribute utility theory to design alternative conservation strategies (e.g., prioritize only northern bobwhite recovery or assign equal weight to each species' recovery). Eastern meadowlarks and field sparrows were more likely to respond to landscape-scale resource patch adjacencies than landscape-scale patch densities. Northern bobwhite responded to both landscape-scale resource patch adjacencies and densities and responded strongly to increased grassland density. Effects of landscape features on local abundance decreased as distance increased and had negligible influence at 0.8 km for eastern meadowlarks (0.7-1.2 km 95% Bayesian credibility intervals [BCI]), 2.5 km for field sparrows (1.5-5.8 km 95% BCI), and 8.4 km for bobwhite (6.4-26 km 95% BCI). Northern bobwhites were predicted to benefit greatly from future grassland conservation regardless of conservation priorities, but eastern meadowlark and field sparrow were not. Our results suggest similar species can respond differently to broad-scale conservation practices because of species-specific, distance-dependent relationships with landscape structure. Our framework is quantitative, conceptually simple, customizable, and predictive and can be used to optimize conservation in heterogeneous ecosystems while considering landscape-scale processes and explicit prioritization of species recovery.

La recuperación de las aves de pastizal en los paisajes agrícolas es una obligación mundial. Los paisajes agrícolas son complejos y el valor de los fragmentos con recursos puede variar sustancialmente entre especies. La magnitud espacial a la que las características del paisaje afectan a las poblaciones (es decir, la escala del efecto) también puede diferir entre especies. Existe la necesidad de una planeación de la conservación a escala regional que considere la escala de paisaje y las respuestas específicas de especie de aves de pastizal al cambio ambiental. Desarrollamos una estrategia espacialmente explícita para optimizar la conservación de pastizales en el contexto de los paisajes de especies específicas y la priorización de la recuperación de especies y la aplicamos a un programa de conservación en Kentucky (E.U.A.). Usamos un modelo jerárquico de muestreo a distancia con una escala integrada del efecto pronosticador para estimar la relación entre la estructura del paisaje y la abundancia de la alondra oriental de pradera (Sturnella magna), el gorrión de campo (Spizella pusilla) y la codorniz norteña (Colinus virginianus). Usamos un novedoso procedimiento de optimización espacialmente explícito basado en la teoría de utilidad multicaracterística para diseñar estrategias de conservación alternativas (p. ej.: priorizar solamente la recuperación de la codorniz norteña o asignar una importancia idéntica a la recuperación de cada especie). La alondra y el gorrión tuvieron una mayor probabilidad de responder a la proximidad de fragmentos con recursos a escala de paisaje que a la densidad de fragmentos a escala de paisaje. La codorniz respondió tanto a la proximidad de fragmentos con recursos a escala de paisaje como a la densidad y también respondió fuertemente al incremento en la densidad del pastizal. Los efectos de las características del paisaje sobre la abundancia local disminuyeron conforme incrementó la distancia, representando una influencia insignificante a los 0.8 km para la alondra (0.7-1.2 km 95% de intervalos de credibilidad bayesiana [ICB]), a los 2.5 km para el gorrión (1.5-5.8 km 95% ICB) y a los 8.4 km para la codorniz (6.4-26 km 95% ICB). Se pronosticó que la codorniz se beneficiaría enormemente con la conservación futura de los pastizales sin importar las prioridades de conservación, pero no fue el caso para la alondra y el gorrión. Nuestros resultados sugieren que especies similares pueden responder de manera diferente a las prácticas de conservación a escalas generalizadas debido a las relaciones específicas de especie y dependientes de la distancia con la estructura del paisaje. Nuestro marco de trabajo es cuantitativo, conceptualmente simple, adaptable y predictivo y puede usarse para optimizar la conservación en los ecosistemas heterogéneos a la vez que considera los procesos a escala de paisaje y la priorización explícita de la recuperación de las especies.

Snake co-occurrence patterns are best explained by habitat and hypothesized effects of interspecific interactions.

Snakes often occur in species-rich assemblages, and sympatry is thought to be facilitated primarily by low diet overlap, not interspecific interactions. We selected, a priori, three species pairs consisting of species that are morphologically and taxonomically similar and may therefore be likely to engage in interspecific, consumptive competition. We then examined a large-scale database of snake detection/nondetection data and used occupancy modelling to determine whether these species occur together more or less frequently than expected by chance while accounting for variation in detection probability among species and incorporating important habitat categories in the models. For some snakes, we obtained evidence that the probabilities that habitat patches are used are influenced by the presence of potentially competing congeneric species. Specifically, timber rattlesnakes (Crotalus horridus) were less likely than expected by chance to use areas that also contained eastern diamond-backed rattlesnakes (Crotalus adamanteus) when the proportion of evergreen forest was relatively high. Otherwise, they occurred together more often than expected by chance. Complex relationships were revealed between habitat use, detection probabilities and occupancy probabilities of North American racers (Coluber constrictor) and coachwhips (Coluber flagellum) that indicated the probability of competitive exclusion increased with increasing area of grassland habitat, although there was some model uncertainty. Cornsnakes (Pantherophis guttatus or Pantherophis slowinskii) and ratsnakes (Pantherophis alleghaniensis, Pantherophis spiloides, or Pantherophis obsoletus) exhibited differences in habitat selection, but we obtained no evidence that patterns of use for this species pair were influenced by current interspecific interactions. Overall, our results are consistent with the hypothesis that competitive interactions influence snake assemblage composition; the strength of these effects was affected by landscape-scale habitat features. Furthermore, we suggest that current interspecific interactions may influence snake occupancy, challenging the paradigm that contemporary patterns of snake co-occurrence are largely a function of diet partitioning that arose over evolutionary time.

Landscape-level influences of terrestrial snake occupancy within the southeastern United States.

Habitat loss and degradation are thought to be the primary drivers of species extirpations, but for many species we have little information regarding specific habitats that influence occupancy. Snakes are of conservation concern throughout North America, but effective management and conservation are hindered by a lack of basic natural history information and the small number of large-scale studies designed to assess general population trends. To address this information gap, we compiled detection/nondetection data for 13 large terrestrial species from 449 traps located across the southeastern United States, and we characterized the land cover surrounding each trap at multiple spatial scales (250-, 500-, and 1000-m buffers). We used occupancy modeling, while accounting for heterogeneity in detection probability, to identify habitat variables that were influential in determining the presence of a particular species. We evaluated 12 competing models for each species, representing various hypotheses pertaining to important habitat features for terrestrial snakes. Overall, considerable interspecific variation existed in important habitat variables and relevant spatial scales. For example, kingsnakes (Lampropeltis getula) were negatively associated with evergreen forests, whereas Louisiana pinesnake (Pituophis ruthveni) occupancy increased with increasing coverage of this forest type. Some species were positively associated with grassland and scrub/shrub (e.g., Slowinski's cornsnake, Elaphe slowinskii) whereas others, (e.g., copperhead, Agkistrodon contortrix, and eastern diamond-backed rattlesnake, Crotalus adamanteus) were positively associated with forested habitats. Although the species that we studied may persist in varied landscapes other than those we identified as important, our data were collected in relatively undeveloped areas. Thus, our findings may be relevant when generating conservation plans or restoration goals. Maintaining or restoring landscapes that are most consistent with the ancestral habitat preferences of terrestrial snake assemblages will require a diverse habitat matrix over large spatial scales.