Two aspects of patch geometry-area and isolation-currently dominate the field of metapopulation dynamics. Under this area-and-isolation paradigm, models commonly assume that the probability of local extinction decreases as patch area increases and that the probability of colonization increases as patch connectivity increases. Environmental variables other than patch area and isolation are assumed to have relatively little effect on metapopulation dynamics. Our work on a metapopulation of the butterfly Speyeria nokomis apacheana highlights the need for a broader view of metapopulation dynamics. In this system, neither occupancy nor turnover patterns were best modeled as functions of patch area or isolation. Instead, other measures of habitat quality explained the most variance in occupancy and turnover. Our study also revealed temporal variation in the factors associated with occupancy and turnover. This variation can cause the results of analyses to vary with the temporal scale of analysis. For example, factors associated with turnover in this system differed among single-year and multiple-year analyses. We emphasize that factors other than patch geometry may drive extinction and colonization processes in metapopulations, especially in systems that experience substantial natural and anthropogenic environmental variability.Evaluación del Papel de la Calidad, Área y Aislamiento de Parches en la Predicción de la Dinámica Metapoblacional Resumen: Dos aspectos de la geometría de parches -área y aislamiento-dominan actualmente el campo de la dinámica metapoblacional. Bajo este paradigma de "área y aislamiento", los modelos comúnmente suponen que la probabilidad de una extinción local disminuye si el área del parche aumenta y la probabilidad de colonización aumenta si la conectividad del parche aumenta. Se asume que otras variables ambientales diferentes al área y al aislamiento del parche tienen relativamente poco efecto en la dinámica metapoblacional. Nuestro trabajo en una metapoblación de la mariposa Speyeria nokomis apacheana resalta la necesidad de una visión más amplia de las dinámicas metapoblacionales. En este sistema, no se modelaron bien ni la ocupación ni los patrones de rendimiento como funciones del área o aislamiento del parche. Por lo contrario, otras medidas de calidad del hábitat explicaron la mayor parte de la variación en cuanto a ocupación y rendimiento. Nuestro estudio también reveló una variación temporal en los factores asociados con la ocupación y el rendimiento. Esta variación puede hacer que los resultados de los análisis varíen con la escala temporal del análisis. Por ejemplo, los factores asociados con el rendimiento en este sistema discreparon en los análisis entre años individuales y entre años múltiples. Señalamos que factores diferentes a la geometría del parche pueden conducir a procesos de extinción y colonización en metapoblaciones, especialmente en sistemas que experimentan una variabilidad ambiental natural y antropogénica substancial. §

Contemporary climate change is expected to affect the distributions of most species, but the nature, tempo, and mechanics of contemporary range shifts are still largely speculative. Here, we use fine-scale distributional records developed over the past Century, combined with spatially comprehensive microclimatic data, to demonstrate a dramatic shift in the range of a climate-sensitive mammal and to infer the increasingly important role of climate in local extinctions of this species across a 38.2 million-ha area. Changes in the distribution of the American pika (Ochotona princeps) throughout the Great Basin ecoregion were characterized using records from 1898-2008, revealing a nearly five-fold increase in the rate of local extinction and an 11-fold increase in the rate of upslope range retraction during the last ten years, compared with during the 20th Century. Four of ten local pika extinctions have occurred since 1999, and across this ecoregion the low-elevation range boundary for this species is now moving upslope at an average rate of about 145 m per decade. The rapid, ecoregional range shift of this small, talus-dwelling species stands in remarkable contrast with the dynamics and determinants of endangerment previously observed for most terrestrial species, and to earlier extinction determinants for O. princeps in this region. Further investigation of widely distributed species will clarify rates at which biotic response to environmental change is occurring, and how factors driving that change are evolving in different portions of the earth.

Biotic responses to climate change will vary among taxa and across latitudes, elevational gradients, and degrees of insularity. However, due to factors such as phenotypic plasticity, ecotypic variation, and evolved tolerance to thermal stress, it remains poorly understood whether losses should be greatest in populations experiencing the greatest climatic change or living in places where the prevailing climate is closest to the edge of the species' bioclimatic envelope (e.g., at the hottest, driest sites). Research on American pikas (Ochotona princeps) in montane areas of the Great Basin during 1994-1999 suggested that 20th-century population extirpations were predicted by a combination of biogeographic, anthropogenic, and especially climatic factors. Surveys during 2005-2007 documented additional extirpations and within-site shifts of pika distributions at remaining sites. To evaluate the evidence in support of alternative hypotheses involving effects of thermal stress on pikas, we placed temperature sensors at 156 locations within pika habitats in the vicinity of 25 sites with historical records of pikas in the Basin. We related these time series of sensor data to data on ambient temperature from weather stations within the Historical Climate Network. We then used these highly correlated relationships, combined with long-term data from the same weather stations, to hindcast temperatures within pika habitats from 1945 through 2006. To explain patterns of loss, we posited three alternative classes of direct thermal stress: (1) acute cold stress (number of days below a threshold temperature); (2) acute heat stress (number of days above a threshold temperature); and (3) chronic heat stress (average summer temperature). Climate change was defined as change in our thermal metrics between two 31-yr periods: 1945-1975 and 1976-2006. We found that patterns of persistence were well predicted by metrics of climate. Our best models suggest some effects of climate change; however, recent and long-term metrics of chronic heat stress and acute cold stress, neither previously recognized as sources of stress for pikas, were some of the best predictors of pika persistence. Results illustrate that extremely rapid distributional shifts can be explained by climatic influences and have implications for conservation topics such as reintroductions and early-warning indicators.

Although climate acts as a fundamental constraint on the distribution of organisms, understanding how this relationship between climate and distribution varies over a species' range is critical for addressing the potential impacts of accelerated climate change on biodiversity. Bioclimatic niche models provide compelling evidence that many species will experience range shifts under scenarios of global change, yet these broad, macroecological perspectives lack specificity at local scales, where unique combinations of environment, biota, and history conspire against generalizations. We explored how these idiosyncrasies of place affect the climate-distribution relationship of the American pika (Ochotona princeps) by replicating intensive field surveys across bioclimatic gradients in eight U.S. national parks. At macroecological scales, the importance of climate as a constraint on pika distribution appears unequivocal; forecasts suggest that the species' range will contract sharply in coming decades. However, the species persists outside of its modeled bioclimatic envelope in many locations, fueling uncertainty and debate over its conservation status. Using a Bayesian hierarchical approach, we modeled variation in local patterns of pika distribution along topographic position, vegetation cover, elevation, temperature, and precipitation gradients in each park landscape. We also accounted for annual turnover in site occupancy probabilities. Topographic position and vegetation cover influenced occurrence in all parks. After accounting for these factors, pika occurrence varied widely among parks along bioclimatic gradients. Precipitation by itself was not a particularly influential predictor. However, measures of heat stress appeared most influential in the driest parks, suggesting an interaction between the strength of climate effects and the position of parks along precipitation gradients. The combination of high elevation, cold temperatures, and high precipitation lowered occurrence probabilities in some parks, suggesting an upper elevational limit for pikas in some environments. Our results demonstrate that the idiosyncrasies of place influence both the nature and strength of the climate-distribution relationship for the American pika. Fine-grained, but geographically extensive, studies replicated across multiple landscapes offer insights important to assessing the impacts of climate change that otherwise may be masked at macroecological scales. The hierarchical approach to modeling provides a coherent conceptual and technical framework for gaining these insights.

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