Elevational Ranges of Montane Birds and Deforestation in the Western Andes of Colombia

Deforestation causes habitat loss, fragmentation, degradation, and can ultimately cause extinction of the remnant species. Tropical montane birds face these threats with the added natural vulnerability of narrower elevational ranges and higher specialization than lowland species. Recent studies assess the impact of present and future global climate change on species’ ranges, but only a few of these evaluate the potentially confounding effect of lowland deforestation on species elevational distributions. In the Western Andes of Colombia, an important biodiversity hotspot, we evaluated the effects of deforestation on the elevational ranges of montane birds along altitudinal transects. Using point counts and mist-nets, we surveyed six altitudinal transects spanning 2200 to 2800m. Three transects were forested from 2200 to 2800m, and three were partially deforested with forest cover only above 2400m. We compared abundance-weighted mean elevation, minimum elevation, and elevational range width. In addition to analysing the effect of deforestation on 134 species, we tested its impact within trophic guilds and habitat preference groups. Abundance-weighted mean and minimum elevations were not significantly different between forested and partially deforested transects. Range width was marginally different: as expected, ranges were larger in forested transects. Species in different trophic guilds and habitat preference categories showed different trends. These results suggest that deforestation may affect species’ elevational ranges, even within the forest that remains. Climate change will likely exacerbate harmful impacts of deforestation on species’ elevational distributions. Future conservation strategies need to account for this by protecting connected forest tracts across a wide range of elevations.     

The geographical range of British birds expands during 15 years of warming

Capsule Abundance monitoring data suggest that the short-term response of breeding birds to recent warming in Great Britain has been range expansion, caused by poleward shifts of leading range margins and no significant shifts of trailing range margins.

Aims To quantify latitudinal and elevational shifts of breeding bird populations in Great Britain and test for differential shifts in range margins during a period of warming (1994–2009).

Methods We modelled the population density of 80 species as a smooth function of latitude, longitude, elevation and year. Reference points on the distribution curve were used to describe latitudinal and elevational shifts.

Results Across species, poleward shifts in the leading range margin were greater than in the range-centre. The trailing range margin was largely static, providing evidence for significant range expansion. The magnitude of latitudinal range shift lagged behind the equivalent shift in temperature, suggesting that species may be accumulating a climatic debt. There was no evidence for consistent elevational shifts.

Conclusion Contrary to the generally expected long-term consequences of climate change of range contraction, we show that the short-term response to recent warming has been range expansion. This suggests the mechanisms of short-term and long-term consequences of climate change may differ.     

Can the effect of species ecological traits on birds' altitudinal changes differ between geographic areas?

The altitudinal distribution of mountain birds has recently changed following different patterns in space and time, probably due to the variability of the ongoing environmental processes. Although several studies have highlighted the effect of climate warming in affecting birds altitudinal responses, in the Alps, land abandonment and the consequential forest regrowth may have played a fundamental role.We applied the response curve shape method to investigate changes in the altitudinal distribution of breeding birds over a ten-year period in two different alpine areas (Central and Western Italian Alps) and we performed a log-linear analysis to depict the differential responses of species grouped according to their breeding habitat preferences.The patterns of change remarkably differed according to species ecological traits and between mountain areas. We did not highlight clear altitudinal changes in the Central Alps for any ecological groups, while in the Western Alps, woodland birds showed an expansion pattern and grassland birds suffered a retraction pattern. Since the two alpine areas did not suffer a significant temperature increase, but experienced different woodland cover dynamics, we believe that forest regrowth played a key role in shaping the different bird altitudinal responses between the two sites.Our findings illustrate the effect of ecological traits in shaping altitudinal changes and the role of local environmental factors in affecting spatial variation. Particularly, we strongly suggest considering woodland cover expansion as a key driver of bird altitudinal changes in alpine areas.     

The role of climate in constraining the elevational range of the Water Pipit Anthus spinoletta in an alpine environment

The study of determinants of species’ ranges along elevational gradients may shed light on the ecological factors that constrain their distribution and fundamental niche. We analysed the influence of the climate, habitat at different spatial scales and topography on Water Pipit Anthus spinoletta density in mountain landscapes across a wide elevational gradient. Variables associated with spring and annual temperature values were the main determinants of Water Pipit density, especially at the lower distributional limit (700–1200 m asl), where the species avoided warmer areas. At high‐elevation sites (1600–2300 m asl), the main constraint to the species’ distribution was habitat structure and composition, with steep rocky areas being avoided. Highest densities were found in open but locally heterogeneous habitat at intermediate to high elevations, and the habitat variables that played a major role at the landscape scale were medium‐tall shrublands and woodlands, but with contrasting effects depending on elevation. These results suggest that different sets of variables may constrain density, and effects may differ at the upper and lower elevational limits, with climate being more important at lower elevations and local habitat more important at higher elevations. Ongoing global warming is likely to cause an upward shift in range boundaries of alpine species, but local habitat features could constrain the upward expansion, resulting in range contractions accompanying range shift.     

Ecological gradient of sexual selection: elevation and song elaboration in finches

Ecological gradients in natural and sexual selection often result in evolutionary diversification of morphological, life history, and behavioral traits. In particular, elevational changes in habitat structure and climate not only covary with intensity of sexual selection in many taxa, but may also influence evolution of mating signals. Here we examined variation in courtship song in relation to elevation of breeding across cardueline finches-a subfamily of birds that occupies the widest elevational range of extant birds and shows extensive variation in life histories and sexual selection along this range. We predicted that decrease in sexual selection intensity with elevation of breeding documented in this clade would result in a corresponding evolutionary reduction in elaboration of courtship songs. We controlled for the effects of phylogeny, morphology, and habitat structure to uncover a predicted elevational decline in courtship song elaboration; species breeding at lower elevations sang more elaborated and louder songs compared to their sister species breeding at higher elevations. In addition, lower elevation species had longer songs with more notes, whereas frequency components of song did not vary with elevation. We suggest that changes in sexual selection account for the observed patterns of song variation and discuss how elevational gradient in sexual selection may facilitate divergence in mating signals potentially reinforcing or promoting speciation.     

Species traits and the response of open‐habitat species to forest edge in landscape mosaics

Human driven changes in land‐use have increased the need to understand how landscape structure affects species distribution. We studied how forest edges affected the distribution of birds in grasslands recently encroached by forest patches. We investigated how species’ biological traits influenced their response to vegetation change near forest edges. We censured birds along 300‐m line transects run into the open habitat perpendicularly to forest edges. We recorded habitat variables and landscape context along each transect and characterized edges and forest patches. We recorded 33 bird species in 153 transects for a total of 654 individuals. We analyzed species response to edges with generalized linear mixed models. Habitat preference was prevalent to explain species response to forest edges. The abundance of open‐habitat birds such as skylark Alauda arvensis decreased significantly in the vicinity of edges. This negative response extended within 150 m from the edge. The effect was disproportionately higher in open‐habitat species with high conservation concern. The abundance of species feeding or/and breeding in both forest and open habitat, such as woodlarks Lullula arborea, sharply increased near edges (positive edge response). Abundance of shrub and non‐shrub dependent species increased with distance to edge. The two species groups did no differ in abundance/distance to edge relationship. Intensity of species response to forest edges varied among transects in relation to transect vegetation characteristics. Edge length or aspect, diet and nest height had no direct effect. We discuss the possible role of variation in resources and nest predation risk to explain observed patterns.     

Large-Scale Range Collapse of Hawaiian Forest Birds under Climate Change and the Need 21st Century Conservation Options

Hawaiian forest birds serve as an ideal group to explore the extent of climate change impacts on at-risk species. Avian malaria constrains many remaining Hawaiian forest bird species to high elevations where temperatures are too cool for malaria’s life cycle and its principal mosquito vector. The impact of climate change on Hawaiian forest birds has been a recent focus of Hawaiian conservation biology, and has centered on the links between climate and avian malaria. To elucidate the differential impacts of projected climate shifts on species with known varying niches, disease resistance and tolerance, we use a comprehensive database of species sightings, regional climate projections and ensemble distribution models to project distribution shifts for all Hawaiian forest bird species. We illustrate that, under a likely scenario of continued disease-driven distribution limitation, all 10 species with highly reliable models (mostly narrow-ranged, single-island endemics) are expected to lose >50% of their range by 2100. Of those, three are expected to lose all range and three others are expected to lose >90% of their range. Projected range loss was smaller for several of the more widespread species; however improved data and models are necessary to refine future projections. Like other at-risk species, Hawaiian forest birds have specific habitat requirements that limit the possibility of range expansion for most species, as projected expansion is frequently in areas where forest habitat is presently not available (such as recent lava flows). Given the large projected range losses for all species, protecting high elevation forest alone is not an adequate long-term strategy for many species under climate change. We describe the types of additional conservation actions practitioners will likely need to consider, while providing results to help with such considerations.     

Warming and provenance limit tree recruitment across and beyond the elevation range of subalpine forest

Climate niche models project that subalpine forest ranges will extend upslope with climate warming. These projections assume that the climate suitable for adult trees will be adequate for forest regeneration, ignoring climate requirements for seedling recruitment, a potential demographic bottleneck. Moreover, local genetic adaptation is expected to facilitate range expansion, with tree populations at the upper forest edge providing the seed best adapted to the alpine. Here, we test these expectations using a novel combination of common gardens, seeded with two widely distributed subalpine conifers, and climate manipulations replicated at three elevations. Infrared heaters raised temperatures in heated plots, but raised temperatures more in the forest than at or above treeline because strong winds at high elevation reduced heating efficiency. Watering increased season‐average soil moisture similarly across sites. Contrary to expectations, warming reduced Engelmann spruce recruitment at and above treeline, as well as in the forest. Warming reduced limber pine first‐year recruitment in the forest, but had no net effect on fourth‐year recruitment at any site. Watering during the snow‐free season alleviated some negative effects of warming, indicating that warming exacerbated water limitations. Contrary to expectations of local adaptation, low‐elevation seeds of both species initially recruited more strongly than high‐elevation seeds across the elevation gradient, although the low‐provenance advantage diminished by the fourth year for Engelmann spruce, likely due to small sample sizes. High‐ and low‐elevation provenances responded similarly to warming across sites for Engelmann spruce, but differently for limber pine. In the context of increasing tree mortality, lower recruitment at all elevations with warming, combined with lower quality, high‐provenance seed being most available for colonizing the alpine, portends range contraction for Engelmann spruce. The lower sensitivity of limber pine to warming indicates a potential for this species to become more important in subalpine forest communities in the coming centuries.     

Current and Potential Future Elevational Distributions of Birds Associated with Pinyon–Juniper Woodlands in the Central Great Basin, U.S.A.

We examined the relationship of breeding birds to elevation across and within four adjacent mountain ranges in the central Great Basin, a cold desert in western North America. Data came from 7 years of point counts at elevations from 1,915 to 3,145 m. We focused on eight passerine species that in this region are associated frequently with Pinus monophylla–Juniperus spp. (pinyon–juniper) woodland. Mean elevation of species' presence differed significantly among mountain ranges for all species except Spizella passerina (Chipping Sparrow); all species except Spizella breweri (Brewer's Sparrow) occurred at the highest mean elevation in the Toquima Range. Observed patterns were consistent with the elevational distribution of pinyon–juniper woodlands that provide nesting and foraging habitat for these species. Across the Great Basin, driven in part by climate change, pinyon–juniper woodland is increasing in density and expanding its distribution at lower elevations. However, breeding habitat for species dependent on mature trees may not be available in expansion woodlands for several decades, and increased tree densities may have negative effects on bird species that are dependent on shrubs within open pinyon–juniper woodlands. Responses of individual species to elevation differed from the response of assemblage-level patterns. Responses to biotic and abiotic variables within guilds of birds are sufficiently diverse, and responses of individual species sufficiently heterogeneous, that one management strategy is unlikely to meet the needs of all species in the group.     

Elevational changes in the avian community of a Mesoamerican cloud forest park

Harboring many range‐restricted and specialized species, high elevation tropical cloud forests are diverse habitats represented in many protected areas. Despite this, many such areas receive little practical protection from deforestation and land conversion. Moreover, montane species may be more sensitive to climate change owing to various factors affecting community assembly across elevational gradients. Few studies have used annual monitoring to assess how biological communities in cloud forests may be shifting in response to habitat or climate change or assessed the efficacy of protected areas in buffering these effects. We analyzed avifaunal community trends in a 10‐yr dataset of constant‐effort bird point‐count data in a cloud forest national park in Honduras, Central America. We found that species richness and diversity increased at higher elevations, but decreased at lower elevations. Abundances of most dietary and forest‐dependency groups exhibited similar trends, and many key cloud forest species shifted upslope and/or increased in abundance. Taken together, our results suggest that the avian community is moving upslope and species composition is changing. Results for species richness and diversity were similar when only nondegraded transects were considered, suggesting the role of climate change as an important driver. At lower elevations, however, many species may be negatively affected by increased habitat degradation, favoring species with low forest dependency. Continued habitat conversion and climate change could push the cloud forest bird community further upslope, potentially resulting in increased competition, mortality, and even extirpation of some species. Increased protection is unlikely to mitigate the effects of climate change.     

Enhanced shrub growth in the Arctic increases habitat connectivity for browsing herbivores

Habitat connectivity is a key factor influencing species range dynamics. Rapid warming in the Arctic is leading to widespread heterogeneous shrub expansion, but impacts of these habitat changes on range dynamics for large herbivores are not well understood. We use the climate–shrub–moose system of northern Alaska as a case study to examine how shrub habitat will respond to predicted future warming, and how these changes may impact habitat connectivity and the distribution of moose (Alces alces). We used a 19 year moose location dataset, a 568 km transect of field shrub sampling, and forecasted warming scenarios with regional downscaling to map current and projected shrub habitat for moose on the North Slope of Alaska. The tall‐shrub habitat for moose exhibited a dendritic spatial configuration correlated with river corridor networks and mean July temperature. Warming scenarios predict that moose habitat will more than double by 2099. Forecasted warming is predicted to increase the spatial cohesion of the habitat network that diminishes effects of fragmentation, which improves overall habitat quality and likely expands the range of moose. These findings demonstrate how climate change may increase habitat connectivity and alter the distributions of shrub herbivores in the Arctic, including creation of novel communities and ecosystems.     

Range dynamics of small mammals along an elevational gradient over an 80‐year interval

One expected response to observed global warming is an upslope shift of species elevational ranges. Here, we document changes in the elevational distributions of the small mammals within the Ruby Mountains in northeastern Nevada over an 80‐year interval. We quantified range shifts by comparing distributional records from recent comprehensive field surveys (2006–2008) to earlier surveys (1927–1929) conducted at identical and nearby locations. Collector field notes from the historical surveys provided detailed trapping records and locality information, and museum specimens enabled confirmation of species' identifications. To ensure that observed shifts in range did not result from sampling bias, we employed a binomial likelihood model (introduced here) using likelihood ratios to calculate confidence intervals around observed range limits. Climate data indicate increases in both precipitation and summer maximum temperature between sampling periods. Increases in winter minimum temperatures were only evident at mid to high elevations. Consistent with predictions of change associated with climate warming, we document upslope range shifts for only two mesic‐adapted species. In contrast, no xeric‐adapted species expanded their ranges upslope. Rather, they showed either static distributions over time or downslope contraction or expansion. We attribute these unexpected findings to widespread land‐use driven habitat change at lower elevations. Failure to account for land‐use induced changes in both baseline assessments and in predicting shifts in species distributions may provide misleading objectives for conservation policies and management practices.     

A weak upward elevational shift in the distributions of breeding birds in the Italian Alps

Aim To test whether bird assemblages are shifting upwards in their elevational distribution in synchrony with current climate warming and/or habitat changes. Location A gradient of elevation in the Italian Alps (Alta Valsessera, Piedmont). Methods We used data from two recent atlas surveys performed on a 1 × 1 km grid at an 11‐year interval (1992–94 and 2003–05). We modelled the elevational gradient of avifaunal composition, using a sample‐based approach, in an effort to detect evidence for an upward elevational shift of bird zonation. Changes in species richness were controlled for. The results from this analysis were compared with those obtained using a species‐based approach. Changes in climate and landscape between the two surveys were assessed using local meteorological data and Corine Land Cover maps, respectively. Results We detected small avifaunal changes between the two surveys: (1) mean elevations increased for the majority of species, but the average change was not significantly different from zero; (2) the species richness increased, but this was mainly due to an increase in sampling effort; and (3) a change in species composition was detected, which was at the limit of significance and corresponded on average to a 29‐m upward elevational shift in the distribution of the avifauna. The shift was the same for open land and forest bird communities. During the same period, the mean temperature increased by c. 1 °C in the area, and a slight trend towards vegetation closure by woody plants was detected. Main conclusions The use of fine‐scale breeding bird atlases in mountainous regions, together with ordination methods, provides a sensitive tool to test and measure elevational shifts in species ranges, but the results have to be interpreted carefully. In our case, the observed elevational shift in the distributions of the avifauna cannot unambiguously be attributed to climate warming. This shift is smaller than expected from the regional increase in temperature, which raises the question of how closely bird distributions match climate change.     

Elevational gradients in bird diversity in the Eastern Himalaya: an evaluation of distribution patterns and their underlying mechanisms

Background

Understanding diversity patterns and the mechanisms underlying those patterns along elevational gradients is critically important for conservation efforts in montane ecosystems, especially those that are biodiversity hotspots. Despite recent advances, consensus on the underlying causes, or even the relative influence of a suite of factors on elevational diversity patterns has remained elusive.

Methods and Principal Findings

We examined patterns of species richness, density and range size distribution of birds, and the suite of biotic and abiotic factors (primary productivity, habitat variables, climatic factors and geometric constraints) that governs diversity along a 4500-m elevational gradient in the Eastern Himalayan region, a biodiversity hotspot within the world''s tallest mountains. We used point count methods for sampling birds and quadrats for estimating vegetation at 22 sites along the elevational gradient. We found that species richness increased to approximately 2000 m, then declined. We found no evidence that geometric constraints influenced this pattern, whereas actual evapotranspiration (a surrogate for primary productivity) and various habitat variables (plant species richness, shrub density and basal area of trees) accounted for most of the variation in bird species richness. We also observed that ranges of most bird species were narrow along the elevation gradient. We find little evidence to support Rapoport''s rule for the birds of Sikkim region of the Himalaya.

Conclusions and Significance

This study in the Eastern Himalaya indicates that species richness of birds is highest at intermediate elevations along one of the most extensive elevational gradients ever examined. Additionally, primary productivity and factors associated with habitat accounted for most of the variation in avian species richness. The diversity peak at intermediate elevations and the narrow elevational ranges of most species suggest important conservation implications: not only should mid-elevation areas be conserved, but the entire gradient requires equal conservation attention.     

Spatial structure and dynamics of breeding bird populations at a distribution margin,southern California

Aim Local‐scale processes at species distribution margins can affect larger‐scale distribution dynamics, but are rarely studied. The objective of this research was to elucidate the nature of distribution limits by studying the comparative structure, dynamics and environmental associations of breeding bird populations at their distribution margin. We hypothesized that climate is principally responsible for setting distribution limits, whereas biotic habitat features are more strongly associated with distribution patterns within the range. Location Southern California, USA. Methods During 2005–2007 we studied the distribution patterns of breeding birds in three study areas, each spanning a low‐elevation (200–1800 m) desert scrub‐to‐chaparral gradient. We used logistic regression with hierarchical partitioning to assess the independent effects of environmental variables (e.g. climate versus habitat) on distributions. We tested for shifts in the relative importance of these environmental variables in determining distribution limits versus within‐range patterns, and we also compared higher‐ and lower‐elevation groups of species. Results Distribution patterns were highly variable among species, but were remarkably static over the three study areas and 3‐year study period. Across species, habitat floristic variables performed relatively well at explaining distribution patterns. For higher‐elevation species (chaparral birds), climate was relatively important in setting their lower distribution limits, and there was a shift to a greater importance of biotic habitat (mainly habitat structural variables) for determining within‐range patterns. Relationships were more mixed for lower‐elevation species (desert scrub birds), but with respect to distribution limits, biotic habitat variables tended to be more important relative to climate than we observed for chaparral birds. Main conclusions Along this warm, arid elevational gradient, higher‐elevation chaparral birds are more limited by climate at their lower margin than are lower‐elevation desert birds at their upper margin, suggesting that climate plays a strong role (relative to other values) in excluding non‐desert birds from desert. However, given the strong differences among species, predictive distribution models will need to be individually tailored, and for most species biotic habitat variables were of greater importance than climate in determining limits. This research highlights the usefulness of studying environmental relationships at distribution margins and the importance of considering biotic relationships in forecasting distribution shifts under changing climates.     

Signals of range expansions and contractions of vascular plants in the high Alps: observations (1994–2004) at the GLORIA* master site Schrankogel,Tyrol, Austria

High mountain ecosystems are defined by low temperatures and are therefore considered to react sensitively to climate warming. Responding to observed changes in plant species richness on high peaks of the European Alps, an extensive setup of 1 m × 1 m permanent plots was established at the alpine‐nival ecotone (between 2900 and 3450 m) on Mount Schrankogel, a GLORIA master site in the central Tyrolean Alps, Austria, in 1994. Recording was repeated in a representative selection of 362 quadrats in 2004. Ten years after the first recording, we observed an average change in vascular plant species richness from 11.4 to 12.7 species per plot, an increase of 11.8% (or of at least 10.6% at a 95% confidence level). The increase in species richness involved 23 species (about 43% of all taxa found at the ecotone), comprising both alpine and nival species and was pronouncedly higher in plots with subnival/nival vegetation than in plots with alpine grassland vegetation. Only three species showed a decrease in plot occupancy: one was an annual species, one was rare, and one a common nival plant that decreased in one part of the area but increased in the uppermost part. Species cover changed in relation to altitudinal preferences of species, showing significant declines of all subnival to nival plants, whereas alpine pioneer species increased in cover. Recent climate warming in the Alps, which has been twice as high as the global average, is considered to be the primary driver of the observed differential changes in species cover. Our results indicate an ongoing range contraction of subnival to nival species at their rear (i.e. lower) edge and a concurrent expansion of alpine pioneer species at their leading edge. Although this was expected from predictive distribution models and different temperature‐related habitat preferences of alpine and nival species, we provide first evidence on – most likely – warming‐induced species declines in the high European Alps. The projected acceleration of climate warming raises concerns that this phenomenon could become the major threat to biodiversity in high mountains.     

Climate and satellite-derived land cover for predicting breeding bird distribution in the Great Lakes Basin

Aim We examined relationships between breeding bird distribution of 10 forest songbirds in the Great Lakes Basin, large‐scale climate and the distribution of land cover types as estimated by advanced very high resolution radiometer (AVHRR) and multi‐spectral scanner (MSS) land cover classifications. Our objective was to examine the ability of regional climate, AVHRR (1 km resolution) land cover and MSS (200 m resolution) land cover to predict the distribution of breeding forest birds at the scale of the Great Lakes Basin and at the resolution of Breeding Bird Atlas data (5–10 km²). Specifically we addressed the following questions. (1) How well do AVHRR or MSS classifications capture the variation in distribution of bird species? (2) Is one land cover classification more useful than the other for predicting distribution? (3) How do models based on climate compare with models based on land cover? (4) Can the combination of both climate and land cover improve the predictive ability of these models. Location Modelling was conducted over the area of the Great Lakes Basin including parts of Ontario, Canada and parts of Illinois, Indiana, Michigan, New York, Ohio, Pennsylvania Wisconsin, and Minnesota, USA. Methods We conducted single variable logistic regression with the forest classes of AVHRR and MSS land cover using evidence of breeding as the response variable. We conducted multiple logistic regression with stepwise selection to select models from five sets of explanatory variables (AVHRR, MSS, climate, AVHRR + climate, MSS + climate). Results Generally, species were related to both AVHRR and MSS land cover types in the direction expected based on the known local habitat use of the species. Neither land cover classification appeared to produce consistently more intuitive results. Good models were generated using each of the explanatory data sets examined here. And at least one but usually all five variable sets produced acceptable or excellent models for each species. Main conclusions Both climate and large scale land cover were effective predictors of the distribution of the 10 forest bird species examined here. Models generated from these data had good classification accuracy of independent validation data. Good models were produced from all explanatory data sets or combinations suggesting that the distribution of climate, AVHRR land cover, and MSS land cover all captured similar variance in the distribution of the birds. It is difficult to separate the effects of climate and vegetation on the species’ distributions at this scale.     

Evidence that climate sets the lower elevation range limit in a high‐elevation endemic salamander

A frequent assumption in ecology is that biotic interactions are more important than abiotic factors in determining lower elevational range limits (i.e., the “warm edge” of a species distribution). However, for species with narrow environmental tolerances, theory suggests the presence of a strong environmental gradient can lead to persistence, even in the presence of competition. The relative importance of biotic and abiotic factors is rarely considered together, although understanding when one exerts a dominant influence on controlling range limits may be crucial to predicting extinction risk under future climate conditions. We sampled multiple transects spanning the elevational range limit of Plethodon shenandoah and site and climate covariates were recorded. A two‐species conditional occupancy model, accommodating heterogeneity in detection probability, was used to relate variation in occupancy with environmental and habitat conditions. Regional climate data were combined with datalogger observations to estimate the cloud base heights and to project future climate change impacts on cloud elevations across the survey area. By simultaneously accounting for species’ interactions and habitat variables, we find that elevation, not competition, is strongly correlated with the lower elevation range boundary, which had been presumed to be restricted mainly as a result of competitive interactions with a congener. Because the lower elevational range limit is sensitive to climate variables, projected climate change across its high‐elevation habitats will directly affect the species’ distribution. Testing assumptions of factors that set species range limits should use models which accommodate detection biases.     

An elevational shift in butterfly species richness and composition accompanying recent climate change

The geographic ranges of many species have shifted polewards and uphill in elevation associated with climate warming, leading to increases in species richness at high latitudes and elevations. However, few studies have addressed community‐level responses to climate change across the entire elevational gradients of mountain ranges, or at warm lower latitudes where ecological diversity is expected to decline. Here, we show uphill shifts in butterfly species richness and composition in the Sierra de Guadarrama (central Spain) between 1967–1973 and 2004–2005. Butterfly communities with comparable species compositions shifted uphill by 293 m (± SE 26), consistent with an upward shift of approximately 225 m in mean annual isotherms. Species richness had a humped relationship with elevation, but declined between surveys, particularly at low elevations. Changes to species richness and composition primarily reflect the loss from lower elevations of species whose regional distributions are restricted to the mountains. The few colonizations by specialist low‐elevation species failed to compensate for the loss of high‐elevation species, because there are few low‐elevation species in the region and the habitat requirements of some of these prevent them from colonizing the mountain range. As a result, we estimated a net decline in species richness in approximately 90% of the region, and increasing community domination by widespread species. The results suggest that climate warming, combined with habitat loss and other drivers of biological change, could lead to significant losses in ecological diversity in mountains and other regions where species encounter their lower latitudinal‐range margins.     

广西大明山鸟类群落组成、区系成分和垂直分布

为了了解鸟类组成和海拔分布状况,利用样线法和固定调查点法于2007~2015年对广西大明山的鸟类进行了研究。在大明山共记录鸟类337种,隶属于17目56科。繁殖鸟类(包括留鸟和夏候鸟)共计234种,占大明山鸟类种数的69.4%,具有明显优势,构成了大明山鸟类区系组成的主体。大明山具有典型的华南区向华中区过渡的鸟类区系特征,67.1%的繁殖鸟类属于东洋型的种类。随着海拔的增加,东洋型的种类逐渐减少。依据海拔梯度和植被的不同,可以将大明山鸟类分成6个类群,鸟类总种数和繁殖鸟类种数均以海拔500~900 m的范围内最多,海拔200~500 m范围内鸟类次之。由于大明山地处热带南缘,本研究将为今后监测气候变暖对鸟类的影响提供依据。