Environmental filtering increases in intensity at both ends of climatic gradients,though driven by different factors,across woody vegetation types of the southwest USA

Species distributions are theorized to be more intensively constrained by abiotic factors in severe than in benign environments. A similar concept can be applied to assemblages of species: environmental filtering is expected to increase in intensity in colder and drier environments. To assess the filtering effects of climate on vegetation at a regional scale, climate niche values were estimated for 338 woody species across 93 vegetation types from arid sub‐tropical to alpine ecosystems of the southwest USA. The standardized range and spacing of climatic niche values in each vegetation type – used as estimates of the intensity of climatic and micro‐environmental filtering, respectively – were correlated with the mean niche values of those vegetation types – used as surrogates for climatic gradients – in order to assess how filtering of vegetation composition varies along broad climatic gradients. The range of climatic niche values was narrower than expected in most vegetation types, indicating significant climatic filtering, with frost having the strongest average effect. Niche spacing differed little from null expectations. Variation in the intensity of climatic filtering along gradients of the same climate variable was primarily asymmetrical, and provided support for the hypothesis that abiotic filtering is most intense in cold and growing season dry environments. However, filtering patterns of at least one climatic factor along gradients of other climatic factors ran counter to the trend of increasing filter intensity in cold or dry environments. In other words, climatic factors exhibited interactive effects on vegetation filtering, often in antagonistic ways. The majority of these interactions were compatible with interspecific niche relationships that correspond with anatomical and physiological tradeoffs among drought, frost and heat tolerances. Filtering patterns and interspecific tradeoffs are likely to vary across taxa and biomes, and application of the methods presented here could help to explain such variation.     

Do climate envelope models transfer? A manipulative test using dung beetle introductions

Climate envelope models (CEMs) are widely used to forecast future shifts in species ranges under climate change, but these models are rarely validated against independent data, and their fundamental assumption that climate limits species distributions is rarely tested. Here, we use the data on the introduction of five South African dung beetle species to Australia to test whether CEMs developed in the native range can predict distribution in the introduced range, where the confounding effects of dispersal limitation, resource limitation and the impact of natural enemies have been removed, leaving climate as the dominant constraint. For two of the five species, models developed in the native range predict distribution in the introduced range about as well as models developed in the introduced range where we know climate limits distribution. For the remaining three species, models developed in the native range perform poorly, implying that non-climatic factors limit the native distribution of these species and need to be accounted for in species distribution models. Quantifying relevant non-climatic factors and their likely interactions with climatic variables for forecasting range shifts under climate change remains a challenging task.     

The abiotic and biotic factors limiting establishment of predatory fishes at their expanding northern range boundaries in Ontario,Canada

There is a poor understanding of the importance of biotic interactions in determining species distributions with climate change. Theory from invasion biology suggests that the success of species introductions outside of their historical ranges may be either positively (biotic acceptance) or negatively (biotic resistance) related to native biodiversity. Using data on fish community composition from two survey periods separated by approximately 28 years during which climate was warming, we examined the factors influencing the establishment of three predatory centrarchids: Smallmouth Bass (Micropterus dolomieu), Largemouth Bass (M. salmoides), and Rock Bass (Ambloplites rupestris) in lakes at their expanding northern range boundaries in Ontario. Variance partitioning demonstrated that, at a regional scale, abiotic factors play a stronger role in determining the establishment of these species than biotic factors. Pairing lakes within watersheds where each species had established with lakes sharing similar abiotic conditions where the species had not established revealed both positive and negative relationships between the establishment of centrarchids and the historical presence of other predatory species. The establishment of these species near their northern range boundaries is primarily determined by abiotic factors at a regional scale; however, biotic factors become important at the lake‐to‐lake scale. Studies of exotic species invasions have previously highlighted how spatial scale mediates the importance of abiotic vs. biotic factors on species establishment. Our study demonstrates how concepts from invasion biology can inform our understanding of the factors controlling species distributions with changing climate.     

Differential response to abiotic stress controls species distributions at biogeographic transition zones

Understanding range limits is critical to predicting species responses to climate change. Subtropical environments, where many species overlap at their range margins, are cooler, more light‐limited and variable than tropical environments. It is thus likely that species respond variably to these multi‐stressor regimes and that factors other than mean climatic conditions drive biodiversity patterns. Here, we tested these hypotheses for scleractinian corals at their high‐latitude range limits in eastern Australia and investigated the role of mean climatic conditions and of parameters linked to abiotic stress in explaining the distribution and abundance of different groups of species. We found that environmental drivers varied among taxa and were predominantly linked to abiotic stress. The distribution and abundance of tropical species and gradients in species richness (alpha diversity) and turnover (beta diversity) were best explained by light limitation, whereas minimum temperatures and temperature fluctuations best explained gradients in subtropical species, species nestedness and functional diversity. Variation in community structure (considering species composition and abundance) was most closely linked to the combined thermal and light regime. Our study demonstrates the role of abiotic stress in controlling the distribution of species towards their high‐latitude range limits and suggests that, at biogeographic transition zones, robust predictions of the impacts of climate change require approaches that account for various aspects of physiological stress and for species abundances and characteristics. These findings support the hypothesis that abiotic stress controls high‐latitude range limits and caution that projections solely based on mean temperature could underestimate species’ vulnerabilities to climate change.     

Non-climatic constraints on upper elevational plant range expansion under climate change

We are limited in our ability to predict climate-change-induced range shifts by our inadequate understanding of how non-climatic factors contribute to determining range limits along putatively climatic gradients. Here, we present a unique combination of observations and experiments demonstrating that seed predation and soil properties strongly limit regeneration beyond the upper elevational range limit of sugar maple, a tree species of major economic importance. Most strikingly, regeneration beyond the range limit occurred almost exclusively when seeds were experimentally protected from predators. Regeneration from seed was depressed on soil from beyond the range edge when this soil was transplanted to sites within the range, with indirect evidence suggesting that fungal pathogens play a role. Non-climatic factors are clearly in need of careful attention when attempting to predict the biotic consequences of climate change. At minimum, we can expect non-climatic factors to create substantial time lags between the creation of more favourable climatic conditions and range expansion.     

Annual temperature variation influences the vulnerability of montane bird communities to land‐use change

Understanding how and why species respond to land‐use change is one of the central challenges in conservation biology, yet the causes of variation in the responses of species to land‐use change remain unclear. We tested whether adaptation to different abiotic environments influenced the vulnerability of bird communities to agricultural expansion in the Himalayan mountain range, which exhibits a strong east–west gradient in annual temperature variation. We did so by surveying bird communities in forest and agriculture at opposite ends of that gradient. We contrasted metrics of species richness, diversity, community composition and forest dependency across land‐use types and regions, and tested whether species’ thermal sensitivity influenced their response to the replacement of forest with agriculture. Agricultural land in the relatively aseasonal east harboured significantly fewer bird species than did forests, a pattern that is starkly reversed in the highly seasonal west. For species common to both regions, eastern populations used forest ~35% more than did western populations. While western species were less constrained by temperature than eastern species, western species with narrow thermal tolerances were also more forest dependent. Selection across a stark environmental gradient on a common species pool appears to have altered the vulnerability of Himalayan birds to forest loss, with communities in the relatively aseasonal east much more sensitive to forest conversion than those in the west. Adaptation to local environmental conditions appears to mediate species’ responses to land use change, with thermal specialists more vulnerable to forest loss than species with greater thermal tolerances. Species’ responses to global change may differ predictably along abiotic gradients even within a single region or biodiversity hotspot, and such variation must be addressed in conservation planning.     

Tree demography suggests multiple directions and drivers for species range shifts in mountains of Northeastern United States

Climate change is expected to lead to upslope shifts in tree species distributions, but the evidence is mixed partly due to land‐use effects and individualistic species responses to climate. We examined how individual tree species demography varies along elevational climatic gradients across four states in the northeastern United States to determine whether species elevational distributions and their potential upslope (or downslope) shifts were controlled by climate, land‐use legacies (past logging), or soils. We characterized tree demography, microclimate, land‐use legacies, and soils at 83 sites stratified by elevation (~500 to ~1200 m above sea level) across 12 mountains containing the transition from northern hardwood to spruce‐fir forests. We modeled elevational distributions of tree species saplings and adults using logistic regression to test whether sapling distributions suggest ongoing species range expansion upslope (or contraction downslope) relative to adults, and we used linear mixed models to determine the extent to which climate, land use, and soil variables explain these distributions. Tree demography varied with elevation by species, suggesting a potential upslope shift only for American beech, downslope shifts for red spruce (more so in cool regions) and sugar maple, and no change with elevation for balsam fir. While soils had relatively minor effects, climate was the dominant predictor for most species and more so for saplings than adults of red spruce, sugar maple, yellow birch, cordate birch, and striped maple. On the other hand, logging legacies were positively associated with American beech, sugar maple, and yellow birch, and negatively with red spruce and balsam fir – generally more so for adults than saplings. All species exhibited individualistic rather than synchronous demographic responses to climate and land use, and the return of red spruce to lower elevations where past logging originally benefited northern hardwood species indicates that land use may mask species range shifts caused by changing climate.     

The shape of abundance distributions across temperature gradients in reef fishes

Improving predictions of ecological responses to climate change requires understanding how local abundance relates to temperature gradients, yet many factors influence local abundance in wild populations. We evaluated the shape of thermal‐abundance distributions using 98 422 abundance estimates of 702 reef fish species worldwide. We found that curved ceilings in local abundance related to sea temperatures for most species, where local abundance declined from realised thermal ‘optima’ towards warmer and cooler environments. Although generally supporting the abundant‐centre hypothesis, many species also displayed asymmetrical thermal‐abundance distributions. For many tropical species, abundances did not decline at warm distribution edges due to an unavailability of warmer environments at the equator. Habitat transitions from coral to macroalgal dominance in subtropical zones also influenced abundance distribution shapes. By quantifying the factors constraining species’ abundance, we provide an important empirical basis for improving predictions of community re‐structuring in a warmer world.     

Intraspecific trait variation across elevation predicts a widespread tree species' climate niche and range limits

Global change is widely altering environmental conditions which makes accurately predicting species range limits across natural landscapes critical for conservation and management decisions. If climate pressures along elevation gradients influence the distribution of phenotypic and genetic variation of plant functional traits, then such trait variation may be informative of the selective mechanisms and adaptations that help define climatic niche limits. Using extensive field surveys along 16 elevation transects and a large common garden experiment, we tested whether functional trait variation could predict the climatic niche of a widespread tree species (Populus angustifolia) with a double quantile regression approach. We show that intraspecific variation in plant size, growth, and leaf morphology corresponds with the species' total climate range and certain climatic limits related to temperature and moisture extremes. Moreover, we find evidence of genetic clines and phenotypic plasticity at environmental boundaries, which we use to create geographic predictions of trait variation and maximum values due to climatic constraints across the western US. Overall, our findings show the utility of double quantile regressions for connecting species distributions and climate gradients through trait‐based mechanisms. We highlight how new approaches like ours that incorporate genetic variation in functional traits and their response to climate gradients will lead to a better understanding of plant distributions as well as identifying populations anticipated to be maladapted to future environments.     

The range implications of lizard traits in changing environments

Aim Most predictions of species ranges are based on correlating current species localities to environmental conditions. These correlative models do not explicitly include a species' biology. In contrast, some mechanistic models link traits to energetics and population dynamics to predict species distributions. These models enable one to ask whether considering a species' biology is important for predicting its range. I implement mechanistic models to investigate how a species' morphology, physiology and life history influence its range. Location North America. Methods I compare the mechanistic model predictions with those of correlative models for eight species of North American lizards in both current environments and following a uniform 3 °C temperature warming. I then examine the implications of superimposing habitat and elevation requirements on constraints associated with environmental tolerances. Results In the mechanistic model, species with a narrower thermal range for activity are both predicted and observed to have more restricted distributions. Incorporating constraints on habitat and elevation further restricts species distributions beyond areas that are thermally suitable. While correlative models generally outperform mechanistic models at predicting current distributions, the performance of mechanistic models improves when incorporating additional factors. In response to a 3 °C temperature warming, the northward range shifts predicted by the mechanistic model vary between species according to trait differences and are of a greater extent than those predicted by correlative models. Main conclusions These findings highlight the importance of species traits for understanding the dynamics of species ranges in changing environments. The analysis demonstrates that mechanistic models may provide an important complement to correlative models for predicting range dynamics, which may underpredict climate‐induced range shifts.     

Mechanistic forecasts of species responses to climate change: The promise of biophysical ecology

A core challenge in global change biology is to predict how species will respond to future environmental change and to manage these responses. To make such predictions and management actions robust to novel futures, we need to accurately characterize how organisms experience their environments and the biological mechanisms by which they respond. All organisms are thermodynamically connected to their environments through the exchange of heat and water at fine spatial and temporal scales and this exchange can be captured with biophysical models. Although mechanistic models based on biophysical ecology have a long history of development and application, their use in global change biology remains limited despite their enormous promise and increasingly accessible software. We contend that greater understanding and training in the theory and methods of biophysical ecology is vital to expand their application. Our review shows how biophysical models can be implemented to understand and predict climate change impacts on species' behavior, phenology, survival, distribution, and abundance. It also illustrates the types of outputs that can be generated, and the data inputs required for different implementations. Examples range from simple calculations of body temperature at a particular site and time, to more complex analyses of species' distribution limits based on projected energy and water balances, accounting for behavior and phenology. We outline challenges that currently limit the widespread application of biophysical models relating to data availability, training, and the lack of common software ecosystems. We also discuss progress and future developments that could allow these models to be applied to many species across large spatial extents and timeframes. Finally, we highlight how biophysical models are uniquely suited to solve global change biology problems that involve predicting and interpreting responses to environmental variability and extremes, multiple or shifting constraints, and novel abiotic or biotic environments.     

Temperature tracking by North Sea benthic invertebrates in response to climate change

Climate change is a major threat to biodiversity and distributions shifts are one of the most significant threats to global warming, but the extent to which these shifts keep pace with a changing climate is yet uncertain. Understanding the factors governing range shifts is crucial for conservation management to anticipate patterns of biodiversity distribution under future anthropogenic climate change. Soft‐sediment invertebrates are a key faunal group because of their role in marine biogeochemistry and as a food source for commercial fish species. However, little information exists on their response to climate change. Here, we evaluate changes in the distribution of 65 North Sea benthic invertebrate species between 1986 and 2000 by examining their geographic, bathymetric and thermal niche shifts and test whether species are tracking their thermal niche as defined by minimum, mean or maximum sea bottom (SBT) and surface (SST) temperatures. Temperatures increased in the whole North Sea with many benthic invertebrates showing north‐westerly range shifts (leading/trailing edges as well as distribution centroids) and deepening. Nevertheless, distribution shifts for most species (3.8–7.3 km yr^?1 interquantile range) lagged behind shifts in both SBT and SST (mean 8.1 km yr^?1), resulting in many species experiencing increasing temperatures. The velocity of climate change (VoCC) of mean SST accurately predicted both the direction and magnitude of distribution centroid shifts, while maximum SST did the same for contraction of the trailing edge. The VoCC of SBT was not a good predictor of range shifts. No good predictor of expansions of the leading edge was found. Our results show that invertebrates need to shift at different rates and directions to track the climate velocities of different temperature measures, and are therefore lagging behind most temperature measures. If these species cannot withstand a change in thermal habitat, this could ultimately lead to a drop in benthic biodiversity.     

Wildlife and climate change: assessing the sensitivity of selected species to simulated doubling of atmospheric CO2

We explored, using computer simulations, the sensitivity of four mammal species (elk, Cervus canadensis ; white-tailed deer, Odocoileus virginianus ; Columbian ground squirrel, Spermophilus columbianus ; and chipmunk, Tamias striatus ) within the continental USA to the effect of anticipated levels of global climate change brought about by a doubling of atmospheric CO₂. Sensitivity to the direct effects of climate change were evaluated using a climate-space approach to delineate the range of thermal conditions tolerable by each species. Sensitivity to indirect effects were evaluated by quantifying the association of each species to the current vegetation distribution within the continental USA and using this association to assess whether wildlife species distributions might shift in response to vegetation shifts under climate change. Results indicate that altered thermal conditions alone should have little or no effect on the wildlife species' distributions as physiological tolerance to heat load would allow them to survive. Analyses of the effects of vegetation change indicate that deer and chipmunks should retain their current distributions and possibly expand westward in the USA. For Elk and ground squirrels, there is a possibility that their current distributions would shrink and there is little possibility that each species would spread to new regions. This work emphasizes that the distributions of the four mammalian species are likely to be influenced more by vegetation changes than by thermal conditions. Future efforts to understand the effects of global change on wildlife species should focus on animal–habitat and climate–vegetation linkages.     

Physiology in ecological niche modeling: using zebra mussel's upper thermal tolerance to refine model predictions through Bayesian analysis

Climate change and human-mediated dispersal are increasingly influencing species’ geographic distributions. Ecological niche models (ENMs) are widely used in forecasting species’ distributions, but are weak in extrapolation to novel environments because they rely on available distributional data and do not incorporate mechanistic information, such as species’ physiological response to abiotic conditions. To improve accuracy of ENMs, we incorporated physiological knowledge through Bayesian analysis. In a case study of the zebra mussel Dreissena polymorpha, we used native and global occurrences to obtain native and global models representing narrower and broader understanding of zebra mussel’ response to temperature. We also obtained thermal limit and survival information for zebra mussel from peer-reviewed literature and used the two types of information separately and jointly to calibrate native models. We showed that, compared to global models, native models predicted lower relative probability of presence along zebra mussel's upper thermal limit, suggesting the shortcoming of native models in predicting zebra mussel's response to warm temperature. We also found that native models showed improved prediction of relative probability of presence when thermal limit was used alone, and best approximated global models when both thermal limit and survival data were used. Our result suggests that integration of physiological knowledge enhances extrapolation of ENM in novel environments. Our modeling framework can be generalized for other species or other physiological limits and may incorporate evolutionary information (e.g. evolved thermal tolerance), thus has the potential to improve predictions of species’ invasive potential and distributional response to climate change.     

Finding answers in the dark: caves as models in ecology fifty years after Poulson and White

The use of semi‐isolated habitats such as oceanic islands, lakes and mountain summits as model systems has played a crucial role in the development of evolutionary and ecological theory. Soon after the discovery of life in caves, different pioneering authors similarly recognized the great potential of these peculiar habitats as biological model systems. In their 1969 paper in Science, ‘The cave environment’, Poulson and White discussed how caves can be used as natural laboratories in which to study the underlying principles governing the dynamics of more complex environments. Together with other seminal syntheses published at the time, this work contributed to establishing the conceptual foundation for expanding the scope and relevance of cave‐based studies. Fifty years after, the aim of this review is to show why and how caves and other subterranean habitats can be used as eco‐evolutionary laboratories. Recent advances and directions in different areas are provided, encompassing community ecology, trophic‐webs and ecological networks, conservation biology, macroecology and climate change biology. Special emphasis is given to discuss how caves are only part of the extended network of fissures and cracks that permeate most substrates and, thus, their ecological role as habitat islands is critically discussed. Numerous studies have quantified the relative contribution of abiotic, biotic and historical factors in driving species distributions and community turnovers in space and time, from local to regional scales. Conversely, knowledge of macroecological patterns of subterranean organisms at a global scale remains largely elusive, due to major geographical and taxonomical biases. Also, knowledge regarding subterranean trophic webs and the effect of anthropogenic climate change on deep subterranean ecosystems is still limited. In these research fields, the extensive use of novel molecular and statistical tools may hold promise for quickly producing relevant information not accessible hitherto.     

Early signs of range disjunction of submountainous plant species: an unexplored consequence of future and contemporary climate changes

Poleward and upward species range shifts are the most commonly anticipated and studied consequences of climate warming. However, these global responses to climate change obscure more complex distribution change patterns. We hypothesize that the spatial arrangement of mountain ranges and, consequently, climatic gradients in Europe, will result in range disjunctions. This hypothesis was investigated for submountainous forest plant species at two temporal and spatial scales: (i) under future climate change (between 1950–2000 and 2061–2080 periods) at the European scale and (ii) under contemporary climate change (between 1914–1987 and 1997–2013 periods) at the French scale. We selected 97 submountainous forest plant species occurring in France, among which distribution data across Europe are available for 25 species. By projecting future distribution changes for the 25 submountainous plant species across Europe, we demonstrated that range disjunction is a likely consequence of future climate change. To assess whether it is already taking place, we used a large forest vegetation‐plot database covering the entire French territory over 100 years (1914–2013) and found an average decrease in frequency (?0.01 ± 0.004) in lowland areas for the 97 submountainous species – corresponding to a loss of 6% of their historical frequency – along with southward and upward range shifts, suggesting early signs of range disjunctions. Climate‐induced range disjunctions should be considered more carefully since they could have dramatic consequences on population genetics and the ability of species to face future climate changes.     

Upslope Range Shifts of Andean Dung Beetles in Response to Deforestation: Compounding and Confounding Effects of Microclimatic Change

Warmer, and sometimes drier, conditions associated with global climate change are driving many species to shift poleward and/or upslope. I hypothesized that microclimatic changes related to deforestation cause similar shifts for forest species persisting within degraded landscapes. This appears to be the first study to examine this novel hypothesis. I examined elevational distributions of dung beetle communities along parallel intact and disturbed elevational gradients from 290 to 3450 m asl in the Andes of southeastern Peru. Deforested sites were consistently warmer and drier than forested sites. To maintain the same ambient temperature as in forest, species in a deforested landscape would need to shift on average 489±59 m upslope. Dung beetle species showed a mean upslope range shift of 132±64 m (maximum=743 m) in the deforested landscape. Eight species occurred farther upslope in the degraded landscape, while none shifted downslope. In addition to upper range limit expansions, six species shifting upslope also showed range contractions or population declines at their lower range boundary. High elevation and disturbance‐tolerant species did not show range shifts. These findings suggest that land‐use change may both confound and compound the influence of global climate change on biodiversity. Synergies between habitat degradation and climate change could more than double previous range shift projections for this century, leading to unexpectedly rapid changes in biodiversity, especially for sensitive organisms such as tropical insects. On the other hand, range shifts caused by habitat degradation may be mistakenly attributed to global climate change. Abstract in Spanish is available in the online version of this article.     

Response of marine communities to local temperature changes

As global climate change and variability drive shifts in species’ distributions, ecological communities are being reorganized. One approach to understand community change in response to climate change has been to characterize communities by a collective thermal preference, or community temperature index (CTI), and then to compare changes in CTI with changes in temperature. However, important questions remain about whether and how responsive communities are to changes in their local thermal environments. We used CTI to analyze changes in 160 marine assemblages (fish and invertebrates) across the rapidly‐changing Northeast U.S. Continental Shelf Large Marine Ecosystem and calculated expected community change based on historical relationships between species presence and temperature from a separate training dataset. We then compared interannual and long‐term temperature changes with expected community responses and observed community responses over both temporal scales. For these marine communities, we found that community composition as well as composition changes through time could be explained by species associations with bottom temperature. Individual species had non‐linear responses to changes in temperature, and these nonlinearities scaled up to a nonlinear relationship between CTI and temperature. On average, CTI increased by 0.36°C (95% CI: 0.34–0.38°C) for every 1°C increase in bottom temperature, but the relationship between CTI and temperature also depended on community composition. In addition, communities responded more strongly to interannual variation than to long‐term trends in temperature. We recommend that future research into climate‐driven community change accounts for nonlinear responses and examines ecological responses across a range of temporal and geographical scales.     

Altitude effects on spatial components of vascular plant diversity in a subarctic mountain tundra

Environmental gradients are caused by gradual changes in abiotic factors, which affect species abundances and distributions, and are important for the spatial distribution of biodiversity. One prominent environmental gradient is the altitude gradient. Understanding ecological processes associated with altitude gradients may help us to understand the possible effects climate change could have on species communities. We quantified vegetation cover, species richness, species evenness, beta diversity, and spatial patterns of community structure of vascular plants along altitude gradients in a subarctic mountain tundra in northern Sweden. Vascular plant cover and plant species richness showed unimodal relationships with altitude. However, species evenness did not change with altitude, suggesting that no individual species became dominant when species richness declined. Beta diversity also showed a unimodal relationship with altitude, but only for an intermediate spatial scale of 1 km. A lack of relationships with altitude for either patch or landscape scales suggests that any altitude effects on plant spatial heterogeneity occurred on scales larger than individual patches but were not effective across the whole landscape. We observed both nested and modular patterns of community structures, but only the modular patterns corresponded with altitude. Our observations point to biotic regulations of plant communities at high altitudes, but we found both scale dependencies and inconsistent magnitude of the effects of altitude on different diversity components. We urge for further studies evaluating how different factors influence plant communities in high altitude and high latitude environments, as well as studies identifying scale and context dependencies in any such influences.