Changes in habitat specificity of species at their climatic range boundaries

Species are thought to have more restricted niches towards their range boundaries, although this has rarely been quantified systematically. We analysed transect data for 41 butterfly species along climatic gradients within Britain and show that 71% of species have broader niches at sites with milder winters. Shifts in habitat associations are considerable across most species' ranges; averaged across all 41 species, we estimate that if 26% of individuals were associated with the favoured habitat on the species' warmest transect, then 70% of individuals would be confined to this habitat on the species' coldest transect. Species with more southerly distributions in Britain showed the greatest changes in their habitat associations. We conclude that geographic variation in realized niche breadth is common and relatively large, especially near range boundaries, and should be taken into account in conserving species under changing climates.     

Impacts of past habitat loss and future climate change on the range dynamics of South African Proteaceae

Aim

To assess how habitat loss and climate change interact in affecting the range dynamics of species and to quantify how predicted range dynamics depend on demographic properties of species and the severity of environmental change.

Location

South African Cape Floristic Region.

Methods

We use data‐driven demographic models to assess the impacts of past habitat loss and future climate change on range size, range filing and abundances of eight species of woody plants (Proteaceae). The species‐specific models employ a hybrid approach that simulates population dynamics and long‐distance dispersal on top of expected spatio‐temporal dynamics of suitable habitat.

Results

Climate change was mainly predicted to reduce range size and range filling (because of a combination of strong habitat shifts with low migration ability). In contrast, habitat loss mostly decreased mean local abundance. For most species and response measures, the combination of habitat loss and climate change had the most severe effect. Yet, this combined effect was mostly smaller than expected from adding or multiplying effects of the individual environmental drivers. This seems to be because climate change shifts suitable habitats to regions less affected by habitat loss. Interspecific variation in range size responses depended mostly on the severity of environmental change, whereas responses in range filling and local abundance depended mostly on demographic properties of species. While most surviving populations concentrated in areas that remain climatically suitable, refugia for multiple species were overestimated by simply overlying habitat models and ignoring demography.

Main conclusions

Demographic models of range dynamics can simultaneously predict the response of range size, abundance and range filling to multiple drivers of environmental change. Demographic knowledge is particularly needed to predict abundance responses and to identify areas that can serve as biodiversity refugia under climate change. These findings highlight the need for data‐driven, demographic assessments in conservation biogeography.

     

Responses of 'resistant' vertebrates to habitat loss and fragmentation: the importance of niche breadth and range boundaries

Abstract. An ability to predict species' sensitivities to habitat loss and fragmentation has important conservation implications, and numerous hypotheses have been proposed to explain interspecific differences observed in human-dominated landscapes. We used occupancy data collected on 32 species of vertebrates (16 mammals and 16 amphibians) in an agricultural landscape of Indiana, USA, to compare hypotheses that focus on different causal mechanisms underlying interspecific variation in responses to habitat alteration: (1) body size; (2) morphology and development; (3) behaviour; (4) niche breadth; (5) proximity to range boundary; and multiple-process models combining main effects and interactions of hypotheses (1)–(2) and (4)–(5). The majority of habitat alteration occurred over a century ago and coincided with extinction of several species; thus, our study dealt only with variation in responses of extant species that often are considered 'resistant' to human modifications of native habitat. Corrected Akaike scores and Akaike weights provided strongest support for models incorporating niche breadth and proximity to range boundary. Measures of dietary and habitat breadth obtained from the literature were negatively correlated with sensitivity to habitat alteration. Additionally, greater sensitivity was observed for species occurring at the periphery of their geographical ranges, especially at northern or western margins. Body size, morphological, developmental and behavioural traits were inferior predictors of tolerance to fragmentation for the species and landscape we examined. Our findings reinforce the importance of niche breadth as a predictor of species' responses to habitat alteration. They also highlight the importance of viewing the effects of habitat loss and fragmentation in a landscape within a biogeographical context that considers a species' level of adaptation to local environmental conditions.     

Predicting the non‐linear collapse of plant–frugivore networks due to habitat loss

Habitat loss can trigger cascades of secondary extinctions, changing the organization of interacting assemblages. Until recently, most extinction models in interaction systems had limited ecological realism. Here, we estimate a realistic sequence of species extinctions resulting from habitat loss to assess its impacts on the structure of frugivory networks from the Brazilian Atlantic Forest. We show that realistic and random extinctions led to similar patterns. We also identified a threshold in the response of network structure to habitat loss. When forest cover was reduced to less than 40% of the landscape, network organization changed dramatically. Hence, the number of species being lost, rather than the order of species extinctions, is the key determinant of its impacts on the organization of frugivory networks. We highlight the need to conserve around 40% of forest cover to keep the basic organization of frugivory networks, a threshold already reached at the best‐preserved Brazilian Atlantic Forest bioregion.     

The roles of landscape context, niche breadth, and range boundaries in predicting species responses to habitat alteration

Extant species in human‐dominated landscapes differ in their sensitivity to habitat loss and fragmentation, although extinctions induced by environmental alteration reduce variation and result in a surviving subset of species with some degree of ‘resistance’. Here, we test the degree to which variable responses to habitat alteration are (1) essentially an inherent property of a taxon subject to constraints imposed by its geographical range, as suggested by Swihart et al. (2003), (2) a function of the landscape in which a species occurs, or (3) a function of spatial trends occurring on large scales. We used data collected on 33 vertebrate species during 2001–04 across the upper Wabash River basin, Indiana, in 35 square ‘landscapes’, each 23 km² in size. Six species of forest rodent, six species of grassland rodents, seven species of bats, eight species of aquatic turtles, and six species of amphibians were sampled at 504, 212, 590, 228, and 625 patches, respectively. The fraction of patches of primary habitat (e.g. forests for tree squirrels, wetlands for aquatic turtles) occupied by a target species was used as a response variable. On a basin‐wide scale, 47% of variation in proportional occupancy among species could be explained by taxon‐specific variables; occupancy rates were related positively to niche breadth and negatively to the proximity of a geographical range boundary. After controlling for species effects, landscape‐level occupancy rates varied significantly for 16 of 33 species, with variation partitioned among landscape variables alone (mean = 11% of variation), spatial trend variables alone (26%), and both variable sets jointly (8%). Among landscape variables, percentage forest cover positively affected occupancy rates of three bat species and a tree squirrel. Variation in occupancy rates among landscapes was consistent with large‐scale spatial trends for 13 species. Our findings demonstrate the general importance of niche breadth as a predictor of species responses to habitat alteration and highlight the importance of viewing the effects of habitat loss and fragmentation at multiple spatial scales.     

Temporal variation in responses of species to four decades of climate warming

Many species are expanding at their leading‐edge range boundaries in response to climate warming. Species are known to respond individualistically to climate change, but there has been little consideration of whether responses are consistent over time. We compared responses of 37 southerly distributed British butterflies over two study periods, first between 1970–1982 and 1995–1999 and then between 1995–1999 and 2005–2009, when mean annual temperature increased regionally by 0.03 °C yr^?1 (a significant rate of increase) and 0.01 °C yr^?1(a nonsignificant increase) respectively. Our study species might be expected to benefit from climate warming. We measured three responses to climate to investigate this; changes in range margin, distribution area and abundance. In general, the responses of species were inconsistent over time. Species that increased their distribution areas during the first period tended to do so again during the second period, but the relationship was weak. Changes in range margins and abundance were not consistent. In addition, only 5/37 species showed qualitatively similar responses in all three response variables over time (three species increased and two species declined in all variables in both periods). Overall rates of range expansion and distribution area change were significantly greater in the second study period, despite the lower rate of warming, perhaps due to species exploiting climate‐distribution lags remaining from the earlier, warmer period. However, there was a significantly greater decline in abundance during the second study period, so range expansions northwards were not necessarily accompanied by increases in distribution area and/or abundance. Hence, species ranges have been thinning as they have expanded northwards. The idiosyncratic responses of these species likely reflect the balance of climatic and habitat drivers of species distribution and abundance changes.     

Interactions between climate and habitat loss effects on biodiversity: a systematic review and meta‐analysis

Climate change and habitat loss are both key threatening processes driving the global loss in biodiversity. Yet little is known about their synergistic effects on biological populations due to the complexity underlying both processes. If the combined effects of habitat loss and climate change are greater than the effects of each threat individually, current conservation management strategies may be inefficient and at worst ineffective. Therefore, there is a pressing need to identify whether interacting effects between climate change and habitat loss exist and, if so, quantify the magnitude of their impact. In this article, we present a meta‐analysis of studies that quantify the effect of habitat loss on biological populations and examine whether the magnitude of these effects depends on current climatic conditions and historical rates of climate change. We examined 1319 papers on habitat loss and fragmentation, identified from the past 20 years, representing a range of taxa, landscapes, land‐uses, geographic locations and climatic conditions. We find that current climate and climate change are important factors determining the negative effects of habitat loss on species density and/or diversity. The most important determinant of habitat loss and fragmentation effects, averaged across species and geographic regions, was current maximum temperature, with mean precipitation change over the last 100 years of secondary importance. Habitat loss and fragmentation effects were greatest in areas with high maximum temperatures. Conversely, they were lowest in areas where average rainfall has increased over time. To our knowledge, this is the first study to conduct a global terrestrial analysis of existing data to quantify and test for interacting effects between current climate, climatic change and habitat loss on biological populations. Understanding the synergistic effects between climate change and other threatening processes has critical implications for our ability to support and incorporate climate change adaptation measures into policy development and management response.     

Combined exposure to hydroelectric expansion,climate change and forest loss jeopardies amphibians in the Brazilian Amazon

Aim

Human‐driven impacts constantly threat amphibians, even in largely protected regions such as the Amazon. The Brazilian Amazon is home to a great diversity of amphibians, several of them currently threatened with extinction. We investigated how climate change, deforestation and establishment of hydroelectric dams could affect the geographic distribution of Amazonian amphibians by 2030 and midcentury.

Location

The Brazilian Amazon.

Methods

We overlapped the geographic distribution of 255 species with the location of hydroelectric dams, models of deforestation and climate change scenarios for the future.

Results

We found that nearly 67% of all species and 54% of species with high degree of endemism within the Legal Brazilian Amazon would lose habitats due to the hydroelectric overlapping. In addition, deforestation is also a potential threat to amphibians, but had a smaller impact compared to the likely changes in climate. The largest potential range loss would be caused by the likely increase in temperature. We found that five amphibian families would have at least half of the species with over 50% of potential distribution range within the Legal Brazilian Amazon limits threatened by climate change between 2030 and 2050.

Main conclusions

Amphibians in the Amazon are highly vulnerable to climate change, which may cause, directly or indirectly, deleterious biological changes for the group. Under modelled scenarios, the Brazilian Government needs to plan for the development of the Amazon prioritizing landscape changes of low environmental impact and economic development to ensure that such changes do not cause major impacts on amphibian species while reducing the emission of greenhouse gases.

     

The loss of indirect interactions leads to cascading extinctions of carnivores

Species extinctions are biased towards higher trophic levels, and primary extinctions are often followed by unexpected secondary extinctions. Currently, predictions on the vulnerability of ecological communities to extinction cascades are based on models that focus on bottom‐up effects, which cannot capture the effects of extinctions at higher trophic levels. We show, in experimental insect communities, that harvesting of single carnivorous parasitoid species led to a significant increase in extinction rate of other parasitoid species, separated by four trophic links. Harvesting resulted in the release of prey from top‐down control, leading to increased interspecific competition at the herbivore trophic level. This resulted in increased extinction rates of non‐harvested parasitoid species when their host had become rare relative to other herbivores. The results demonstrate a mechanism for horizontal extinction cascades, and illustrate that altering the relationship between a predator and its prey can cause wide‐ranging ripple effects through ecosystems, including unexpected extinctions.     

苜蓿草地生境丧失与破碎化对昆虫物种丧失与群落重建的影响

生境破碎化包括生境丧失与破碎化两个相对独立的过程,为探讨这两个过程各自对生物多样性的影响,本文利用苜蓿草地实验模型系统(EMS)构建了36个小区研究不同生境丧失与破碎化对昆虫群落及不同类群的影响,包括18个破碎化小区与18个连续小区,破碎化小区全部采用1 m×1 m(H=1)破碎,连续小区苜蓿连片(H=0),生境丧失采...     

汶川地震对都江堰地区大熊猫生境的影响

为了明确汶川地震破坏区的空间分布特征及其对大熊猫生境的影响,选择在都江堰地区采用遥感数据解译和GIS模型分析相结合的方法进行了此项研究。研究结果表明：汶川地震及其产生的滑坡、泥石流等次生灾害造成的植被破坏区面积为12862hm^2,其中78．64％的破坏区位于龙溪虹口自然保护区内部。地震破坏区在空间上主要分布在海拔1400—2400m,坡度20～55°之间的山坡上。地震造成都江堰地区21．63％的大熊猫生境丧失,其中海拔2200～3000m之间的大熊猫生境丧失比例较大。大熊猫生境破碎化程度严重,震后的生境斑块数量是震前的7．7倍。龙溪虹口自然保护区的大熊猫生境丧失更为严重,其丧失比例为32．15％,而保护区外部的大熊猫生境丧失较轻,其丧失比例为9．83％。地震造成该地区大熊猫生境丧失严重,生境破碎化加剧,为了增加大熊猫可利用的生境,在震后恢复重建中应当避免在大熊猫生境中开展旅游。     

Winter home range and habitat use by porcupines in Alaska

Habitat selection results from trade-offs between availability and use of resources under constraints of predation, competition, or other threats, which can vary spatially and temporally. For northern herbivores, winter food availability and quality can limit population size and may drive habitat preference. North American porcupines (Erethizon dorsatum) are widespread generalist herbivores that range from Mexico to the northern reaches of Alaska. During the long Alaskan winter, porcupines deal with high energetic demands resulting from low ambient temperatures while subsisting on low quality forage. We tracked free-ranging porcupines over 3 winters in southcentral Alaska to determine habitat selection and home range size in relation to diet. Porcupines maintained larger than expected home ranges, and selected for conifer-hardwood forests at the home range level. Individual variation among porcupines was too large to determine a pattern of microhabitat selection among trees. Regardless, direct observations revealed that porcupines used only white spruce and paper birch trees for foraging. White spruce may provide some nutritional and thermoregulatory advantage over paper birch; however, porcupines did feed on paper birch cambium, suggesting some nutritional requirement is met by eating paper birch. Porcupines most likely feed on paper birch cambium when detoxification pathways used to process plant toxins in white spruce needles are saturated. Maintaining mixed conifer-hardwood forests in southcentral Alaska would provide suitable winter habitat for porcupines and may alleviate damage to single species stands of conifers or hardwoods that are preferred by commercial forestry operations. © 2012 The Wildlife Society.     

Modelling the effect of habitat fragmentation on range expansion in a butterfly

There is an increasing need for conservation programmes to make quantitative predictions of biodiversity responses to changed environments. Such predictions will be particularly important to promote species recovery in fragmented landscapes, and to understand and facilitate distribution responses to climate change. Here, we model expansion rates of a test species (a rare butterfly, Hesperia comma) in five landscapes over 18 years (generations), using a metapopulation model (the incidence function model). Expansion rates increased with the area, quality and proximity of habitat patches available for colonization, with predicted expansion rates closely matching observed rates in test landscapes. Habitat fragmentation constrained expansion, but in a predictable way, suggesting that it will prove feasible both to understand variation in expansion rates and to develop conservation programmes to increase rates of range expansion in such species.     

Tree range expansion in eastern North America fails to keep pace with climate warming at northern range limits

Rising global temperatures are suggested to be drivers of shifts in tree species ranges. The resulting changes in community composition may negatively impact forest ecosystem function. However, long‐term shifts in tree species ranges remain poorly documented. We test for shifts in the northern range limits of 16 temperate tree species in Quebec, Canada, using forest inventory data spanning three decades, 15° of longitude and 7° of latitude. Range shifts were correlated with climate warming and dispersal traits to understand potential mechanisms underlying changes. Shifts were calculated as the change in the 95th percentile of latitudinal occurrence between two inventory periods (1970–1978, 2000–2012) and for two life stages: saplings and adults. We also examined sapling and adult range offsets within each inventory, and changes in the offset through time. Tree species ranges shifted predominantly northward, although species responses varied. As expected shifts were greater for tree saplings, 0.34 km yr^?1, than for adults, 0.13 km yr^?1. Range limits were generally further north for adults compared to saplings, but the difference diminished through time, consistent with patterns observed for range shifts within each life stage. This suggests caution should be exercised when interpreting geographic range offsets between life stages as evidence of range shifts in the absence of temporal data. Species latitudinal velocities were on average <50% of the velocity required to equal the spatial velocity of climate change and were mostly unrelated to dispersal traits. Finally, our results add to the body of evidence suggesting tree species are mostly limited in their capacity to track climate warming, supporting concerns that warming will negatively impact the functioning of forest ecosystems.     

Precipitation buffers temperature-driven local extinctions of moths at warm range margins

Species' distributions are moving polewards in response to climate change, and although range expansions of relatively warm-adapted species are widely reported, reports of range retractions in cool-adapted species are less common. Here, we analysed species' distribution shifts for 76 cool-adapted moths in Great Britain using citizen science occurrence records from the National Moth Recording Scheme over a 40-year period. Although we find evidence for trailing edge shifts to higher latitudes, shifts in species' range centroids are oriented towards the north-west, and are more closely correlated with directional changes in total precipitation than average temperature. We also found that species' local extinction risk is higher in areas where temperature is high and precipitation is low, but this risk diminishes as precipitation increases. Adaptation efforts should therefore focus on maintaining or increasing water availability as the climate continues to change.     

Effects of climate warming on polar bears: a review of the evidence

Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze‐up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long‐term survival. To maintain viable subpopulations, polar bears depend on sea ice as a platform from which to hunt seals for long enough each year to accumulate sufficient energy (fat) to survive periods when seals are unavailable. Less time to access to prey, because of progressively earlier breakup in spring, when newly weaned ringed seal (Pusa hispida) young are available, results in longer periods of fasting, lower body condition, decreased access to denning areas, fewer and smaller cubs, lower survival of cubs as well as bears of other age classes and, finally, subpopulation decline toward eventual extirpation. The chronology of climate‐driven changes will vary between subpopulations, with quantifiable negative effects being documented first in the more southerly subpopulations, such as those in Hudson Bay or the southern Beaufort Sea. As the bears' body condition declines, more seek alternate food resources so the frequency of conflicts between bears and humans increases. In the most northerly areas, thick multiyear ice, through which little light penetrates to stimulate biological growth on the underside, will be replaced by annual ice, which facilitates greater productivity and may create habitat more favorable to polar bears over continental shelf areas in the short term. If the climate continues to warm and eliminate sea ice as predicted, polar bears will largely disappear from the southern portions of their range by mid‐century. They may persist in the northern Canadian Arctic Islands and northern Greenland for the foreseeable future, but their long‐term viability, with a much reduced global population size in a remnant of their former range, is uncertain.     

How fire interacts with habitat loss and fragmentation

Biodiversity faces many threats and these can interact to produce outcomes that may not be predicted by considering their effects in isolation. Habitat loss and fragmentation (hereafter ‘fragmentation’) and altered fire regimes are important threats to biodiversity, but their interactions have not been systematically evaluated across the globe. In this comprehensive synthesis, including 162 papers which provided 274 cases, we offer a framework for understanding how fire interacts with fragmentation. Fire and fragmentation interact in three main ways: (i) fire influences fragmentation (59% of 274 cases), where fire either destroys and fragments habitat or creates and connects habitat; (ii) fragmentation influences fire (25% of cases) where, after habitat is reduced in area and fragmented, fire in the landscape is subsequently altered because people suppress or ignite fires, or there is increased edge flammability or increased obstruction to fire spread; and (iii) where the two do not influence each other, but fire interacts with fragmentation to affect responses like species richness, abundance and extinction risk (16% of cases). Where fire and fragmentation do influence each other, feedback loops are possible that can lead to ecosystem conversion (e.g. forest to grassland). This is a well-documented threat in the tropics but with potential also to be important elsewhere. Fire interacts with fragmentation through scale-specific mechanisms: fire creates edges and drives edge effects; fire alters patch quality; and fire alters landscape-scale connectivity. We found only 12 cases in which studies reported the four essential strata for testing a full interaction, which were fragmented and unfragmented landscapes that both span contrasting fire histories, such as recently burnt and long unburnt vegetation. Simulation and empirical studies show that fire and fragmentation can interact synergistically, multiplicatively, antagonistically or additively. These cases highlight a key reason why understanding interactions is so important: when fire and fragmentation act together they can cause local extinctions, even when their separate effects are neutral. Whether fire–fragmentation interactions benefit or disadvantage species is often determined by the species' preferred successional stage. Adding fire to landscapes generally benefits early-successional plant and animal species, whereas it is detrimental to late-successional species. However, when fire interacts with fragmentation, the direction of effect of fire on a species could be reversed from the effect expected by successional preferences. Adding fire to fragmented landscapes can be detrimental for species that would normally co-exist with fire, because species may no longer be able to disperse to their preferred successional stage. Further, animals may be attracted to particular successional stages leading to unexpected responses to fragmentation, such as higher abundance in more isolated unburnt patches. Growing human populations and increasing resource consumption suggest that fragmentation trends will worsen over coming years. Combined with increasing alteration of fire regimes due to climate change and human-caused ignitions, interactions of fire with fragmentation are likely to become more common. Our new framework paves the way for developing a better understanding of how fire interacts with fragmentation, and for conserving biodiversity in the face of these emerging challenges.