Panmixia across elevation in thermally sensitive Andean dung beetles

Janzen's seasonality hypothesis predicts that organisms inhabiting environments with limited climatic variability will evolve a reduced thermal tolerance breadth compared with organisms experiencing greater climatic variability. In turn, narrow tolerance breadth may select against dispersal across strong temperature gradients, such as those found across elevation. This can result in narrow elevational ranges and generate a pattern of isolation by environment or neutral genetic differentiation correlated with environmental variables that are independent of geographic distance. We tested for signatures of isolation by environment across elevation using genome‐wide SNP data from five species of Andean dung beetles (subfamily Scarabaeinae) with well‐characterized, narrow thermal physiologies, and narrow elevational distributions. Contrary to our expectations, we found no evidence of population genetic structure associated with elevation and little signal of isolation by environment. Further, elevational ranges for four of five species appear to be at equilibrium and show no decay of genetic diversity at range limits. Taken together, these results suggest physiological constraints on dispersal may primarily operate outside of a stable realized niche and point to a lower bound on the spatial scale of local adaptation.     

Cryptic species and hidden ecological interactions of halictine bees along an elevational gradient

Changes of abiotic and biotic conditions along elevational gradients represent serious challenges to organisms which may promote the turnover of species, traits and biotic interaction partners. Here, we used molecular methods to study cuticular hydrocarbon (CHC) profiles, biotic interactions and phylogenetic relationships of halictid bees of the genus Lasioglossum along a 2,900 m elevational gradient at Mt. Kilimanjaro, Tanzania. We detected a strong species turnover of morphologically indistinguishable taxa with phylogenetically clustered cryptic species at high elevations, changes in CHC profiles, pollen resource diversity, and a turnover in the gut and body surface microbiome of bees. At high elevations, increased proportions of saturated compounds in CHC profiles indicate physiological adaptations to prevent desiccation. More specialized diets with higher proportions of low‐quality Asteraceae pollen imply constraints in the availability of food resources. Interactive effects of climatic conditions on gut and surface microbiomes, CHC profiles, and pollen diet suggest complex feedbacks among abiotic conditions, ecological interactions, physiological adaptations, and phylogenetic constraints as drivers of halictid bee communities at Mt. Kilimanjaro.     

An experimental assessment of the upper elevational limit of flowering plants in the western Himalayas

Transplant experiments are a useful tool both for determining species’ ranges and understanding their cause, yet such experiments have seldom been performed in areas where plants reach extremely high elevations. We examined the position of the upper elevational limits of vascular plants in E Ladakh, India, by transplanting individuals of 14 subnival species from 5800–5850 m elevation to a control site at the same elevation, as well as to edaphically suitable sites at 5960 m (subnival belt with sparse plant cover), to 6030 m (the highest elevation reached by vascular plants in the area) and to 6160 m elevation (no vascular plants observed). Two years later, transplants of 13 species survived at the control elevation, whereas 5 species survived at 5960 m, 2 species (Waldheimia tridactylites, Poa attenuata) at 6030 m, and none at 6160 m. The highest elevation at which transplanted flowering plants survived corresponds well to the observed elevational limit. Soil temperature data at the sites suggest that the growing season, defined as the period with mean daily soil temperature above zero, lasted nearly 3 months at 5960 m, ca 1.5 month at 6030 m, but <3 weeks at 6160 m, moreover interrupted at the highest elevation by several days with temperatures remaining below zero. The experiment confirmed the observed sharp limit of vegetation, set not by any physical barrier per se (e.g. not by the top of the massif), but instead by physiological constraints of the species. The result provides support for the assumptions of mid‐domain effect models that domain limits are defined by shared organismal adaptations in relation to environmental gradients, in this case tolerance to freezing temperature.     

Divergence of thermal physiological traits in terrestrial breeding frogs along a tropical elevational gradient

Critical thermal limits are thought to be correlated with the elevational distribution of species living in tropical montane regions, but with upper limits being relatively invariant compared to lower limits. To test this hypothesis, we examined the variation of thermal physiological traits in a group of terrestrial breeding frogs (Craugastoridae) distributed along a tropical elevational gradient. We measured the critical thermal maximum (CT_max; n = 22 species) and critical thermal minimum (CT_min; n = 14 species) of frogs captured between the Amazon floodplain (250 m asl) and the high Andes (3,800 m asl). After inferring a multilocus species tree, we conducted a phylogenetically informed test of whether body size, body mass, and elevation contributed to the observed variation in CT_max and CT_min along the gradient. We also tested whether CT_max and CT_min exhibit different rates of change given that critical thermal limits (and their plasticity) may have evolved differently in response to different temperature constraints along the gradient. Variation of critical thermal traits was significantly correlated with species’ elevational midpoint, their maximum and minimum elevations, as well as the maximum air temperature and the maximum operative temperature as measured across this gradient. Both thermal limits showed substantial variation, but CT_min exhibited relatively faster rates of change than CT_max, as observed in other taxa. Nonetheless, our findings call for caution in assuming inflexibility of upper thermal limits and underscore the value of collecting additional empirical data on species’ thermal physiology across elevational gradients.     

Islands in the sky or squeezed at the top? Ecological causes of elevational range limits in montane salamanders

Many animal and plant taxa reach their highest endemism and species richness in montane regions. The study of elevational range limits is central to understanding this widespread pattern and to predicting the responses of montane species to climate change. Yet, because large‐scale manipulations of the distributions of most species are difficult, the causes of species’ elevational range limits (e.g. competitive interactions, physiological specialization) are poorly understood. Here, we harness the power of new mechanistic approaches to dissect the factors that underlie the elevational replacement of two salamander species in the Appalachian Highlands. Our results challenge the long‐held idea that competitive interactions drive the lower elevational range limits of montane species and that physiological stress prevents low‐elevation species from expanding to high elevations. We show that physiological constraints drive the lower elevational range limit of the montane‐endemic species, Plethodon jordani. Conversely, we find that competition with P. jordani prevents the low‐elevation species, P. teyahalee, from expanding its range to include higher‐elevation habitats. These results are broadly consistent with the biogeography and behavior of other montane species, suggesting that similar mechanisms underlie patterns of elevational zonation across a variety of taxa and montane regions. To the extent that our findings are taxonomically and geographically widespread, these results challenge the idea that competitive release at species’ lower elevational range limits is driving the downslope range shifts exhibit by some montane taxa. Instead, our results raise the sobering possibility that even small changes in climate might cause erosion of the ranges of many high‐elevation species.     

Scale‐dependent thermal tolerance variation in Australian mountain grasshoppers

Physiological variation among and within species is thought to play a key role in determining distribution patterns across environmental gradients. We tested inter‐ and intraspecific variation in cold and heat tolerances for three grasshopper species (genus Kosciuscola) with overlapping elevation distributions, across their respective ranges in the Australian mountains. Of the three cold tolerance traits measured, the critical thermal minimum was the only trait to vary among species, with greater cold tolerance associated with a distribution extending to a higher elevation. Cold tolerance limits were regularly exceeded in exposed microhabitats, suggesting a role for cold adaptation in structuring species distribution patterns. In contrast to cold tolerance, heat tolerance variation was primarily partitioned within species. For two species, populations from treeless alpine habitat were more heat tolerant than their lower‐elevation counterparts, supporting recent models that suggest greater exposure to temperature extremes at higher elevations. These contrasting patterns of physiological variation among and within species emphasise the importance of considering variation within species when attempting to understand how species distributions are affected by thermal extremes.     

Thermal physiology explains the elevational range for a lizard,Eutropis longicaudata,in Taiwan

1The decrease of temperatures along an elevation gradient imposes physiological constraints on reptiles that ultimately determine their distribution ranges. Forest patterns are likely to interact with this process, but very few studies have examined their contribution in determining distribution limits.2We examined the role played by thermal physiology and forest cover in determining the elevational ranges of a lizard, Eutropis longicaudata. We integrated this species’ thermal traits in simulating its maximum activity time under different conditions of forest cover and elevation using a NicheMapR model. In addition, we evaluated the influence of winter temperatures on the range limit by examining the simulated soil temperatures at the occurrence sites.3Laboratory experiments showed that E. longicaudata has a high preferred body temperature and low cold tolerance. The model predicts that maximum activity time decreases with elevation and forest cover. Although unforested areas may provide longer active time in all simulated elevations, mountain areas in Taiwan are heavily forested and are predicted to allow only a very short period of activity above 1000 m elevation.4All sightings were indeed located in areas below 1000 m elevation, in which the predicted average soil temperature is above 10 °C in January in cold years.5Our results show that reptile physiological response does respond strongly to the change of microclimate induced by forest cover and elevation. Overall, this suggests that forest cover is a major determinant of some reptiles’ elevational range.     

Thermal constraints on embryonic development as a proximate cause for elevational range limits in two Mediterranean lacertid lizards

Local adaptation and range restrictions in alpine environments are central topics in biogeographic research with important implications for predicting impacts of global climate change on organisms. Temperature is strongly coupled to elevation and greatly affects life history traits of oviparous reptiles in mountain environments. Thus, species may encounter barriers for expanding their ranges if they are unable to adapt to the changing thermal conditions encountered along elevational gradients. We sought to determine whether thermal requirements for embryonic development provide a plausible explanation for elevational range limits of two species of lacertid lizards that have complementary elevational ranges in a Mediterranean mountain range (Psammodromus algirus is found at elevations below 1600 m and Iberolacerta cyreni is found at elevations above 1600 m). We combined experimental incubation of eggs in the laboratory with modelled estimates of nest temperature in the field. In both species, increasing temperature accelerated development and produced earlier hatching dates. The species associated with warmer environments (P. algirus) experienced an excessive hatching delay under the lowest incubation temperature. Moreover, newborns from eggs incubated at low temperatures showed poor body condition and very slow rates of postnatal growth. In contrast, eggs of the strictly alpine species I. cyreni exhibited shorter incubation periods than P. algirus that allowed hatching before the end of the active season even under low incubation temperatures. This was countered by lower reproductive success at higher temperatures, due to lower hatching rates and higher incidence of abnormal phenotypes. Elevational range limits of both species coincided well with threshold temperatures for deleterious effects on embryonic development. We suggest that incubation temperature is a major ecophysiological factor determining the elevational range limits of these oviparous lizards with predictable consequences for mountain distributions under future warmer climates.     

Patterns of ant species richness along elevational gradients in an arid ecosystem

Aim In this study, we examine patterns of local and regional ant species richness along three elevational gradients in an arid ecosystem. In addition, we test the hypothesis that changes in ant species richness with elevation are related to elevation‐dependent changes in climate and available area. Location Spring Mountains, Nevada, U.S.A. Methods We used pitfall traps placed at each 100‐m elevational band in three canyons in the Spring Mountains. We compiled climate data from 68 nearby weather stations. We used multiple regression analysis to examine the effects of annual precipitation, average July precipitation, and maximum and minimum July temperature on ant species richness at each elevational band. Results We found that patterns of local ant species richness differed among the three gradients we sampled. Ant species richness increased linearly with elevation along two transects and peaked at mid‐elevation along a third transect. This suggests that patterns of species richness based on data from single transects may not generalize to larger spatial scales. Cluster analysis of community similarity revealed a high‐elevation species assemblage largely distinct from that of lower elevations. Major changes in the identity of ant species present along elevational gradients tended to coincide with changes in the dominant vegetation. Regional species richness, defined here as the total number of unique species within an elevational band in all three gradients combined, tended to increase with increasing elevation. Available area decreased with increasing elevation. Area was therefore correlated negatively with ant species richness and did not explain elevational patterns of ant species richness in the Spring Mountains. Mean July maximum and minimum temperature, July precipitation and annual precipitation combined to explain 80% of the variation in ant species richness. Main conclusions Our results suggest that in arid ecosystems, species richness for some taxa may be highest at high elevations, where lower temperatures and higher precipitation may support higher levels of primary production and cause lower levels of physiological stress.     

Linking species thermal tolerance to elevational range shifts in upland dung beetles

Climate warming has been proposed as the main cause of the recent range shifts seen in many species. Although species' thermal tolerances are thought to play a key role in determining responses to climate change, especially in ectotherms, empirical evidence is still limited. We investigate the connection between species' thermal tolerances, elevational range and shifts in the lower elevational limit of dung beetle species (Coleoptera, Aphodiidea) in an upland region in the northwest of England. We measured thermal tolerances in the laboratory, and used current and historical distribution data to test specific hypotheses about the area's three dominant species, particularly the species most likely to suffer from warming: Agollinus lapponum. We found marked differences between species in their minimum and maximum thermal tolerance and in their elevational range and patterns of abundance. Overall, differences in thermal limits among species matched the abundance patterns along the elevation gradient expected if distributions were constrained by climate. Agollinus lapponum abundance increased with elevation and this species showed lower maximum and minimum thermal limits than Acrossus depressus, for which abundance declined with elevation. Consistent with lower tolerance to high temperature, we recorded an uphill retreat of the low elevation limit of A. lapponum (177 m over 57 yr) in line with the increase in summer temperature observed in the region over the same period. Moreover, this species has been replaced at low and mid‐elevations by the other two warm‐tolerant species (A. depressus and Agrilinus ater). Our results provide empirical evidence that species' thermal tolerance constrains elevational ranges and contributes to explain the observed responses to climate warming. A mechanistic understanding of how climate change directly affects species, such as the one presented here, will provide a robust base to inform predictions of how individual species and whole assemblages may change in the future.     

Elevational gradients of small mammal diversity on the northern slopes of Mt. Qilian, China

Aim Small mammal species richness and relative abundance vary along elevational gradients, but there are different patterns that exist. This study reports the patterns of distribution and abundance of small mammals along the broader elevational gradient of Mt. Qilian range. Location The study was conducted in the Mt. Qilian range, north‐western China, from June to August 2001. Methods Removal trapping was conducted using a standardized technique at 7 sites ranging between 1600 and 3900 m elevation within three transects. Correlation, regression and graphical analyses were used to evaluate the diversity patterns along this elevational gradient. Results In total, 586 individuals representing 18 nonvolant small mammal species were collected during 20 160 trap nights. Species composition was different among the three transects with 6 (33%) of the species found only within one transect. Elevational distribution and relative abundance of small rodents showed substantial spatial variation, with only 2 species showing nonsignificant capture frequencies across elevations. Despite these variations, some general patterns of elevational distribution emerged: humped‐shape relationships between species diversity and elevation were noted in all three transects with diversity peaks at middle elevations. In addition, relative abundance was negatively correlated with elevation. Conclusions Results indicate that maximum richness and diversity of nonvolant small mammals occurred at mid‐elevations where several types of plants reached their maximum diversity and primary productivity, and where rainfall and humidity reached a maximum. It is demonstrated that the mid‐elevation bulge is a general feature of at least a large portion of the biota on the Mt. Qilian range.     

Environmental heterogeneity shapes physiological traits in tropical direct‐developing frogs

1. Tropical ectotherm species tend to have narrower physiological limits than species from temperate areas. As a consequence, tropical species are considered highly vulnerable to climate change since minor temperature increases can push them beyond their physiological thermal tolerance. Differences in physiological tolerances can also be seen at finer evolutionary scales, such as among populations of ectotherm species along elevation gradients, highlighting the physiological sensitivity of such organisms.
2. Here, we analyze the influence of elevation and bioclimatic domains, defined by temperature and precipitation, on thermal sensitivities of a terrestrial direct‐developing frog (Craugastor loki) in a tropical gradient. We address the following questions: (a) Does preferred temperature vary with elevation and among bioclimatic domains? (b) Do thermal tolerance limits, that is, critical thermal maximum and critical thermal minimum vary with elevation and bioclimatic domains? and (c) Are populations from high elevations more vulnerable to climate warming?
3. We found that along an elevation gradient body temperature decreases as environmental temperature increases. The preferred temperature tends to moderately increase with elevation within the sampled bioclimatic domains. Our results indicate that the ideal thermal landscape for this species is located at midelevations, where the thermal accuracy (d_b) and thermal quality of the environment (d_e) are suitable. The critical thermal maximum is variable across elevations and among the bioclimatic domains, decreasing as elevation increases. Conversely, the critical thermal minimum is not as variable as the critical thermal maximum.
4. Populations from the lowlands may be more vulnerable to future increases in temperature. We highlight that the critical thermal maximum is related to high temperatures exhibited across the elevation gradient and within each bioclimatic domain; therefore, it is a response to high environmental temperatures.

     

Harvestman (Arachnida: Opiliones) species distribution along three Neotropical elevational gradients: an alternative rescue effect to explain Rapoport's rule?

Aim Relationships between elevation and litter‐dweller harvestman (Arachnida: Opiliones) species richness along three elevational gradients in the Brazilian Atlantic Forest were evaluated. Specifically, three candidate explanatory factors for the observed patterns were tested: (1) the mid‐domain effect, (2) the Rapoport effect, and (3) the influence of environmental variables on species density and specimen abundance. Location Cuscuzeiro, Corcovado and Capricórnio mountains, in Ubatuba (23°26′ S, 45°04′ W), a coastal municipality in São Paulo state, south‐eastern Brazil. Methods We recorded harvestman species and abundance through active sampling using 8 × 8‐m plots in both summer and winter. At each plot we measured the temperature, humidity and mean litter depth. Harvestman species richness per elevational band was the sum of all species recorded in each band, plus the species supposed to occur due to the interpolation of the upper and lower elevational records. Differences between observed and expected species richness per elevational band, based on the mid‐domain effect, were examined through a Monte Carlo simulation. The Rapoport effect was evaluated using both the midpoint method and a new procedure proposed here, the ‘specimen method’. We applied multiple regression analysis to evaluate the contribution of each environmental variable (elevation, temperature, humidity and litter depth) on species density and specimen abundance per plot. Results Harvestman abundance and species richness decreased at higher elevations in the three mountains. The decrease in species richness was not monotonic and showed a plateau of high species richness at lower elevations. The number of harvestman species per elevational band does not fit that predicted by the mid‐domain effect based solely on geometric constraints assuming hard boundaries. Species with their midpoints at higher elevations tended to cover broader elevational range sizes. Both the midpoint method and the specimen method detected evidence of the Rapoport effect in the data. At fine spatial scales, temperature and humidity had positive effects on species density and specimen abundance, while mean litter depth had no clear effect. These relationships, however, were not constant between seasons. Main conclusions Our results suggest that harvestman species density declines at higher elevations due to restrictions imposed by temperature and humidity. We found a pattern in species range distribution as predicted by the elevational Rapoport effect. However, the usual rescue effect proposed to explain the Rapoport effect does not apply in our study. Since the majority of harvestman species covering broader elevational ranges do not exhibit reduced abundance at low elevations, an alternative rescue effect is proposed here. According to this alternative rescue effect, the decrease in species richness at higher elevations occurs due to differential upper limits of species with source populations below mid‐elevations. The seasonal differences in the relationships between environmental variables and species richness/specimen abundance per plot is an indication that species occurrence on elevational gradients is seasonally dependent. Thus relationships and hypotheses based on data recorded over short time periods, or in a single season, should be viewed cautiously.     

Variation in insulative feather structure in songbirds replacing each other along a tropical elevation gradient

High‐elevation organisms are expected to evolve physiological adaptations to cope with harsh environmental conditions. Yet, evidence for such adaptive differences, especially compared to closely related lowland taxa occurring along the same elevational gradient, is rare. Revisiting an anecdotal natural history observation by O. Bangs from 1899 and based on new measurements of museum specimens, we confirmed that the high‐elevation hermit wood wren (Henicorhina anachoreta) from the Sierra Nevada de Santa Marta, Colombia, has longer, more insulative feathers on the chest and back, than its lower‐elevation counterpart the grey‐breasted wood wren (H. leucophrys). However, we did not find evidence for the same specializations in subspecies of H. leucophrys that live at high elevations on other elevational gradients in the Colombian Andes, although similar adaptive solutions have arisen in separate mountain systems like the Himalayas. Adaptations in plumage may be associated with the recurrence of elevational species replacements throughout the tropics.     

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.     

Elevational gradients in ant species richness: area, geometry, and Rapoport's rule

Studying the distributions of plants and animals along environmental gradients can illuminate the factors governing and maintaining species diversity. There are two general predictions of how species richness and elevation are related: either species richness decreases monotonically with increasing elevation or richness peaks at mid-elevations. Several processes might contribute to this pattern. In this paper, I examine patterns in ant species richness along elevational gradients in three states in the western US: Colorado, Nevada, and Utah. I test for the effects of available area and the geometric constraints model on species richness patterns. I also test Rapoport's rescue hypothesis, which relates the extent of species' elevational ranges to patterns in species richness. In each state, species richness peaked at mid-elevations. Area explained more variation in species richness than the geometric constraints model in Colorado and Utah, but not in Nevada. Area and geometric constraints together explained 90%, 99%, and 57% of the variation in species richness in Colorado, Nevada, and Utah, respectively. Even though there were peaks at mid-elevations, I still found a strong Rapoport effect. This work suggests that the influences of area and geometric constraints cannot be overlooked when examining patterns in species richness along environmental gradients.     

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.     

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.     

Patterns and drivers of intraspecific variation in avian life history along elevational gradients: a meta‐analysis

Elevational gradients provide powerful natural systems for testing hypotheses regarding the role of environmental variation in the evolution of life‐history strategies. Case studies have revealed shifts towards slower life histories in organisms living at high elevations yet no synthetic analyses exist of elevational variation in life‐history traits for major vertebrate clades. We examined (i) how life‐history traits change with elevation in paired populations of bird species worldwide, and (ii) which biotic and abiotic factors drive elevational shifts in life history. Using three analytical methods, we found that fecundity declined at higher elevations due to smaller clutches and fewer reproductive attempts per year. By contrast, elevational differences in traits associated with parental investment or survival varied among studies. High‐elevation populations had shorter and later breeding seasons, but longer developmental periods implying that temporal constraints contribute to reduced fecundity. Analyses of clutch size data, the trait for which we had the largest number of population comparisons, indicated no evidence that phylogenetic history constrained species‐level plasticity in trait variation associated with elevational gradients. The magnitude of elevational shifts in life‐history traits were largely unrelated to geographic (altitude, latitude), intrinsic (body mass, migratory status), or habitat covariates. Meta‐population structure, methodological issues associated with estimating survival, or processes shaping range boundaries could potentially explain the nature of elevational shifts in life‐history traits evident in this data set. We identify a new risk factor for montane populations in changing climates: low fecundity will result in lower reproductive potential to recover from perturbations, especially as fewer than half of the species experienced higher survival at higher elevations.