Why tropical forest lizards are vulnerable to climate warming

Narrow safety margin in the phyllosphere during thermal extremes

The thermal limits of terrestrial ectotherms vary more locally than globally. Local microclimatic variations can explain this pattern, but the underlying mechanisms remain unclear. We show that cryptic microclimatic variations at the scale of a single leaf determine the thermal limit in a community of arthropod herbivores living on the same host plant. Herbivores triggering an increase in transpiration, thereby cooling the leaf, had a lower thermal limit than those decreasing leaf transpiration and causing the leaf to warm up. These subtle mechanisms have major consequences for the safety margin of these herbivores during thermal extremes. Our findings suggest that temperate species may be more vulnerable to heat waves than previously thought.

The thermal limit of ectotherms provides an estimate of vulnerability to climate change. It differs between contrasting microhabitats, consistent with thermal ecology predictions that a species’ temperature sensitivity matches the microclimate it experiences. However, observed thermal limits may differ between ectotherms from the same environment, challenging this theory. We resolved this apparent paradox by showing that ectotherm activity generates microclimatic deviations large enough to account for differences in thermal limits between species from the same microhabitat. We studied upper lethal temperature, effect of feeding mode on plant gas exchange, and temperature of attacked leaves in a community of six arthropod species feeding on apple leaves. Thermal limits differed by up to 8 °C among the species. Species that caused an increase in leaf transpiration (+182%), thus cooling the leaf, had a lower thermal limit than those that decreased leaf transpiration (−75%), causing the leaf to warm up. Therefore, cryptic microclimatic variations at the scale of a single leaf determine the thermal limit in this community of herbivores. We investigated the consequences of these changes in plant transpiration induced by plant–insect feedbacks for species vulnerability to thermal extremes. Warming tolerance was similar between species, at ±2 °C, providing little margin for resisting increasingly frequent and intense heat waves. The thermal safety margin (the difference between thermal limit and temperature) was greatly overestimated when air temperature or intact leaf temperature was erroneously used. We conclude that feedback processes define the vulnerability of species in the phyllosphere, and beyond, to thermal extremes.

Potential Effects of Future Climate Changes on Brazilian Cool-Adapted Stoneflies (Insecta: Plecoptera)

The continuous pursuit of welfare and economic development through the exploitation of natural resources by human societies consequently resulted in the ongoing process of climate change. Changes in the distribution of species towards the planet's poles and mountain tops are some of the expected to biological consequences of this process. Here, we assessed the potential effects of future climate change on four cool-adapted Gripopterygidae (Insecta: Plecoptera) species [Gripopteryx garbei Navás 1936, G. cancellata (Pictet 1841), Tupiperla gracilis (Burmeister 1839), and T. tessellata (Brauer 1866)] from Southeastern Brazilian Atlantic forest. As species adapted to cold conditions, in the future scenarios of climate change, we expected these organisms to shrink/change their distributions ranges towards areas with suitable climatic conditions in Southern Brazilian regions, when compared with their predicted distributions in present climatic conditions. We used seven principal components derived from 19 environmental variables from Worldclim database for the present scenario and also seven principal components obtained from 17 different Atmosphere-Ocean Global Circulation Models (AOGCMs), considering the most severe emission scenario for green-house gases to predict the species' distributions. Depending on the climatic scenario considered, there were polewards distribution range changes of the species. Additionally, we also observed an important decrease in the amount of protected modeled range for the species in the future scenarios. Considering that this Brazilian region may become hotter in the future and have its precipitation regime changed, as observed in the severe 2013-2014 drought, we believe these species adapted to high altitudes will be severely threatened in the future.

Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms

The urban heat island effect, where urban areas exhibit higher temperatures than less-developed suburban and natural habitats, occurs in cities across the globe and is well understood from a physical perspective and at broad spatial scales. However, very little is known about how thermal variation caused by urbanization influences the ability of organisms to live in cities. Ectotherms are sensitive to environmental changes that affect thermal conditions, and therefore, increased urban temperatures may pose significant challenges to thermoregulation and alter temperature-dependent activity. To evaluate whether these changes to the thermal environment affect the persistence and dispersal of ectothermic species in urban areas, we studied two species of Anolis lizards (Anolis cristatellus and Anolis sagrei) introduced to Miami-Dade County, FL, USA, where they occur in both urban and natural habitats. We calculated canopy openness and measured operative temperature (T_e ), which estimates the distribution of body temperatures in a non-thermoregulating population, in four urban and four natural sites. We also captured lizards throughout the day and recorded their internal body temperature (T_b ). We found that urban areas had more open canopies and higher T_e compared to natural habitats. Laboratory trials showed that A. cristatellus preferred lower temperatures than A. sagrei. Urban sites currently occupied by each species appear to lower thermoregulatory costs for both species, but only A. sagreihad field T_b that were more often within their preferred temperature range in urban habitats compared to natural areas. Furthermore, based on available T_e within each species' preferred temperature range, urban sites with only A. sagrei appear less suitable for A. cristatellus, whereas natural sites with only A. cristatellus are less suitable for A. sagrei. These results highlight how the thermal properties of urban areas contribute to patterns of persistence and dispersal, particularly relevant for studying species invasions worldwide.

Plasticity for desiccation tolerance across Drosophila species is affected by phylogeny and climate in complex ways

Comparative analyses of ectotherm susceptibility to climate change often focus on thermal extremes, yet responses to aridity may be equally important. Here we focus on plasticity in desiccation resistance, a key trait shaping distributions of Drosophila species and other small ectotherms. We examined the extent to which 32 Drosophila species, varying in their distribution, could increase their desiccation resistance via phenotypic plasticity involving hardening, linking these responses to environment, phylogeny and basal resistance. We found no evidence to support the seasonality hypothesis; species with higher hardening plasticity did not occupy environments with higher and more seasonal precipitation. As basal resistance increased, the capacity of species to respond via phenotypic plasticity decreased, suggesting plastic responses involving hardening may be constrained by basal resistance. Trade-offs between basal desiccation resistance and plasticity were not universal across the phylogeny and tended to occur within specific clades. Phylogeny, environment and trade-offs all helped to explain variation in plasticity for desiccation resistance but in complex ways. These findings suggest some species have the ability to counter dry periods through plastic responses, whereas others do not; and this ability will depend to some extent on a species' placement within a phylogeny, along with its basal level of resistance.

Temperature shapes the costs, benefits and geographic diversification of sexual coloration in a dragonfly

The environment shapes the evolution of secondary sexual traits by determining how their costs and benefits vary across the landscape. Given the thermal properties of dark coloration generally, temperature should crucially influence the costs, benefits and geographic diversification of many secondary sexual colour patterns. We tested this hypothesis using sexually selected wing coloration in a dragonfly. We find that greater wing coloration heats males - the magnitude of which improves flight performance under cool conditions but dramatically reduces it under warm conditions. In a colder region of the species' range, behavioural observations of a wild population show that these thermal effects translate into greater territorial acquisition on thermally variable days. Finally, geo-referenced photographs taken by citizen scientists reveal that this sexually selected wing coloration is dramatically reduced in the hottest portions of the species' range. Collectively, our results underscore temperature's capacity to promote and constrain the evolution of sexual coloration.

Comparing thermal performance curves across traits: how consistent are they?

Thermal performance curves (TPCs) are intended to approximate the relationship between temperature and fitness, and are commonly integrated into species distributional models for understanding climate change responses. However, TPCs may vary across traits because selection and environmental sensitivity (plasticity) differ across traits or because the timing and duration of the temperature exposure, here termed time-scale, may alter trait variation. Yet the extent to which TPCs vary temporally and across traits is rarely considered in assessments of climate change responses. Using a common garden approach, we estimate TPCs for standard metabolic rate (SMR), and activity in Drosophila melanogaster at three test temperatures (16, 25 and 30 °C), using flies from each of six developmental temperatures (16, 18, 20, 25, 28 and 30 °C). We examined the effects of time-scale of temperature exposure (mins/hours vs days/weeks) in altering the TPC shape, position and commonly used descriptors of the TPC- thermal optimum (TOPT), thermal limits (TMIN and TMAX) and thermal breadth (TBR). In addition we collated previously published estimates of TPCs for fecundity and egg-to-adult viability in D. melanogaster. We found that the descriptors of the TPCs varied across traits (egg-to-adult viability, SMR, activity and fecundity), but variation in TPCs within these traits was small across studies when measured at the same time-scales. The time-scale at which traits were measured contributed to greater variation in TPCs than the observed variance across traits, although the relative importance of time-scale differed depending on the trait (activity vs fecundity). Variation in the TPC across traits and time-scales suggests that TPCs using single traits may not be an accurate predictor of fitness and thermal adaptation across environments.

Are lizards sensitive to anomalous seasonal temperatures? Long-term thermobiological variability in a subtropical species

Alterations in thermal niches have been widely associated with the Anthropocene erosion of reptiles' diversity. They entail potential physiological constraints for organisms' performance, which can lead to activity restrictions and impact fitness and demography. Reptiles are ectotherms which rely on seasonal periodicity to maximize the performance of biological functions. Despite it, the ecological implications of shifts in local temperatures are barely explored at the seasonal scale. This study aims to assess how changes in air temperature and substrate temperature affect the activity, body temperature (Tb) and thermoregulation patterns of the sand lizard, Liolaemus arambarensis (an endangered, microendemic species from southern Brazil), throughout a four-year period. Field surveys were conducted monthly on a restricted population in a sand-dune habitat. The annual fluctuations of the seasonal temperatures led to significant changes in the activity and Tb of L. arambarensis and shaped thermoregulation trends, suggesting biological plasticity as a key factor in the face of such variability. Lizards tended to maintain seasonal Tb in mild and harsh seasons through increased warming/cooling efforts. Anomalous winter conditions seemed especially critical for individual performance due to their apparent high impact favouring/constraining activity. Activity and thermoregulation were inhibited in frigid winters, probably due to a vulnerable physiology to intense cold spells determined by higher preferred body temperatures than Tb. Our results warn of a complex sensitivity in lizards to anomalous seasonal temperatures, which are potentially enhanced by climate change. The current work highlights the importance of multiannual biomonitoring to disentangle long-term responses in the thermal biology of reptiles and, thereby, to integrate conservation needs in the scope of global change.

Anticipatory parental effects in a subtropical lizard in response to experimental warming

Parental effects may produce adaptive or maladaptive plasticity that either facilitates persistence or increases the extinction risk of species and populations in a changing climate. However, empirical evidence of transgenerational adaptive plastic responses to climate change is still scarce. Here we conducted thermal manipulation experiments with a factorial design in a Chinese lacertid lizard (Takydromus septentrionalis) to identify the fitness consequences of parental effects in response to climate warming. Compared to present climate conditions, a simulated warming climate significantly advanced the timing of oviposition, depressed the immune capability of post-partum females, and decreased the hatching success of embryos, but did not affect female reproductive output (clutch size and egg mass). These results indicate that maternal warming negatively affects female health, and embryonic hatchability. More interestingly, we found that offspring from parents exposed to warming environments survived well under a simulated warming climate, but not under a present climate scenario. Accordingly, our study demonstrates anticipatory parental effects in response to a warming climate in an ectothermic vertebrate. However, the fitness consequences of this parental effect will depend on future climate change scenarios.

Microhabitat selection and communal nesting in the insular Psychedelic Rock Gecko, Cnemaspis psychedelica, in Southern Vietnam with updated information on trade

The Psychedelic Rock Gecko,Cnemaspispsychedelica, was described in 2010 and certainly belongs to the most spectacular gecko discoveries worldwide. The species is endemic to two small offshore islands in Rach Gia Bay. Its striking colour pattern makes the species highly attractive for the international pet market. The existentCnemaspispopulation is negatively affected by habitat degradation and predation by introduced macaques. We herein provide the first characterisation of microhabitat selection of this species, including seasonal variation on Hon Khoai and Hon Tuong islands, Ca Mau Province, Vietnam. We found that characteristics of the selected microhabitat, such as substrate type, temperature and canopy cover slightly differed between the wet and dry seasons. We also demonstrated age-related differences in the selection of perch heights. Communal nesting was, for the first time, reported forC.psychedelica, as well as natural predation by a snake species (Lycodoncapucinus). In addition, we documented ongoing habitat destruction on Hon Khoai Island and recorded illegal trade of live Psychedelic Rock Geckos for the first time on local pet markets in both northern and southern Vietnam. Our findings highlight the need for improved conservation measures in order to reduce anthropogenic impacts on wild populations ofC.psychedelica.

Unraveling the influences of climate change in Lepidosauria (Reptilia)

In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans and many species have shifted their geographic ranges, seasonal activities, migration patterns, abundances and interactions in response to these changes. Projections of future climate change are uncertain, but the Earth's warming is likely to exceed 4.8 °C by the end of 21th century. The vulnerability of a population, species, group or system due to climate change is a function of impact of the changes on the evaluated system (exposure and sensitivity) and adaptive capacity as a response to this impact, and the relationship between these elements will determine the degree of species vulnerability. Predicting the potential future risks to biodiversity caused by climate change has become an extremely active field of research, and several studies in the last two decades had focused on determining possible impacts of climate change on Lepidosaurians, at a global, regional and local level. Here we conducted a systematic review of published studies in order to seek to what extent the accumulated knowledge currently allow us to identify potential trends or patterns regarding climate change effects on lizards, snakes, amphisbaenians and tuatara. We conducted a literature search among online literature databases/catalogues and recorded 255 studies addressing the influence of climate change on a total of 1918 species among 49 Lepidosaurian's families. The first study addressing this subject is dated 1999. Most of the studies focused on species distribution, followed by thermal biology, reproductive biology, behavior and genetics. We concluded that an integrative approach including most of these characteristics and also bioclimatic and environmental variables, may lead to consistent and truly effective strategies for species conservation, aiming to buffer the climate change effects on this group of reptiles.

Intraspecific variation in lizard heat tolerance alters estimates of climate impact

Research addressing the effects of global warming on the distribution and persistence of species generally assumes that population variation in thermal tolerance is spatially constant or overridden by interspecific variation. Typically, this rationale is implicit in sourcing one critical thermal maximum (CT_max ) population estimate per species to model spatiotemporal cross-taxa variation in heat tolerance. Theory suggests that such an approach could result in biased or imprecise estimates and forecasts of impact from climate warming, but limited empirical evidence in support of those expectations exists. We experimentally quantify the magnitude of intraspecific variation in CT_max among lizard populations, and the extent to which incorporating such variability can alter estimates of climate impact through a biophysical model. To do so, we measured CT_max from 59 populations of 15 Iberian lizard species (304 individuals). The overall median CT_max across all individuals from all species was 42.8°C and ranged from 40.5 to 48.3°C, with species medians decreasing through xeric, climate-generalist and mesic taxa. We found strong statistical support for intraspecific differentiation in CT_max by up to a median of 3°C among populations. We show that annual restricted activity (operative temperature > CT_max ) over the Iberian distribution of our study species differs by a median of >80 hr per 25-km² grid cell based on different population-level CT_max estimates. This discrepancy leads to predictions of spatial variation in annual restricted activity to change by more than 20 days for six of the study species. Considering that during restriction periods, reptiles should be unable to feed and reproduce, current projections of climate-change impacts on the fitness of ectotherm fauna could be under- or over-estimated depending on which population is chosen to represent the physiological spectra of the species in question. Mapping heat tolerance over the full geographical ranges of single species is thus critical to address cross-taxa patterns and drivers of heat tolerance in a biologically comprehensive way.

How much starvation, desiccation and oxygen depletion can Drosophila melanogaster tolerate before its upper thermal limits are affected?

Heat tolerance is commonly assessed as the critical thermal maximum (CTmax) using the dynamic method exposing organisms to a gradually increasing (ramping) temperature until organisms fall into a coma. The CTmax estimate is dependent on the ramping rate, with decreased rates leading to longer treatments and ultimately lower CTmax estimates. There is a current discussion surrounding the physiological dynamics of the effect of the time of exposure by temperature interaction on these estimates. Besides temperature the time of exposure to limited food (starvation), desiccation, and reduced levels of oxygen or increased levels of CO₂ may, in interaction with ramping rate, act as confounding factors when assessing upper thermal limits using the dynamic method. Here we test the role of the different potentially confounding factors for assaying thermal tolerance using a ramping assay under four different ramping rates, varying from 0.01 °C/min to 0.2 °C/min. We find that CTmax values are higher at faster ramping rates and that oxygen or CO₂ concentration does not show any negative effect on the CTmax values obtained within the experimental pre-treatment period (32 h). Both water (up to 6 h) and food (up to 42 h) deprivation prior to assay showed a negative correlation with thermal tolerance of the flies. For both traits, we found a significant interaction with ramping rate, most likely due to prolonged assays at lower rates. However, as little water was lost during the ramping assay and as food deprivation only modestly affected CTmax values, results were very robust to the conditions experienced during the assay (even at slow rates) and mainly affected by the conditions experienced prior to performing the assay. Thus, for the most commonly applied experimental conditions CTmax estimates are unlikely to be biased or confounded by ramping rate, starvation, desiccation or deteriorating atmospheric composition.

Climate-driven declines in arthropod abundance restructure a rainforest food web

A number of studies indicate that tropical arthropods should be particularly vulnerable to climate warming. If these predictions are realized, climate warming may have a more profound impact on the functioning and diversity of tropical forests than currently anticipated. Although arthropods comprise over two-thirds of terrestrial species, information on their abundance and extinction rates in tropical habitats is severely limited. Here we analyze data on arthropod and insectivore abundances taken between 1976 and 2012 at two midelevation habitats in Puerto Rico's Luquillo rainforest. During this time, mean maximum temperatures have risen by 2.0 °C. Using the same study area and methods employed by Lister in the 1970s, we discovered that the dry weight biomass of arthropods captured in sweep samples had declined 4 to 8 times, and 30 to 60 times in sticky traps. Analysis of long-term data on canopy arthropods and walking sticks taken as part of the Luquillo Long-Term Ecological Research program revealed sustained declines in abundance over two decades, as well as negative regressions of abundance on mean maximum temperatures. We also document parallel decreases in Luquillo's insectivorous lizards, frogs, and birds. While El Niño/Southern Oscillation influences the abundance of forest arthropods, climate warming is the major driver of reductions in arthropod abundance, indirectly precipitating a bottom-up trophic cascade and consequent collapse of the forest food web.

Effect of temperature on the locomotor performance of species in a lizard assemblage in the Puna region of Argentina

Locomotion is relevant to the ecology of reptiles because of its presumed influence on an organism's Darwinian fitness. Moreover, in ectothermic species, physiological performance capacity is affected by body temperature. We analyzed two components of locomotor performance in three species of lizards, Phymaturus extrilidus, Liolaemus parvus, and Liolaemus ruibali, in the Puna environment of Argentina. First, we estimated the thermal sensitivity of locomotion by measuring sprint speed at four different body temperatures. We included two measures of sprint speed: initial velocity and long sprint for sustained runs. Based on these data, we calculated the optimal temperature for performance and the optimal performance breadth. We also estimated endurance capacity at a single temperature. Maximum sprint speed for L. parvus was greater than L. ruibali and P. extrilidus in both initial velocity and long sprint. In contrast, L. parvus exhibited lower levels of endurance than L. ruibali and P. extrilidus. However, endurance in L. ruibali exceeded that of P. extrilidus. The species differed in the optimal temperature for the initial velocity with the lowest for L. ruibali (31.8 °C) followed by P. extrilidus (33.25 °C) and then L. parvus (36.25 °C). The optimal temperature for long sprint varied between 32 and 36 °C for all species. We found that all species attained maximum performance at body temperatures commonly experienced during daily activity, which was higher than the thermal quality of the environment. We found evidence for thermal sensitivity in locomotor performance in these species. However, we also show that the broad thermal breadth of performance suggests that the lizards are capable of sustaining near optimal levels of locomotor performance at ambient temperatures that would appear to be suboptimal. Thus, this lizard assemblage is capable of coping with the highly variable climatic conditions in the Puna region of Argentina.

Main factors affecting lacertid lizard thermal ecology

The thermal ecology of ectotherms has been studied for almost 2 centuries, but additional attention is currently being paid to it, to understand how organisms deal with the environment in a climate change context. A consensus is still far away due to the large number of factors involved and their complex interactions. In this context, 3 analyses in lacertid lizards were carried out: (i) a meta-analysis, to test for differences between body and air temperatures from 71 populations; (ii) a meta-analysis concerning correlations between body and air temperatures from 60 populations; and (iii) a multimodel inference of thermoregulation effectiveness indices from 45 populations. The importance of different factors, including body size, habitat, insularity, altitude, climate and season, was evaluated in all analyses to model the response variables. A strong seasonality effect was observed, with a consistent pattern of less effective thermoregulation in summer compared to other seasons. Altitude was the second most important factor, with a consistent higher thermoregulation effort in populations occurring at high elevations (>1000 m above sea level). Other factors, such as insularity or body size, can also be important, but did not exhibit a clear pattern. Finally, thermoregulation was less affected by climate and habitat type.

Thermal ecology and activity patterns of six species of tropical night lizards (Squamata: Xantusiidae: Lepidophyma) from Mexico

Activity patterns in ectotherms rely on the structure of the thermal environment and thermoregulatory opportunities during activity periods. A dichotomy between diurnal and nocturnal ectotherms is not clear in every case, and temperature can directly affect the daily activity period in these organisms during both photophase and scotophase. In the present study we evaluate the thermal ecology of six tropical night lizards (genus Lepidophyma) from Mexico. Our results indicate a thermoconformer strategy in most of the studied species. In these species, thermal tolerances are associated with environmental temperatures to which they are exposed. Furthermore, thermal quality of the environment directly determines the daily activity period. Therefore, we argue that diurnal activity in Lepidophyma species is determined by local thermal conditions.

Thermal ecology and microhabitat use of an arboreal lizard in two different Pantanal wetland phytophysionomies (Brazil)

Temperature is one of the main environmental variables shaping the evolution and biology of terrestrial ectotherms. The Pantanal is the largest continuous wetland in the World. However, a lack of knowlegde still exists on the thermal ecology of terrestrial ectothems from this wetland. In this context, the thermal ecology of the lizard Tropidurus lagunablanca Carvalho, 2016 (Squamata, Tropiduridae) was investigated in the Brazilian Pantanal. The thermal ecology and microhabitat use of lizards from a riparian forest was compared to lizards from a park savanna. At both studied areas, air and body temperatures of lizards did not differ between sexes. Mean T. lagunablanca body temperatures were higher at the savanna compared to the forest, while air temperatures were similar in both habitats. The main substrates were tree trunks, with a frequency of approximately 90% of the observations. Lizards from the savanna used higher perches than those from the forest despite -in average- trees were higher at the forest. Lizard sun and shade exposure was similar for both areas. Lizards from both habitats showed similar strong linear relationships between body and air temperatures. However, lizard behaviour of using tree trunk perches differently under different sunlight situations suggests that these lizards actively thermoregulate. Further research on the thermoregulation abilities of this species, with a null hypotesis and behavioral observations will shed light on lizard thermal biology. Studies on the ecophysiological aspects of these lizards should be a priority to understand how they will react to climate change and which conservation measures will be more effective concerning their preservation.

Climate and foraging mode explain interspecific variation in snake metabolic rates

The energy cost of self-maintenance is a critical facet of life-history strategies. Clarifying the determinant of interspecific variation in metabolic rate (MR) at rest is important to understand and predict ecological patterns such as species distributions or responses to climatic changes. We examined variation of MR in snakes, a group characterized by a remarkable diversity of activity rates and a wide distribution. We collated previously published MR data (n = 491 observations) measured in 90 snake species at different trial temperatures. We tested for the effects of metabolic state (standard MR (SMR) versus resting MR (RMR)), foraging mode (active versus ambush foragers) and climate (temperature and precipitation) while accounting for non-independence owing to phylogeny, body mass and thermal dependence. We found that RMR was 40% higher than SMR, and that active foragers have higher MR than species that ambush their prey. We found that MR was higher in cold environments, supporting the metabolic cold adaptation hypothesis. We also found an additive and positive effect of precipitation on MR suggesting that lower MR in arid environments may decrease dehydration and energetic costs. Altogether, our findings underline the complex influences of climate and foraging mode on MR and emphasize the relevance of these facets to understand the physiological impact of climate change.

Optimal Representation of Anuran Call Spectrum in Environmental Monitoring Systems Using Wireless Sensor Networks

The analysis and classification of the sounds produced by certain animal species, notably anurans, have revealed these amphibians to be a potentially strong indicator of temperature fluctuations and therefore of the existence of climate change. Environmental monitoring systems using Wireless Sensor Networks are therefore of interest to obtain indicators of global warming. For the automatic classification of the sounds recorded on such systems, the proper representation of the sound spectrum is essential since it contains the information required for cataloguing anuran calls. The present paper focuses on this process of feature extraction by exploring three alternatives: the standardized MPEG-7, the Filter Bank Energy (FBE), and the Mel Frequency Cepstral Coefficients (MFCC). Moreover, various values for every option in the extraction of spectrum features have been considered. Throughout the paper, it is shown that representing the frame spectrum with pure FBE offers slightly worse results than using the MPEG-7 features. This performance can easily be increased, however, by rescaling the FBE in a double dimension: vertically, by taking the logarithm of the energies; and, horizontally, by applying mel scaling in the filter banks. On the other hand, representing the spectrum in the cepstral domain, as in MFCC, has shown additional marginal improvements in classification performance.

Heritability of climate-relevant traits in a rainforest skink

There is justified concern about the impact of global warming on the persistence of tropical ectotherms. There is also growing evidence for strong selection on climate-relevant physiological traits. Understanding the evolutionary potential of populations is especially important for low dispersal organisms in isolated populations, because these populations have little choice but to adapt. Despite this, direct estimates of heritability and genetic correlations for physiological traits in ectotherms-which will determine their evolutionary responses to selection-are sparse, especially for reptiles. Here we examine the heritabilities and genetic correlations for a set of four morphological and six climate-relevant physiological traits in an isolated population of an Australian rainforest lizard, Lampropholis coggeri. These traits show considerable variation across populations in this species, suggesting local adaptation. From laboratory crosses, we estimated very low to moderate heritability of temperature-related physiological traits (h² < 0.31), but significant and higher heritability of desiccation resistance (h²~0.42). These values contrasted with uniformly higher heritabilities (h² > 0.51) for morphological traits. At the phenotypic level, there were positive associations among the morphological traits and between thermal limits. Growth rate was positively correlated with thermal limits, but there was no indication that morphology and physiology were linked in any other way. We found some support for a specialist-generalist trade-off in the thermal performance curve, but otherwise there was no evidence for evolutionary constraints, suggesting broadly labile multivariate trait structure. Our results indicate little potential to respond to selection on thermal traits in this population and provide new insights into the capacity of tropical ectotherms to adapt in situ to rapid climate change.

Searching for Biotic Multipliers of Climate Change

SYNOPSIS

As climates change, biologists need to prioritize which species to understand, predict, and protect. One way is to identify key species that are both sensitive to climate change and that disproportionately affect communities and ecosystems. These "biotic multipliers" provide efficient targets for research and conservation. Here, we propose eight mechanistic hypotheses related to impact and sensitivity that suggest that top consumers might often act as biotic multipliers of climate change. For impact, top consumers often affect communities and ecosystems through strong top-down effects. For sensitivity, metabolic theory and data suggest that photosynthesis and respiration differ in temperature responses, potentially increasing the sensitivity of consumers relative to plants. Larger-bodied organisms are typically more thermally sensitive than smaller ones, suggesting how large top consumers might be more sensitive than their smaller prey. In addition, traits related to predation are more sensitive than defensive traits to temperature. Top consumers might also be more sensitive because they often lag behind prey in phenological responses. The combination of low population sizes and demographic traits of top consumers could make them more sensitive to disturbances like climate change, which could slow their recovery. As top consumers are positioned at the top of the food chain, many small effects can accumulate from other trophic levels to affect top consumers. Finally, top consumers also often disperse more frequently and farther than prey, potentially leading to greater sensitivity to climate-induced changes in ranges and subsequent impacts on invaded communities. Overall, we expect that large, ectothermic top consumers and mobile predators might frequently be biotic multipliers of climate change. However, this prediction depends on the particular features of species, habitats, and ecosystems. In specific cases, herbivores, plants, or pathogens might be more sensitive than top consumers or have greater community impacts. To predict biotic multipliers, we need to compare sensitivities and impacts across trophic groups in a broader range of ecosystems as well as perform experiments that uncouple proposed mechanisms. Overall, the biotic multiplier concept offers an alternative prioritization scheme for research and conservation that includes impacts on communities and ecosystems.

Is the future already here? The impact of climate change on the distribution of the eastern coral snake (Micrurus fulvius)

Anthropogenic climate change is a significant global driver of species distribution change. Although many species have undergone range expansion at their poleward limits, data on several taxonomic groups are still lacking. A common method for studying range shifts is using species distribution models to evaluate current, and predict future, distributions. Notably, many sources of ‘current’ climate data used in species distribution modeling use the years 1950–2000 to calculate climatic averages. However, this does not account for recent (post 2000) climate change. This study examines the influence of climate change on the eastern coral snake (Micrurus fulvius). Specifically, we: (1) identified the current range and suitable environment of M. fulvius in the Southeastern United States, (2) investigated the potential impacts of climate change on the distribution of M. fulvius, and (3) evaluated the utility of future models in predicting recent (2001–2015) records. We used the species distribution modeling program Maxent and compared both current (1950–2000) and future (2050) climate conditions. Future climate models showed a shift in the distribution of suitable habitat across a significant portion of the range; however, results also suggest that much of the Southeastern United States will be outside the range of current conditions, suggesting that there may be no-analog environments in the future. Most strikingly, future models were more effective than the current models at predicting recent records, suggesting that range shifts may already be occurring. These results have implications for both M. fulvius and its Batesian mimics. More broadly, we recommend future Maxent studies consider using future climate data along with current data to better estimate the current distribution.

Thermal niche evolution across replicated Anolis lizard adaptive radiations

Elucidating how ecological and evolutionary mechanisms interact to produce and maintain biodiversity is a fundamental problem in evolutionary ecology. Here, we focus on how physiological evolution affects performance and species coexistence along the thermal niche axis in replicated radiations of Anolis lizards best known for resource partitioning based on morphological divergence. We find repeated divergence in thermal physiology within these radiations, and that this divergence significantly affects performance within natural thermal environments. Morphologically similar species that co-occur invariably differ in their thermal physiology, providing evidence that physiological divergence facilitates species coexistence within anole communities. Despite repeated divergence, phylogenetic comparative analyses indicate that physiological traits have evolved more slowly than key morphological traits related to the structural niche. Phylogenetic analyses also reveal that physiological divergence is correlated with divergence in broad-scale habitat climatic features commonly used to estimate thermal niche evolution, but that the latter incompletely predicts variation in the former. We provide comprehensive evidence for repeated adaptive evolution of physiological divergence within Anolis adaptive radiations, including the complementary roles of physiological and morphological divergence in promoting community-level diversity. We recommend greater integration of performance-based traits into analyses of climatic niche evolution, as they facilitate a more complete understanding of the phenotypic and ecological consequences of climatic divergence.

Phylogenetic homogenization of amphibian assemblages in human-altered habitats across the globe

Habitat conversion is driving biodiversity loss and restructuring species assemblages across the globe. Responses to habitat conversion vary widely, however, and little is known about the degree to which shared evolutionary history underlies changes in species richness and composition. We analyzed data from 48 studies, comprising 438 species on five continents, to understand how taxonomic and phylogenetic diversity of amphibian assemblages shifts in response to habitat conversion. We found that evolutionary history explains the majority of variation in species' responses to habitat conversion, with specific clades scattered across the amphibian tree of life being favored by human land uses. Habitat conversion led to an average loss of 139 million years of amphibian evolutionary history within assemblages, high species and lineage turnover at landscape scales, and phylogenetic homogenization at the global scale (despite minimal taxonomic homogenization). Lineage turnover across habitats was greatest in lowland tropical regions where large species pools and stable climates have perhaps given rise to many microclimatically specialized species. Together, our results indicate that strong phylogenetic clustering of species' responses to habitat conversion mediates nonrandom structuring of local assemblages and loss of global phylogenetic diversity. In an age of rapid global change, identifying clades that are most sensitive to habitat conversion will help prioritize use of limited conservation resources.

Under the weather?-The direct effects of climate warming on a threatened desert lizard are mediated by their activity phase and burrow system

For ectotherms such as lizards, the importance of behavioural thermoregulation in avoiding thermal extremes is well-established and is increasingly acknowledged in modern studies of climate warming and its impacts. Less appreciated and understood are the buffering roles of retreat sites and activity phase, in part because of logistical challenges of studying below-ground activity. Burrowing and nocturnal activity are key behavioural adaptations that have enabled a diverse range of reptiles to survive extreme environmental temperatures within hot desert regions. Yet, the direct impact of recent global warming on activity potential has been hypothesised to have caused extinctions in desert lizards, including the Australian arid zone skink Liopholis kintorei. We test the relevance of this hypothesis through a detailed characterisation of the above- and below-ground thermal and hydric microclimates available to, and used by, L. kintorei. We integrate operative temperatures with observed body temperatures to construct daily activity budgets, including the inference of subterranean behaviour. We then assess the likelihood that contemporary and future local extinctions in this species, and those of similar burrowing habits, could be explained by the direct effects of warming on its activity budget and exposure to thermal extremes. We found that L. kintorei spent only 4% of its time active on the surface, primarily at dusk, and that overall potential surface activity will be increased, not restricted, with climate warming. The burrow system provides an exceptional buffer to current and future maximum extremes of temperature (≈40°C reduction from potential surface temperatures), and desiccation (burrows near 100% humidity). Therefore, any climate warming impacts on this species are likely to be indirect. Our findings reflect the general buffering capacity of underground microclimates, therefore, our conclusions for L. kintorei are more generally applicable to nocturnal and crepuscular ectotherms, and highlight the need to consider the buffering properties of retreat sites and activity phase when forecasting climate change impacts.

Thermal physiology of Amazonian lizards (Reptilia: Squamata)

We summarize thermal-biology data of 69 species of Amazonian lizards, including mode of thermoregulation and field-active body temperatures (Tb). We also provide new data on preferred temperatures (Tpref), voluntary and thermal-tolerance ranges, and thermal-performance curves (TPC's) for 27 species from nine sites in the Brazilian Amazonia. We tested for phylogenetic signal and pairwise correlations among thermal traits. We found that species generally categorized as thermoregulators have the highest mean values for all thermal traits, and broader ranges for Tb, critical thermal maximum (CTmax) and optimal (Topt) temperatures. Species generally categorized as thermoconformers have large ranges for Tpref, critical thermal minimum (CTmin), and minimum voluntary (VTmin) temperatures for performance. Despite these differences, our results show that all thermal characteristics overlap between both groups and suggest that Amazonian lizards do not fit into discrete thermoregulatory categories. The traits are all correlated, with the exceptions of (1) Topt, which does not correlate with CTmax, and (2) CTmin, and correlates only with Topt. Weak phylogenetic signals for Tb, Tpref and VTmin indicate that these characters may be shaped by local environmental conditions and influenced by phylogeny. We found that open-habitat species perform well under present environmental conditions, without experiencing detectable thermal stress from high environmental temperatures induced in lab experiments. For forest-dwelling lizards, we expect warming trends in Amazonia to induce thermal stress, as temperatures surpass the thermal tolerances for these species.

How sensitive are temperate tadpoles to climate change? The use of thermal physiology and niche model tools to assess vulnerability

Ectotherms are vulnerable to climate change, given their dependence on temperature, and amphibians are particularly interesting because of their complex life cycle. Tadpoles may regulate their body temperature by using suitable thermal microhabitats. Thus, their physiological responses are the result of adjustment to the local thermal limits experienced in their ponds. We studied three anuran tadpole species present in Argentina and Chile: Pleurodema thaul and Pleurodema bufoninum that are seasonal and have broad geographic ranges, and Batrachyla taeniata, a geographically restricted species with overwintering tadpoles. Species with restricted distribution are more susceptible to climate change than species with broader distribution that may cope with potential climatic changes in the environments in which they occur. We aim to test whether these species can buffer the potential effects of climate warming. We used ecological niche models and the outcomes of their thermal attributes (critical thermal limits, optimal temperature, and locomotor performance breadth) as empirical evidence of their capacity. We found that Pleurodema species show broader performance curves, related to their occurrence, while the geographically restricted B. taeniata shows a narrower thermal breadth, but is faster in warmer conditions. The modeled distributions and empirical physiological results suggest no severe threats for these three anurans. However, the risk level is increasing and a retraction of their distribution range might be possible for Pleurodema species, and some local population extinctions may happen, particularly for the narrowly distributed B. taeniata.

Dispersal and population state of an endangered island lizard following a conservation translocation

Population size is widely used as a unit of ecological analysis, yet to estimate population size requires accounting for observed and latent heterogeneity influencing dispersion of individuals across landscapes. In newly established populations, such as when animals are translocated for conservation, dispersal and availability of resources influence patterns of abundance. We developed a process to estimate population size using N-mixture models and spatial models for newly established and dispersing populations. We used our approach to estimate the population size of critically endangered St. Croix ground lizards (Ameiva polops) five years after translocation of 57 individuals to Buck Island, an offshore island of St. Croix, United States Virgin Islands. Estimates of population size incorporated abiotic variables, dispersal limits, and operative environmental temperature available to the lizards to account for low species detection. Operative environmental temperature and distance from the translocation site were always important in fitting the N-mixture model indicating effects of dispersal and species biology on estimates of population size. We found that the population is increasing its range across the island by 5-10% every six months. We spatially interpolated site-specific abundance from the N-mixture model to the entire island, and we estimated 1,473 (95% CI, 940-1,802) St. Croix ground lizards on Buck Island in 2013 corresponding to survey results. This represents a 26-fold increase since the translocation. We predicted the future dispersal of the lizards to all habitats on Buck Island, with the potential for the population to increase by another five times in the future. Incorporating biologically relevant covariates as explicit parameters in population models can improve predictions of population size and the future spread of species introduced to new localities.

Adaptation to a latitudinal thermal gradient within a widespread copepod species: the contributions of genetic divergence and phenotypic plasticity

Understanding how populations adapt to heterogeneous thermal regimes is essential for comprehending how latitudinal gradients in species diversification are formed, and how taxa will respond to ongoing climate change. Adaptation can occur by innate genetic factors, by phenotypic plasticity, or by a combination of both mechanisms. Yet, the relative contribution of such mechanisms to large-scale latitudinal gradients of thermal tolerance across conspecific populations remains unclear. We examine thermal performance in 11 populations of the intertidal copepod Tigriopus californicus, ranging from Baja California Sur (Mexico) to British Columbia (Canada). Common garden experiments show that survivorship to acute heat-stress differs between populations (by up to 3.8°C in LD₅₀ values), reflecting a strong genetic thermal adaptation. Using a split-brood experiment with two rearing temperatures, we also show that developmental phenotypic plasticity is beneficial to thermal tolerance (by up to 1.3°C), and that this effect differs across populations. Although genetic divergence in heat tolerance strongly correlates with latitude and temperature, differences in the plastic response do not. In the context of climate warming, our results confirm the general prediction that low-latitude populations are most susceptible to local extinction because genetic adaptation has placed physiological limits closer to current environmental maxima, but our results also contradict the prediction that phenotypic plasticity is constrained at lower latitudes.

A positive relationship between spring temperature and productivity in 20 songbird species in the boreal zone

Anthropogenic climate warming has already affected the population dynamics of numerous species and is predicted to do so also in the future. To predict the effects of climate change, it is important to know whether productivity is linked to temperature, and whether species' traits affect responses to climate change. To address these objectives, we analysed monitoring data from the Finnish constant effort site ringing scheme collected in 1987-2013 for 20 common songbird species together with climatic data. Warm spring temperature had a positive linear relationship with productivity across the community of 20 species independent of species' traits (realized thermal niche or migration behaviour), suggesting that even the warmest spring temperatures remained below the thermal optimum for reproduction, possibly due to our boreal study area being closer to the cold edge of all study species' distributions. The result also suggests a lack of mismatch between the timing of breeding and peak availability of invertebrate food of the study species. Productivity was positively related to annual growth rates in long-distance migrants, but not in short-distance migrants. Across the 27-year study period, temporal trends in productivity were mostly absent. The population sizes of species with colder thermal niches had decreasing trends, which were not related to temperature responses or temporal trends in productivity. The positive connection between spring temperature and productivity suggests that climate warming has potential to increase the productivity in bird species in the boreal zone, at least in the short term.

Thermal biology mediates responses of amphibians and reptiles to habitat modification

Human activities often replace native forests with warmer, modified habitats that represent novel thermal environments for biodiversity. Reducing biodiversity loss hinges upon identifying which species are most sensitive to the environmental conditions that result from habitat modification. Drawing on case studies and a meta-analysis, we examined whether observed and modelled thermal traits, including heat tolerances, variation in body temperatures, and evaporative water loss, explained variation in sensitivity of ectotherms to habitat modification. Low heat tolerances of lizards and amphibians and high evaporative water loss of amphibians were associated with increased sensitivity to habitat modification, often explaining more variation than non-thermal traits. Heat tolerances alone explained 24-66% (mean = 38%) of the variation in species responses, and these trends were largely consistent across geographic locations and spatial scales. As habitat modification alters local microclimates, the thermal biology of species will likely play a key role in the reassembly of terrestrial communities.

Natural selection on thermal preference, critical thermal maxima and locomotor performance

Climate change is resulting in a radical transformation of the thermal quality of habitats across the globe. Whereas species have altered their distributions to cope with changing environments, the evidence for adaptation in response to rising temperatures is limited. However, to determine the potential of adaptation in response to thermal variation, we need estimates of the magnitude and direction of natural selection on traits that are assumed to increase persistence in warmer environments. Most inferences regarding physiological adaptation are based on interspecific analyses, and those of selection on thermal traits are scarce. Here, we estimate natural selection on major thermal traits used to assess the vulnerability of ectothermic organisms to altered thermal niches. We detected significant directional selection favouring lizards with higher thermal preferences and faster sprint performance at their optimal temperature. Our analyses also revealed correlational selection between thermal preference and critical thermal maxima, where individuals that preferred warmer body temperatures with cooler critical thermal maxima were favoured by selection. Recent published estimates of heritability for thermal traits suggest that, in concert with the strong selective pressures we demonstrate here, evolutionary adaptation may promote long-term persistence of ectotherms in altered thermal environments.