Thermal Niche Breadth Research Articles

Local Climatic Effects on Colonisation and Extinction Drive Changes in Mountain Butterfly Communities

ABSTRACTAimThe capacity of cool refugia to protect cold‐adapted species against climate change may depend on both their initial climatic conditions and how quickly these change. We test how local climatic conditions influence mountain butterfly communities via their effects on colonisation and local extinction.LocationFour mountain ranges in Central Spain.MethodsWe used community temperature index (CTI), based on the climatic niches of constituent species (species temperature index, STI), to estimate thermal affinities for butterfly communities sampled in 1984–2005 to 2017–2022. We related CTI to local temperature, estimated using the model Microclima, and tested for changes to local temperature and CTI over time. We used standard deviation in CTI (CTISD) and species richness to detect effects of colonisation and local extinction on community change. Finally, we tested for differences in thermal affinity and thermal niche breadth (STISD) between species undergoing local extinction or colonisation at each site.ResultsCTI was positively related to local temperature in both periods. However, there were regional differences in rates of change in CTI and local temperature. CTI increased overall, even though temperatures decreased at many sites; and CTI increases were greatest in historically cool sites. Neither CTISD nor species richness changed overall, suggesting that communities experienced equivalent numbers of colonisations and extinctions. Colonising species had warmer thermal affinities than those undergoing local extinction, and species with broader thermal niches increased their occupancy most over time.Main ConclusionsLocal climatic conditions influenced changes to community composition based on species thermal tolerances, resulting in the loss of communities where cool‐affinity species predominated, and a narrower range of community thermal affinities overall. Our results suggest that a regional perspective to identifying climate change refugia is needed to provide a wide range of local climate conditions and rates of change to help adapt conservation to climate change.

On the Brink of Change? Environmental Drivers of Voluntary Thermal Maximum in South American Pitvipers

ABSTRACTAimWe test the relationship between the voluntary thermal maximum (VTMax; the temperature at which an individual actively retreats to a colder site) and geographical/environmental features in the distribution of South American pitvipers. Additionally, we explore the evolution of environmental temperatures and VTMax in species' ranges.LocationSouth America.TaxonSouth American pitvipers of the genera Bothrops and Bothrocophias.MethodsWe experimentally measured the VTMax of 15 species of South American pitvipers. We explored the relationship between VTMax and geographical/environmental features (e.g., latitude, topographic complexity and temperature) with PGLS regressions. Additionally, we explored the evolution of maximum (TMax) and minimum (TMin) environmental temperatures, as well as the Thermal Niche Breadth (TNB) and VTMax, using ancestral state reconstruction and testing for phylogenetic signal.ResultsMean VTMax values for South American pitvipers clustered primarily within the 34°C–36°C range, exhibiting little variation among species or clades. No significant correlations were found between VTMax and climatic or geographic variables. Furthermore, our analysis revealed that these snakes are absent from regions where maximum temperatures surpass their preferred thermal tolerances. Ancestral state reconstruction indicated divergent evolutionary pathways for thermal limits among species, independent of phylogenetic relationships.Main ConclusionsSouth American pitvipers unexpectedly exhibit similar voluntary thermal maximum values across a wide range of habitats and despite distinct phylogenetic relationships. Our results indicate that there is no strong climatic niche conservatism for South American pitvipers, with a likely weak selective pressure of VTMax.

Local climate change velocities and evolutionary history explain multidirectional range shifts in a North American butterfly assemblage.

Species are often expected to shift their distributions either poleward or upslope to evade warming climates and colonise new suitable climatic niches. However, from 18-years of fixed transect monitoring data on 88 species of butterfly in the midwestern United States, we show that butterflies are shifting their centroids in all directions, except towards regions that are warming the fastest (southeast). Butterflies shifted their centroids at a mean rate of 4.87 km year-1. The rate of centroid shift was significantly associated with local climate change velocity (temperature by precipitation interaction), but not with mean climate change velocity throughout the species' ranges. Species tended to shift their centroids at a faster rate towards regions that are warming at slower velocities but increasing in precipitation velocity. Surprisingly, species' thermal niche breadth (range of climates butterflies experience throughout their distribution) and wingspan (often used as metric for dispersal capability) were not correlated with the rate at which species shifted their ranges. We observed high phylogenetic signal in the direction species shifted their centroids. However, we found no phylogenetic signal in the rate species shifted their centroids, suggesting less conserved processes determine the rate of range shift than the direction species shift their ranges. This research shows important signatures of multidirectional range shifts (latitudinal and longitudinal) and uniquely shows that local climate change velocities are more important in driving range shifts than the mean climate change velocity throughout a species' entire range.

Thermal tolerance as a driver of reef fish community structure at the isolated tropical Mid-Atlantic Ridge Islands

Reef fish communities are shaped by historical and ecological factors, including abiotic and biotic mechanisms at different spatial scales, determining species composition, abundance and biomass. The oceanic islands in the Mid-Atlantic Ridge (St. Peter and St. Paul's Archipelago - SPSPA, Ascension, and St. Helena), exhibiting differences in community structure along a 14-degree latitudinal and a 10 °C thermal gradient. We investigate the influence of sea surface temperature, area, age, isolation and phosphate on reef fish community structures. Reef fish trophic structure varies significantly across the islands, with planktivores and herbivore-detritivores showing the highest abundances in SPSPA and Ascension, while less abundant in St. Helena, aligning with the thermal gradient. Variations in reef fish community structures were predominantly influenced by thermal regimes, corroborating the expansion of species' thermal niche breadth at higher latitudes and lower temperatures. This study highlights that in addition to biogeographic factors, temperature is pivotal on shaping oceanic island reef fish community structure.

Warming underpins community turnover in temperate freshwater and terrestrial communities

Rising temperatures are leading to increased prevalence of warm-affinity species in ecosystems, known as thermophilisation. However, factors influencing variation in thermophilisation rates among taxa and ecosystems, particularly freshwater communities with high diversity and high population decline, remain unclear. We analysed compositional change over time in 7123 freshwater and 6201 terrestrial, mostly temperate communities from multiple taxonomic groups. Overall, temperature change was positively linked to thermophilisation in both realms. Extirpated species had lower thermal affinities in terrestrial communities but higher affinities in freshwater communities compared to those persisting over time. Temperature change’s impact on thermophilisation varied with community body size, thermal niche breadth, species richness and baseline temperature; these interactive effects were idiosyncratic in the direction and magnitude of their impacts on thermophilisation, both across realms and taxonomic groups. While our findings emphasise the challenges in predicting the consequences of temperature change across communities, conservation strategies should consider these variable responses when attempting to mitigate climate-induced biodiversity loss.

Multi-dimensional temperature sensitivity of protected tropical mountain rain forests

IntroductionTropical mountain rain forests (TMRF, natural forests at > 300 m asl) are globally important for biodiversity and ecosystem services and are believed to be highly vulnerable to climate change. But there are no specific approaches for rigorous assessment of their vulnerability at the landscape and local scales necessary for management for adaptation. We address the challenge of evaluating the ecological sensitivity to temperature of TMRF, applying a multidimensional approach in protected areas over a 440–2,950 m asl altitudinal gradient in Costa Rica, synthesizing results of a long-term research programme (2012-present). We evaluate the sensitivity to the current spatial temperature gradient of eleven ecosystem properties in three categories: forest composition and diversity, thermal characteristics of forest stands and forest structure and dynamics.MethodsData are from 29 to 32 plots of 50 m x 50 m (0.25 ha) distributed over the gradient, in which all trees, palms and tree ferns ≥ 10 dbh are identified to species and measured for recruitment, growth and mortality. An experimental study of leaf litter decomposition rates was carried out in twelve plots. Current and future (SSP 585, 2070) values of mean annual temperatures MAT were obtained from online climate surfaces. Thermal characteristics of forest stands were determined using MATs of species occurrences in GBIF and include a new index, the Community Thermal Capital Index (CTCI), calculated as CTI-MAT.ResultsWe classified degrees of sensitivity to temperature as very weak, weak, moderate or substantial. All eleven ecosystem properties are substantially sensitive, so changes in their values are expected under rising temperatures. Species density, the community temperature index CTI, tree recruitment and mortality rates and leaf litter decomposition rates are positively related to temperature, while the community weighted mean thermal niche breadth, the CTCI, net basal area increments, stand basal area and carbon in aboveground biomass are negatively related. Results point to zones of vulnerability in the protected areas.DiscussionIn montane forests, positive values of the CTCI–climate credit– robust basal area growth and very low mortality and leaf litter decomposition rates suggest healthy ecosystems and no risk of mountaintop extinction. Lowland forests may be vulnerable to degradation and biotic attrition, showing current basal area loss, high mortality and climate debts. National and local actors are participating in a process of adoption of the sensitivity analysis and recommendations regarding zones of vulnerability.

Changes in thermal niche position and breadth of bird assemblages in Spain in relation to increasing temperatures

AbstractAimAnimal communities around the world are responding to climate change by altering their taxonomic composition, mainly through an increase in the colonisation rate of warm‐dwelling species and the local extinction of cold‐dwelling ones. We assessed whether the taxonomic composition of bird assemblages in peninsular Spain has changed in accordance with the recent increase in temperature. We also evaluated the role of species thermal affinities and population dynamics on these changes.LocationPeninsular Spain.TaxonBirds.MethodsWe compared assemblages reported in the last Spanish breeding bird atlases (1998–2002 vs. 2014–2018) in 10 × 10 km squares. We described species' thermal niches by overlaying global species breeding distributions and world temperature metrics (based on mean, minimum, maximum and range), and then aggregated them to obtain a set of community thermal indices for each assemblage (CTIs and CTR for ranges). Long‐term average temperatures and local current temperatures were related to changes in CTIs using spatial GLMMs, which considered habitat change. We identified the species most responsible for variation in assemblages and regressed species' influence on thermal affinities and population dynamics.ResultsCTIs increased with temperature and warm‐dwelling species became more prevalent to the detriment of cold‐dwelling ones. However, we found a counteracting effect of temperature and habitat. Cold‐dwelling forest species were among the most influential species, mainly through colonisation, while warm‐dwelling farmland species contributed through local extinctions (both attenuated local increases in CTI). The mean thermal breadth of assemblages (CTR) decreased with temperatures.Main conclusionsThe taxonomic composition of bird assemblages shifted in line with the main expectations due to global change (thermophilisation), mainly due to local colonisation of warm‐dwelling species, although it did not show the pattern of thermal homogenisation suggested elsewhere. Our results add further evidence of the interplay between climate warming and land‐use change in the ongoing adjustment of animal communities.

Colonizing polar environments: thermal niche evolution in Collembola

Temperature is a primary driver to define the ecophysiological activity and performance of ectotherms. Thus, thermal tolerance limits have a profound effect in determining geographic ranges. In regions with extreme cold temperatures, lower thermal limits of species are a key physiological trait for survival. Moreover, thermal niche breadth also plays an important role in allowing organisms to withstand climatic variability and confers species with broader potential to establish in new regions. Here we study the evolution of thermal tolerance limits among Collembola (Arthropoda) and explore how they are affected by the colonization of polar environments. In addition, we test the hypothesis that globally invasive species are more eurythermal than non‐invasive ones. Critical thermal limits (CTmin and CTmax), classic measurements of thermal tolerance, were compiled from the literature and complemented with experimental assays for springtail species. Genetic data of the mitochondrial gene cytochrome oxidase subunit 1 (COI) was used to assemble a phylogeny. Our results show that polar springtails have lower CTmin and lower CTmax compared to species from temperate and tropical regions, consistent with the Polar pressure hypothesis. We found no phylogenetic signal for CTmax, but low values of phylogenetic signal for CTmin. Globally invasive species do not have significantly broader thermal tolerance breadth (CTrange) than non‐invasive ones, thus not supporting the predictions of the Eurythermality hypothesis. We conclude that polar springtails have evolved their thermal niches in order to adapt to extremely cold environments, which has led to decreasing both upper and lower thermal tolerance limits.

Seasonal Variation in the Thermoregulation Pattern of an Insular Agamid Lizard.

Ectotherms, including lizards, rely on behavioral thermoregulation to maintain their body temperature within an optimal range. The benign climate of islands is expected to favor the thermoregulation efficiency of reptiles throughout their activity period. In this study, we investigated the seasonal variation in thermoregulation in an insular population of the roughtail rock agama (Laudakia stellio) on Naxos Island, Greece. We measured body, operative, and preferred temperatures across three seasons (spring, summer, and autumn), and we evaluated the effectiveness of thermoregulation, using the Hertz index (E). Our results revealed that the effectiveness of thermoregulation was significantly influenced by seasonality. E was quite high in summer (0.97) and spring (0.92), and lowest in autumn (0.81). Accordingly, the quality of the thermal environment was significantly low during autumn, and maximum during summer. However, despite the environmental temperature fluctuations, lizards exhibited remarkable stability in body temperatures. They also adjusted their preferred temperatures seasonally and doubled the thermal niche breadth they occupied during summer, thus enhancing thermoregulation efficiency. Whether or not these adjustments are plastic or fixed local adaptations remains to be explored in further research across multiple years and seasons, including additional insular populations.

Thermal niche breadth and their relationship with sturnira bat species diversification

The interaction between climatic conditions and the ability of organisms to maintain homeostasis regulates the distribution of species on the planet. However, its influence on macroevolutionary dynamics is not well understood. It has been suggested that diversification rates will be different in lineages with narrow thermal niches (specialists) to diversification rates in generalist lineages, but the evidence for this is elusive. Here, we tested this hypothesis by using the most diverse (in species richness and geographic range variation) tropical bat genus within the Phyllostomidae family. We estimated the realized thermal niche breadth of Sturnira species from their geographic range and categorized them as generalists, cold specialists, or warm specialists. We compared dynamic evolutionary models that differ in 1) niche breadth evolution, 2) parental niche breadth inheritance, and 3) whether niche breadth evolution is associated with shifts in diversification rates. Our best-performing model indicates that most Sturnira species arose as specialists in warm climates and that over time, their niche breadth broadens, and just a subset of those species becomes specialists in cold environments. We found that the evolution of realized thermal niche breadth causes fluctuations in per-lineage rates of diversification, where warm specialists boast the highest speciation rates. However, we found no evidence of these changes in niche neither triggering nor being a result of speciation events themselves; this suggests that diversification events in Sturnira could instead depend on allopatric speciation processes such as the development of geographic barriers.

Some like it hot: Thermal preference of the groundwater amphipod Niphargus longicaudatus (Costa, 1851) and climate change implications

Groundwater is a crucial resource for humans and the environment, but its global human demand currently exceeds available volumes by 3.5 times. Climate change is expected to exacerbate this situation by increasing the frequency of droughts along with human impacts on groundwater ecosystems. Despite prior research on the quantitative effects of climate change on groundwater, the direct impacts on groundwater biodiversity, especially obligate groundwater species, remain largely unexplored. Therefore, investigating the potential impacts of climate change, including groundwater temperature changes, is crucial for the survival of obligate groundwater species. This study aimed to determine the thermal niche breadth of the crustacean amphipod species Niphargus longicaudatus by using the chronic method. We found that N. longicaudatus has a wide thermal niche with a natural performance range of 7–9 °C, which corresponds to the thermal regime this species experiences within its distribution range in Italy. The observed range of preferred temperature (PT) was different from the mean annual temperature of the sites from which the species has been collected, challenging the idea that groundwater species are only adapted to narrow temperature ranges. Considering the significant threats of climate change to groundwater ecosystems, these findings provide crucial information for the conservation of obligate groundwater species, suggesting that some of them may be more resilient to temperature changes than previously thought. Understanding the fundamental thermal niche of these species can inform conservation efforts and management strategies to protect groundwater ecosystems and their communities.

Compositional shifts of alpine plant communities across the high Andes

AbstractAimClimate change is transforming mountain summit plant communities worldwide, but we know little about such changes in the High Andes. Understanding large‐scale patterns of vegetation changes across the Andes, and the factors driving these changes, is fundamental to predicting the effects of global warming. We assessed trends in vegetation cover, species richness (SR) and community‐level thermal niches (CTN) and tested whether they are explained by summits' climatic conditions and soil temperature trends.LocationHigh Andes.Time periodBetween 2011/2012 and 2017/2019.Major taxa studiedVascular plants.MethodsUsing permanent vegetation plots placed on 45 mountain summits and soil temperature loggers situated along a ~6800 km N‐S gradient, we measured species and their relative percentage cover and estimated CTN in two surveys (intervals between 5 and 8 years). We then estimated the annual rate of changes for the three variables and used generalized linear models to assess their relationship with annual precipitation, the minimum air temperatures of each summit and rates of change in the locally recorded soil temperatures.ResultsOver time, there was an average loss of vegetation cover (mean = −0.26%/yr), and a gain in SR across summits (mean = 0.38 species m2/yr), but most summits had significant increases in SR and vegetation cover. Changes in SR were positively related to minimum air temperature and soil temperature rate of change. Most plant communities experienced shifts in their composition by including greater abundances of species with broader thermal niches and higher optima. However, the measured changes in soil temperature did not explain the observed changes in CTN.Main conclusionsHigh Andean vegetation is changing in cover and SR and is shifting towards species with wider thermal niche breadths. The weak relationship with soil temperature trends could have resulted from the short study period that only marginally captures changes in vegetation through time.

Seed germination thermal niche differs among nine populations of an annual plant: A modeling approach.

Germination timing is an important determinant of survival and niche breadth of plants. The annual plant Nigella sativa occurs in diverse environments along a steep temperature gradient and thus is a suitable model for the study of germination behavior in response to temperature. We used a modeling approach to compare the germination thermal niche of seeds of nine populations of N. sativa produced in a common garden. Germination time courses were obtained by a newly developed process‐based model, and thermal niche was visualized by plotting germination breadth as a function of after‐ripening time. Seeds were sampled five times: immature (2 weeks before maturity), mature, and afterripened for 1, 2, and 5 months. Immature and mature seeds had a greater depth of dormancy than afterripened seeds, as estimated by lower values of high‐limit temperatures (T h). Afterripening increased germination percentage, synchrony, and thermal niche breadth of all nine populations. The highest asynchrony was for immature and mature seeds, and afterripening enhanced synchrony. Based on the new graphical method, N. sativa has Type 1 nondeep physiological dormancy, and thus, the germination niche is narrow at seed maturity, leading to a delayed germination strategy that is highly dependent on thermal time accumulated during afterripening. Our findings show that there is considerable variation in the germination thermal niche among populations. Temperature regimes in the natural habitats of N. sativa have played a significant role in shaping variation in thermal niche breadth for seed germination of this annual species. The models used in our study precisely predict germination behavior and thermal niche under different environmental conditions. The germination synchrony model also can estimate germination pattern and degree of dormancy during the year, suggesting a useful method for quantification of germination strategies.

Temperature variability interacts with mean temperature to influence the predictability of microbial phenotypes.

Despite their relatively high thermal optima (T opt), tropical taxa may be particularly vulnerable to a rising baseline and increased temperature variation because they live in relatively stable temperatures closer to their T opt. We examined how microbial eukaryotes with differing thermal histories responded to temperature fluctuations of different amplitudes (0 control, ±2, ±4°C) around mean temperatures below or above their T opt. Cosmopolitan dinoflagellates were selected based on their distinct thermal traits and included two species of the same genus (tropical and temperate Coolia spp.), and two strains of the same species maintained at different temperatures for >500 generations (tropical Amphidinium massartii control temperature and high temperature, CT and HT, respectively). There was a universal decline in population growth rate under temperature fluctuations, but strains with narrower thermal niche breadth (temperate Coolia and HT) showed ~10% greater reduction in growth. At suboptimal mean temperatures, cells in the cool phase of the fluctuation stopped dividing, fixed less carbon (C) and had enlarged cell volumes that scaled positively with elemental C, N, and P and C:Chlorophyll‐a. However, at a supra‐optimal mean temperature, fixed C was directed away from cell division and novel trait combinations developed, leading to greater phenotypic diversity. At the molecular level, heat‐shock proteins, and chaperones, in addition to transcripts involving genome rearrangements, were upregulated in CT and HT during the warm phase of the supra‐optimal fluctuation (30 ± 4°C), a stress response indicating protection. In contrast, the tropical Coolia species upregulated major energy pathways in the warm phase of its supra‐optimal fluctuation (25 ± 4°C), indicating a broadscale shift in metabolism. Our results demonstrate divergent effects between taxa and that temporal variability in environmental conditions interacts with changes in the thermal mean to mediate microbial responses to global change, with implications for biogeochemical cycling.

Limited acclimation of leaf traits and leaf temperatures in a subtropical urban heat island.

The consequences of rising temperatures for trees will vary between species based on their abilities to acclimate their leaf thermoregulatory traits and photosynthetic thermal tolerances. We tested the hypotheses that adult trees in warmer growing conditions (i) acclimate their thermoregulatory traits to regulate leaf temperatures, (ii) acclimate their thermal tolerances such that tolerances are positively correlated with leaf temperature and (iii) that species with broader thermal niche breadths have greater acclimatory abilities. To test these hypotheses, we measured leaf traits and thermal tolerances of seven focal tree species across steep thermal gradients in Miami's urban heat island. We found that some functional traits varied significantly across air temperatures within species. For example, leaf thickness increased with maximum air temperature in three species, and leaf mass per area and leaf reflectance both increased with air temperature in one species. Only one species was marginally more homeothermic than expected by chance due to acclimation of its thermoregulatory traits, but this acclimation was insufficient to offset elevated air temperatures. Thermal tolerances acclimated to higher maximum air temperatures in two species. As a result of limited acclimation, leaf thermal safety margins (TSMs) were narrower for trees in hotter areas. We found some support for our hypothesis that species with broader thermal niches are better at acclimating to maintain more stable TSMs across the temperature gradients. These findings suggest that trees have limited abilities to acclimate to high temperatures and that thermal niche specialists may be at a heightened risk of thermal stress as global temperatures continue to rise.

Integrating laboratory experiments and biogeographic modelling approaches to understand sensitivity to ocean warming in rare and common marine annelids.

Among ectotherms, rare species are expected to have a narrower thermal niche breadth and reduced acclimation capacity and thus be more vulnerable to global warming than their common relatives. To assess these hypotheses, we experimentally quantified the thermal sensitivity of seven common, uncommon, and rare species of temperate marine annelids of the genus Ophryotrocha to assess their vulnerability to ocean warming. We measured the upper and lower limits of physiological thermal tolerance, survival, and reproductive performance of each species along a temperature gradient (18, 24, and 30°C). We then combined this information to produce curves of each species' fundamental thermal niche by including trait plasticity. Each thermal curve was then expressed as a habitat suitability index (HSI) and projected for the Mediterranean Sea and temperate Atlantic Ocean under a present day (1970-2000), mid- (2050-2059) and late- (2090-2099) 21st Century scenario for two climate change scenarios (RCP2.6 and RCP8.5). Rare and uncommon species showed a reduced upper thermal tolerance compared to common species, and the niche breadth and acclimation capacity were comparable among groups. The simulations predicted an overall increase in the HSI for all species and identified potential hotspots of HSI decline for uncommon and rare species along the warm boundaries of their potential distribution, though they failed to project the higher sensitivity of these species into a greater vulnerability to ocean warming. In the discussion, we provide some caveats on the implications of our results for conservation efforts.

Decreased thermal niche breadth as a trade-off of antibiotic resistance

Evolutionary theory predicts that adaptations, including antibiotic resistance, should come with associated fitness costs; yet, many resistance mutations seemingly contradict this prediction by inducing no growth rate deficit. However, most growth assays comparing sensitive and resistant strains have been performed under a narrow range of environmental conditions, which do not reflect the variety of contexts that a pathogenic bacterium might encounter when causing infection. We hypothesized that reduced niche breadth, defined as diminished growth across a diversity of environments, can be a cost of antibiotic resistance. Specifically, we test whether chloramphenicol-resistant Escherichia coli incur disproportionate growth deficits in novel thermal conditions. Here we show that chloramphenicol-resistant bacteria have greater fitness costs at novel temperatures than their antibiotic-sensitive ancestors. In several cases, we observed no resistance cost in growth rate at the historic temperature but saw diminished growth at warmer and colder temperatures. These results were consistent across various genetic mechanisms of resistance. Thus, we propose that decreased thermal niche breadth is an under-documented fitness cost of antibiotic resistance. Furthermore, these results demonstrate that the cost of antibiotic resistance shifts rapidly as the environment changes; these context-dependent resistance costs should select for the rapid gain and loss of resistance as an evolutionary strategy.

Joint effects of environmental filtering and dispersal limitation on the species assemblage of the Tibetan Plateau

AbstractAimMountains harbour a rich and non‐random cluster of species, yet knowledge of the species' biological attributes that support their coexistence in the montane community is limited. Here, we investigated the association of species occurrence on the Tibetan Plateau with their morphological, ecological or evolutionary constraints.LocationTibetan Plateau (TP).TaxonMammals and birds.MethodsWe tested whether species occurrence on the TP correlates with morphological, ecological or evolutionary constraints using the spatial distribution, phylogeny, dispersal ability and thermal niche property data for 1353 terrestrial vertebrates (383 mammals and 970 birds). We used standard (non‐phylogenetic) and phylogenetic logistic regressions to elucidate the relative contributions of these attributes of species to explaining their occurrence on the TP. We assessed the geographical patterns of the community structures on the TP and fitted linear mixed models to explore the underlying eco‐evolutionary forces.ResultsThe TP species exhibited a higher cold tolerance, wider thermal niche breadth and higher rate of niche evolution than non‐TP species. We supported the assumption that the TP species were not a random subset from the species pool, but were structured jointly by environmental filtering and dispersal limitation. While dispersal and ecological processes underlying species assemblages varied spatially and among taxa, we found that species in stressful environments were limited by environmental filtering, whereas dispersal limitation was more pronounced under favourable climatic conditions.Main conclusionsOur study finds that environmental filtering and dispersal limitation jointly shape the species assemblage on the TP. These findings provide significant insights into community assembly processes on the TP and other montane ecosystems on Earth, especially those that are sensitive to global warming.

Elevational gradients do not affect thermal tolerance at local scale in populations of livebearing fishes of the genus Limia (Cyprinodontiformes: Poeciliinae)

One of the main assumptions of Janzen’s mountain passes hypothesis is that due the low overlap in temperature regimes between low and high elevations in the tropics, organisms living in high-altitude evolve narrow tolerance for colder temperatures while low-altitude species develop narrow tolerance for warmer temperatures. Some studies have questioned the generality of the assumptions and predictions of this hypothesis suggesting that other factors different to temperature gradients between low and high elevations may explain altitudinal distribution of species in the tropics. In this study we test some predictions of the Janzen’s hypothesis at local scales through the analysis of the individual thermal niche breadth in populations of livebearing fishes of the genus Limia and its relationship with their altitudinal distribution in some islands of the Greater Antilles. We assessed variation in tolerance to extreme temperatures (measured as critical thermal minimum (CTmin) and maximum (CTmax) and compared thermal breadth for populations of eight species of Limia occurring in three Caribbean islands and that occupy different altitudinal distribution. Our results showed that species analyzed had significant differences in thermal limits and ranges. Generally, species distributed in high and low elevations did not differ in thermal limits and showed a wider range of thermal tolerance. However, species living in mid-elevations had narrower range of temperature tolerance. We found no significant effect of phylogeny on CTmin, CTmax and thermal ranges among species. This study did not provide evidence supporting Janzen’s hypothesis at a local scale since thermal tolerance and altitudinal distribution of Limia species were not related to temperature gradients expected in nature. Phylogeny also did not explain the patterns we observed. We suggest that biotic factors such as species interactions, diet specializations, and others should be considered when interpreting current distribution patterns of Limia species.

Ecological Characterisation of Native Isolates of Heterorhabditis indica from Viti Levu, Fiji Islands.

Entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are obligate parasites of soil inhibiting insects. EPNs are being widely researched as promising biocontrol agents for a wide range of agricultural pests. It is known that strains of EPNs isolated from different geographical regions differ in their attributes, such as host-finding ability, host range, infectivity, reproduction, and environmental stress tolerance. A precise knowledge of these factors is therefore an essential pre-requisite for devising successful strategies to use these nematodes in biological control programmes. Thus, ecological characterisation of the EPN Heterorhabditis indica (Rhabditida: Heterorhabditidae) newly isolated and representing the only species of EPN reported from the island of Viti Levu, Fiji was carried out using Galleria mellonella larvae (L) (Pyralidae: Galleriinae) as hosts to allow comparisons between bioassays conducted in different laboratories around the world. Temperature data showed that native isolates of H. indica are warm-adapted nematodes with thermal range for infectivity between 15˚C and 35˚C and can reproduce between 20˚C and 30˚C. They are highly virulent with LC50 values against G. mellonella ranging from 2.8 IJ to 3.8 IJ/larva. However, they showed poor desiccation tolerance and fail to infect hosts in soil with moisture levels below 8%. They showed a moderate level of hypoxic tolerance and can be stored at 15˚C for 4 months. Results also showed great variability within the selected native isolates of H. indica. Beneficial traits for selected isolates were added up to identify a superior candidate. The current study also suggested that the thermal niche breadth for infection can differ among conspecific strains of an EPN species. The results of this experimental study on ecological aspects of these native isolates of H. indica should form a basis for their potential use in biological control of insect pests in Fiji.