Cooler Habitats Research Articles

Thermal tolerance of giant salmonfly nymphs (Pteronarcys californica) varies across populations in a regulated river.

Warming of aquatic ecosystems is transforming the distribution, phenology and growth of the organisms dependent upon these ecosystems. Aquatic insects such as stoneflies are especially vulnerable to warming because the aquatic nymph stage of their life cycle depends on cool, well-oxygenated, flowing water habitat. We tracked thermal effects on available aerobic capacity of the aquatic nymph stage of an iconic and vulnerable stonefly species, the giant salmonfly (Pteronarcys californica), to compare habitat thermal regime measurements for two salmonfly populations from habitats separated by a gradient in summer weekly maximum temperatures. Contrary to expectations, the thermal optima range of the warmer habitat population was cooler than for the cooler habitat population. We posit that this unexpected interpopulation variation in thermal response is more strongly driven by diel and seasonal thermal variability than by the highest summer temperatures experienced within respective habitats. Additionally, we show that summer daily maximum temperatures could result in periodic limits in available aerobic capacity to support work of the warmer habitat nymphs and may be the mechanism underlying reduced abundance relative to the upstream cooler habitat population. Our findings provide insight into potential thermal and metabolic mechanisms that could regulate the success of ecological and culturally important aquatic insect species experiencing global change. We conclude that thermal regimes and thermal variation, not just mean and maximum temperatures, are critical drivers of aquatic insect responses to water temperatures.

Diversity, Ecology and Phytogeography of Bryophytes across Temperate Forest Communities-Insight from Mt. Papuk (Croatia, SE Europe).

It has been widely documented that the complex structure of forest ecosystems supports considerable bryophyte species and functional diversity. In this study, we assessed the diversity, distribution and ecological and phytogeographical features of bryophytes across a gradient of temperate forest types on Mt. Papuk. This is the largest and highest mountain in the lowland, Pannonian part of Croatia, with high geological diversity and various temperate forests covering 95% of the mountain. According to the predominant tree species (oak vs. beech), geological bedrock (calcareous vs. siliceous) and soil reaction (alkaline vs. acidic), 21 study plots were classified into four distinct forest types. In all, 184 bryophyte species (35 liverworts and 149 mosses) were recorded. Although the forest types investigated did not differ significantly with respect to species richness, each was characterized by a considerable number of diagnostic bryophyte species. According to our results, one of the main ecological factors determining the variability of the forest bryophyte composition was geological bedrock and the associated soil reaction. Basiphilous forests developed on carbonate bedrock harbored more thermophilous and nitrophilous bryophytes and were characterized by southern-temperate and Mediterranean-Atlantic biogeographic elements. In contrast, acidophilous forests growing on silicate bedrock were characterized by wide-boreal and boreo-arctic-montane elements, i.e., bryophytes indicating cooler habitats and nitrogen-deficient soils. Based on the results, we hypothesized that the main latitudinal biogeographic distinction between southern and northern biogeographic elements is driven more by geological substrate than by the main tree species in forest communities. The present study confirmed previous findings that bryophytes are good and specific habitat indicators and show associations with different forest types, which can help to understand the complexity, ecological microconditions and biogeographic characteristics of forest communities.

Hypothesised life cycle adaptation of stonefly (Plecoptera) in response to increased water temperatures

Water temperature is the most important and critical factor for freshwater invertebrates and it fluctuates with an increase in air temperature. In this study, the effect of water temperature on egg development was clarified in Stavsolus japonicus, and the response to climate change in stoneflies with long egg periods were considered. Water temperatures prior to 43 days before hatching likely do not affect egg development in Stavsolus japonicus. Instead, they use egg diapause as an adaptive strategy to survive hot summer conditions. Increased water temperatures may cause migration to higher elevations for stoneflies that have lower adaptability in their egg development period, with populations eventually becoming stranded where no higher elevation or cooler habitat is available. Species extinction is expected to increase with increasing temperatures, leading to reduced biodiversity in many ecosystems. Indirect effects of water warming on maturation and reproduction may lead to substantial reductions in benthic invertebrate populations.

Environmental temperature predicts resting metabolic rates in tropidurinae lizards.

Interspecific variation in metabolic rates may be associated with climate, habitat structure, and resource availability. Despite a strong link between ecology and physiology, there is a dearth in the understanding of how the costs of body maintenance change during ecological transitions. We focused on an ecologically diverse group of neotropical lizards (Tropidurinae) to investigate whether and how resting metabolic rate (RMR) evolved under divergent micro- and macrohabitat conditions. Using a phylogenetic framework, we tested whether species from hot and dry habitats had lower RMRs in relation to those from cooler and mesic habitats, and investigated whether microhabitat usage had an effect over body mass-adjusted RMRs. Our results suggest that RMRs are not phylogenetically structured in Tropidurinae. We found no correlation between metabolism, precipitation, and microhabitat usage. Species from warmer habitats had lower RMR compared to those from cooler habitats, supporting a mechanism of negative compensation in metabolic responses to temperature. Ectotherms from warmer habitats can limit energetic demand and expenditure through reduced RMR, whereas those from cooler habitats may sustain activity despite thermal constraints via increased RMR. Our work highlights the role of temperature in shaping metabolic responses in lizards, giving additional support to the notion that physiology and ecological contexts are intertwined.

Temperature-buffering by oyster habitat provides temporal stability for rocky shore communities

Intertidal rocky shores are considered among the most thermally stressful marine ecosystems, where many species live close to their upper thermal limit and depend on access to cool microclimates to persist through heat events. In such environments, the provision of cool microclimates by habitat-forming species enables persistence of associated species during high temperature events. We assessed whether, by maintaining cool microclimates through heat events, habitat formed by rock oysters (Saccostrea cucullata) provides temporal stability to associated invertebrate communities over periods of extreme temperatures. On three tropical rocky shores of Hong Kong, which experiences a monsoonal climate, we compared changes in microclimates and invertebrate communities associated with oyster and bare rock habitats between the cool and hot seasons. Oyster habitats were, across both seasons, consistently characterised by lower maximum temperatures and greater thermal stability than bare rock habitats. Invertebrate communities in the bare rock habitat were less diverse and abundant in the hot than the cool season, but communities in the cooler habitats provided by oysters did not display temporal change. These results demonstrate that microclimates formed by oysters provide temporal stability to associated communities across periods of temperature change and are key determinants of species distributions in thermally stressful environments. The conservation and restoration of oyster habitats may, therefore, build resilience in associated ecological communities subject to ongoing environmental change.

Evolution of Dispersal, Habit, and Pollination in Africa Pushed Apocynaceae Diversification After the Eocene-Oligocene Climate Transition

Apocynaceae (the dogbane and milkweed family) is one of the ten largest flowering plant families, with approximately 5,350 species and diverse morphology and ecology, ranging from large trees and lianas that are emblematic of tropical rainforests, to herbs in temperate grasslands, to succulents in dry, open landscapes, and to vines in a wide variety of habitats. Despite a specialized and conservative basic floral architecture, Apocynaceae are hyperdiverse in flower size, corolla shape, and especially derived floral morphological features. These are mainly associated with the development of corolline and/or staminal coronas and a spectrum of integration of floral structures culminating with the formation of a gynostegium and pollinaria—specialized pollen dispersal units. To date, no detailed analysis has been conducted to estimate the origin and diversification of this lineage in space and time. Here, we use the most comprehensive time-calibrated phylogeny of Apocynaceae, which includes approximately 20% of the species covering all major lineages, and information on species number and distributions obtained from the most up-to-date monograph of the family to investigate the biogeographical history of the lineage and its diversification dynamics. South America, Africa, and Southeast Asia (potentially including Oceania), were recovered as the most likely ancestral area of extant Apocynaceae diversity; this tropical climatic belt in the equatorial region retained the oldest extant lineages and these three tropical regions likely represent museums of the family. Africa was confirmed as the cradle of pollinia-bearing lineages and the main source of Apocynaceae intercontinental dispersals. We detected 12 shifts toward accelerated species diversification, of which 11 were in the APSA clade (apocynoids, Periplocoideae, Secamonoideae, and Asclepiadoideae), eight of these in the pollinia-bearing lineages and six within Asclepiadoideae. Wind-dispersed comose seeds, climbing growth form, and pollinia appeared sequentially within the APSA clade and probably work synergistically in the occupation of drier and cooler habitats. Overall, we hypothesize that temporal patterns in diversification of Apocynaceae was mainly shaped by a sequence of morphological innovations that conferred higher capacity to disperse and establish in seasonal, unstable, and open habitats, which have expanded since the Eocene-Oligocene climate transition.

The Importance of Including Water Temperature Simulations in a 2D Fish Habitat Model for the St. Lawrence River

Extreme climatic conditions likely caused a massive fish mortality during the summer of 2001 in the St. Lawrence River. To corroborate this hypothesis, we used a physical habitat simulation approach incorporating hydraulic and water temperature models. Spawning Habitat Suitability Indices (HSI) for common carp (Cyprinus carpio) were developed using fuzzy logic and applied to the model outputs to estimate habitat weighted usable area during the event. The results revealed that areas suitable for common carp spawning (HSI > 0.3) were severely reduced by high water temperatures, which exceeded 28 °C during the mortality event. During the mortality event, the amount of suitable habitat was reduced to <200 ha/day, representing less than 15% of the maximum potential suitable habitat in the study reach. In addition, the availability of cooler habitats that could have been used as thermal refuges was also reduced. These results indicate that the high water temperature in spawning areas and reduced accessibility to thermal refuge habitats exposed the carp to substantial physiological and environmental stress. The high water temperatures were highly detrimental to the fish and eventually led to the observed mortalities. This study demonstrates the importance of including water temperature in habitat suitability models.

Thermal Preferences of Cowpea Seed Beetles (Callosobruchus maculatus): Effects of Sex and Nuptial Gift Transfers.

Simple SummaryThe thermal environment is crucial for organismal functioning, and many cold-blooded organisms, including insects, behaviorally regulate their body temperature. Why do insects inhabit given thermal conditions? We propose that access to water affects thermal preference and that insects with poor access to water inhabit colder environments, which reduces evaporation and preserves water. We studied the seed beetle Callosobruchus maculatus, which, as adults, do not drink or eat; however, males provide their mates with sperm, as well as nuptial gifts, including nutrients and water sources. We compared preferred temperatures between males and females that had access to mates or remained unmated and measured the sizes of the transferred gifts. We found that females preferred higher temperatures than males, but these preferences did not change due to mating or the transfer of larger or smaller gifts. It appears that males and females receive and lose certain amounts of water during mating, but they do not alter their thermal preferences according to the amount of water they receive or lose.The thermal environment influences insect performance, but the factors affecting insect thermal preferences are rarely studied. We studied Callosobruchus maculatus seed beetles and hypothesized that thermal preferences are influenced by water balance, with individuals with limited water reserves preferring cooler habitats to reduce evaporative water loss. Adult C. maculatus, in their flightless morph, do not consume food or water, but a copulating male provides a female with a nuptial gift of ejaculate containing nutrients and water. We hypothesized that gift recipients would prefer warmer habitats than gift donors and that both sexes would plastically adjust their thermal preferences according to the size of the transferred gift. We measured the thermal preference in each sex in individuals that were mated once or were unmated. In the mated group, we measured the sizes of the nuptial gifts and calculated proportional body mass changes in each mate during copulation. Supporting the role of water balance in thermal preference, females preferred warmer habitats than males. Nevertheless, thermal preferences in either sex were not affected by mating status or gift size. It is likely that high rates of mating and gift transfers in C. maculatus living under natural conditions promoted the evolution of constitutive sex-dependent thermal preferences.

The ecophysiological plasticity of Aedes aegypti and Aedes albopictus concerning overwintering in cooler ecoregions is driven by local climate and acclimation capacity.

Aedes aegypti and Aedes albopictus transmit diseases such as dengue, and are of major public health concern. Driven by climate change and global trade/travel both species have recently spread to new tropic/subtropic regions and Ae. albopictus also to temperate ecoregions. The capacity of both species to adapt to new environments depends on their ecophysiological plasticity, which is the width of functional niches where a species can survive. Mechanistic distribution models often neglect to incorporate ecophysiological plasticity especially in regards to overwintering capacity in cooler habitats. To portray the ecophysiological plasticity concerning overwintering capability, we conducted temperature experiments with multiple populations of both species originating from an altitudinal gradient in South Asia and tested as follows: the cold tolerance of eggs (-2°C- 8days and-6°C- 2days) without and with an experimental winter onset (acclimation: 10°C- 60days), differences between a South Asian and a European Ae. albopictus population and the temperature response in life cycles (13°C, 18°C, 23°C, 28°C). Ecophysiological plasticity in overwintering capacity in Ae. aegypti is high in populations originating from low altitude and in Ae. albopictus populations from high altitude. Overall, ecophysiological plasticity is higher in Ae. albopictus compared to Ae. aegypti. In both species acclimation and in Ae. albopictus temperate continental origin had a huge positive effect on survival. Our results indicate that future mechanistic prediction models can include data on winter survivorship of both, tropic and subtropic Ae. aegypti, whereas for Ae. albopictus this depends on the respective temperate, tropical region the model is focusing on. Future research should address cold tolerance in multiple populations worldwide to evaluate the full potential of the ecophysiological plasticity in the two species. Furthermore, we found that Ae. aegypti can survive winter cold especially when acclimated and will probably further spread to colder ecoregions driven by climate change.

Spatial Distribution Changes and Habitat Use in Red Porgy in Waters off the Southeast U.S. Atlantic Coast

AbstractDespite 30 years of relatively strict management measures, the Red Porgy Pagrus pagrus population off the southeast U.S. Atlantic coast has not met rebuilding goals and was still categorized as overfished over a decade after a moratorium (SEDAR 2020). The lack of recovery indicates that limiting fishing pressure is not enough to effectively manage population levels. Population size may be driven by spatial or habitat associations independent of fishing pressure. We defined spatial distribution and habitat associations of Red Porgy adults and recruits by using a 23‐year, fishery‐independent trap catch time series (1996–2019). Abundance of recruits was below the long‐term average, and adults were declining for the last 8 years of the time series. In addition, the spatial distribution of recruits tended to contract to deeper waters in the center of the region when abundance was low, whereas adults remained relatively consistent in their spatial and depth distribution regardless of abundance. The independence between effective area occupied and adult abundance supports that adults persisted throughout the region, whereas recruit area occupied was proportional to abundance. Recruits and adults overlapped spatially, but there was some partitioning of habitats: recruits were more abundant in less‐complex habitats (low benthic biota coverage and low availability of hard substrate) relative to more complex habitats, and adults were more abundant in more complex or warm habitats than in less‐complex or cooler habitats. When overall abundance was reduced, adult abundance in more complex habitats became more similar to abundance in less‐complex habitats, while there was little to no change in recruit habitat use. The center of the region had a high overlap of adults and recruits, particularly in times of reduced recruitment. If fishers cannot target adults only, there is high potential for bycatch mortality or reduced fitness for recruits, which would further reduce the likelihood of recovery.

Does social thermal regulation constrain individual thermal tolerance in an ant species?

In ants, social thermal regulation is the collective maintenance of a nest temperature that is optimal for individual colony members. In the thermophilic ant Aphaenogaster iberica, two key behaviours regulate nest temperature: seasonal nest relocation and variable nest depth. Outside the nest, foragers must adapt their activity to avoid temperatures that exceed their thermal limits. It has been suggested that social thermal regulation constrains physiological and morphological thermal adaptations at the individual level. We tested this hypothesis by examining the foraging rhythms of six populations of A. iberica, which were found at different elevations (from 100 to 2,000m) in the Sierra Nevada mountain range of southern Spain. We tested the thermal resistance of individuals from these populations under controlled conditions. Janzen's climatic variability hypothesis (CVH) states that greater climatic variability should select for organisms with broader temperature tolerances. We found that the A. iberica population at 1,300m experienced the most extreme temperatures and that ants from this population had the highest heat tolerance (LT50=57.55°C). These results support CVH's validity at microclimatic scales, such as the one represented by the elevational gradient in this study. Aphaenogaster iberica maintains colony food intake levels across different elevations and mean daily temperatures by shifting its rhythm of activity. This efficient colony-level thermal regulation and the significant differences in individual heat tolerance that we observed among the populations suggest that behaviourally controlled thermal regulation does not constrain individual physiological adaptations for coping with extreme temperatures.

Environmental effects on daytime sheltering behaviors of California horn sharks (Heterodontus francisci)

California horn sharks (Heterodontus francisci) are relatively small (122 cm maximum total length; TL), nocturnally active sharks that have been observed refuging in shelters during the day; however, little is known about how they select their daytime resting shelters, and what factors may drive their degree of shelter fidelity. Depending on body size, thermal tolerance, and ability to avoid predators, horn sharks may need to balance tradeoffs when selecting a quality shelter. This study quantified vertical daytime distributions via dive surveys and shelter fidelity via acoustic telemetry during June – August 2016 and June – November 2017 in a temperate rocky reef (33˚26’ N, -118˚29’ W). Immature individuals ( 58 cm TL) were found in deeper (> 10 m), cooler habitats sheltering in larger caves and rock ledges. The sizes and relative abundances of sharks varied between land-associated and offshore-isolated reefs, indicating habitat type may be a likely driver of ontogenetic shifts in shelter behavior. No sharks returned to their shelters in 2016 coinciding with the period of El Nino conditions (increased temperature, shifts in community assemblage), yet shelter fidelity was 47% in 2017 under non-El Nino conditions. By quantifying sheltering behavior in a residential mesopredator, this study provides a framework for understanding how environmental conditions influence horn shark behaviors and their potential impacts on their community.

Will like replace like? Linking thermal performance to ecological function across predator and herbivore populations.

The inability of species to adapt to changing climate may cause ecological communities to disassemble and lose ecological functioning. However, theory suggests that communities may be resilient whenever populations within species exhibit variation in thermal plasticity or adaptation whereby thermally tolerant populations replace thermally sensitive ones. But will they maintain the functional roles of the populations being replaced? This study evaluated whether "like replaces like" functionally by measuring how four populations of a grasshopper herbivore and its co-occurring spider predator cope with environmental warming. The study occurred across a latitudinal gradient bounded by southerly, warmer Connecticut and northerly, cooler New Hampshire, USA. The study compared the survival rates, thermal performance, habitat usage, and food chain interactions of each grasshopper and spider population between its home field site (field of origin) and a Connecticut transplant site, and the native Connecticut population. Three grasshopper populations exhibited physiological plasticity by adjusting metabolic rates. The fourth population selected cooler habitat locations. Spider populations did not alter their metabolism and instead selected cooler habitat locations, thereby altering spatial overlap with their prey and food chain interactions. Grasshopper populations that coped physiologically consumed plants in different ratios than the fourth population and the Connecticut population. Hence, "like may not replace like" whenever populations adapt physiologically to warming.

Hot eats and cool creeks: juvenile Pacific salmonids use mainstem prey while in thermal refuges

Thermal refuges form important habitat for cold-water fishes in the face of rising temperatures. As fish become concentrated in refuges, food resources may become depleted. In this study, we used invertebrate drift sampling and fish density surveys to quantify potential in-refuge food limitation, temperature-sensitive radio-tagging studies to quantify thermal habitat use, and isotopic analyses to determine diet sources for juvenile Pacific salmonids using thermal refuges in California’s Klamath River. Juvenile salmonids using refuges formed by tributary junctions with the mainstem river obtained the majority (range = 47%–97%) of their diet from mainstem prey sources. Mean steelhead (Oncorhynchus mykiss) body temperatures were significantly cooler (∼3.5 °C) than diet-inferred foraging temperatures. Thus, while fish seek cooler habitat for physiological benefits, they rely primarily on mainstem prey. Moreover, consistently high densities of fish in refuges (mean = 3.5 fish·m−2) could lead to density-dependent food limitation. Thus, mobile consumers like fish can exploit existing heterogeneity associated with cold-water refuges by gaining thermal benefits from a food-limited cold-water habitat while deriving the majority of their prey from the warm mainstem river.

Identifying priority habitats and monitoring species for conservation and restoration of lentic Odonata habitats: assemblage nestedness on Amami‐Oshima Island, Japan

AbstractWe investigated Odonata faunal and habitat characteristics (forest cover, emergent, submerged, floating‐leaved and floating plant covers, pond area, NO3−, chemical oxygen demand, and presence/absence of a nonnative fish) in 10 ponds on Amami‐Oshima Island. In total, 26 species of six odonate families were found, and we detected significant nestedness of species composition among the ponds (22 species in the most species‐rich pond, and 8 species in the most species‐poor pond). Species found only in the most species‐rich ponds were: Anax nigrofasciatus nigrofasciatus, Acisoma panorpoides panorpoides, Agriocnemis famina oryzae, Rhyothemis severini, Anasiaeschna martini, Hemicordulia okinawaensis, Lyriothemis elegantissima, and Hydrobasileus croceus (hereafter referred to as the rare species). These rare species are generally known to preferentially inhabit ponds with lush emergent plants and/or to prefer cooler habitats shaded by forest cover, such as Anax nigrofasciatus nigrofasciatus, Anac. martini, He. okinawaensis, and L. elegantissima. In contrast, the common species also found in species‐poor ponds were: Ischnura senegalensis, Pantala flavescens, Anax parthenope julis, Ictinogomphus pertinax, and Tramea verginia, which are known to prefer an open water surface as spawning habitat. These differences in habitat preference between the rare and common species may be among the major reasons for the significant positive effects of percent forest cover and emergent plants on Odonata species richness. These results suggest that nestedness helped identify precise habitat characteristics and rare species that should be considered for conservation and restoration of lentic habitats on Amami‐Oshima Island.

Conservation planning for the extraordinary and Endangered Spesbona damselfly

The damselfly Spesbona angusta is one of the world’s rarest insects, is Red Listed as Endangered, and occurs today at only one known locality in the Cape Floristic Region (CFR), South Africa. It has some unusual characteristics, including rapid and reversible colour change in both sexes, and a larva with frilled lamellae that lives in a micro-habitat free of competitors and large anisopteran enemies. We define here the characteristics of its habitat and record some other unusual behavioural traits, including the adult male’s ability to sail on the water surface, very strong site selection for oviposition, and female approach to males, all in the context of its conservation. We used satellite imagery to determine the location of habitats within its locality. We further used infrared imagery to identify warmer and cooler habitats within the area. Details of its occurence were mapped, based on observational data acquired throughout the flight season. From this, we were able to establish that its population moves around its locality, and we also establish its environmental requirements for conservation. We also indicate its umbrella value for representing two other threatened odonate species, Endangered Proischnura polychromatica and Vulnerable Syncordulia legator, as well as some other CFR endemic odonates. Conservation of this species requires continual monitoring and removal of invasive alien trees as a priority. Translocation should also be considered as various risks to this one locality are high. A potential site is identified.

Pressure as a Limiting Factor for Life.

Facts concerning the stability and functioning of key biomolecular components suggest that cellular life should no longer be viable above a few thousand atmospheres (200–300 MPa). However, organisms are seen to survive in the laboratory to much higher pressures, extending into the GPa or even tens of GPa ranges. This is causing main questions to be posed concerning the survival mechanisms of simple to complex organisms. Understanding the ultimate pressure survival of organisms is critical for food sterilization and agricultural products conservation technologies. On Earth the deep biosphere is limited in its extent by geothermal gradients but if life forms exist in cooler habitats elsewhere then survival to greater depths must be considered. The extent of pressure resistance and survival appears to vary greatly with the timescale of the exposure. For example, shock experiments on nanosecond timescales reveal greatly enhanced survival rates extending to higher pressure. Some organisms could survive bolide impacts thus allowing successful transport between planetary bodies. We summarize some of the main questions raised by recent results and their implications for the survival of life under extreme compression conditions and its possible extent in the laboratory and throughout the universe.

An Acoustic Analysis of the Genus Microhyla (Anura: Microhylidae) of Sri Lanka.

Vocalizing behavior of frogs and toads, once quantified, is useful for systematics, rapid species identification, behavioral experimentation and conservation monitoring. But yet, for many lineages vocalizations remain unknown or poorly quantified, especially in diversity rich tropical regions. Here we provide a quantitative acoustical analysis for all four Sri Lankan congeners of the genus Microhyla. Three of these species are endemic to the island, but Microhyla ornata is regionally widespread. Two of these endemics, M. karunaratnei (Critically Endangered) and M. zeylanica (Endangered), are highly threatened montane isolates; the other, M. mihintalei, is relatively common across the dry lowlands. We recorded and analyzed 100 advertisement calls from five calling males for each species, except for M. zeylanica, which only had 53 calls from three males suitable for analyses. All four species call in choruses and their vocal repertoires are simple compared to most frogs. Their calls contain multiple pulses and no frequency modulation. We quantified eight call characters. Call duration and number of pulses were higher for the two montane isolates (inhabiting cooler habitats at higher altitudes) compared to their lowland congeners. Microhyla zeylanica has the longest call duration (of 1.8 ± 0.12 s) and the highest number of pulses (of 61–92 pulses). The smallest of the species, Microhyla karunaratnei (16.2–18.3 mm), has the highest mean dominant frequency (3.3 ± 0.14 kHz) and pulse rate (77 ± 5.8 pulses per second). The calls separate well in the Principal Component space: PC1 axis is mostly explained by the number of pulses per call and call duration; PC2 is mostly explained by the pulse rate. A canonical means plot of a Discriminant Function analysis shows non-overlapping 95% confidence ellipses. This suggests that some call parameters can be used to distinguish these species effectively. We provide detailed descriptions for eight call properties and compare these with congeners for which data is available. This work provides a foundation for comparative bioacoustic analyses and species monitoring while facilitating the systematics of Microhyla across its range.

What do metabolic rates tell us about thermal niches? Mechanisms driving crayfish distributions along an altitudinal gradient.

Humans are rapidly altering thermal landscapes, so a central challenge to organismal ecologists is to better understand the thermal niches of ectotherms. However, there is much disagreement over how we should go about this. Some ecologists assume that a statistical model of abundance as a function of habitat temperature provides a sufficient approximation of the thermal niche, but ecophysiologists have shown that the relationship between fitness and temperature can be complicated, and have stressed the need to elucidate the causal mechanisms underlying the response of species to thermal change. Towards this end, we studied the distribution of two crayfishes, Euastacus woiwuru and Euastacus armatus, along an altitudinal gradient, and for both species conducted experiments to determine the temperature-dependence of: (1) aerobic scope (the difference between maximum and basal metabolic rate; purported to be a proxy of the thermal niche); and (2) burst locomotor performance (primarily fuelled using anaerobic pathways). E. woiwuru occupied cooler habitats than E. armatus, but we found no difference in aerobic scope between these species. In contrast, locomotor performance curves differed significantly and strongly between species, with peak locomotor performances of E. woiwuru and E. armatus occurring at ~10 and ~18 °C, respectively. Crayfish from different thermal landscapes may have similar aerobic thermal performance curves but different anaerobic thermal performance curves. Our results support a growing body of literature implying different components of ectotherm fitness have different thermal performance curves, and further challenge our understanding of the ecology and evolution of thermal niches.

Dispersal response to climate change: scaling down to intraspecific variation

AbstractRange shift, a widespread response to climate change, will depend on species abilities to withstand warmer climates. However, these abilities may vary within species and such intraspecific variation can strongly impact species responses to climate change. Facing warmer climates, individuals should disperse according to their thermal optimum with consequences for species range shifts. Here, we studied individual dispersal of a reptile in response to climate warming and preferred temperature using a semi‐natural warming experiment. Individuals with low preferred temperatures dispersed more from warmer semi‐natural habitats, whereas individuals with higher preferred temperatures dispersed more from cooler habitats. These dispersal decisions partly matched phenotype‐dependent survival rates in the different thermal habitats, suggesting adaptive dispersal decisions. This process should result into a spatial segregation of thermal phenotypes along species moving ranges which should facilitate local adaptation to warming climates. We therefore call for range shift models including intraspecific variation in thermal phenotype and dispersal decision.