Interspecific Differences In Response Research Articles

Invertebrates from naturally brackish areas are less impacted by road salt and alternative deicers

AbstractRoad salt (NaCl) is the most common deicer used to melt snow and ice from roadways in cold climates, but its use results in runoff of sodium and chloride ions into sewers and into soil and freshwater ecosystems. Road salt causes harmful effects on wetland habitats, which host an abundance of macroinvertebrate species. Alternatives to road salt, such as beet juice, are commercially available, but their impact on invertebrates is less well studied. We examined the impact of road salt alternatives on four invertebrate species (Daphnia pulex, Eisenia fetida, Heterocypris sp., and Culicoides sp. larvae), some of which come from a naturally brackish area. Our expectation was that road salt alternatives (beet salt, molasses, pickle juice, and sand) would be less toxic to the animals than traditional road salt. This study comprised two experiments: the first exposed individuals of the four invertebrate species to road salt alternatives, and the second exposed the invertebrates to a range of road salt concentrations. Only individuals of D. pulex were negatively impacted by road salt. The other invertebrates were not significantly affected by any salt alternative, demonstrating interspecific differences in response to salt. Species found in naturally salty environments were more tolerant of both road salt and alternatives. This research shows species‐ and habitat‐specific responses to road salt alternatives, which has implications for municipalities looking to salt roads without negatively impacting freshwater ecosystems.

Scalable phylogenetic Gaussian process models improve the detectability of environmental signals on local extinctions for many Red List species

Abstract Conservation biologists have a daunting task of understanding the causes of species decline associated with anthropogenic factors and predicting the extinction risk of a growing number of endangered species. By reducing variances of estimates with information on closely related species, phylogenetic information among species can bridge gaps in information on species with small range sizes when modelling large numbers of endangered species. However, modelling many species with the Gaussian process (GP), which underlies the evolutionary process of phylogenetic random effects, remains a challenge owing to the computational burden in estimating the large variance–covariance matrix. Here, we applied a phylogenetic generalised mixed model with random slopes and random intercepts to 1010 endangered vascular plant taxa in Japan following phylogenetic GPs implemented by nearest neighbour GP (NNGP) approximation. NNGP enables flexibility in changing the proximity on the phylogenetic tree of species from which information is borrowed to reduce the variances of estimates with a realistic computational burden. We evaluated the effectiveness of phylogenetic models by comparing the predictive performance and descriptive power of phylogenetic and non‐phylogenetic models and identified the anthropogenic factors contributing to the decline of each of the studied endangered species. We found that the model with phylogenetic information had better prediction performance than the model without phylogenetic information. The results showed that across all explanatory variables, the phylogenetic model could detect interspecific differences in response to environmental factors in a number of species more clearly. Combined with the phylogenetic signal results, we could also detect a phylogenetic bias in the species that could benefit from the positive effects of protected areas but reduce the local extinctions of 95% of all studied taxa. In conclusion, our model, considering phylogenetic information with NNGP, allows the elucidation of factors causing the decline of many endangered species. In future analyses, the estimation of extinction probability linked to environmental change might be applied to future climate–land use scenarios, advancing the comprehensive assessment of biodiversity degradation and threats to species at multiple scales.

Differences in the reproductive output and larval survival of Rocky Mountain wood ticks (Dermacentor andersoni) and American dog ticks (Dermacentor variabilis) from prairie populations near their northern distributional limits in western Canada.

The effects of temperature and relative humidity (RH) on female reproductive output, egg development and larval survival were determined for Rocky Mountain wood ticks (Dermacentor andersoni) from a prairie population (Chin Lakes, Alberta, Canada) near the northern distribution limit of this species. The responses of D. andersoni eggs and unfed larvae to different temperature (25 or 32°C) and RH (35, 55, 75, 85 or 95%) regimes were compared to our previously published data (Diyes et al. 2021) for a northern prairie population of American dog ticks (Dermacentor variabilis). Oviposition by D. andersoni females took 21-30 days at 25°C and 95% RH compared to 10-21 days for D. variabilis. The number of eggs laid by female ticks was strongly dependent on their engorgement weight, and D. andersoni females produced more eggs than D. variabilis females of an equivalent body weight. Eggs of D. andersoni took less time to develop at 32°C than 25°C with ≥ 85% RH, and hatched faster than those of D. variabilis. Larval survival times declined as temperature increased and RH decreased, but D. andersoni survived longer at 32°C and ≤ 75% RH than D. variabilis. The interspecific differences in responses to the same temperature and humidity regimes indicate that D. andersoni is xerophilic, whereas D. variabilis is hydrophilic. Hence, 'prairie' populations of the Rocky Mountain wood tick occur in the drier grassland ecoregions but are absent in Aspen Parklands Ecoregion which is located to the north and east of the distributional range of D. andersoni.

A size‐based perspective on the decoupling between compositional and functional changes in planktonic communities

AbstractRecent studies have shown a decoupling in the way community composition and functions respond to environmental changes. A common pattern observed is that aggregated functions at the community level are more stable than community composition, which is likely the result of functional compensatory dynamics driven by interspecific differences in response to environmental change. However, the mechanisms by which these patterns emerge remain largely unexplored. Here we investigated in a mesocosm experiment for four weeks the compositional and functional responses of edible phytoplankton (<64 μm) and cladoceran zooplankton communities to climate warming (a constant increase of +3.5°C plus heat wave) and eutrophication (nutrient additions) from a size‐based perspective. Our results show that warming increases small‐sized taxa and decreases large‐sized taxa within both phytoplankton and zooplankton community composition. We found that such opposite responses of different‐sized taxa contributed to the stability of planktonic community functions and thereby resulted in a decoupling between compositional and functional changes. We also found that nutrient additions increased the abundance of all‐sized algal taxa, while phytoplankton community function remained stable. Nutrient additions did not alter the zooplankton community, neither compositionally nor functionally. Under the combined stress of warming and nutrient additions, the compositional and functional responses of planktonic communities were mainly driven by warming. In a broader perspective, our findings reveal a size‐dependent compensation mechanism and suggest that functional stability relies on compensatory effects among different‐sized taxa, and it is therefore important that communities host a large range of taxa differing in size to withstand an increasingly more variable environment in the future.

Community phenology of insects on oak: local differentiation along a climatic gradient

AbstractClimate change is advancing the onset of phenological events, with the rate of advance varying among species and trophic levels. In addition, local populations of the same species may show genetic differences in their response to seasonal cues. If populations of interacting species differ in their response, then climate change may result in geographically varying shifts in the community‐level distribution of interaction strength. We explored the magnitude of trophic‐ and species‐level responses to temperature in a tritrophic system comprising pedunculate oak, insect herbivores, and their associated parasitoids. We sampled local realizations of this community at five sites along a transect spanning fifteen degrees of latitude. Samples from each trophic level at each site were exposed to the same set of five climatic regimes during overwintering in climate chambers. We then recorded the number of days and degree‐days required for oak acorns to develop and insects to emerge. In terms of dates of events, phenology differed among populations. In terms of degree‐days, we found that for two species pairs, the heat sum required to develop in spring differed by an additional ˜500 degree‐days between trophic levels when overwintering at the highest temperature. For three species, within‐population variation in the number of degree‐days required for emergence was higher at warmer temperatures. Our findings suggest that changing temperatures can modify interactions within a community by altering the relative phenology of interacting species and that some interactions are more vulnerable than others to a shift in temperature. The geographic variation in the phenological response of a species suggests that there is a genetic component in determining the phenology of local populations. Such local variation blended with interspecific differences in responses makes it complex to understand how communities will respond to warmer temperatures.

Dynamic table‐visiting behavior of birds at outdoor restaurants and cafés

AbstractFear of humans and its effect on animal behavior is increasingly being recognized as an important structuring force in ecological landscapes, with consequences for ecological interactions and communities. When aggressive, physically dominant species are displaced by anthropogenic disturbance, physically weaker species exploit competitor and predator downtimes to forage in previously risky places. Birds feeding at outdoor restaurants and cafés in association with humans are exposed to fluctuating levels of perceived danger caused by frequently changing densities of human diners. Consequently, birds must make decisions about which dining tables to visit based on trade‐offs between foraging gain and perceived danger from avian competitors and humans. We tested the hypothesis that interspecific differences in response to perceived danger, combined with varying densities of human diners, dynamically alter which bird species predominates at dining tables. We found that house sparrows (Passer domesticus) tolerated higher human diner‐densities than larger‐sized, more physically dominant Eurasian jackdaws (Coloeus monedula). Sparrows were usually the first birds to visit diner‐occupied tables and spent more time there than jackdaws. However, at diner‐abandoned tables, this pattern changed: During low diner‐densities at surrounding tables, jackdaws were usually the predominant species in first visits and minutes spent visiting, while at high diner‐densities sparrows usually predominated. Moreover, along a gradient of increasing human diner‐density, sparrows gradually replaced jackdaws as the predominant species in first visits and time at abandoned tables. However, at diner‐occupied tables, once a sparrow chose which table to visit, factors other than diner‐density influenced its choice of where to forage there (table‐top or ground). To our knowledge, our research is the first scientific study of table‐visiting behavior by birds at outdoor restaurants and cafés, and the first to reveal interspecific differences in table‐visiting behavior by birds there.

Regeneration growth and crown architecture of European beech and silver fir depend on gap characteristics and light gradient in the mixed montane old-growth stands

Light is a vital factor affecting tree growth, survival and reproduction. In forests, natural and anthropogenic disturbances are the main drivers of abrupt changes in environmental conditions, including solar irradiance. We examined interspecific differences in the responses of European beech and silver fir to canopy gap characteristics and positions within gaps across various life stages (small seedlings, tall seedlings and saplings) in old-growth stands in Świętokrzyski National Park, Central Poland. Additionally, we analyzed sapling architectural responses to light. Regeneration densities were strongly affected by gap characteristics. The largest interspecific differences in responses to gap characteristics were found for small seedlings, which indicated their different preferences not only for light conditions created within gaps, but also toward various microsites distributed on a fine-scale after gap creation. Small beech seedlings responded only to the position within the gap, but small fir seedlings reacted in a more complex way, including such variables as gap size, shape and distance from a gap border. Gap size and the distance from its border had the most noticeable positive effect on tall seedlings and saplings, indicating that successful transition of regeneration to taller life stages may be possible only in larger gaps and in places further from a canopy border. Light conditions did not affect sapling length to diameter ratio. However, both direct and diffuse light had a negative effect on beech and fir crown area and length. Fir had wider but shorter crowns compared with beech in the whole light spectrum. This result indicates that these two species might have contrasting strategies regarding light interception, with fir being better adapted to increase a crown laterally, and with beech either being more tolerant to self-shading than fir or able to keep a favorable spatial leaf arrangement to avoid self-shading. Beech had the highest height growth increments in low levels of direct light, but its height growth was positively affected by diffuse light. Fir height growth rates showed no response to direct light, but were highest in medium levels of diffuse light. No effect of light on beech height to lateral growth rate ratio was found. The effect of direct light on this parameter for fir was negative, and nonlinear in the case of diffuse light, with the highest ratios observed in medium light levels. Our results stress the need of using both direct and diffuse light when analyzing light effects on sapling architecture.

Signal from the noise: model‐based interpretation of variable correspondence between active and passive samplers

AbstractCombining information from active and passive sampling of mobile animals is challenging because active‐sampling data are affected by limited detection of rare or sparse taxa, while passive‐sampling data reflect both density and movement. We propose that a model‐based analysis allows information to be combined between these methods to interpret variation in the relationship between active estimates of density and passive measurements of catch per unit effort to yield novel information on activity rates (distance/time). We illustrate where discrepancies arise between active and passive methods and demonstrate the model‐based approach with seasonal surveys of fish assemblages in the Florida Everglades, where data are derived from concurrent sampling with throw traps, an enclosure‐type sampler producing point estimates of density, and drift fences with unbaited minnow traps that measure catch per unit effort (CPUE). We compared incidence patterns generated by active and passive sampling, used hierarchical Bayesian modeling to quantify the detection ability of each method, characterized interspecific and seasonal variation in the relationship between density and passively measuredCPUE, and used a predator encounter‐rate model to convert variableCPUE–density relationships into ecological information on activity rates. Activity rate information was used to compare interspecific responses to seasonal hydrology and to quantify spatial variation in non‐native fish activity. Drift fences had higher detection probabilities for rare and sparse species than throw traps, causing discrepancies in the estimated spatial distribution of non‐native species from passively measuredCPUEand actively measured density. Detection probability of the passive sampler, but not the active sampler, varied seasonally with changes in water depth. The relationship betweenCPUEand density was sensitive to fluctuating depth, with most species not having a proportional relationship betweenCPUEand density until seasonal declines in depth. Activity rate estimates revealed interspecific differences in response to declining depths and identified locations and species with high rates of activity. We propose that variation in catchability from methods that passively measureCPUEcan be sources of ecological information on activity. We also suggest that model‐based combining of data types could be a productive approach for analyzing correspondence of incidence and abundance patterns in other applications.

The effect of tree diversity on the resistance and recovery of forest stands in the French Alps may depend on species differences in hydraulic features

As climate change should lead to an increase in the vulnerability and the sensitivity of forests to extreme climatic events, quantifying and predicting their response to more severe droughts remains a key task for foresters. Furthermore, recent works have suggested that tree diversity may affect forest ecosystem functioning, including their response to extreme events. In this study we aimed at testing whether the growth response of forest stands to stressful climatic events varied between mixed and monospecific stands, under various environmental conditions. We focused on beech-fir forests (Fagus sylvatica [L.] and Abies alba [L.]) and beech-oak forests (F. sylvatica [L.] and Quercus pubescent [L.]) in the French Alps. We used a dendrochronological dataset sampled in forest plots organized by triplets (one mixture and two monospecific stands) distributed in six sites along a latitudinal gradient. We tested (1) whether stand diversity (two-species stands vs monospecific stands) modulates the stands’ response to drought events in terms of productivity, (2) whether species identity may drive the diversity effect on resistance and recovery, and (3) whether this can be explained by interspecific interactions. We found that (1) interspecific differences in response to extreme drought events (possibly due to interspecific differences in hydraulic characteristics) can induce a mixture effect on stand growth, although it appeared (2) to be strongly depending on species identity (positive effect only found for beech-fir mixed stands), while (3) there were no significant non-additive effects of diversity on stand resistance and recovery, except for some specific cases. Overall, our study shows that promoting selected mixed stands management may buffer extreme drought effect on stand productivity.

Water depth-dependent notonectid predatory impacts across larval mosquito ontogeny.

Context-dependencies can modulate the strength of predatory interactions and often remain unquantified. In particular, differences in water depth within aquatic systems could influence predator efficiencies towards prey which utilise three-dimensional space through the water column. Differences in prey size could drive prey size-refuge effects, influencing the efficacy of natural enemies towards vector species. We thus quantify the predatory impact of two notonectid predators, Anisops breddini and Anisops sardeus, towards four different larval instars of Culex quinquefasciatus prey across a water depth gradient, using functional responses (FRs). Consumption rates differed significantly between the predators, and interspecific differences in responses to variations in water depth were emergent. Both notonectids were able to handle C. quinquefasciatus prey across all instar stages, yet predation rates were generally higher towards early as opposed to late instar prey. Anisops sardeus was most voracious, and differential predation rates of this species were most pronounced in shallow waters. Type II FRs were displayed by notonectids in the majority of treatments; however, Type III FRs were emergent in specific treatment groups, with potential implications for prey population stability. Both capture rates and handling times were often greater at greater depths, and thus maximum feeding rates reduced as depth increased. Our results further demonstrate substantial predatory impacts of notonectid predators towards mosquito, and quantify biotic and abiotic context-dependencies which modulate their impact. Given notonectids are capable of aerial dispersal between ephemeral aquatic habitats of varied volumes, their promotion in aquatic systems could help reduce proliferations of medically important mosquitoes. © 2019 Society of Chemical Industry.

Effects of enhanced ultraviolet-B radiation, water deficit, and their combination on UV-absorbing compounds and osmotic adjustment substances in two different moss species.

A simulation experiment was conducted to explore the influence of enhanced ultraviolet-B (UV-B) radiation, water deficit, and their combination on UV-absorbing compounds and osmotic adjustment substances of mosses Bryum argenteum and Didymodon vinealis isolated from biological soil crusts (BSCs) growing in a revegetated area of the Tengger Desert, China. Four levels of UV-B radiation and two gradients of water regime were employed. Compared with their controls, amounts of total flavonoids, chlorophyll,carotenoids, soluble sugars, and soluble proteins significantly decreased (p < 0.05), but proline content significantly increased (p < 0.05), when exposed to either enhanced UV-B or water deficit. The negative effects of enhanced UV-B were alleviated when water deficit was applied. There were increases in UV-absorbing compounds and osmotic adjustment substances when exposed to a combination of enhanced UV-B and water deficit compared with single stresses, except for the proline content in D. vinealis. In addition, our results also indicated interspecific differences in response to enhanced UV-B, water deficit, and their combination. Compared with B. argenteum, D. vinealis was more resistant to enhanced UV-B and water deficit singly and in combination. These results suggest that the damage of enhanced UV-B on both species might be alleviated by water deficit. This alleviation is important for understanding the response of BSCs to UV-B radiation in future global climate change. This also provides novel insights into assessment damages of UV-B to BSC stability in arid and semiarid regions.

Differential impact of hotter drought on seedling performance of five ecologically distinct pine species

Increasing temperature and drought intensity is inducing the phenomenon of the so-called “hotter drought”, which is expected to increase in frequency over the coming decades across many areas of the globe, and is expected to have major implications for forest systems. Consequences of hotter drought could be especially relevant for closely related species overlapping their distributions, since differences in response can translate into range shifts. We assessed the effect of future climatic conditions on the performance of five ecologically distinct pine species common in Europe: Pinus halepensis, P. pinaster, P. nigra, P. sylvestris and P. uncinata. We hypothesised that Mediterranean species inhabiting dry, low-elevation sites will be less affected by the expected warming and drought increase than species inhabiting cold-wet sites. We performed a controlled conditions experiment simulating current and projected temperature and precipitation, and analysed seedling responses in terms of survival, growth, biomass allocation, maximum photochemical efficiency (Fv/Fm) and plant water potential (Ψ). Either an increase in temperature or a reduction in water input alone reduced seedling performance, but the highest impact occurred when these two factors acted in combination. Warming and water limitation reduced Ψ, whereas warming alone reduced biomass allocation to roots and Fv/Fm. However, species responded differentially to warmer and drier conditions, with lowland Mediterranean pines (P. halepensis and P. pinaster) showing higher survival and performance than mountain species. Interspecific differences in response to warmer, drier conditions could contribute to changes in the relative dominance of these pine species in Mediterranean regions where they co-occur and a hotter, drier climate is anticipated.

Constitutive and cold-induced resistance of rye and wheat seedlings to oxidative stress

The influence of cold hardening of rye (Secale cereale L.) and wheat (Triticum aestivum L.) seedlings on their resistance to the oxidative stress (OS) agents, namely, 50 mM hydrogen peroxide or 5 mM iron (II) sulfate was studied. Unhardened rye seedlings were more resistant to hydrogen peroxide than those of wheat, since their growth was less inhibited, and they accumulated lesser amounts of lipid peroxidation products after a treatment with H2O2. The interspecific differences in responses to FeSO4 were less significant. The unhardened seedlings of rye, in comparison with those of wheat, possessed more active guaiacol peroxidase (GPO) and more levels of anthocyanins and proline. In response to the OS agents, the unhardened rye seedlings enhanced activities of superoxide dismutase and catalase, whereas the wheat seedlings enhanced GPO activity and proline content. The cold hardening (6 days at 2°C) increased activities of antioxidant (AO) enzymes, contents of proline, sugars, and anthocyanins in seedlings of both species, and made the seedlings more resistant to the OS agents. After the cold hardening, rye seedlings were more resistant to OS than wheat seedlings. The hardened seedlings of both species activated the AO enzymes in response to H2O2 or FeSO4 greater than the unhardened ones. However, the hardened wheat seedlings, in contrast to the unhardened ones, did not augment the proline content in contact with the OS agents. The conclusion was drawn on different contributions of AO enzymes and low-molecular weight compounds to the basal and induced by the cold—hardening resistances of rye and wheat seedlings to OS.

Energetic costs and implications of the intake of plant secondary metabolites on digestive and renal morphology in two austral passerines

Seed-eating birds have a diet of high nutritional value; however, they must cope with plant secondary metabolites (PSM). We postulated that the detoxification capacity of birds is associated with a metabolic cost, given that the organs responsible for detoxification significantly contribute to energetic metabolism. We used an experimental approach to assess the effects of phenol-enriched diets on two passerines with different feeding habits: the omnivorous rufous-collared sparrow (Zonotrichia capensis) and the granivorous common diuca-finch (Diuca diuca). The birds were fed with one of three diets: control diet, supplemented with tannic acid, or supplemented with Opuntia ficus-indica phenolic extract (a common food of the sparrow but not the finch). After 5weeks of exposure to the diets, we measured basal metabolic rates (BMR), energy intake, glucuronic acid output and digestive and kidney structure. In both species, detoxification capacity expressed as glucuronic acid output was higher in individuals consuming phenol-enriched diets compared to the control diet. However, whereas sparrows increase energy intake and intestinal mass when feeding on phenol-enriched diets, finches had lower intestinal mass and energy intake remains stable. Furthermore, sparrows had higher BMR on phenol-enriched diets compared to the control group, whereas in the finches BMR remains unchanged. Interspecific differences in response to phenols intake may be determined by the dietary habits of these species. While both species can feed on moderate phenolic diets for 5weeks, energy costs may differ due to different responses in food intake and organ structure to counteract the effects of PSM intake.

Effects of short-term low temperature stress on chlorophyll fluorescence transients in Antarctic lichen species

Chlorophyll fluorescence is an effective tool for investigating characteristics of any photosynthesizing organisms and its responses due to different stressors. Here, we have studied a short-term temperature response on two Antarctic green algal lichen species: Umbilicaria antarctica, and Physconia muscigena. We measured slow chlorophyll fluorescence transients in the species during slow a cooling of thallus temperature from 20°C to 5°C with a 10 min. acclimation at each temperature in dark. The measurements were supplemented with saturation pulses for the analysis of chlorophyll fluorescence parameters: maximum yield of PS II photochemistry (FV/FM), effective quantum yield of PS II photochemistry (FPSII) and non-photochemical quenching (NPQ). In response to decreasing thallus temperature, we observed species-specific changes in chlorophyll fluorescence levels P, S, M, T reached during chlorophyll fluorescence transient as well as in the shape of the chlorophyll fluorescence transients. With a decrease in temperature, the time at which M and T chlorophyll fluorescence levels were reached, increased. These changes were attributed to redox state of plastoquinon pool, changes in Calvin-Benson cycle activity, non-photochemical quenching components, state transition in particular. In this study, we present some chlorophyll fluorescence ratios (P/M, M/T, P/T) and chlorophyll fluorescence increase rates (FR1, i.e. O to P, and FR2 - i.e. S to M) as the parameters reflecting direct temperature effects on chloroplastic apparatus of lichen alga sensitively. We proposed that species-specific changes in the slow phase of chlorophyll fluorescence transients could be potentially used as indicators of low temperature effects in photosynthetic apparatus of lichen algal photobionts. Interspecific differences in response to low temperature might be evaluated using the approach as well.

Response of Six Turf Species to Cadmium Stress: Displaying the Most Tolerant Cultivar

Response of Six Turf Species to Cadmium Stress: Displaying the Most Tolerant Cultivar This study was accomplished to monitor the interspecific differences in response to cadmium (Cd) stress among six turfgrass species through investigating the seed germination, seedling growth and some biochemical characteristics. After an environmentally controlled experiment under different Cd treatments (0, 100, 200 and 300 µM), Agropyron elongatum showed the highest germination percentage (80.33%) under 300 µM Cd, followed by Lollium perenne with 72.59%. The lowest germination parameters including germination vigor, index and percentage were found in Festuca ovina, which referred as the more sensitive species to Cd than other studied turfgrasses. The highest shoot growth followed by the lowest chlorophyll degradation was observed in Agropyron elongatum, Festuca rubra and Lolium perenne respectively. Furthermore, the low chlorophyll degradation and the high seedling growth in turf species were correlated with increasing in some antioxidant enzymes activities. It might display the crucial indirect effect of Cd, that is, oxidative stress. Overall, Agropyron elongatum is introduced as the most tolerant cool-season turfgrass among studied species, which could be considered for engaging in advanced studies of heavy metal stresses......

Life on the edge: survival and behavioural responses of freshwater gill‐breathing snails to declining water level and substratum drying

Summary Reductions in water level and temporary exposure of substratum to air are two of the most important factors structuring communities in temperate near‐shore zones. Snails are suitable model organisms to study responses of aquatic communities to water‐level fluctuations, as they often inhabit near‐shore zones and are relatively mobile. In a laboratory study, we investigated survival and behavioural responses (horizontal migration and burrowing) of three freshwater gill‐breathing snails: Viviparus viviparus (L.) (large and small individuals), Bithynia tentaculata (L.) and Potamopyrgus antipodarum (Gray) to substratum drying. We studied the effect of distance to a suitable habitat (24 and 48 cm) and rate of dewatering (gradual: eight days or sudden) on horizontal migrations of snails as well as their burrowing depth. Large V. viviparus individuals were best adapted to dewatering: they were resistant to drying (surviving more than 3 weeks of air exposure) and migrated in response to decreasing water level and/or burrowed into the substratum. Their horizontal movement was negatively related to the rate of dewatering and distance needed to get to a submerged area. However, they were able to migrate to some extent even after a sudden dewatering and to reach a distant submerged refuge. Small V. viviparus exhibited similar behavioural responses as large individuals, but were less resistant to drying, surviving approximately one week of air exposure. Neither B. tentaculata nor P. antipodarum exhibited behavioural adaptations to desiccation, although resistance to drying differed markedly from approximately 3 weeks for B. tentaculata to 3–4 days for P. antipodarum. Resistance to drying and behavioural adaptations are two factors enabling benthic organisms to survive in harsh near‐shore environments. Our study revealed marked intra‐ and interspecific differences in response to dewatering, depending on body size, distance to a refuge and rate of dewatering. Appropriate physiological and behavioural responses may increase fitness of organisms under changing environmental conditions and contribute to their survival.

Body size-dependent toxicokinetics and toxicodynamics could explain intra- and interspecies variability in sensitivity

Ecological risk assessment of chemicals aims at quantifying the likelihood of adverse effects posed to non-target populations and the communities they constitute, often based on lethal concentration estimates for standard test species. There may, however, be intra- and interspecific differences in responses to chemical exposure. Here with the help of a toxicokinetic-toxicodynamic model, we explored whether differential body sizes might explain the observed variability in sensitivity between species and between life-stages of each individual species, for three model organisms, Daphnia magna, Chaoborus crystallinus and Mesocyclops leuckarti. While body size-dependent toxicokinetics could be used to predict intraspecies variation in sensitivity, our results also suggest that changes in both toxicokinetic and toxicodynamic parameters might be needed to describe differential species sensitivity. Accounting for biological traits, like body size, in mechanistic effect models will allow more accurate predictions of chemical effects in size structured populations, ultimately providing mechanistic explanations for species sensitivity distributions.

Species mixture increases the effect of drought on tree ring density, but not on ring width, in Quercus petraea–Pinus sylvestris stands

Mixing species has been proposed as a forest management option to mitigate the effects of the increase in summer drought episodes predicted by climate change models in temperate zones. Studying how the relationship between tree rings and summer drought episodes is modified by species mixture is of primary importance in this context. Based on a dendroclimatology study, we (i) qualified and quantified the relationship between ring width (RW) or mean ring density (MRD) and soil water deficit (SWD) in a ring-porous species, Quercus petraea, and a coniferous species, Pinus sylvestris, and (ii) determined if the relationships between tree ring characteristics and SWD are modified in mixtures. We found inter-specific differences in RW patterns depending on the seasonality of the drought periods: RW in Q. petraea responded mainly to SWD from May to July, and RW in P. sylvestris to SWD from May to September. The ring-width of both species was strongly reduced by SWD; however, inter-specific differences in response to SWD seasonality triggered RW variations of opposite directions between the two species, for several years. In contrast, MRD for both species was dependent on the SWD from June to July. MRD in Q. petraea increased slightly with SWD whereas MRD in P. sylvestris decreased strongly with SWD. The relationship between RW and SWD was not modified in mixtures compared to pure stands. We found that the effect of SWD on MRD was stronger in mixtures. The impact of SWD on species may be worsened in mixtures, but mixture of species with different growth sensitivities to the seasonality of the drought periods and to the drought intensity might help to buffer the effects of climatic fluctuations on the overall mixed stands productivity compared to pure stands.

Contrasting stress responses of two co-occurring chipmunk species (Tamias alpinus and T. speciosus)

Glucocorticoid (GC) hormones are important mediators of responses to environmental conditions. Accordingly, differences in GC physiology may contribute to interspecific variation in response to anthropogenically-induced patterns of climate change. To begin exploring this possibility, we validated the use of fecal cortisol/corticosterone metabolites (FCM) to measure baseline glucocorticoid levels in two species of co-occurring chipmunks that have exhibited markedly different patterns of response to environmental change. In Yosemite National Park, the alpine chipmunk (Tamias alpinus) has undergone a significant upward contraction of its elevational range over the past century; in contrast, the lodgepole chipmunk (Tamiasspeciosus) has experienced no significant change in elevational distribution over this period. To determine if GC levels in these species vary in response to external stimuli and to assess whether these responses differ between species, we compared FCM levels for the same individuals (1) at the time of capture in the field, (2) after a short period of captivity, and (3) after adrenocorticotropic hormone (ACTH), (4) handling, and (5) trapping challenges conducted while these animals were held in captivity. Our analyses indicate that T. alpinus was more responsive to several of these changes in external conditions. Although both species displayed a significant FCM response to ACTH challenge, only T. alpinus showed a significant response to our handling challenge and to captive housing conditions. These findings underscore the importance of species-specific validation studies and support the potential for studies of GC physiology to generate insights into interspecific differences in response to environmental change.