Biological traits predict shifts in geographical ranges of freshwater invertebrates during climatic warming and drying

Aim To test the ability of biological traits to predict climate‐related changes in geographical ranges of running‐water invertebrates. Location The Australian state of New South Wales and the Australian Capital Territory. Methods I analysed data from 8928 biomonitoring samples collected during a 16‐year period of generally rising air temperatures and declining precipitation. I used quantile regression to test for expansions and contractions on the climatically cooler, warmer, drier and wetter edges of the ranges of 120 invertebrate taxa, and correlated these shifts with the traits of thermophily (degree of preference for high versus low temperature) and rheophily (preference for flowing versus still water). Results The most commonly inferred range shifts were cool‐edge expansion plus warm‐edge contraction (71 taxa) and wet‐edge expansion plus dry‐edge contraction (71), but contractions from both cool and warm extremes (36) and from both dry and wet extremes (28) were also frequent. High‐temperature preference was associated with cool‐edge expansion and low‐temperature preference with wet‐edge expansion and contraction from all other extremes. A preference for flow was associated with wet‐edge expansion and dry‐edge contraction. Main conclusions Trait analysis has potential for predicting which species will expand their ranges and which will contract, but needs to be coupled with assessment of how the landscape provides each species with opportunities to track or avoid climate change. Improved quantification of climatically relevant traits and integration of trait analysis with species distribution modelling are likely to be beneficial.     

The smell of change: warming affects species interactions mediated by chemical information

Knowledge of how temperature influences an organism's physiology and behaviour is of paramount importance for understanding and predicting the impacts of climate change on species' interactions. While the behaviour of many organisms is driven by chemical information on which they rely on to detect resources, conspecifics, natural enemies and competitors, the effects of temperature on infochemical‐mediated interactions remain largely unexplored. Here, we experimentally show that temperature strongly influences the emission of infochemicals by ladybeetle larvae, which, in turn, modifies the oviposition behaviour of conspecific females. Temperature also directly affects female perception of infochemicals and their oviposition behaviour. Our results suggest that temperature‐mediated effects on chemical communication can influence flows across system boundaries (e.g. immigration and emigration) and thus alter the dynamics and stability of ecological networks. We therefore argue that investigating the effects of temperature on chemical communication is a crucial step towards a better understanding of the functioning of ecological communities facing rapid environmental changes.     

生态学代谢理论: 基于个体新陈代谢过程解释物种多样性的地理格局

新陈代谢是生物的基本生理过程。生态学代谢理论(metabolic theory of ecology)基于生物个体大小和环境温度对个体新陈代谢过程的影响, 使用尺度推移(scaling)的方法来解释多种生态学格局和过程。James Borwn等将这一理论用于解释物种多样性的大尺度格局, 并从机制上解释了物种多样性与环境温度的关系。这一理论提出了两个明确的预测: (1)物种多样性的对数与绝对温度的倒数之间呈线性关系; (2) 这一线性关系的斜率为–0.6至–0.7。这一理论自提出以来, 饱受争议, 经过了正反两方面经验数据的检验, 目前仍未形成一致的结论。虽然这一理论仍面临着一些有待解决的问题, 但它以崭新的思路和方法有别于以往的基于统计学方法的研究。人们过去对该理论的实证检验忽略了两个重要的约束条件, 即除温度以外的环境条件处于理想状态和群落处于平衡状态, 而这两个约束条件是理解该理论的基础。本文对生态学代谢理论的理论框架、预测和含义, 以及以往的检验结果进行阐述, 在此基础上提出了作者对该理论的若干认识和未来研究中应考虑的若干问题。     

Behavioural effects of temperature on ectothermic animals: unifying thermal physiology and behavioural plasticity

Temperature imposes significant constraints on ectothermic animals, and these organisms have evolved numerous adaptations to respond to these constraints. While the impacts of temperature on the physiology of ectotherms have been extensively studied, there are currently no frameworks available that outline the multiple and often simultaneous pathways by which temperature can affect behaviour. Drawing from the literature on insects, we propose a unified framework that should apply to all ectothermic animals, generalizing temperature's behavioural effects into: (1) kinetic effects, resulting from temperature's bottom‐up constraining influence on metabolism and neurophysiology over a range of timescales (from short to long term), and (2) integrated effects, where the top‐down integration of thermal information intentionally initiates or modifies a behaviour (behavioural thermoregulation, thermal orientation, thermosensory behavioural adjustments). We discuss the difficulty in distinguishing adaptive behavioural changes from constraints when observing animals' behavioural responses to temperature. We then propose two complementary approaches to distinguish adaptations from constraints, and categorize behaviours according to our framework: (i) ‘kinetic null modelling’ of temperature's effects on behaviour; and (ii) behavioural ecology experiments using temperature‐insensitive mutants. Our framework should help to guide future research on the complex relationship between temperature and behaviour in ectothermic animals.     

Towards a mechanistic understanding of temperature and enrichment effects on species interaction strength,omnivory and food‐web structure

Revealing the links between species functional traits, interaction strength and food‐web structure is of paramount importance for understanding and predicting the relationships between food‐web diversity and stability in a rapidly changing world. However, little is known about the interactive effects of environmental perturbations on individual species, trophic interactions and ecosystem functioning. Here, we combined modelling and laboratory experiments to investigate the effects of warming and enrichment on a terrestrial tritrophic system. We found that the food‐web structure is highly variable and switches between exploitative competition and omnivory depending on the effects of temperature and enrichment on foraging behaviour and species interaction strength. Our model contributes to identifying the mechanisms that explain how environmental effects cascade through the food web and influence its topology. We conclude that considering environmental factors and flexible food‐web structure is crucial to improve our ability to predict the impacts of global changes on ecosystem diversity and stability.     

Effects of constant and fluctuating incubation temperatures on hatching success and hatchling traits in the diamondback terrapin (Malaclemys terrapin) in the context of the warming climate

As global temperatures continue to rise, so too will the nest temperatures of many species of turtles. Yet for most turtle species, including the estuarine diamondback terrapin (Malaclemys terrapin), there is limited information on embryonic sensitivity to elevated temperature. We incubated eggs of M. terrapin at three, mean temperatures (31, 34, 37 °C) under two thermal exposure regimes (constant or semi-naturally fluctuating temperature) and measured hatching success, developmental rate, and hatchling size. Hatching success was 100% at 31 °C and 67% at 34 °C, respectively; at 37 °C, all eggs failed early in the incubation period. These values were unaffected by exposure regime. The modeled LT₅₀ (temperature that was lethal to 50% of the test population) was 34.0 °C in the constant and 34.2 °C in the fluctuating thermal regime, reflecting a steep decline in survival between 33 and 35 °C. Hatchlings having been incubated at a constant 34 °C hatched sooner than those incubated at 31 °C under either constant or fluctuating temperature. Hatchlings were smaller in straight carapace length (CL) and width after having been incubated at 34 °C compared to 31 °C. Larger (CL) hatchlings resulted from fluctuating temperature conditions relative to constant temperature conditions, regardless of mean temperature. Based upon recent temperatures in natural nests, the M. terrapin population studied here appears to possess resiliency to several degrees of elevated mean nest temperatures, beyond which, embryonic mortality will likely sharply increase. When considered within the mosaic of challenges that Maryland's M. terrapin face as the climate warms, including ongoing habitat losses due to sea level rise and impending thermal impacts on bioenergetics and offspring sex ratios, a future increase in embryonic mortality could be a critical factor for a population already experiencing ecological and physiological challenges due to climate change.     

Interacting effects of ocean acidification and warming on growth and DMS‐production in the haptophyte coccolithophore Emiliania huxleyi

The production of the marine trace gas dimethyl sulfide (DMS) provides 90% of the marine biogenic sulfur in the atmosphere where it affects cloud formation and climate. The effects of increasing anthropogenic CO₂ and the resulting warming and ocean acidification on trace gas production in the oceans are poorly understood. Here we report the first measurements of DMS‐production and data on growth, DMSP and DMS concentrations in pH‐stated cultures of the phytoplankton haptophyte Emiliania huxleyi. Four different environmental conditions were tested: ambient, elevated CO₂ (+CO₂), elevated temperature (+T) and elevated temperature and CO₂ (+TCO₂). In comparison to the ambient treatment, average DMS production was about 50% lower in the +CO₂ treatment. Importantly, temperature had a strong effect on DMS production and the impacts outweighed the effects of a decrease in pH. As a result, the +T and +TCO₂ treatments showed significantly higher DMS production of 36.2 ± 2.58 and 31.5 ± 4.66 μmol L^?1 cell volume (CV) h^?1 in comparison with the +CO₂ treatment (14.9 ± 4.20 μmol L^?1 CV h^?1). As the cultures were aerated with an air/CO₂ mixture, DMS was effectively removed from the incubation bottles so that concentration remained relatively low (3.6–6.1 mmol L^?1 CV). Intracellular DMSP has been shown to increase in E. huxleyi as a result of elevated temperature and/or elevated CO₂ and our results are in agreement with this finding: the ambient and +CO₂ treatments showed 125 ± 20.4 and 162 ± 27.7 mmol L^?1 CV, whereas +T and +TCO₂ showed significantly increased intracellular DMSP concentrations of 195 ± 15.8 and 211 ± 28.2 mmol L^?1 CV respectively. Growth was unaffected by the treatments, but cell diameter decreased significantly under elevated temperature. These results indicate that DMS production is sensitive to CO₂ and temperature in E. huxleyi. Hence, global environmental change that manifests in ocean acidification and warming may not result in decreased DMS as suggested by earlier studies investigating the effect of elevated CO₂ in isolation.     

Interactions between temperature and nutrients across levels of ecological organization

Temperature and nutrient availability play key roles in controlling the pathways and rates at which energy and materials move through ecosystems. These factors have also changed dramatically on Earth over the past century as human activities have intensified. Although significant effort has been devoted to understanding the role of temperature and nutrients in isolation, less is known about how these two factors interact to influence ecological processes. Recent advances in ecological stoichiometry and metabolic ecology provide a useful framework for making progress in this area, but conceptual synthesis and review are needed to help catalyze additional research. Here, we examine known and potential interactions between temperature and nutrients from a variety of physiological, community, and ecosystem perspectives. We first review patterns at the level of the individual, focusing on four traits – growth, respiration, body size, and elemental content – that should theoretically govern how temperature and nutrients interact to influence higher levels of biological organization. We next explore the interactive effects of temperature and nutrients on populations, communities, and food webs by synthesizing information related to community size spectra, biomass distributions, and elemental composition. We use metabolic theory to make predictions about how population‐level secondary production should respond to interactions between temperature and resource supply, setting up qualitative predictions about the flows of energy and materials through metazoan food webs. Last, we examine how temperature–nutrient interactions influence processes at the whole‐ecosystem level, focusing on apparent vs. intrinsic activation energies of ecosystem processes, how to represent temperature–nutrient interactions in ecosystem models, and patterns with respect to nutrient uptake and organic matter decomposition. We conclude that a better understanding of interactions between temperature and nutrients will be critical for developing realistic predictions about ecological responses to multiple, simultaneous drivers of global change, including climate warming and elevated nutrient supply.     

Phenology, ontogeny and the effects of climate change on the timing of species interactions

Climate change is altering the phenology of many species and the timing of their interactions with other species, but the impacts of these phenological shifts on species interactions remain unclear. Classical approaches to the study of phenology have typically documented changes in the timing of single life-history events, while phenological shifts affect many interactions over entire life histories. In this study, we suggest an approach that integrates the phenology and ontogeny of species interactions with a fitness landscape to provide a common mechanistic framework for investigating phenological shifts. We suggest that this ontogeny–phenology landscape provides a flexible method to document changes in the relative phenologies of interacting species, examine the causes of these phenological shifts, and estimate their consequences for interacting species.
Ecology Letters (2010) 13: 1–10     

Quantifying the effects of ecological constraints on trait expression using novel trait‐gradient analysis parameters

Complex processes related to biotic and abiotic forces can impose limitations to assembly and composition of plant communities. Quantifying the effects of these constraints on plant functional traits across environmental gradients, and among communities, remains challenging. We define ecological constraint (C_i) as the combined, limiting effect of biotic interactions and environmental filtering on trait expression (i.e., the mean value and range of functional traits). Here, we propose a set of novel parameters to quantify this constraint by extending the trait‐gradient analysis (TGA) methodology. The key parameter is ecological constraint, which is dimensionless and can be measured at various scales, for example, on population and community levels. It facilitates comparing the effects of ecological constraints on trait expressions across environmental gradients, as well as within and among communities. We illustrate the implementation of the proposed parameters using the bark thickness of 14 woody species along an aridity gradient on granite outcrops in southwestern Australia. We found a positive correlation between increasing environmental stress and strength of ecological constraint on bark thickness expression. Also, plants from more stressful habitats (shrublands on shallow soils and in sun‐exposed locations) displayed higher ecological constraint for bark thickness than plants in more benign habitats (woodlands on deep soils and in sheltered locations). The relative ease of calculation and dimensionless nature of C_i allow it to be readily implemented at various scales and make it widely applicable. It therefore has the potential to advance the mechanistic understanding of the ecological processes shaping trait expression. Some future applications of the new parameters could be investigating the patterns of ecological constraints (1) among communities from different regions, (2) on different traits across similar environmental gradients, and (3) for the same trait across different gradient types.     

Assessment of the effects of environmental change on the performance and density of Bistorta vivipara: the use of multivariate analysis and experimental manipulation

1 Studies of plant performance in relation to local variability in environmental conditions can be used to predict the responses of species to environmental change.
2 We used redundancy analysis to study how interpopulation variation in average plant weight, flower and bulbil number, bulbil weight and population density among 28 populations of Bistorta vivipara was related to variation in 15 environmental factors. We also examined the responses of plants to a 4-year experimental increase in temperature.
3 Significant differences in average plant performance were found between populations. Variance partitioning of the response data showed that environmental factors explained 45% of the variation in plant performance and density between populations, whereas variation due to transect position was small (10.8%). Soil pH, altitude and season length were the most influential of the environmental variables, and explained 23%, 21% and 14%, respectively, of the variation. Plant performance was in general negatively correlated with these variables, whereas plant density increased along the pH and altitude gradients, suggesting that environmental factors associated with elevation (temperature and vegetation cover) and pH (soil fertility) had opposing effects on individual performance and density. Season length was highly important for average bulbil weight.
4 Plants growing in open top chambers had significantly enhanced growth and produced significantly heavier bulbils than those in control plots, whereas flower and bulbil number were unaffected by experimentally increased temperatures. Plant density was equal for warmed and control plots.
5 Although warming may increase bulbil weight and plant size in B. vivipara , the response to climate change is complicated by the fact that population densities may decrease due to intensified competition for light caused by a denser vegetation cover.     

Geographical and experimental contexts modulate the effect of warming on top‐down control: a meta‐analysis

Ecologists have extensively investigated the effect of warming on consumer–resource interactions, with experiments revealing that warming can strengthen, weaken or have no net effect on top‐down control of resources. These experiments have inspired a body of theoretical work to explain the variation in the effect of warming on top‐down control. However, there has been no quantitative attempt to reconcile theory with outcomes from empirical studies. To address the gap between theory and experiment, we performed a meta‐analysis to examine the combined effect of experimental warming and top‐down control on resource biomass and determined potential sources of variation across experiments. We show that differences in experimental outcomes are related to systematic variation in the geographical distribution of studies. Specifically, warming strengthened top‐down control when experiments were conducted in colder regions, but had the opposite effect in warmer regions. Furthermore, we found that differences in the thermoregulation strategy of the consumer and openness of experimental arenas to dispersal can contribute to some deviation from the overall geographical pattern. These results reconcile empirical findings and support the expectation of geographical variation in the response of consumer–resource interactions to warming.     

Cold‐adapted species in a warming world – an explorative study on the impact of high winter temperatures on a continental butterfly

Increasing evidence suggests that global warming significantly alters the range and phenology of plants and animals. Whereas thermophilous species usually benefit from rising temperatures, the living conditions of taxa adapted to cooler or continental climates are deteriorating. The woodland ringlet butterfly, Erebia medusa Fabricius (Lepidoptera: Nymphalidae) is one of the continental species that are supposed to be adversely affected by climate change, especially by rising winter temperatures. Here, we conduct an explorative study on the effects of low, moderate, and high winter temperatures on the pre‐adult and adult stages of E. medusa in a laboratory experiment. Compared to the two other temperature regimes, the warm winter treatment led to an earlier termination of diapause and higher larval weights at the end of the winter, but significantly lower survival rates. The after‐effects of the warm treatment included lower weight of the pupae and adult females, shorter forewings of adult males, and earlier emergence of both adult males and females. In natural environments, which are characterized by a much greater thermal variability and a much higher frequency of soil freeze‐thaw events compared to our experiment, the effects of rising winter temperatures might be stronger than in this study. Thus, we conclude that warmer winters pose a non‐negligible long‐term threat to E. medusa.     

Additive effects of temperature and infection with an acanthocephalan parasite on the shredding activity of Gammarus fossarum (Crustacea: Amphipoda): the importance of aggregative behavior

Climate change can have critical impacts on the ecological role of keystone species, leading to subsequent alterations within ecosystems. The consequences of climate change may be best predicted by understanding its interaction with the cumulative effects of other stressors, although this approach is rarely adopted. However, whether this interaction is additive or interactive can hardly be predicted from studies examining a single factor at a time. In particular, biotic interactions are known to induce modifications in the functional role of many species. Here, we explored the effect of temperature on leaf consumption by a keystone freshwater shredder, the amphipod Gammarus fossarum. This species is found at high densities in the wild and relies on aggregation as an antipredator behavior. In addition, gammarids regularly harbor acanthocephalan parasites that are known to induce multiple effects on their hosts, including modifications on their functional role. We thus assessed the cumulative effect of both intraspecific interactions and parasitism. Consumption tests were conducted on gammarids, either naturally infected with Pomphorhynchus tereticollis or uninfected, feeding alone or in groups. Our results show that increased temperatures induced a significant increase in consumption, but only to a certain extent. Interestingly, consumption at the highest temperature depended on amphipod density: Whereas a decrease was observed for single individuals, no such effect on feeding was observed for individuals in groups. In addition, infection by acanthocephalan parasites per se significantly negatively impacted the shredding role of gammarids. Overall, the combined effects of parasitism and temperature appeared to be additive. Thus, future studies focusing on the impact of climate change on the functional role of keystone species may benefit from a multimodal approach under realistic conditions to derive accurate predictions.     

Mechanistic insights into the effects of climate change on larval cod

Understanding the biophysical mechanisms that shape variability in fisheries recruitment is critical for estimating the effects of climate change on fisheries. In this study, we used an Earth System Model (ESM) and a mechanistic individual‐based model (IBM) for larval fish to analyze how climate change may impact the growth and survival of larval cod in the North Atlantic. We focused our analysis on five regions that span the current geographical range of cod and are known to contain important spawning populations. Under the SRES A2 (high emissions) scenario, the ESM‐projected surface ocean temperatures are expected to increase by >1 °C for 3 of the 5 regions, and stratification is expected to increase at all sites between 1950–1999 and 2050–2099. This enhanced stratification is projected to decrease large (>5 μm ESD) phytoplankton productivity and mesozooplankton biomass at all 5 sites. Higher temperatures are projected to increase larval metabolic costs, which combined with decreased food resources will reduce larval weight, increase the probability of larvae dying from starvation and increase larval exposure to visual and invertebrate predators at most sites. If current concentrations of piscivore and invertebrate predators are maintained, larval survival is projected to decrease at all five sites by 2050–2099. In contrast to past observed responses to climate variability in which warm anomalies led to better recruitment in cold‐water stocks, our simulations indicated that reduced prey availability under climate change may cause a reduction in larval survival despite higher temperatures in these regions. In the lower prey environment projected under climate change, higher metabolic costs due to higher temperatures outweigh the advantages of higher growth potential, leading to negative effects on northern cod stocks. Our results provide an important first large‐scale assessment of the impacts of climate change on larval cod in the North Atlantic.