Influence of climate variability on plant production and N‐mineralization in Central US grasslands

Abstract. We assessed the influence of annual and seasonal climate variability over soil organic matter (SOM), above‐ground net primary production (ANPP) and in situ net nitrogen (N) mineralization in a regional field study across the International Geosphere Biosphere Programme (IGBP) North American mid‐latitude transect (Koch et al. 1995). We hypothesized that while trends in SOM are strongly correlated with mean climatic parameters, ANPP and net N‐mineralization are more strongly influenced by annual and seasonal climate because they are dynamic processes sensitive to short‐term variation in temperature and water availability. Seasonal and monthly deviations from long‐term climatic means, particularly precipitation, were greatest at the semi‐arid end of the transect. ANPP is sensitive to this climatic variability, but is also strongly correlated with mean annual climate parameters. In situ net N‐mineralization and nitrification were weakly influenced by soil water content and temperature during the incubation and were less sensitive to seasonal climatic variables than ANPP, probably because microbial transformations of N in the soil are mediated over even finer temporal scales. We found no relationship between ANPP and in situ net N‐mineralization. These results suggests that methods used to estimate in situ net N‐mineralization are inadequate to represent N‐availability across gradients where microbial biomass, N‐immobilization or competition among plants and microbes vary.     

The thermoregulatory benefits of the communal nest of sociable weavers Philetairus socius are spatially structured within nests

Structures built by animals, such as nests, mounds and burrows, are often the product of cooperative investment by more than one individual. Such structures may be viewed as a public good, since all individuals that occupy them share the benefits they provide. However, access to the benefits generated by the structure may vary among individuals and is likely to be an important determinant of social organisation. Here we use the massive, communal nests of sociable weavers Philetairus socius, to investigate whether their thermoregulatory function varies in relation to the size of communal nests, and the position of individual nest chambers within the communal structure. We then examine whether this spatial variation in thermoregulatory function predicts the social organisation of colonies. First, we show that the sociable weavers’ communal nests buffer variation in ambient temperature, and reduce temperature variability within nest chambers. The extent of this buffering effect depends significantly on the position of nest chambers within the communal structure, and on the depth to which chambers are embedded within the nest mass. We detected no effect of nest volume on thermoregulatory benefits, suggesting that there are likely to be additional, non‐thermoregulatory benefits leading to communal nests. Finally, our results indicate that there may be competition for access to the benefits of the public good, since older birds occupied the chambers with the highest thermoregulatory benefits, where breeding activity was also more common. We discuss how the spatial structure of the benefits of the public good might influence social organisation in the unique communal lifestyle of sociable weavers.     

Evolutionary refugia and ecological refuges: key concepts for conserving Australian arid zone freshwater biodiversity under climate change

Refugia have been suggested as priority sites for conservation under climate change because of their ability to facilitate survival of biota under adverse conditions. Here, we review the likely role of refugial habitats in conserving freshwater biota in arid Australian aquatic systems where the major long‐term climatic influence has been aridification. We introduce a conceptual model that characterizes evolutionary refugia and ecological refuges based on our review of the attributes of aquatic habitats and freshwater taxa (fishes and aquatic invertebrates) in arid Australia. We also identify methods of recognizing likely future refugia and approaches to assessing the vulnerability of arid‐adapted freshwater biota to a warming and drying climate. Evolutionary refugia in arid areas are characterized as permanent, groundwater‐dependent habitats (subterranean aquifers and springs) supporting vicariant relicts and short‐range endemics. Ecological refuges can vary across space and time, depending on the dispersal abilities of aquatic taxa and the geographical proximity and hydrological connectivity of aquatic habitats. The most important are the perennial waterbodies (both groundwater and surface water fed) that support obligate aquatic organisms. These species will persist where suitable habitats are available and dispersal pathways are maintained. For very mobile species (invertebrates with an aerial dispersal phase) evolutionary refugia may also act as ecological refuges. Evolutionary refugia are likely future refugia because their water source (groundwater) is decoupled from local precipitation. However, their biota is extremely vulnerable to changes in local conditions because population extinction risks cannot be abated by the dispersal of individuals from other sites. Conservation planning must incorporate a high level of protection for aquifers that support refugial sites. Ecological refuges are vulnerable to changes in regional climate because they have little thermal or hydrological buffering. Accordingly, conservation planning must focus on maintaining meta‐population processes, especially through dynamic connectivity between aquatic habitats at a landscape scale.     

Differing contributions of density dependence and climate to the population dynamics of three eruptive herbivores

1. Although both endogenous and exogenous processes regulate populations, the current understanding of the contributions from density dependence and climate to the population dynamics of eruptive herbivores remains limited. 2. Using a 17‐year time series of three cereal aphid species [Rhopalosiphum padi L., Metopolophium dirhodum (Walker), and Diuraphis noxia (Kurdumov)] compiled from a trapping network spanning the northwestern U.S.A., temporal and spatial patterns associated with population fluctuations, and modelled density dependence in aphid abundances were tested. These models were used to analyse correlations between climate and aphid abundances in the presence and absence of residual variance as a result of density‐dependent effects. 3. The temporal dynamics of aphid population fluctuations indicated periodicity, with no clear evidence for a spatial pattern underlying population fluctuations. 4. Aphid abundances oscillated in a manner consistent with delayed density dependence for all three aphid species, although the strength of these feedbacks differed among species. 5. Diuraphis noxia abundances were negatively correlated with increasing temperatures in the absence of density‐dependent effects, whereas M. dirhodum abundances were positively correlated with increasing cumulative precipitation in the presence of density‐dependent effects; yet, R. padi abundances were unrelated to climate variables irrespective of population feedbacks. 6. Our analysis suggests that endogenous feedbacks differentially regulate aphid populations in the northwestern U.S.A., and these feedbacks may operate at an expansive spatial scale. It is concluded that the contributions of density dependence and climate to aphid population dynamics are species‐specific in spite of similar ecological niches, with implications for assessing species responses to climate variability.     

Spatial heterogeneity in the effects of climate change on the population dynamics of a Mediterranean tortoise

Climatic shifts may increase the extinction risk of populations, especially when they are already suffering from other anthropogenic impacts. Our ability to predict the consequences of climate change on endangered species is limited by our scarce knowledge of the effects of climate variability on the population dynamics of most organisms and by the uncertainty of climate projections, which depend strongly on the region of the earth being considered. In this study, we analysed a long‐term monitoring programme (1988–2009) of Hermann's tortoise (Testudo hermanni) aimed at evaluating the consequences of the drastic changes in temperature and precipitation patterns predicted for the Mediterranean region on the demography of a long‐lived species with low dispersal capability and already suffering a large number of threats. Capture–recapture modelling of a population in the Ebro Delta (NE Spain) allowed us to assess the effect of climate variability on the survival of tortoises. Winter rainfall was found to be the major driver of juvenile and immature survival, whereas that of adults remained high and constant across the study. Furthermore, local climate series obtained ad hoc from regional climate simulations, for this and 10 additional Mediterranean locations where tortoises occurred, provided us with reliable future climate forecasts, which were used to simulate the fate of these populations under three precipitation scenarios (mean, wet and dry) using stochastic population modelling. We show that a shift to a more arid climate would have negative consequences for population persistence, enhancing juvenile mortality and increasing quasiextinction risk because of a decrease in recruitment. These processes varied depending on the population and the climate scenario we considered, but our results suggest that unless other human‐induced causes of mortality are suppressed (e.g. poaching, fire, habitat fragmentation), climate variability will increase extinction risk within most of the species’ current range.     

A continental-scale analysis of tree cover in African savannas

Aim We present a continental‐scale analysis that explores the processes controlling woody community structure in tropical savannas. We analyse how biotic and abiotic factors interact to promote and modify tree cover, examine alternative ecological hypotheses and quantify disturbance effects using satellite estimates of tree cover. Location African savannas. Methods Tree cover is represented as a resource‐driven potential cover related to rainfall and soil characteristics perturbed by natural and human factors such as fire, cattle grazing, human population and cultivation. Within this framework our approach combines semi‐empirical modelling and information theory to identify the best models. Results Woody community structure across African savannas is best represented by a sigmoidal response of tree cover to mean annual precipitation (MAP), with a dependency on soil texture, which is modified by the separate effects of fire, domestic livestock, human population density and cultivation intensity. This model explains c. 66% of the variance in tree cover and appears consistent across the savanna regions of Africa. Main conclusions The analysis provides a new understanding of the importance and interaction of environmental and disturbance factors that create the broad spatial patterns of tree cover observed in African savannas. Woody cover increases with rainfall, but is modified by disturbances. These ‘perturbation’ effects depend on MAP regimes: in arid savannas (MAP < 400 mm) they are generally small (< 1% decrease in cover), while in semi‐arid and mesic savannas (400–1600 mm), perturbations result in an average 2% (400 mm) to 23% (1600 mm) decrease in cover; fire frequency and human population have more influence than cattle, and cultivation appears, on average, to lead to small increases in woody cover. Wet savannas (1600–2200 mm) are controlled by perturbations that inhibit canopy closure and reduce tree cover by, on average, 24–34%. Full understanding of the processes determining savanna structure requires consideration of resource limitation and disturbance dynamics.     

Niche models tell half the story: spatial context and life‐history traits influence species responses to global change

Aim While niche models are typically used to assess the vulnerability of species to climate change, they have been criticized for their limited assessment of threats other than climate change. We attempt to evaluate this limitation by combining niche models with life‐history models to investigate the relative influence of climate change and a range of fire regimes on the viability of a long‐lived plant population. Specifically, we investigate whether range shift due to climate change is a greater threat to an obligate seeding fire‐prone shrub than altered fire frequency and how these two threatening processes might interact. Location Australian sclerophyll woodland and heathland. Methods The study species is Leucopogon setiger, an obligate seeding fire‐prone shrub. A spatially explicit stochastic matrix model was constructed for this species and linked with a dynamic niche model and fire risk functions representing a suite of average fire return intervals. We compared scenarios with a variety of hypothetical patches, a patch framework based upon current habitat suitability and one with dynamic habitat suitability based on climate change scenarios A1FI and A2. Results Leucopogon setiger was found to be sensitive to fire frequency, with shorter intervals reducing expected minimum abundances (EMAs). Spatial decoupling of fires across the landscape reduced the vulnerability of the species to shortened fire frequencies. Shifting habitat, while reducing EMAs, was less of a threat to the species than frequent fire. Main conclusions Altered fire regime, in particular more frequent fires relative to the historical regime, was predicted to be a strong threat to this species, which may reflect a vulnerability of obligate seeders in general. Range shifts induced by climate change were a secondary threat when habitat reductions were predicted. Incorporating life‐history traits into habitat suitability models by linking species distribution models with population models allowed for the population‐level evaluation of multiple stressors that affect population dynamics and habitat, ultimately providing a greater understanding of the impacts of global change than would be gained by niche models alone. Further investigations of this type could elucidate how particular bioecological factors can affect certain types of species under global change.     

Cumulative effects of land use,altered fire regime and climate change on persistence of Ceanothus verrucosus,a rare,fire‐dependent plant species

Mediterranean ecosystems are among the highest in species richness and endemism globally and are also among the most sensitive to climate and land‐use change. Fire is an important driver of ecosystem processes in these systems; however, fire regimes have been substantially changed by human activities. Climate change is predicted to further alter fire regimes and species distributions, leading to habitat loss and threatening biodiversity. It is currently unknown what the population‐level effects of these landscape‐level changes will be. We linked a spatially explicit stochastic population model to dynamic bioclimate envelopes to investigate the effects of climate change, habitat loss and fragm entation and altered fire regime on population abundances of a long‐lived obligate seeding shrub, Ceanothus verrucosus, a rare endemic species of southern California. We tested a range of fire return intervals under the present and two future climate scenarios. We also assessed the impact of potential anthropogenic land‐use change by excluding land identified as developable by local governments. We found that the 35–50 year fire return interval resulted in the highest population abundances. Expected minimum population abundance (EMA) declined gradually as fire return interval increased, but declined dramatically for shorter fire intervals. Simulated future development resulted in a 33% decline in EMA, but relatively stable population trajectories over the time frame modeled. Relative changes in EMA for alternative fire intervals were similar for all climate and habitat loss scenarios, except under the more severe climate scenario which resulted in a change in the relative ranking of the fire scenarios. Our results show climate change to be the most serious threat facing obligate seeding shrubs embedded in urban landscapes, resulting in population decline and increased local extirpation, and that likely interactions with other threats increase risks to these species. Taking account of parameter uncertainty did not alter our conclusions.     

Nonlinearity in interspecific interactions in response to climate change: Cod and haddock as an example

Climate change has profound ecological effects, yet our understanding of how trophic interactions among species are affected by climate change is still patchy. The sympatric Atlantic haddock and cod are co‐occurring across the North Atlantic. They compete for food at younger stages and thereafter the former is preyed by the latter. Climate change might affect the interaction and coexistence of these two species. Particularly, the increase in sea temperature (ST) has been shown to affect distribution, population growth and trophic interactions in marine systems. We used 33‐year long time series of haddock and cod abundances estimates from two data sources (acoustic and trawl survey) to analyse the dynamic effect of climate on the coexistence of these two sympatric species in the Arcto‐Boreal Barents Sea. Using a Bayesian state‐space threshold model, we demonstrated that long‐term climate variation, as expressed by changes of ST, affected species demography through different influences on density‐independent processes. The interaction between cod and haddock has shifted in the last two decades due to an increase in ST, altering the equilibrium abundances and the dynamics of the system. During warm years (ST over ca. 4°C), the increase in the cod abundance negatively affected haddock abundance while it did not during cold years. This change in interactions therefore changed the equilibrium population size with a higher population size during warm years. Our analyses show that long‐term climate change in the Arcto‐Boreal system can generate differences in the equilibrium conditions of species assemblages.     

Rapid evolution of thermal plasticity in mountain lake Daphnia populations

Populations at risk of extinction due to climate change may be rescued by adaptive evolution or plasticity. Selective agents, such as introduced predators, may enhance or constrain plastic or adaptive responses to temperature. We tested responses of Daphnia to temperature by collecting populations from lakes across an elevational gradient in the presence and absence of fish predators (long‐term selection). We subsequently grew these populations at two elevations in field mesocosms over two years (short‐term selection), followed by a common‐garden experiment at two temperatures in the lab to measure life‐history traits. Both long‐term and short‐term selection affected traits, suggesting that genetic variation of plasticity within populations enabled individuals to rapidly evolve plasticity in response to high temperature. We found that short‐term selection by high temperature increased plasticity for growth rate in all populations. Fecundity was higher in populations from fishless lakes and body size showed greater plasticity in populations from warm lakes (long‐term selection). Neither body size nor fecundity were affected by short‐term thermal selection. These results demonstrate that plasticity is an important component of the life‐history response of Daphnia, and that genetic variation within populations enabled rapid evolution of plasticity in response to selection by temperature.     

Direct and indirect effects of grazing constrain shrub encroachment in semi‐arid Patagonian steppes

Question: What are the long‐term effects of grazing exclusion on the population structure and dynamics of, and interactions among, three dominant shrub species? Location: Grass‐shrub Patagonian steppe, Chubut, Argentina. Methods: Permanent plots were established in grazed paddocks and paddocks excluded from grazing in representative Patagonian rangelands. Shrub abundance, population size‐structure, short‐term (two 3‐yr periods) and long‐term (matrix models) population dynamics, and neighborhood interactions of three native and codominant shrub species (Mulinum spinosum, Senecio filaginoides and Adesmia volckmanni) were measured and analysed using different statistical approaches. Results: The total density of shrubs was 74% higher in paddocks excluded from grazing, owing mainly to increases in Mulinum (80%) and Senecio (68%) species. However, differences in size structure between ungrazed and grazed paddocks were only detected in Mulinum. Demographic rates differed between shrub species, time‐periods and grazing conditions. In particular, recruitment in the short term (especially in wet years) and population growth rate in the long term (λ) were higher in paddocks excluded from grazing only in Mulinum populations. Senecio populations showed a marginal increase in recruitment and mortality independent of the grazing condition in the wet and dry period. Grazing exclusion modified the balance of neighborhood interactions among the three shrub species. In grazing‐exclusion paddocks, there was a balance between positive and negative interspecific interactions, while in grazed paddocks there were more negative intraspecific and interspecific interactions, resulting in a net negative balance of neighborhood interactions. Conclusions: Our understanding of woody encroachment in arid rangelands can be informed through evaluation of direct and indirect effects of grazing exclusion on the abundance and demography of dominant woody species. In Patagonian arid steppes, the occurrence of woody encroachment in rangelands excluded from grazing can be explained by altered responses in plant‐animal and plant‐plant interactions among shrub species.     

Uncertainty in predicting range dynamics of endemic alpine plants under climate warming

Correlative species distribution models have long been the predominant approach to predict species’ range responses to climate change. Recently, the use of dynamic models is increasingly advocated for because these models better represent the main processes involved in range shifts and also simulate transient dynamics. A well‐known problem with the application of these models is the lack of data for estimating necessary parameters of demographic and dispersal processes. However, what has been hardly considered so far is the fact that simulating transient dynamics potentially implies additional uncertainty arising from our ignorance of short‐term climate variability in future climatic trends. Here, we use endemic mountain plants of Austria as a case study to assess how the integration of decadal variability in future climate affects outcomes of dynamic range models as compared to projected long‐term trends and uncertainty in demographic and dispersal parameters. We do so by contrasting simulations of a so‐called hybrid model run under fluctuating climatic conditions with those based on a linear interpolation of climatic conditions between current values and those predicted for the end of the 21st century. We find that accounting for short‐term climate variability modifies model results nearly as differences in projected long‐term trends and much more than uncertainty in demographic/dispersal parameters. In particular, range loss and extinction rates are much higher when simulations are run under fluctuating conditions. These results highlight the importance of considering the appropriate temporal resolution when parameterizing and applying range‐dynamic models, and hybrid models in particular. In case of our endemic mountain plants, we hypothesize that smoothed linear time series deliver more reliable results because these long‐lived species are primarily responsive to long‐term climate averages.     

Canopy scale measurements of CO2 and water vapor exchange along a precipitation gradient in southern Africa

Short‐term measurements of carbon dioxide, water, and energy fluxes were collected at four locations along a mean annual precipitation gradient in southern Africa during the wet (growing) season with the purpose of determining how the observed vegetation–atmosphere exchange properties are functionally related to the long‐term climatic conditions. This research was conducted along the Kalahari Transect (KT), one in the global set of International Geosphere‐Biosphere Program transects, which covers a north–south aridity gradient, all on a homogenous sand formation. Eddy covariance instruments were deployed on a permanent tower in Mongu, Zambia (879 mm of rainfall per year), as well as on a portable tower in Maun (460 mm yr^?1), Okwa River Crossing (407 mm yr^?1), and Tshane (365 mm yr^?1), Botswana for several days at each site. The relationships between CO₂ flux, F_c, and photosynthetically active radiation were described well by a hyperbolic fit to the data at all locations except for Mongu, the wettest site. Here, there appeared to be an air temperature effect on F_c. While daytime values of F_c routinely approached or exceeded ?20 μmol m^?2 s^?1 at Mongu, the magnitude of F_c remained less than ?10 μmol m^?2 s^?1 when the air temperature was above 27°C. Canopy resistances to water vapor transfer, r_c, displayed an overall decline from the wetter sites to the more arid sites, but the differences in r_c could be almost exclusively accounted for by the decrease in leaf area index (LAI) from north to south along the KT. Ecosystem water use efficiency (WUE), defined as the ratio of net carbon flux to evapotranspiration, showed a general decrease with increasing vapor pressure deficit, D, for all of the sites. The magnitudes of WUE at a given D, however, were dissimilar for the individual sites and were found to be stratified according to the position of the sites along the long‐term aridity gradient. For example, Mongu, which has the wettest climate, has a much lower WUE for like levels of D than Tshane, which historically has the most arid climate. Given the similar inferred stomatal resistances between the sites, the disparate carbon uptake behavior for the grass vs. woody vegetation is the likely cause for the observed differences in WUE along the aridity gradient. The short‐term flux measurements provide a framework for evaluating the vegetation's functional adaptation to the long‐term climate and provide information that may be useful for predicting the dynamic response of the vegetation to future climate change.     

Implication of climate change for the persistence of raptors in arid savanna

Arid savannas are regarded as one of the ecosystems most likely to be affected by climate change. In these dry conditions, even top predators like raptors are affected by water availability and precipitation. However, few research initiatives have addressed the question of how climate change will affect population dynamics and extinction risk of particular species in arid ecosystems. Here, we use an individual‐oriented modeling approach to conduct experiments on the population dynamics of long lived raptors. We investigate the potential impact of precipitation variation caused by climate change on raptors in arid savanna using the tawny eagle (Aquila rapax) in the southern Kalahari as a case study. We simulated various modifications of precipitation scenarios predicted for climate change, such as lowered annual precipitation mean, increased inter‐annual variation and increased auto‐correlation in precipitation. We found a high impact of these modifications on extinction risk of tawny eagles, with reduced population persistence in most cases. Decreased mean annual precipitation and increased inter‐annual variation both caused dramatic decreases in population persistence. Increased auto‐correlation in precipitation led only to slightly accelerated extinction of simulated populations. Finally, for various patterns of periodically fluctuating precipitation, we found both increased and decreased population persistence. In summary, our results suggest that the impacts on raptor population dynamics and survival caused by climate change in arid savannas will be great. We emphasize that even if under climate change the mean annual precipitation remains constant but the inter‐annual variation increases the persistence of raptor populations in arid savannas will decrease considerably. This suggests a new dimension of climate change driven impacts on population persistence and consequently on biodiversity. However, more investigations on particular species and/or species groups are needed to increase our understanding of how climate change will impact population dynamics and how this will influence species diversity and biodiversity.     

Seasonal climate effects on the survival of a hibernating mammal

Global climate change and associated regional climate variability is impacting the phenology of many species, ultimately altering individual fitness and population dynamics. Yet, few studies have considered the effects of pertinent seasonal climate variability on phenology and fitness. Hibernators may be particularly susceptible to changes in seasonal climate since they have a relatively short active season in which to reproduce and gain enough mass to survive the following winter. To understand whether and how seasonal climate variability may be affecting hibernator fitness, we estimated survival from historical (1964–1968) and contemporary (2014–2017) mark–recapture data collected from the same population of Uinta ground squirrels (UGS, Urocitellus armatus), a hibernator endemic to the western United States. Despite a locally warming climate, the phenology of UGS did not change over time, yet season‐specific climate variables were important in regulating survival rates. Specifically, older age classes experienced lower survival when winters or the following springs were warm, while juveniles benefited from warmer winter temperatures. Although metabolic costs decrease with decreasing temperature in the hibernacula, arousal costs increase with decreasing temperature. Our results suggest that this trade‐off is experienced differently by immature and mature individuals. We also observed an increase in population density during that time period, suggesting resources are less limited today than they used to be. Cheatgrass is now dominating the study site and may provide a better food source to UGS than native plants did historically.     

Northward displacement of optimal climate conditions for ecotypes of Eriophorum vaginatum L. across a latitudinal gradient in Alaska

Plants are often genetically specialized as ecotypes attuned to local environmental conditions. When conditions change, the optimal environment may be physically displaced from the local population, unless dispersal or in situ evolution keep pace, resulting in a phenomenon called adaptational lag. Using a 30‐year‐old reciprocal transplant study across a 475 km latitudinal gradient, we tested the adaptational lag hypothesis by measuring both short‐term (tiller population growth rates) and long‐term (17‐year survival) fitness components of Eriophorum vaginatum ecotypes in Alaska, where climate change may have already displaced the optimum. Analyzing the transplant study as a climate transfer experiment, we showed that the climate optimum for plant performance was displaced ca. 140 km north of home sites, although plants were not generally declining in size at home sites. Adaptational lag is expected to be widespread globally for long‐lived, ecotypically specialized plants, with disruptive consequences for communities and ecosystems.     

Fine‐scale refuges can buffer demographic and genetic processes against short‐term climatic variation and disturbance: a 22‐year case study of an arboreal marsupial

Ecological disturbance and climate are key drivers of temporal dynamics in the demography and genetic diversity of natural populations. Microscale refuges are known to buffer species’ persistence against environmental change, but the effects of such refuges on demographic and genetic patterns in response to short‐term environmental variation are poorly understood. We quantified demographic and genetic responses of mountain brushtail possums (Trichosurus cunninghami) to rainfall variability (1992–2013) and to a major wildfire. We hypothesized that there would be underlying differences in demographic and genetic processes between an unburnt mesic refuge and a topographically exposed zone that was burnt in 2009. Fire caused a 2‐year decrease in survival in the burnt zone, but the population grew after the fire due to immigration, leading to increased expected heterozygosity. We documented a fire‐related behavioural shift, where the rate of movement by individuals in the unburnt refuge to the burnt zone decreased after fire. Irrespective of the fire, there were long‐term differences in demographic and genetic parameters between the mesic/unburnt refuge and the nonmesic/burnt zone. Survival was high and unaffected by rainfall in the refuge, but lower and rainfall‐dependent in the nonmesic zone. Net movement of individuals was directional, from the mesic refuge to the nonmesic zone, suggesting fine‐scale source–sink dynamics. There were higher expected heterozygosity (H_E) and temporal genetic stability in the refuge, but lower H_E and marked temporal genetic structure in the exposed habitat, consistent with reduced generational overlap caused by elevated mortality and immigration. Thus, fine‐scale refuges can mediate the short‐term demographic and genetic effects of climate and ecological disturbance.     

Long‐term patterns of invertebrate abundance and relationships to environmental factors in arid Australia

Resource pulses are a key feature of semi‐arid and arid ecosystems and are generally triggered by rainfall. While rainfall is an acknowledged driver of the abundance and distribution of larger animals, little is known about how invertebrate communities respond to rain events or to vegetative productivity. Here we investigate Ordinal‐level patterns and drivers of ground‐dwelling invertebrate abundance across 6 years of sampling in the Simpson Desert, central Australia. Between February 1999 and February 2005, a total of 174 381 invertebrates were sampled from 32 Orders. Ants were the most abundant taxon, comprising 83% of all invertebrates captured, while Collembola at 10.3% of total captures were a distant second over this period. Temporal patterns of the six invertebrate taxa specifically analysed (Acarina, ants, Araneae, Coleoptera, Collembola and Thysanura) were dynamic over the sampling period, and patterns of abundance were taxon‐specific. Analyses indicate that all six taxa showed a positive relationship with the cover of non‐Triodia vegetation. Other indicators of vegetative productivity (seeding and flowering) also showed positive relationships with certain taxa. Although the influence of rainfall was taxon‐dependent, no taxon was affected by short‐term rainfall (up to 18 days prior to survey). The abundance of Acarina, ants, and Coleoptera increased with greater long‐term rainfall (up to 18 months prior to survey), whilst Araneae showed the opposite effect. Temperature and dune zone (dune crest vs. swale) also had taxon‐specific effects. These results show that invertebrates in arid ecosystems are influenced by a variety of abiotic factors, at multiple scales, and that responses to rainfall are not as strong or as predictable as those seen for other taxa. Our results highlight the diversity of invertebrates in our study region and emphasize the need for targeted long‐term sampling to enhance our understanding of the ecology of these taxa and the role they play in arid ecosystems.     

Anticipating the spatio‐temporal response of plant diversity and vegetation structure to climate and land use change in a protected area

Vegetation is a key driver of ecosystem functioning (e.g. productivity and stability) and of the maintenance of biodiversity (e.g. creating habitats for other species groups). While vegetation sensitivity to climate change has been widely investigated, its spatio‐temporally response to the dual effects of land management and climate change has been ignored at landscape scale. Here we use a dynamic vegetation model called FATE‐HD, which describes the dominant vegetation dynamics and associated functional diversity, in order to anticipate vegetation response to climate and land‐use changes in both short and long‐term perspectives. Using three contrasted management scenarios for the Ecrins National Park (French Alps) developed in collaboration with the park managers, and one regional climate change scenario, we tracked the dynamics of vegetation structure (forest expansion) and functional diversity over 100 yr of climate change and a further 400 additional years of stabilization. As expected, we observed a slow upward shift in forest cover distribution, which appears to be severely impacted by pasture management (i.e. maintenance or abandonment). The time lag before observing changes in vegetation cover was the result of demographic and seed dispersal processes. However, plant diversity response to environmental changes was rapid. After land abandonment, local diversity increased and spatial turnover was reduced, whereas local diversity decreased following land use intensification. Interestingly, in the long term, as both climate and management scenarios interacted, the regional diversity declined. Our innovative spatio‐temporally explicit framework demonstrates that the vegetation may have contrasting responses to changes in the short and the long term. Moreover, climate and land‐abandonment interact extensively leading to a decrease in both regional diversity and turnover in the long term. Based on our simulations we therefore suggest a continuing moderate intensity pasturing to maintain high levels of plant diversity in this system.     

Resilience to extreme temperature events: acclimation capacity and body condition of a polymorphic fish in response to thermal stress

Considerable attention has been given to the potential impacts of global climate change on biodiversity. In the present study, we combine understudied themes by examining the ability of a freshwater fish (polymorphic for heat‐sensitivity) to respond to short‐term thermal stress mimicking an extreme temperature event. We simultaneously measured the effect of thermal stress on the body condition of heat‐sensitive and heat‐tolerant forms to evaluate an existing hypothesis regarding the underlying mechanism by which temperature affects the maintenance of genetic variation in this species. Surprisingly, the heat‐sensitive allelic variant increased in body condition equally as much as a heat‐tolerant variant under acute heat stress. More importantly, the heat‐sensitive variant exhibited a significant response to thermal stress, with an upward shift of greater than 2 °C in critical thermal maximum. Our findings suggest a complexity to the relationship between thermal stress and male body condition that may depend on an interaction with other factors such as resource level. Although the evolutionary fate of species with respect to climate change is typically evaluated in terms long‐term adaptive response, short‐term selection events could drastically reduce fitness and reduce evolutionary potential. Our results suggest that heat‐sensitive species may have considerably greater resilience to the short‐term, extreme perturbations to the environment that are expected under climate change. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 504–510.