Community structure and composition in response to climate change in a temperate steppe

Climate change would have profound influences on community structure and composition, and subsequently has impacts on ecosystem functioning and feedback to climate change. A field experiment with increased temperature and precipitation was conducted to examine effects of experimental warming, increased precipitation and their interactions on community structure and composition in a temperate steppe in northern China since April 2005. Increased precipitation significantly stimulated species richness and coverage of plant community. In contrast, experimental warming markedly reduced species richness of grasses and community coverage. Species richness was positively dependent upon soil moisture (SM) across all treatments and years. Redundancy analysis (RDA) illustrated that SM dominated the response of community composition to climate change at the individual level, suggesting indirect effects of climate change on plant community composition via altering water availability. In addition, species interaction also mediated the responses of functional group coverage to increased precipitation and temperature. Our observations revealed that both abiotic (soil water availability) and biotic (interspecific interactions) factors play important roles in regulating plant community structure and composition in response to climate change in the semiarid steppe. Therefore these factors should be incorporated in model predicting terrestrial vegetation dynamics under climate change.     

The challenge of novel abiotic conditions for species undergoing climate-induced range shifts

Coincident with recent global warming, species have shifted their geographic distributions to cooler environments, generally by moving along thermal axes to higher latitudes, higher elevations or deeper waters. While these shifts allow organisms to track their thermal niche, these three thermal axes also covary with non-climatic abiotic factors that could pose challenges to range-shifting plants and animals. Such novel abiotic conditions also present an unappreciated pitfall for researchers – from both empirical and predictive viewpoints – who study the redistribution of species under global climate change. Climate, particularly temperature, is often assumed to be the primary abiotic factor in limiting species distributions, and decades of thermal biology research have made the correlative and mechanistic understanding of temperature the most accessible and commonly used response to any abiotic factor. Receiving far less attention, however, is that global gradients in oxygen, light, pressure, pH and water availability also covary with latitude, elevation, and/or ocean depth, and species show strong physiological and behavioral adaptations to these abiotic variables within their historic ranges. Here, we discuss how non-climatic abiotic factors may disrupt climate-driven range shifts, as well as the variety of adaptations species use to overcome abiotic conditions, emphasizing which taxa may be most limited in this capacity. We highlight the need for scientists to extend their research to incorporate non-climatic, abiotic factors to create a more ecologically relevant understanding of how plants and animals interact with the environment, particularly in the face of global climate change. We demonstrate how additional abiotic gradients can be integrated into global climate change biology to better inform expectations and provide recommendations for addressing the challenge of predicting future species distributions in novel environments.     

Habitat shifts of endangered species under altered climate conditions: importance of biotic interactions

Predicting changes in potential habitat for endangered species as a result of global warming requires considering more than future climate conditions; it is also necessary to evaluate biotic associations. Most distribution models predicting species responses to climate change include climate variables and occasionally topographic and edaphic parameters, rarely are biotic interactions included. Here, we incorporate biotic interactions into niche models to predict suitable habitat for species under altered climates. We constructed and evaluated niche models for an endangered butterfly and a threatened bird species, both are habitat specialists restricted to semiarid shrublands of southern California. To incorporate their dependency on shrubs, we first developed climate‐based niche models for shrubland vegetation and individual shrub species. We also developed models for the butterfly's larval host plants. Outputs from these models were included in the environmental variable dataset used to create butterfly and bird niche models. For both animal species, abiotic–biotic models outperformed the climate‐only model, with climate‐only models over‐predicting suitable habitat under current climate conditions. We used the climate‐only and abiotic–biotic models to calculate amounts of suitable habitat under altered climates and to evaluate species' sensitivities to climate change. We varied temperature (+0.6, +1.7, and +2.8 °C) and precipitation (50%, 90%, 100%, 110%, and 150%) relative to current climate averages and within ranges predicted by global climate change models. Suitable habitat for each species was reduced at all levels of temperature increase. Both species were sensitive to precipitation changes, particularly increases. Under altered climates, including biotic variables reduced habitat by 68–100% relative to the climate‐only model. To design reserve systems conserving sensitive species under global warming, it is important to consider biotic interactions, particularly for habitat specialists and species with strong dependencies on other species.     

Simulated shifts in trophic niche breadth modulate range loss of alpine butterflies under climate change

Species currently track suitable abiotic and biotic conditions under ongoing climate change. Adjustments of trophic interactions may provide a mechanism for population persistence, an option that is rarely included in model projections. Here, we model the future distribution, of butterflies in the western Alps of Switzerland under climate change, simulating potential diet expansion resulting from adaptive behavior or new host opportunities. We projected the distribution of 60 butterfly and 298 plant species with species distribution models (SDMs) under three climate change scenarios. From known host plants, we allowed a potential diet expansion based on phylogenetic constraints. We assessed whether diet expansion could reduce the rate of expected regional species extinction under climate change. We found that the risk of species extinctions decreased with a concave upward decreasing shape when expanding the host plant range. A diet expansion to even a few phylogenetically closely related host plants would significantly decrease extinction rates. Yet, even when considering expansion toward all plant species available in the study area, the overall regional extinction risk would remain high. Ecological or evolutionary shifts to new host plants may attenuate extinction risk, but the severe decline of suitable abiotic conditions is still expected to drive many species to local extinction.     

Evidence that climate sets the lower elevation range limit in a high‐elevation endemic salamander

A frequent assumption in ecology is that biotic interactions are more important than abiotic factors in determining lower elevational range limits (i.e., the “warm edge” of a species distribution). However, for species with narrow environmental tolerances, theory suggests the presence of a strong environmental gradient can lead to persistence, even in the presence of competition. The relative importance of biotic and abiotic factors is rarely considered together, although understanding when one exerts a dominant influence on controlling range limits may be crucial to predicting extinction risk under future climate conditions. We sampled multiple transects spanning the elevational range limit of Plethodon shenandoah and site and climate covariates were recorded. A two‐species conditional occupancy model, accommodating heterogeneity in detection probability, was used to relate variation in occupancy with environmental and habitat conditions. Regional climate data were combined with datalogger observations to estimate the cloud base heights and to project future climate change impacts on cloud elevations across the survey area. By simultaneously accounting for species’ interactions and habitat variables, we find that elevation, not competition, is strongly correlated with the lower elevation range boundary, which had been presumed to be restricted mainly as a result of competitive interactions with a congener. Because the lower elevational range limit is sensitive to climate variables, projected climate change across its high‐elevation habitats will directly affect the species’ distribution. Testing assumptions of factors that set species range limits should use models which accommodate detection biases.     

Temporal variation in structural properties of tropical plant-herbivore networks: The role of climatic factors

Plant herbivore interactions can be influenced by abiotic factors such as climate or resource availability. Nevertheless, the influence of climatic variation on the temporal dynamics of plant-herbivore networks has been scarcely studied. In this study we evaluated the influence of temperature and precipitation on the structure and selectiveness of plant-herbivore networks associated to a seasonal tropical ecosystem in the Gulf of Mexico. Although a significant turnover was observed in plant and herbivore species across seasons, high modularity and selectivity of the networks remained relatively constant despite the temporal variation in climatic variables. However, precipitation and temperature was negatively associated with niche overlap for herbivores and positively related to evenness of network interactions. In other words, less stressful conditions are likely to promote the diversification in the use of resources by herbivores, and increase evenness of interactions in the network. An increase in niche overlap and a decrease in the evenness of interactions during the driest and coldest months could be promoted by the presence of less specialized herbivores when availability and quality of host resources is lower.We suggest that the constancy in network selectiveness and modularity facilitates the coexistence of species through the fine distribution of niches and the equitable distribution of food resources in periods of greater precipitation and temperature, when the availability of host plants is greater. Overall, we show for the first time how abiotic factors can influence the emergent structural properties of an antagonistic tropical plant-herbivore network.     

Food Webs and Disease: Is Pathogen Diversity Limited by Vector Diversity?

Classical predator–prey and host–parasite systems have been extensively studied in a food web context. Less attention has been paid to communities that include pathogens and their vectors. We present a coarse-grained, pan-African analysis of the relationships between the abiotic environment (location, precipitation, temperature), the species richness and community composition of ixodid ticks, and the species richness and community composition of pathogens that ticks transmit to humans. We found strong correlations between the abiotic environment and tick species richness, and a weak but significant correlation between the abiotic environment and pathogen species richness. A substantial amount of variation in community composition of parasites and pathogens was not explained by the variables that we considered. A structural equation model that compensated for the indirect effects of climate on the pathogen community via tick community composition suggested that while the environment strongly regulates tick community composition and tick community composition strongly regulates pathogen community composition, abiotic influences on pathogen species richness and community composition are weak. Our results support the view that changes in the broader environment will influence tick-borne pathogens primarily via the influence of the environment on ticks. The interactions that regulate host–vector–pathogen dynamics are of particular relevance in understanding the relationships between environmental change and health concerns, such as the impact of climate change on the occurrence of vector-borne diseases.     

Climate effects and feedback structure determining weed population dynamics in a long-term experiment

Pest control is one of the areas in which population dynamic theory has been successfully applied to solve practical problems. However, the links between population dynamic theory and model construction have been less emphasized in the management and control of weed populations. Most management models of weed population dynamics have emphasized the role of the endogenous process, but the role of exogenous variables such as climate have been ignored in the study of weed populations and their management. Here, we use long-term data (22 years) on two annual weed species from a locality in Central Spain to determine the importance of endogenous and exogenous processes (local and large-scale climate factors). Our modeling study determined two different feedback structures and climate effects in the two weed species analyzed. While Descurainia sophia exhibited a second-order feedback and low climate influence, Veronica hederifolia was characterized by a first-order feedback structure and important effects from temperature and rainfall. Our results strongly suggest the importance of theoretical population dynamics in understanding plant population systems. Moreover, the use of this approach, discerning between the effect of exogenous and endogenous factors, can be fundamental to applying weed management practices in agricultural systems and to controlling invasive weedy species. This is a radical change from most approaches currently used to guide weed and invasive weedy species managements.     

樟翠尺蛾种群动态与植物群落结构及气候因子的关系

在昆虫种群的研究中,Ｇｉｅｉｒ和Ｃｌａｒｋ等曾经提出生命系统的基本概念[1,2],认为生命系统由一个对象种群和作用于这个种群的环境所组成。控制昆虫种群增长的有密度制约因子(如食源)和非密度制约因子(如气候环境)。昆虫和植物之间的关系,历来是生态学研究的重要领域。通过长期的定点监测,研究某种昆虫种群动态与各种生态因子之间的关系,不仅可揭示动物和植物及环境之间互相影响的关系,对保护生物学理论的某些方面将有所发展,而且可为林业生产和环保工作提供如何应用生态学原理控制虫害,保护生物多样性和维护生态平衡的理论依据。樟翠尺…     

Temperature‐dependence of minimum resource requirements alters competitive hierarchies in phytoplankton

Resource competition theory is a conceptual framework that provides mechanistic insights into competition and community assembly of species with different resource requirements. However, there has been little exploration of how resource requirements depend on other environmental factors, including temperature. Changes in resource requirements as influenced by environmental temperature would imply that climate warming can alter the outcomes of competition and community assembly. We experimentally demonstrate that environmental temperature alters the minimum light and nitrogen requirements – as well as other growth parameters – of six widespread phytoplankton species from distinct taxonomic groups. We found that species require the most nitrogen at the highest temperatures while light requirements tend to be lowest at intermediate temperatures, although there are substantial interspecific differences in the exact shape of this relationship. We also experimentally parameterize two competition models, which we use to illustrate how temperature, through its effects on species’ traits, alters competitive hierarchies in multispecies assemblages, determining community dynamics. Developing a mechanistic understanding of how temperature influences the ability to compete for limiting resources is a critical step towards improving forecasts of community dynamics under climate warming.     

Contrasting forms of competition set elevational range limits of species

How abiotic and biotic factors constrain distribution limits at the harsh and benign edges of species ranges is hotly debated, partly because macroecological experiments testing the proximate causes of distribution limits are scarce. It has long been recognized – at least since Darwin’s On the Origin of Species – that a harsh climate strengthens competition and thus sets species range limits. Using thorough field manipulations along a large elevation gradient, we show the mechanisms by which temperature determines competition type, resulting in a transition from interference to exploitative competition from the lower to the upper elevation limits in burying beetles (Nicrophorus nepalensis). This transition is an example of Darwin’s classic hypothesis that benign climates favor direct competition for highly accessible resources while harsh climates result in competition through resources of high rivalry. We propose that identifying the properties of these key resources will provide a more predictive framework to understand the interplay between biotic and abiotic factors in determining geographic range limits.     

Climate change,woodpeckers, and forests: Current trends and future modeling needs

The structure and composition of forest ecosystems are expected to shift with climate‐induced changes in precipitation, temperature, fire, carbon mitigation strategies, and biological disturbance. These factors are likely to have biodiversity implications. However, climate‐driven forest ecosystem models used to predict changes to forest structure and composition are not coupled to models used to predict changes to biodiversity. We proposed integrating woodpecker response (biodiversity indicator) with forest ecosystem models. Woodpeckers are a good indicator species of forest ecosystem dynamics, because they are ecologically constrained by landscape‐scale forest components, such as composition, structure, disturbance regimes, and management activities. In addition, they are correlated with forest avifauna community diversity. In this study, we explore integrating woodpecker and forest ecosystem climate models. We review climate–woodpecker models and compare the predicted responses to observed climate‐induced changes. We identify inconsistencies between observed and predicted responses, explore the modeling causes, and identify the models pertinent to integration that address the inconsistencies. We found that predictions in the short term are not in agreement with observed trends for 7 of 15 evaluated species. Because niche constraints associated with woodpeckers are a result of complex interactions between climate, vegetation, and disturbance, we hypothesize that the lack of adequate representation of these processes in the current broad‐scale climate–woodpecker models results in model–data mismatch. As a first step toward improvement, we suggest a conceptual model of climate–woodpecker–forest modeling for integration. The integration model provides climate‐driven forest ecosystem modeling with a measure of biodiversity while retaining the feedback between climate and vegetation in woodpecker climate change modeling.     

Temperature change and complex dynamics

Density-dependent factors, such as population growth rate and migration, influence dynamic behaviour in ecological models. Temperature, an abiotic and density-independent factor, is also an important determinant of insect population growth. We investigated the endogenous dynamics of a density-dependent response-surface model that included temperature, based on time series for two aphid species. We investigated the effects of temperature and random noise on the model dynamics. In most cases, an increase in temperature resulted in a higher predicted equilibrium density; it could induce complex dynamics. Noise at the level of the natural variation in temperature resulted in extinctions in some models. Our results from these models indicate that aphid populations might become more abundant, and less stable in some circumstances, if there is climate warming. Received: 25 November 1996 / Accepted: 30 June 1997     

Predicting future coexistence in a North American ant community

Global climate change will remodel ecological communities worldwide. However, as a consequence of biotic interactions, communities may respond to climate change in idiosyncratic ways. This makes predictive models that incorporate biotic interactions necessary. We show how such models can be constructed based on empirical studies in combination with predictions or assumptions regarding the abiotic consequences of climate change. Specifically, we consider a well‐studied ant community in North America. First, we use historical data to parameterize a basic model for species coexistence. Using this model, we determine the importance of various factors, including thermal niches, food discovery rates, and food removal rates, to historical species coexistence. We then extend the model to predict how the community will restructure in response to several climate‐related changes, such as increased temperature, shifts in species phenology, and altered resource availability. Interestingly, our mechanistic model suggests that increased temperature and shifts in species phenology can have contrasting effects. Nevertheless, for almost all scenarios considered, we find that the most subordinate ant species suffers most as a result of climate change. More generally, our analysis shows that community composition can respond to climate warming in nonintuitive ways. For example, in the context of a community, it is not necessarily the most heat‐sensitive species that are most at risk. Our results demonstrate how models that account for niche partitioning and interspecific trade‐offs among species can be used to predict the likely idiosyncratic responses of local communities to climate change.     

Accounting for dispersal and biotic interactions to disentangle the drivers of species distributions and their abundances

Although abiotic factors, together with dispersal and biotic interactions, are often suggested to explain the distribution of species and their abundances, species distribution models usually focus on abiotic factors only. We propose an integrative framework linking ecological theory, empirical data and statistical models to understand the distribution of species and their abundances together with the underlying community assembly dynamics. We illustrate our approach with 21 plant species in the French Alps. We show that a spatially nested modelling framework significantly improves the model's performance and that the spatial variations of species presence-absence and abundances are predominantly explained by different factors. We also show that incorporating abiotic, dispersal and biotic factors into the same model bring new insights to our understanding of community assembly. This approach, at the crossroads between community ecology and biogeography, is a promising avenue for a better understanding of species co-existence and biodiversity distribution.     

Interactive effects between plant functional types and soil factors on tundra species diversity and community composition

Plant communities are coupled with abiotic factors, as species diversity and community composition both respond to and influence climate and soil characteristics. Interactions between vegetation and abiotic factors depend on plant functional types (PFT) as different growth forms will have differential responses to and effects on site characteristics. However, despite the importance of different PFT for community assembly and ecosystem functioning, research has mainly focused on vascular plants. Here, we established a set of observational plots in two contrasting habitats in northeastern Siberia in order to assess the relationship between species diversity and community composition with soil variables, as well as the relationship between vegetation cover and species diversity for two PFT (nonvascular and vascular). We found that nonvascular species diversity decreased with soil acidity and moisture and, to a lesser extent, with soil temperature and active layer thickness. In contrast, no such correlation was found for vascular species diversity. Differences in community composition were found mainly along soil acidity and moisture gradients. However, the proportion of variation in composition explained by the measured soil variables was much lower for nonvascular than for vascular species when considering the PFT separately. We also found different relationships between vegetation cover and species diversity according the PFT and habitat. In support of niche differentiation theory, species diversity and community composition were related to edaphic factors. The distinct relationships found for nonvascular and vascular species suggest the importance of considering multiple PFT when assessing species diversity and composition and their interaction with edaphic factors. Synthesis: Identifying vegetation responses to edaphic factors is a first step toward a better understanding of vegetation–soil feedbacks under climate change. Our results suggest that incorporating differential responses of PFT is important for predicting vegetation shifts, primary productivity, and in turn, ecosystem functioning in a changing climate.     

Temporal variation in plant-soil feedback controls succession

Soil abiotic and biotic factors play key roles in plant community dynamics. However, little is known about how soil biota influence vegetation changes over time. Here, we show that the effects of soil organisms may depend on both the successional development of ecosystems and on the successional position of the plants involved. In model systems of plants and soils from different successional stages, we observed negative plant–soil feedback for early-successional plant species, neutral feedback for mid-successional species, and positive feedback for late-successional species. The negative feedback of early-successional plants was independent of soil origin, while late-successional plants performed best in late- and worst in early-successional soil. Increased performance of the subordinate, late-successional plants resulted in enhanced plant community diversity. Observed feedback effects were more related to soil biota than to abiotic conditions. Our results show that temporal variations in plant–soil interactions profoundly contribute to plant community assemblage and ecosystem development.     

Why Do Species Co-Occur? A Test of Alternative Hypotheses Describing Abiotic Differences in Sympatry versus Allopatry Using Spadefoot Toads

Areas of co-occurrence between two species (sympatry) are often thought to arise in regions where abiotic conditions are conducive to both species and are therefore intermediate between regions where either species occurs alone (allopatry). Depending on historical factors or interactions between species, however, sympatry might not differ from allopatry, or, alternatively, sympatry might actually be more extreme in abiotic conditions relative to allopatry. Here, we evaluate these three hypothesized patterns for how sympatry compares to allopatry in abiotic conditions. We use two species of congeneric spadefoot toads, Spea multiplicata and S. bombifrons, as our study system. To test these hypotheses, we created ecological niche models (specifically using Maxent) for both species to create a map of the joint probability of occurrence of both species. Using the results of these models, we identified three types of locations: two where either species was predicted to occur alone (i.e., allopatry for S. multiplicata and allopatry for S. bombifrons) and one where both species were predicted to co-occur (i.e., sympatry). We then compared the abiotic environment between these three location types and found that sympatry was significantly hotter and drier than the allopatric regions. Thus, sympatry was not intermediate between the alternative allopatric sites. Instead, sympatry occurred at one extreme of the conditions occupied by both species. We hypothesize that biotic interactions in these extreme environments facilitate co-occurrence. Specifically, hybridization between S. bombifrons females and S. multiplicata males may facilitate co-occurrence by decreasing development time of tadpoles. Additionally, the presence of alternative food resources in more extreme conditions may preclude competitive exclusion of one species by the other. This work has implications for predicting how interacting species will respond to climate change, because species interactions may facilitate survival in extreme habitats.     

Bottom-up determination of soil collembola diversity and population dynamics in response to interactive climatic factors

Soil invertebrate contributions to decomposition are climate dependent. Understanding the influence of abiotic factors on soil invertebrate population dynamics will strengthen predictions regarding ecosystem functioning under climate change. As well as being important secondary decomposers, mycophagous collembola exert a strong influence on the growth and activity of primary decomposers, particularly fungi. Species-specific grazing preferences for different fungi enable fungal community composition to influence the direct impacts of climate change on collembola populations. We investigate the interactive roles of altered abiotic conditions (warming, wetting and drying) and the identity of the dominant decomposer fungus in determining collembola community dynamics in woodland soil mesocosms. The bottom-up influence of the dominant component of the fungal resource base was an important mediator of the direct climatic impacts on collembola populations. The positive influences of warming and wetting, and the negative influence of drying, on collembola abundance and diversity were much less pronounced in fungal-inoculation treatments, in which populations were reduced compared with uninoculated mesocosms. We conclude that the thick, sclerotised cords of the competitively dominant decomposer fungi reduced the biomass of smaller, more palatable soil fungi, limiting the size of collembola populations and their ability to respond to altered abiotic conditions.     

Exploring the influence of shrubs on herbaceous communities in a Mediterranean climatic context of two spatial scales

Communities of plants determine nonrandom spatial patterns defined by the intervention of abiotic and biotic factors acting at different spatial scales. We consider the influence of shrubs as one of the most important factors (biotic) affecting these spatial patterns at microscale. The macroclimate could be considered one of the most important factors (abiotic) at regional scale. To study the role and the floristic implications of each factor on the global patterns of herbaceous communities, we have developed a stratified sampling design that integrates both micro and macroscale on a 100 Km-long transect (east–west) in western central Spain. The results suggest that macroclimate could be one of the most important factors in determining herbaceous spatial patterns. Moreover, shrubs create a microspatial environmental heterogeneity that could alter such global climate patterns, modifying the spatial affinities established among species. This implies that environmental heterogeneity related to microhabitat could play a key role in spatial patterns at broad spatial scales, and consequently in the dynamics of the distribution and establishment of herbaceous species.