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When fertilizer phosphorus (P) is applied to soils, the P can run off fields and cause harmful algal blooms. Due to its chemistry, much of the added P that does not run off can bind to soil particles and become inaccessible to plants. In natural systems, microbial and faunal decomposers can increase soil P accessibility to plants. We tested the hypothesis that this may also be true in agricultural systems, which could increase P application efficiency and reduce runoff potential. We stimulated soil fauna with sodium (Na+ ) and microbes with carbon (C) by adding corn (Zea mays L.) stover and Na+ solution to plots in conventionally managed corn fields in northwestern Ohio. Stover addition increased microbial biomass by 65 ± 12% and respiration by 400-700%. Application of stover with Na+ increased soil detritivore fauna abundance by 51 ± 20% and likely did not affect the other invertebrate guilds. However, soil biological activity was low compared with natural systems in all treatments and was not correlated with instantaneous measures of P accessibility, though cumulative P accessibility over the course of the growing season was correlated with microbial phosphatase activity (slope = 1.01, p

Decomposition is an essential ecosystem service driven by interacting biotic and abiotic factors. Increasing temperatures due to climate change can affect soil moisture, soil fauna, and subsequently, decomposition. Understanding how projected climate change scenarios will affect decomposition is of vital importance for predicting nutrient cycling and ecosystem health. In this study, we experimentally addressed the question of how the early stages of decomposition would vary along a gradient of projected climate change scenarios. Given the importance of biodiversity for ecosystem service provisioning, we measured the effect of invertebrate exclusion on red maple (Acer rubrum) leaf litter breakdown along a temperature gradient using litterbags in warming chambers over a period of five weeks. Leaf litter decomposed more slowly in the warmer chambers and in the litterbag treatment that minimized invertebrate access. Moreover, increasing air temperature reduced invertebrate abundance and richness, and altered the community composition, independent of exclusion treatment. Using structural equation models, we were able to disentangle the effects of average air temperature on leaf litter loss, finding a direct negative effect of warming on the early stages of decomposition, independent of invertebrate abundance. This result indicates that not only can climate change affect the invertebrate community, but may also directly influence how the remaining organisms interact with their environment and their effectiveness at provisioning ecosystem services. Overall, our study highlights the role of biodiversity in maintaining ecosystem services and contributes to our understanding of how climate change could disrupt nutrient cycling.

Because ectotherm activity and metabolism are sensitive to temperature, terrestrial arthropods may be especially responsive to ongoing climatic warming. Here, we quantified responses of arthropod abundance to two years of warming in an outdoor temperature manipulation experiment at Duke Forest, North Carolina, USA. Nine open‐top chambers were individually heated year‐round from 1.5° to 5.5°C above ambient temperature. From two years of monthly pitfall trapping, we collected and identified 4,468 arthropods representing 24 orders. We initially predicted that arthropods would experience the greatest negative effects of experimental warming during the summer months, when temperatures reach their yearly maximum and arthropods may be close to their maximum thermal tolerance limits. Instead, we found that the strongest negative effects on arthropod abundance occurred during the winter and spring, when ambient temperatures are relatively cooler, whereas the effects of experimental warming on abundance were not significant during the summer or fall. During the spring of 2012, the warmest spring on record for the southeastern USA, total arthropod abundance declined 20% per °C of experimental warming. Abundance declines were driven largely by flies (Diptera), which were the most abundant insect order, representing approximately a third of all arthropods collected. The most abundant arthropod family, Mycetophilidae (fungus gnats), declined 64% per °C of warming during the spring of 2012. Although previous research on climatic warming has focused on the impact of maximum yearly temperatures on organismal performance, our results are more consistent with the cool‐season sensitivity hypothesis, which posits that arthropods adapted for cooler conditions are likely to face the strongest negative effects of warming during the cooler seasons.

Dredging operations produce large amounts of sediments, and when open lake disposal is used, it can pose a threat to water quality. This study examined the potential to use dredged sediment as a farm soil amendment. We conducted greenhouse experiments to determine (a) the physico-chemical health of a farm soil amended with various dredged sediment ratios, (b) nutrient dynamics when the soil blends were subjected to simulated storm events, and (c) the effect of dredged sediment on soybean [Glycine max (L.) Merr.] belowground biomass and yield. The soil blends consisted of 100% farm soil, 90% farm soil to 10% dredged sediment, 80% farm soil to 20% dredged sediment, or 100% dredged sediment. After 123 d, the soybean plants were harvested, and physico-chemical analyses were conducted on the soil, soybeans, and percolated stormwater. We found that dredged sediment amendment improved soil health by increasing soil organic matter, cation exchange capacity, and Ca content and by decreasing bulk density and P concentration in a farm soil with P concentration above the agronomic recommended value. Crop biomass and yield averages increased with increasing dredged sediment ratios. Nutrient loss (P and N) in the percolated solutions from the soil blends showed no significant changes when compared to the percolated solutions in the 100% farm soil treatment, indicating no significant contribution to the export of nutrients in percolated water.

Exploring ways to reduce high-nutrient agricultural runoff is imperative, considering how such runoff reduces water quality and has the potential to cause harmful algal blooms. Ground arthropod communities, particularly detritivores (i.e. consume dead plant or animal tissue matter), are largely ignored as a possible avenue for reducing nutrient runoff. However, stimulating these organisms may help maintain nutrient availability with decreased fertilizer application rates, thereby increasing application efficiency while reducing nutrient runoff potential. With the aim of stimulating the detrital community and soil microbes to ultimately enhance nutrient availability, we added a labile substrate and nutrient source (carcasses of Hexagenia spp. (mayflies), as well as a recalcitrant substrate and nutrient source (Zea mays corn stover), both separately and in combination, to plots on four conventionally managed corn fields in northwest Ohio, U.S.A. Over the seven-week study period, we found that detritivores increased with mayfly additions with or without stover, but arthropods that prey on detritivores only increased with mayfly and corn additions in combination. Soil microbial biomass and enzyme activities did not respond to any treatments, but when mayflies were added microbial respiration increased. Respiration was positively correlated with arthropod abundance. Mayfly additions initially boosted water-soluble ammonium, and, in plots without stover, increased phosphate throughout the experiment. Overall, our results are consistent with other findings of generally low levels of biotic activity on conventional corn fields, making it difficult to stimulate further activity over short time-scales, like the seven-week one in this study. However, our results also indicate that additions of labile detritus enhance detritivores and nutrient availability. Adding labile detritus in combination with recalcitrant detritus, which promotes detritivore predators, may further enhance nutrient cycling rates. Thus, the potential for these amendments to stimulate soil biota to help maintain nutrient availability with decreased fertilizer application rates compels further study on conventional corn fields over longer periods of time or in organic fields with higher baseline activity.

Many studies on herbivores are solely concerned with the damage that they cause to plants. However, the impacts of aboveground herbivores go further, as their additions to the soil affect the soil microbes and subsequently nutrient cycling that feeds back into aboveground production. This chapter focuses on the feedback loop beginning with inputs via invertebrate herbivores and leading to alteration of carbon (C) and nitrogen (N) cycling via soil microbes to change nutrient availability for the surrounding vegetation. This loop eventually leads back to affect the invertebrate herbivores through changes in vegetation. Inputs from invertebrate herbivores can result physically from the invertebrates (e.g., frass, honeydew, carcasses) or from their consumption of vegetation (e.g., impacts on quality of throughfall, litterfall). The consumption activity can also alter the timing, quantity, and quality of organic inputs to the soil, all of which will affect the soil microbial communities in different ways depending on their lability. That lability also drives changes in C and N cycling, altering the available nutrients within the soil. The goal of this chapter is to discuss the feedback loop described above and develop a greater understanding of how aboveground herbivores interact with the belowground microbial community.

(1) Background: Strategies aimed at managing freshwater eutrophication should be based on practices that consider cropland invertebrates, climatic change, and soil nutrient cycling. Specifically, detritivores play a crucial role in the biogeochemical processes of soil through their consumptive and burrowing activities. Here, we evaluated the effectiveness of increasing detritivore abundance as a strategy for nutrient management under varied rainfall. (2) Methods: We manipulated soil macroinvertebrate abundance and rainfall amount in an agricultural mesocosms. We then measured the phosphorus, nitrogen, and carbon levels within the soil, corn, invertebrates, and soil solution. (3) Results: Increasing detritivore abundance in our soil significantly increased corn biomass by 2.49 g (p &lt, 0.001), reduced weed growth by 18.2% (p &lt, 0.001), and decreased soil solution nitrogen and total organic carbon (p &lt, 0.05) and volume by 31.03 mL (p &lt, 0.001). Detritivore abundance also displayed a significant interaction effect with rainfall treatment to influence soil total P (p = 0.0019), total N (p &lt, 0.001), and total C (p = 0.0146). (4) Conclusions: Soil detritivores play an important role in soil nutrient cycling and soil health. Incorporating soil macroinvertebrate abundance into management strategies for agricultural soil may increase soil health of agroecosystems, preserve freshwater ecosystems, and protect the valuable services they both provide for humans.

Climatic warming is altering the behavior of individuals and the composition of communities. However, recent studies have shown that the impact of warming on ectotherms varies geographically: species at warmer sites where environmental temperatures are closer to their upper critical thermal limits are more likely to be negatively impacted by warming than are species inhabiting relatively cooler sites. We used a large‐scale experimental temperature manipulation to warm intact forest ant assemblages in the field and examine the impacts of chronic warming on foraging at a southern (North Carolina) and northern (Massachusetts) site in eastern North America. We examined the influence of temperature on the abundance and recruitment of foragers as well as the number of different species observed foraging. Finally, we examined the relationship between the mean temperature at which a species was found foraging and the critical thermal maximum temperature of that species, relating functional traits to behavior. We found that forager abundance and richness were related to the experimental increase in temperature at the southern site, but not the northern site. Additionally, individual species responded differently to temperature: some species foraged more under warmer conditions, whereas others foraged less. Importantly, these species‐specific responses were related to functional traits of species (at least at the Duke Forest site). Species with higher critical thermal maxima had greater forager densities at higher temperatures than did species with lower critical thermal maxima. Our results indicate that while climatic warming may alter patterns of foraging activity in predictable ways, these shifts vary among species and between sites. More southerly sites and species with lower critical thermal maxima are likely to be at greater risk to ongoing climatic warming.

Identifying the factors that control soil CO2 emissions will improve our ability to predict the magnitude of climate change–soil ecosystem feedbacks. Despite the integral role of invertebrates in belowground systems, they are excluded from climate change models. Soil invertebrates have consumptive and nonconsumptive effects on microbes, whose respiration accounts for nearly half of soil CO2 emissions. By altering the behavior and abundance of invertebrates that interact with microbes, invertebrate predators may have indirect effects on soil respiration. We examined the effects of a generalist arthropod predator on belowground respiration under different warming scenarios. Based on research suggesting invertebrates may mediate soil CO2 emission responses to warming, we predicted that predator presence would result in increased emissions by negatively affecting these invertebrates. We altered the presence of wolf spiders (Pardosa spp.) in mesocosms containing a forest floor community. To simulate warming, we placed mesocosms of each treatment in ten open-top warming chambers ranging from 1.5° to 5.5°C above ambient at Harvard Forest, Massachusetts, USA. As expected, CO2 emissions increased under warming and we found an interactive effect of predator presence and warming, although the effect was not consistent through time. The interaction between predator presence and warming was the inverse of our predictions: Mesocosms with predators had lower respiration at higher levels of warming than those without predators. Carbon dioxide emissions were not significantly associated with microbial biomass. We did not find evidence of consumptive effects of predators on the invertebrate community, suggesting that predator presence mediates response of microbial respiration to warming through nonconsumptive means. In our system, we found a significant interaction between warming and predator presence that warrants further research into mechanism and generality of this pattern to other systems.

The sustainability of ecosystem services depends on a firm understanding of both how organisms provide these services to humans and how these organisms will be altered with a changing climate. Unquestionably a dominant feature of most ecosystems, invertebrates affect many ecosystem services and are also highly responsive to climate change. However, there is still a basic lack of understanding of the direct and indirect paths by which invertebrates influence ecosystem services, as well as how climate change will affect those ecosystem services by altering invertebrate populations. This indicates a lack of communication and collaboration among scientists researching ecosystem services and climate change effects on invertebrates, and land managers and researchers from other disciplines, which becomes obvious when systematically reviewing the literature relevant to invertebrates, ecosystem services, and climate change. To address this issue, we review how invertebrates respond to climate change. We then review how invertebrates both positively and negatively influence ecosystem services. Lastly, we provide some critical future directions for research needs, and suggest ways in which managers, scientists and other researchers may collaborate to tackle the complex issue of sustaining invertebrate-mediated services under a changing climate.

Population changes and shifts in geographic range boundaries induced by climate change have been documented for many insect species. On the basis of such studies, ecological forecasting models predict that, in the absence of dispersal and resource barriers, many species will exhibit large shifts in abundance and geographic range in response to warming. However, species are composed of individual populations, which may be subject to different selection pressures and therefore may be differentially responsive to environmental change. Asystematic responses across populations and species to warming will alter ecological communities differently across space. Common garden experiments can provide a more mechanistic understanding of the causes of compositional and spatial variation in responses to warming. Such experiments are useful for determining if geographically separated populations and co-occurring species respond differently to warming, and they provide the opportunity to compare effects of warming on fitness (survivorship and reproduction). We exposed colonies of two common ant species in the eastern United States, Aphaenogaster rudis and Temnothorax curvispinosus, collected along a latitudinal gradient from Massachusetts to North Carolina, to growth chamber treatments that simulated current and projected temperatures in central Massachusetts and central North Carolina within the next century. Regardless of source location, colonies of A. rudis, a keystone seed disperser, experienced high mortality and low brood production in the warmest temperature treatment. Colonies of T. curvispinosus from cooler locations experienced increased mortality in the warmest rearing temperatures, but colonies from the warmest locales did not. Our results suggest that populations of some common species may exhibit uniform declines in response to warming across their geographic ranges, whereas other species will respond differently to warming in different parts of their geographic ranges. Our results suggest that differential responses of populations and species must be incorporated into projections of range shifts in a changing climate.

The fossil record tells us that many species shifted their geographic distributions during historic climate changes, but this record does not portray the complete picture of future range change in response to climate change. In particular, it does not provide information on how species interactions will affect range shifts. Therefore, we also need modern research to generate understanding of range change. This paper focuses on the role that species interactions play in promoting or preventing geographic ranges shifts under current and future climate change, and we illustrate key points using empirical case studies from an integrated study system. Case studies can have limited generalizability, but they are critical to defining possible outcomes under climate change. Our case studies emphasize host limitation that could reduce range shifts and enemy release that could facilitate range expansion. We also need improvements in modeling that explicitly consider species interactions, and this modeling can be informed by empirical research. Finally, we discuss how species interactions have implications for range management by people.

Effects of climate warming on wild populations of organisms are expected to be greatest at higher latitudes, paralleling greater anticipated increases in temperature in these regions. Yet, these expectations assume that populations in different regions are equally susceptible to the effects of warming. This is unlikely to be the case. Here, we develop a series of predictive models for physiological thermal tolerances in ants based on current and future climates. We found that tropical ants have lower warming tolerances, a metric of susceptibility to climate warming, than temperate ants despite greater increases in temperature at higher latitudes. Using climatic, ecological and phylogenetic data, we refine our predictions of which ants (across all regions) were most susceptible to climate warming. We found that ants occupying warmer and more mesic forested habitats at lower elevations are the most physiologically susceptible to deleterious effects of climate warming. Phylogenetic history was also a strong indicator of physiological susceptibility. In short, we find that ants that live in the canopies of hot, tropical forest are the most at risk, globally, from climate warming. Unfortunately this is where many, perhaps most, ant and other species on Earth live.

Characterization of thermal tolerances of ants, which are both abundant and important in most terrestrial ecosystems, is needed since thermal constraints can inform how a species may respond to local climatic change. Here we identified the thermal tolerances of 16 common ant species of the Northeastern United States and determined relationships between body size, desiccation, and thermal tolerance among species. We hypothesized that maximum heat tolerances of these species would differ and be related to body size and capacity to resist desiccation. We identified four distinct groups of species belonging to one of three subfamilies, Dolichoderinae, Formicinae, or Myrmicinae, with different maximum thermal tolerances. Group “a” had a mean thermal tolerance of approximately 43°C (±1°C), group “b” had a mean thermal tolerance of 40°C (±1°C), group “c” had a mean thermal tolerance of 38°C (±0°C), and group “d” had a mean thermal tolerance of 36°C (±0°C). Groups “a” and “d” consisted of a single species (in the subfamilies Myrmicinae and Formicinae, respectively), while groups “b” and “c” were a mix of species in the subfamilies Myrmicinae, Formicinae, and Dolichoderinae. In the subfamily Formicinae, thermal tolerance increased with body size and critical water content, a metric of desiccation tolerance. In contrast, in the subfamily Myrmicinae, higher thermal tolerance was correlated with intermediate body size and lower critical water content. These findings suggest that the two dominant subfamilies in Northeastern deciduous forests have different relationships between body size, capacity to tolerate desiccation, and thermal tolerances across species. This variation in thermal tolerance suggests that climatic change may impact species differently.

Summary 1. Recent observations indicate that climatic change is altering biodiversity, and models suggest that the consequences of climate change will differ across latitude. However, long-term experimental field manipulations that directly test the predictions about organisms’ responses to climate change across latitude are lacking. Such experiments could provide a more mechanistic understanding of the consequences of climate change on ecological communities and subsequent changes in ecosystem processes, facilitating better predictions of the effects of future climate change. 2. This field experiment uses octagonal, 5-m-diameter (c. 22 m 3 ) open-top chambers to simulate warming at northern (Harvard Forest, Massachusetts) and southern (Duke Forest, North Carolina) hardwood forest sites to determine the effects of warming on ant and other arthropod populations and communities near the edges of their ranges. Each site has 12 plots containing open-top chambers that manipulate air temperature incrementally from ambient to 6 � C above ambient. Because the focus of this study is on mobile, litter- and soil-dwelling arthropods, standard methods for warming chambers (e.g. soil-warming cables or infrared heaters applied to relatively small areas) were inappropriate and new technological approaches using hydronic heating and forced air movement were developed. 3. We monitor population dynamics, species composition, phenology and behaviour of ants and other arthropods occupying these experimental chambers. Microclimatic measurements in each chamber include the following: air temperature (three), soil temperatures (two each in organic and mineral soil), photosynthetically active radiation (PAR), relative humidity and soil moisture (one each). In two chambers, we are also measuring soil heat flux, associated soil temperatures at 2 and 6 cm and volumetric water content. To assess the composition, phenology and abundance of arthropod communities within the experiment, we use monthly pitfall trapping and annual Winkler sampling. We also census artificial and natural ant nests to monitor changes in ant colony size and productivity across the temperature treatments. 4. This experiment is a long-term ecological study that provides opportunities for collaborations across a broad spectrum of ecologists, including those studying biogeochemical, microbial and plant responses to warming. Future studies also may include implementation of multifactorial climate manipulations, examination of interactions across trophic levels and quantification of changes in ecosystem processes.

Many serious ecosystem consequences of climate change will take decades or even centuries to emerge. Long-term ecological responses to global change are strongly regulated by slow processes, such as changes in species composition, carbon dynamics in soil and by long-lived plants, and accumulation of nutrient capitals. Understanding and predicting these processes require experiments on decadal time scales. But decadal experiments by themselves may not be adequate because many of the slow processes have characteristic time scales much longer than experiments can be maintained. This article promotes a coordinated approach that combines long-term, large-scale global change experiments with process studies and modeling. Long-term global change manipulative experiments, especially in high-priority ecosystems such as tropical forests and high-latitude regions, are essential to maximize information gain concerning future states of the earth system. The long-term experiments should be conducted in tandem with complementary process studies, such as those using model ecosystems, species replacements, laboratory incubations, isotope tracers, and greenhouse facilities. Models are essential to assimilate data from long-term experiments and process studies together with information from long-term observations, surveys, and space-for-time studies along environmental and biological gradients. Future research programs with coordinated long-term experiments, process studies, and modeling have the potential to be the most effective strategy to gain the best information on long-term ecosystem dynamics in response to global change.

We describe aspects of the life history ofErynnis propertius(Scudder and Burgess) (Lepidoptera: Hesperiidae) by examining several populations over multiple years. We focused on peripheral populations of this species because they are isolated, are threatened by habitat loss, and may play an important role in driving poleward range expansion under increasing regional temperature. Our findings show that the annual larval growth rate does not vary directly with temperature, adult flight phenology and the timing of key resources respond to average daytime temperatures in spring, and population-density patterns among sites are robust over years across a broad region near the species' northern range limit. In addition, we provide descriptions of all larval instars for this species. This fundamental information about the biology, timing, and abundance of this species will facilitate further experimental study and improved assessment of its conservation status.

Insects are found in abundance nearly everywhere on Earth and provide services important to both the health of our ecosystems (e.g. decomposition, seed dispersal) and to our economy (e.g. pollination, crop pests). Understanding how climate change affects insects is necessary if we are to predict what insect communities will look like in the future and therefore determine how the services they provide will change. Since insect traits such as growth, reproduction, and activity are heavily shaped by environmental conditions, climate change will affect them in many ways. Here we present evidence that insects cope with climate change in one of three major ways: they move to areas that have a more suitable climate; they emerge earlier and are active longer to take advantage of warmer temperatures; and they adapt to withstand new climatic conditions. These changes can lead them to lose interaction partners (i.e. a host plant), develop new interactions, or even become locally extinct. Climate change will affect insect development time, number of generations per year, foraging behaviour, emergence time, and survivorship. Ultimately, climate change will continue to alter the shape of insect communities, with effects varying with geographic location, time, and type of insect.

Insect mutualisms can have disproportionately large impacts on local arthropod and plant communities and their responses to climatic change. The objective of this study was to determine if the presence of insect mutualisms affects host plant and herbivore responses to warming. Using open-top warming chambers at Harvard Forest, Massachusetts, USA, we manipulated temperature and presence of ants and Chaitophorus populicola aphids on Populus tremuloides host plants and monitored ant attendance and persistence of C. populicola, predator abundance, plant stress, and abundance of Myzus persicae, a pest aphid that colonized plants during the experiment. We found that, regardless of warming, C. populicola persistence was higher when tended by ants, and some ant species increased aphid persistence more than others. Warming had negligible direct but strong indirect effects on plant stress. Plant stress decreased with warming only when both ants and C. populicola aphids were present and engaged in mutualism. Plant stress was increased by warming-induced reductions in predator abundance and increases in M. persicae aphid abundance. Altogether, these findings suggest that insect mutualisms could buffer the effects of warming on specialist herbivores and plants, but when mutualisms are not intact, the direct effects of warming on predators and generalist herbivores yield strong indirect effects of warming on plants.

Physiological intolerance of high temperatures places limits on organismal responses to the temperature increases associated with global climatic change. Because ants are geographically widespread, ecologically diverse, and thermophilic, they are an ideal system for exploring the extent to which physiological tolerance can predict responses to environmental change. Here, we expand on simple models that use thermal tolerance to predict the responses of ants to climatic warming. We investigated the degree to which changes in the abundance of ants under warming reflect reductions in the thermal niche space for their foraging. In an eastern deciduous forest system in the United States with approximately 40 ant species, we found that for some species, the loss of thermal niche space for foraging was related to decreases in abundance with increasing experimental climatic warming. However, many ant species exhibited no loss of thermal niche space. For one well-studied species, Temnothorax curvispinosus, we examined both survival of workers and growth of colonies (a correlate of reproductive output) as functions of temperature in the laboratory, and found that the range of thermal tolerances for colony growth was much narrower than for survival of workers. We evaluated these functions in the context of experimental climatic warming and found that the difference in the responses of these two attributes to temperature generates differences in the means and especially the variances of expected fitness under warming. The expected mean growth of colonies was optimized at intermediate levels of warming (2-4°C above ambient); yet, the expected variance monotonically increased with warming. In contrast, the expected mean and variance of the survival of workers decreased when warming exceeded 4°C above ambient. Together, these results for T. curvispinosus emphasize the importance of measuring reproduction (colony growth) in the context of climatic change: indeed, our examination of the loss of thermal niche space with the larger species pool could be missing much of the warming impact due to these analyses being based on survival rather than reproduction. We suggest that while physiological tolerance of temperature can be a useful predictive tool for modeling responses to climatic change, future efforts should be devoted to understanding the causes and consequences of variability in models of tolerance calibrated with different metrics of performance and fitness.

Physiological tolerance of environmental conditions can influence species-level responses to climate change. Here, we used species-specific thermal tolerances to predict the community responses of ant species to experimental forest-floor warming at the northern and southern boundaries of temperate hardwood forests in eastern North America. We then compared the predictive ability of thermal tolerance vs. correlative species distribution models (SDMs) which are popular forecasting tools for modeling the effects of climate change. Thermal tolerances predicted the responses of 19 ant species to experimental climate warming at the southern site, where environmental conditions are relatively close to the ants' upper thermal limits. In contrast, thermal tolerances did not predict the responses of the six species in the northern site, where environmental conditions are relatively far from the ants' upper thermal limits. Correlative SDMs were not predictive at either site. Our results suggest that, in environments close to a species' physiological limits, physiological trait-based measurements can successfully forecast the responses of species to future conditions. Although correlative SDMs may predict large-scale responses, such models may not be accurate for predicting site-level responses.

The fossil record tells us that many species shifted their geographic distributions during historic climate changes, but this record does not portray the complete picture of future range change in response to climate change. In particular, it does not provide information on how species interactions will affect range shifts. Therefore, we also need modern research to generate understanding of range change. This paper focuses on the role that species interactions play in promoting or preventing geographic ranges shifts under current and future climate change, and we illustrate key points using empirical case studies from an integrated study system. Case studies can have limited generalizability, but they are critical to defining possible outcomes under climate change. Our case studies emphasize host limitation that could reduce range shifts and enemy release that could facilitate range expansion. We also need improvements in modeling that explicitly consider species interactions, and this modeling can be informed by empirical research. Finally, we discuss how species interactions have implications for range management by people.

Climatic change is expected to have differential effects on ecological communities in different geographic areas. However, few studies have experimentally demonstrated the effects of warming on communities simultaneously at different locales. We manipulated air temperature with in situ passive warming and cooling chambers and quantified effects of temperature on ant abundance, diversity, and foraging activities (predation, scavenging, seed dispersal, nectivory, granivory) in two deciduous forests at 35° and 43° N latitude in the eastern U.S. In the southern site, the most abundant species, Crematogaster lineolata, increased while species evenness, most ant foraging activities, and abundance of several other ant species declined with increasing temperature. In the northern site, species evenness was highest at intermediate temperatures, but no other metrics of diversity or foraging activity changed with temperature. Regardless of temperature, ant abundance and foraging activities at the northern site were several orders of magnitude lower than those in the southern site.

We must consider the role of multitrophic interactions when examining species' responses to climate change. Many plant species, particularly trees, are limited in their ability to shift their geographic ranges quickly under climate change. Consequently, for herbivorous insects, geographic mosaics of host plant specialization could prohibit range shifts and adaptation when insects become separated from suitable host plants. In this study, we examined larval growth and survival of an oak specialist butterfly (Erynnis propertius) on different oaks (Quercus spp.) that occur across its range to determine if individuals can switch host plants if they move into new areas under climate change. Individuals from Oregon and northern California, USA that feed on Q. garryana and Q. kelloggii in the field experienced increased mortality on Q. agrifolia, a southern species with low nutrient content. In contrast, populations from southern California that normally feed on Q. agrifolia performed well on Q. agrifolia and Q. garryana and poorly on the northern, high elevation Q. kelloggii. Therefore, colonization of southern E. propertius in higher elevations and some northern locales may be prohibited under climate change but latitudinal shifts to Q. garryana may be possible. Where shifts are precluded due to maladaptation to hosts, populations may not accrue warm-adapted genotypes. Our study suggests that, when interacting species experience asynchronous range shifts, historical local adaptation may preclude populations from colonizing new locales under climate change.

The hygric hypothesis postulates that insect discontinuous gas exchange cycles (DGCs) are an adaptation that reduces respiratory water loss (RWL), but evidence is lacking for reduction of water loss by insects expressing DGCs under normal ecological conditions. Larvae ofErynnis propertius(Lepidoptera: Hesperiidae) naturally switch between DGCs and continuous gas exchange (CGE), allowing flow-through respirometry comparisons of water loss between the two modes. Water loss was lower during DGCs than CGE, both between individuals using different patterns and within individuals using both patterns. The hygric cost of gas exchange (water loss associated with carbon dioxide release) and the contribution of respiratory to total water loss were lower during DGCs. Metabolic rate did not differ between DGCs and CGE. Thus, DGCs reduce RWL inE. propertius, which is consistent with the suggestion that water loss reduction could account for the evolutionary origin and/or maintenance of DGCs in insects.

There is a pressing need to predict how species will change their geographic ranges under climate change. Projections typically assume that temperature is a primary fitness determinant and that populations near the poleward (and upward) range boundary are preadapted to warming. Thus, poleward, peripheral populations will increase with warming, and these increases facilitate poleward range expansions. We tested the assumption that poleward, peripheral populations are enhanced by warming using 2 butterflies (Erynnis propertiusandPapilio zelicaon) that co-occur and have contrasting degrees of host specialization and interpopulation genetic differentiation. We performed a reciprocal translocation experiment between central and poleward, peripheral populations in the field and simulated a translocation experiment that included alternate host plants. We found that the performance of both central and peripheral populations ofE. propertiuswere enhanced during the summer months by temperatures characteristic of the range center but that local adaptation of peripheral populations to winter conditions near the range edge could counteract that enhancement. Further, poleward range expansion in this species is prevented by a lack of host plants. InP. zelicaon, the fitness of central and peripheral populations decreased under extreme summer temperatures that occurred in the field at the range center. Performance in this species also was affected by an interaction of temperature and host plant such that host species strongly mediated the fitness of peripheral individuals under differing simulated temperatures. Altogether we have evidence that facilitation of poleward range shifts through enhancement of peripheral populations is unlikely in either study species.

Publisher Summary This chapter demonstrates that the direction and magnitude of the effects of climate change on insect species are multifaceted. Warming from climate change will alter insect development time, voltinism, foraging behavior, emergence time, and survivorship. These changes, which alter population size and distribution, will affect the temporal and spatial dynamics of insect communities. Many insects provide important ecosystem services or affect human activities and the effects of climate change could alter these services or exacerbate these effects. Changes are occurring both spatially and temporally, and these changes result directly from changing climate and indirectly through interactions with species in lower (i.e. plants) and upper (i.e. predators) trophic levels. In addition, trophic cascades can occur such that changes in interactions between herbivores and their host plants affect higher trophic levels, and changes between predators and herbivorous prey can affect primary producers. Further, species traits such as dispersal ability, trophic level and degree of specialization are potentially good predictors of the effects of climate change. The prediction is that future communities will be dominated by mobile generalists, species with fast generation times, those that have high dispersal capabilities or those that have been dispersed around the globe by humans. Many of these species are already pests, and new species could become pests on new host plants or in new locations under climate change. These opportunists may affect important human activities, such as forestry and agriculture, with extensions into the role of forests as carbon sinks. Insects that provide important ecosystems services such as pollination or biological control could not fare as well.

Forest floor food webs play pivotal roles in carbon cycling, but they are rarely considered in models of carbon fluxes, including soil carbon dioxide emissions (respiration), under climatic warming. The indirect effects of invertebrates on heterotrophic (microbial and invertebrate) respiration through interactions with microbial communities are significant and will be altered by warming. However, the interactive effects of invertebrates and warming on heterotrophic respiration in the field are poorly understood. In this study we combined field and common garden laboratory approaches to examine relationships between warming, forest floor food web structure, and heterotrophic respiration. We found that soil animals can overwhelm the effects of warming (to 5 degrees Celsius above ambient) on heterotrophic respiration. In particular, the presence of higher trophic levels and burrowing detritivores strongly determined heterotrophic respiration rates in temperate forest soils. These effects were, however, context-dependent, with greater effects in a lower-latitude site. Without isolating and including the significant impact of invertebrates, climate models will be incomplete, hindering well-informed policy decisions.

To predict changes in species' distributions due to climate change we must understand populations at the poleward edge of species' ranges. Ecologists generally expect range shifts under climate change caused by the expansion of edge populations as peripheral conditions increasingly resemble the range core. We tested whether peripheral populations of two contrasting butterflies, a small-bodied specialist (Erynnis propertius) and a large-bodied generalist (Papilio zelicaon), respond favorably to warmer conditions. Performance of populations related to climate was evaluated in seven peripheral populations spanning 1.2 degrees latitude (160 km) using: (1) population density surveys, an indirect measure of site suitability; and (2) organismal fitness in translocation experiments. There was evidence that population density increased with temperature for P. zelicaon whose population density declined with latitude in 1 of 3 sample years. On the other hand, E. propertius showed a positive relationship of population density with latitude, apparently unrelated to climate or measured habitat variables. Translocation experiments showed increased larval production at increased temperatures for both species, and in P. zelicaon, larval production also increased under drier conditions. These findings suggest that both species may increase at their range edge with warming but the preference for core-like conditions may be stronger in P. zelicaon. Further, populations of E. propertius at the range boundary may be large enough to act as sources of colonists for range expansions, but range expansion in this species may be prevented by a lack of available host plants further north. In total, the species appear to respond differently to climate and other factors that vary latitudinally, factors that will likely affect poleward expansion.

While much progress has been made toward identifying the spectrum of organisms’ responses to climate change, which include distributional, phenological, demographic, behavioural and genetic changes (reviewed in Parmesan 2006), our ability to accurately forecast the magnitude and direction of these changes requires a more mechanistic understanding of the interactions among the abiotic and biotic drivers that determine organismal fitness and performance. More specifically, future work should combine observational, experimental and modelling approaches to: I, quantify the net fitness effects of multiple abiotic variables; II, determine which species’ traits and ⁄ or geographic locations correspond to increased sensitivity; and III, examine the effects of biotic interactions in mediating the responses of organisms and shaping future ecological communities under climate change. For many organisms, particularly insects and other ectotherms, changes in temperature have pronounced effects on life-history traits and fitness (Parmesan, Root & Willig 2000; Bale et al. 2002). In one of the first studies to quantify the net effects of changes in both temperature means and extremes, Buckley & Kingsolver (2012) examine the demographic impacts of climate change on two Colias species (sulphur butterflies) in alpine habitats, one of the biomes most vulnerable to biodiversity losses under rapid climate change (Parry & IPCC 2007). In this issue of Functional Ecology ,B uckley & Kingsolver (2012) incorporate climatic data and demography into a biophysical model to determine whether fitness and activity responses to recent changes in temperature means and extremes correspond to current C. meadii and C. eriphyle lower and upper elevational limits in the Rocky Mountains. Overall, the projections of their biophysical models reveal opposing effects of temperature changes on flight and fecundity and do correspond with the current elevational limits of these two butterfly species, demonstrating that changes in both mean and extreme temperatures set species’ distributional boundaries and therefore need to be considered when forecasting species’ responses to climate change.

Ecological communities are being reshaped by climatic change. Losses and gains of species will alter community composition and diversity but these effects are likely to vary geographically and may be hard to predict from uncontrolled “natural experiments”. In this study, we used open-top warming chambers to simulate a range of warming scenarios for ground-nesting ant communities at a northern (Harvard Forest, MA) and southern (Duke Forest, NC) study site in the eastern US. After 2.5 years of experimental warming, we found no significant effects of accumulated growing degree days or soil moisture on ant diversity or community composition at the northern site, but a decrease in asymptotic species richness and changes in community composition at the southern site. However, fewer than 10% of the species at either site responded significantly to the warming treatments. Our results contrast with those of a comparable natural experiment conducted along a nearby elevational gradient, in which species richness and composition responded strongly to changes in temperature and other correlated variables. Together, our findings provide some support for the prediction that warming will have a larger negative effect on ecological communities in warmer locales at lower latitudes and suggest that predicted responses to warming may differ between controlled field experiments and unmanipulated thermal gradients.

Historical records of species are compared with current records to elucidate effects of recent climate change. However, confounding variables such as succession, land-use change, and species invasions make it difficult to demonstrate a causal link between changes in biota and changes in climate. Experiments that manipulate temperature can overcome this issue of attribution, but long-term impacts of warming are difficult to test directly. Here we combine historical and experimental data to explore effects of warming on ant assemblages in southeastern US. Observational data span a 35-year period (1976-2011), during which mean annual temperatures had an increasing trend. Mean summer temperatures in 2010-2011 were ∼ 2.7 °C warmer than in 1976. Experimental data come from an ongoing study in the same region, for which temperatures have been increased ∼ 1.5-5.5 °C above ambient from 2010 to 2012. Ant species richness and evenness decreased with warming under natural but not experimental warming. These discrepancies could have resulted from differences in timescales of warming, abiotic or biotic factors, or initial species pools. Species turnover tended to increase with temperature in observational and experimental datasets. At the species level, the observational and experimental datasets had four species in common, two of which exhibited consistent patterns between datasets. With natural and experimental warming, collections of the numerically dominant, thermophilic species, Crematogaster lineolata, increased roughly two-fold. Myrmecina americana, a relatively heat intolerant species, decreased with temperature in natural and experimental warming. In contrast, species in the Solenopsis molesta group did not show consistent responses to warming, and Temenothorax pergandei was rare across temperatures. Our results highlight the difficulty of interpreting community responses to warming based on historical records or experiments alone. Because some species showed consistent responses to warming based on thermal tolerances, understanding functional traits may prove useful in explaining responses of species to warming.