Species diversity and structure of phytophagous beetle assemblages along a latitudinal gradient: predicting the potential impacts of climate change

Abstract.  1. Assemblages of phytophagous beetles on Acacia were examined along a 1150 km latitudinal gradient in eastern Australia to investigate the potential effects of climate change on insect communities. The latitudinal gradient was used as a surrogate for differences in temperature. Several possible confounding variables were held constant by selecting comparable sites and emphasising a single host-plant species.
2. Total species richness increased towards the tropics, but there were no significant differences among latitudes for average species density, species richness, Fisher's α , or average Chao-1 index.
3. Beetles sampled along the gradient were classified into four climate change response groups, depending on their latitudinal range and apparent host specificity: cosmopolitan species, generalist feeders , climate generalists , and specialists . These four groups might respond differently to shifting climate zones. Cosmopolitan species (22% of community, found at more than one latitude and on more than one host plant) may be resilient to climate change. Generalist feeders (16%, found only at one latitude but found on more than one Acacia species) may well feed on several species but will have to move with their climatic envelope. Climate generalists (6%, found only on Acacia falcata but found at more than one latitude) may be constrained by the host species' ability to either cope with the changing climate or move with it. Finally, specialists (55%, found only on A. falcata and at only one latitude) may be forced to move poleward concurrently with their host species, or go extinct.
4. The analyses indicate that community structure may be fairly resilient to temperature change. The displacement or local extinction of species, especially the species that are found at only one latitude and on only one host plant, however, may lead to significant changes in community composition.     

Arthropod community structure along a latitudinal gradient: Implications for future impacts of climate change

Abstract The structure of free‐living arthropod communities on the foliage of Acacia falcata was assessed along an extensive latitudinal gradient in eastern Australia. We hypothesized that abundance and biomass of arthropods within feeding groups would increase from temperate latitudes towards the tropics. We also hypothesized that the ratio of carnivores to herbivores would be consistent along the latitudinal gradient. Three sites at each of four latitudes, spanning 9° and 1150 km (Batemans Bay, Sydney, Grafton, Gympie in Australia), were sampled every season for 2 years, using pyrethrum knockdown. Abundance and biomass (based on dry weight) of arthropods within eight feeding groups were measured. The relative size of the feeding groups, and the ratio of carnivores to herbivores were then compared among latitudes and seasons. We found no consistent north to south (tropical to temperate) change in feeding group structure in terms of abundance. A weak latitudinal trend was evident for predator biomass, consisting of a reduction from north to south, but no significant trends in biomass for other feeding groups were found. Relative abundance and relative biomass of both carnivores and herbivores, as well as the ratio of carnivores to herbivores were consistent among latitudes. Finally, we compared a subset of these data to arthropod communities found on congeneric host species at individual sites along the latitudinal gradient. Overall, 68% of comparisons showed no significant differences in abundance or biomass within different feeding groups between host plants and among latitudes. We conclude that arthropod communities show consistencies among latitudes and between congeneric host species, in terms of feeding group and trophic structure. These results have implications for predicting the impacts of future climate change on arthropod communities.     

Temperature adaptation of soil bacterial communities along an Antarctic climate gradient: predicting responses to climate warming

Soil microorganisms, the central drivers of terrestrial Antarctic ecosystems, are being confronted with increasing temperatures as parts of the continent experience considerable warming. Here we determined short‐term temperature dependencies of Antarctic soil bacterial community growth rates, using the leucine incorporation technique, in order to predict future changes in temperature sensitivity of resident soil bacterial communities. Soil samples were collected along a climate gradient consisting of locations on the Antarctic Peninsula (Anchorage Island, 67 °34′S, 68 °08′W), Signy Island (60 °43′S, 45 °38′W) and the Falkland Islands (51 °76′S 59 °03′W). At each location, experimental plots were subjected to warming by open top chambers (OTCs) and paired with control plots on vegetated and fell‐field habitats. The bacterial communities were adapted to the mean annual temperature of their environment, as shown by a significant correlation between the mean annual soil temperature and the minimum temperature for bacterial growth (T_min). Every 1 °C rise in soil temperature was estimated to increase T_min by 0.24–0.38 °C. The optimum temperature for bacterial growth varied less and did not have as clear a relationship with soil temperature. Temperature sensitivity, indicated by Q₁₀ values, increased with mean annual soil temperature, suggesting that bacterial communities from colder regions were less temperature sensitive than those from the warmer regions. The OTC warming (generally <1 °C temperature increases) over 3 years had no effects on temperature relationship of the soil bacterial community. We estimate that the predicted temperature increase of 2.6 °C for the Antarctic Peninsula would increase T_min by 0.6–1 °C and Q₁₀ (0–10 °C) by 0.5 units.     

Evolutionary potential of Chamaecrista fasciculata in relation to climate change. I. Clinal patterns of selection along an environmental gradient in the great plains

Climate change will alter natural selection on native plant populations. Little information is available to predict how selection will change in the future and how populations will respond. Insight can be obtained by comparing selection regimes in current environments to selection regimes in environments similar to those predicted for the future. To mimic predicted temporal change in climate, three natural populations of the annual legume Chamaecrista fasciculata were sampled from a climate gradient in the Great Plains and progeny of formal crosses were reciprocally planted back into common gardens across this climate gradient. In each garden, native populations produced significantly more seed than the other populations, providing strong evidence of local adaptation. Phenotypic selection analysis conducted by site showed that plants with slower reproductive development, more leaves, and thicker leaves were favored in the most southern garden. Evidence of clinal variation in selection regimes was also found; selection coefficients were ordered according to the latitude of the common gardens. The adaptive value of native traits was indicated by selection toward the mean of local populations. Repeated clinal patterns in linear and nonlinear selection coefficients among populations and within and between sites were found. To the extent that temporal change in climate into the future will parallel the differences in selection across this spatial gradient, this study suggests that selection regimes will be displaced northward and different trait values will be favored in natural populations.     

Predicting potential impacts of climate change on the geographical distribution of enchytraeids: a meta-analysis approach

The expectation that atmospheric warming will be most pronounced at higher latitudes means that Arctic and montane systems, with predominantly organic soils, will be particularly influenced by climate change. One group of soil fauna, the enchytraeids, is commonly the major soil faunal component in specific biomes, frequently exceeding above‐ground fauna in biomass terms. These organisms have a crucial role in carbon turnover in organic rich soils and seem particularly sensitive to temperature changes. In order to predict the impacts of climate change on this important group of soil organisms we reviewed data from 44 published papers using a combination of conventional statistical techniques and meta‐analysis. We focused on the effects of abiotic factors on total numbers of enchytraeids (a total of 611 observations) and, more specifically, concentrated on total numbers, vertical distribution and age groupings of the well‐studied species Cognettia sphagnetorum (228 observations). The results highlight the importance of climatic factors, together with vegetation and soil type in determining global enchytraeid distribution; in particular, cold and wet environments with mild summers are consistently linked to greater densities of enchytraeids. Based on the upper temperature distribution limits reported in the literature, and identified from our meta‐analyses, we also examined the probable future geographical limits of enchytraeid distribution in response to predicted global temperature changes using the HadCM3 model climate output for the period between 2010 and 2100. Based on the existing data we identify that a maximum mean annual temperature threshold of 16 °C could be a critical limit for present distribution of field populations, above which their presence would decline markedly, with certain key species, such as C. sphagnetorum, being totally lost from specific regions. We discuss the potential implications for carbon turnover in these organic soils where these organisms currently dominate and, consequently, their future role as C sink/source in response to climate change.     

Investigating the potential impacts of climate change on a marine turtle population

Recent increases in global temperatures have affected the phenology and survival of many species of plants and animals. We investigated a case study of the effects of potential climate change on a thermally sensitive species, the loggerhead sea turtle, at a breeding location at the northerly extent of the range of regular nesting in the United States. In addition to the physical limits imposed by temperature on this ectothermic species, sea turtle primary sex ratio is determined by the temperature experienced by eggs during the middle third of incubation. We recorded sand temperatures and used historical air temperatures (ATs) at Bald Head Island, NC, to examine past and predict future sex ratios under scenarios of warming. There were no significant temporal trends in primary sex ratio evident in recent years and estimated mean annual sex ratio was 58% female. Similarly, there were no temporal trends in phenology but earlier nesting and longer nesting seasons were correlated with warmer sea surface temperature. We modelled the effects of incremental increases in mean AT of up to 7.5°C, the maximum predicted increase under modelled scenarios, which would lead to 100% female hatchling production and lethally high incubation temperatures, causing reduction in hatchling production. Populations of turtles in more southern parts of the United States are currently highly female biased and are likely to become ultra‐biased with as little as 1°C of warming and experience extreme levels of mortality if warming exceeds 3°C. The lack of a demonstrable increase in AT in North Carolina in recent decades coupled with primary sex ratios that are not highly biased means that the male offspring from North Carolina could play an increasingly important role in the future viability of the loggerhead turtle in the Western Atlantic.     

Post-Eocene climate change, niche conservatism, and the latitudinal diversity gradient of New World birds

Aim The aim of this study was to test a variant of the evolutionary time hypothesis for the bird latitudinal diversity gradient derived from the effects of niche conservatism in the face of global climate change over evolutionary time. Location The Western Hemisphere. Methods We used digitized range maps of breeding birds to estimate the species richness at two grain sizes, 756 and 12,100 km². We then used molecular phylogenies resolved to family to quantify the root distance (RD) of each species as a measure of its level of evolutionary development. Birds were classified as ‘basal’ or ‘derived’ based on the RD of their family, and richness patterns were contrasted for the most basal and most derived 30% of species. We also generated temperature estimates for the Palaeogene across the Western Hemisphere to examine how spatial covariation between past and present climates might make it difficult to distinguish between ecological and evolutionary hypotheses for the current richness gradient. Results The warm, wet tropics support many species from basal bird clades, whereas the northern temperate zone and cool or dry tropics are dominated by species from more recent, evolutionarily derived clades. Furthermore, crucial to evaluating how niche conservatism among birds may drive the hemispherical richness gradient, the spatial structure of the richness gradient for basal groups is statistically indistinguishable from the overall gradient, whereas the richness gradient for derived groups is much shallower than the overall gradient. Finally, modern temperatures and the pattern of climate cooling since the Eocene are indistinguishable as predictors of bird species richness. Main conclusions Differences in the richness gradients of basal vs. derived clades suggest that the hemispherical gradient has been strongly influenced by the differential extirpation of species in older, warm‐adapted clades from parts of the world that have become cooler in the present. We propose that niche conservatism and global‐scale climate change over evolutionary time provide a parsimonious explanation for the contemporary bird latitudinal diversity gradient in the New World, although dispersal limitation of some highly derived clades probably plays a secondary role.     

Contrasting patterns of phylogenetic assemblage structure along the elevational gradient for major hummingbird clades

Aim We evaluated the hypothesis that, given niche conservatism, relatedness of co‐occurring hummingbird species of a given clade will increase at greater distances from the elevation where it originated. We also used prior knowledge of flight biomechanics and feeding specialization of hummingbird species (family Trochilidae) to evaluate which environmental variables were important predictors of changes in phylogenetic structure for each hummingbird clade. Location Ecuador. Methods We compiled species lists for 189 local hummingbird assemblages across major environmental gradients in Ecuador from a variety of published and non‐published sources. For the entire family and each of the major hummingbird clades (hermits, emeralds, mangoes, coquettes and brilliants) we quantified the phylogenetic structure of each assemblage using the net relatedness index (NRI). This index calculates the standardized mean of all possible pairwise phylogenetic distances between co‐occurring species. We related NRI for each clade to elevation, precipitation and vegetation‐related variables using generalized additive models. Results Our findings support the prediction of an increase in the co‐occurrence of close relatives away from the elevation of origin at the family level and for assemblages of mangoes and brilliants. The opposite pattern was found for assemblages of coquettes and emeralds. For the hermits, variation in phylogenetic structure was not explained by elevation. Clades with high levels of feeding specialization (hermits and brilliants) always included a vegetation‐related variable as an important predictor of change in phylogenetic structure. Main conclusions We found no overall support for the conservatism and zone of origin hypotheses. Knowledge of each clade’s natural history proved useful for predicting which environmental variables correlated with phylogenetic structure of local assemblages. Clades with the same elevation of origin appear to have radiated along the elevational gradient in association with different environmental factors.     

Changes in fine root biomass of Picea abies forests: predicting the potential impacts of climate change

Aims The impact of global warming on belowground processes, especially on fine root production, is poorly understood in comparison with its aboveground counterpart.Methods Here, we compiled 227 measurements to assess the influence of temperature and precipitation on fine root biomass of Norway spruce (Picea abies [L.] Karst) forest ecosystems in the Eurasia boreal region.Important findings We found that fine root biomass decreased significantly with latitudes. There was a biomass increase of 0.63 Mg ha^-1 and 0.32 Mg ha^-1 for fine roots <2 and <1 mm in diameter, respectively, with 1°C increase of mean annual temperature. There was an increase of 0.5 and 0.1 Mg ha^-1 per 100 mm year^-1 precipitation for the two size classes of fine roots. If the adaption of root production can match the pace of global warming and water is not a limiting factor for plant growth, fine root biomass would be expected to increase by 40–140% in response to the predicted increase in temperature (3–10°C) over the next century. Our analyses highlighted the strongly positive influences of temperature and precipitation on belowground function, suggesting that predicted future climate change could substantially enhance belowground biomass in the boreal region where the greatest warming is anticipated. This potential increase of belowground biomass, coupled with aboveground biomass, may provide a better understanding of climate–ecosystem feedbacks.     

Predators and priority effects suggested as potential drivers of microfauna communities in a community transplantation experiment along an elevational gradient

Transplantation experiments are a useful method to identify responses of organisms to environmental change. However, they are typically restricted to single or few species. Our experiment was carried out using entire bromeliad‐inhabiting microfauna communities which were transplanted along an elevational gradient, simulating environmental change acting on the communities. Additionally, we manipulated trophic interactions, i.e. resource availability and predator presence, thus combining abiotic and biotic effects in a full‐factorial experimental design. Using this experiment, we found a strong signal of original elevation in microfauna community structure (abundance, evenness, functional composition) with a shift from amoeba‐dominated to flagellate‐dominated communities with increasing original elevation. Surprisingly, the transplantation of communities along the elevational gradient did not affect community structure, indicating strong priority effects. Predation decreased microfauna abundance and increased microfauna evenness, specifically in higher original elevation and high resource levels. In summary, our results suggest that microfauna communities in bromeliads might be primarily shaped by priority effects and predator presence. However, interacting effects (between predator presence and resource availability, as well as between predator presence and original elevation) highlight the usefulness of studies with full‐factorial experimental designs to understand community‐structuring processes. Bromeliads and other micro‐ecosystems provide convenient study systems for community level approaches that could be used in future studies concerning the effects of environmental change, for example climate change on community structure.     

Radial growth response of four dominant boreal tree species to climate along a latitudinal gradient in the eastern Canadian boreal forest

To address the central question of how climate change influences tree growth within the context of global warming, we used dendroclimatological analysis to understand the reactions of four major boreal tree species –Populus tremuloides, Betula papyrifera, Picea mariana, and Pinus banksiana– to climatic variations along a broad latitudinal gradient from 46 to 54°N in the eastern Canadian boreal forest. Tree‐ring chronologies from 34 forested stands distributed at a 1° interval were built, transformed into principal components (PCs), and analyzed through bootstrapped correlation analysis over the period 1950–2003 to identify climate factors limiting the radial growth and the detailed radial growth–climate association along the gradient. All species taken together, previous summer temperature (negative influences), and current January and March–April temperatures (positive influences) showed the most consistent relationships with radial growth across the gradient. Combined with the identified species/site‐specific climate factors, our study suggested that moisture conditions during the year before radial growth played a dominant role in positively regulating P. tremuloides growth, whereas January temperature and growing season moisture conditions positively impacted growth of B. papyrifera. Both P. mariana and P. banksiana were positively affected by the current‐year winter and spring or whole growing season temperatures over the entire range of our corridor. Owing to the impacts of different climate factors on growth, these boreal species showed inconsistent responsiveness to recent warming at the transition zone, where B. papyrifera, P. mariana, and P. banksiana would be the most responsive species, whereas P. tremuloides might be the least. Under continued warming, B. papyrifera stands located north of 49°N, P. tremuloides at northern latitudes, and P. mariana and P. banksiana stands located north of 47°N might benefit from warming winter and spring temperatures to enhance their radial growth in the coming decades, whereas other southern stands might be decreasing in radial growth.     

Global climate change in large European rivers: long‐term effects on macroinvertebrate communities and potential local confounding factors

Aquatic species living in running waters are widely acknowledged to be vulnerable to climate‐induced, thermal and hydrological fluctuations. Climate changes can interact with other environmental changes to determine structural and functional attributes of communities. Although such complex interactions are most likely to occur in a multiple‐stressor context as frequently encountered in large rivers, they have received little attention in such ecosystems. In this study, we aimed at specifically addressing the issue of relative long‐term effects of global and local changes on benthic macroinvertebrate communities in multistressed large rivers. We assessed effects of hydroclimatic vs. water quality factors on invertebrate community structure and composition over 30 years (1979–2008) in the Middle Loire River, France. As observed in other large European rivers, water warming over the three decades (+0.9 °C between 1979–1988 and 1999–2008) and to a lesser extent discharge reduction (?80 m³ s^?1) were significantly involved in the disappearance or decrease in taxa typical from fast running, cold waters (e.g. Chloroperlidae and Potamanthidae). They explained also a major part of the appearance and increase of taxa typical from slow flowing or standing waters and warmer temperatures, including invasive species (e.g. Corbicula sp. and Atyaephyra desmarestii). However, this shift towards a generalist and pollution tolerant assemblage was partially confounded by local improvement in water quality (i.e. phosphate input reduction by about two thirds and eutrophication limitation by almost one half), explaining a significant part of the settlement of new pollution‐sensitive taxa (e.g. the caddisfly Brachycentridae and Philopotamidae families) during the last years of the study period. The regain in such taxa allowed maintaining a certain level of specialization in the invertebrate community despite climate change effects.     

Some like it hot! Rapid climate change promotes changes in distribution ranges of Nezara viridula and Nezara antennata in Japan

We compared past and current limits of the distribution range of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), in central Japan. In the early 1960s, the northern limit of the range was in Wakayama Prefecture and was limited by a +5 °C isothermal line for the mean January temperature. In 2006–2007, a new survey demonstrated that this northern limit had shifted northwards by 85 km (i.e., at a mean rate of 19.0 km per decade). The shift was most likely promoted by milder winter conditions. The mean January to February temperature in the region was 1.03–1.91 °C higher in 1998–2007 than in 1960–1969. The number of cold days (with the mean temperature below +5 °C) also significantly decreased, while the annual lowest temperature significantly increased. Nezara viridula was found mostly close to those locations where (i) the mean January temperature exceeded +5 °C, (ii) the mean number of cold days did not exceed 26 in January to February, and (iii) where the mean annual lowest temperature did not drop below –3.0 °C. The general linear model shows that the mean January temperature and number of cold days are the most important factors controlling the northern limit of distribution of N. viridula. All the climatic data suggest that over the last 45 years, environmental conditions have become more favourable for overwintering of N. viridula at many locations in central Japan. This has probably promoted the northward spread of the species, representing a direct response to climate warming. A sympatrically distributed congeneric, Nezara antennata Scott, seems to respond to the warming by a retreat from the ocean coast towards cooler elevated habitats, which might be a complex response to elevated temperature and interspecific mating with N. viridula. It is suggested that the range changes in both species will continue in response to further climate change.     

Flower-heads, herbivores, and their parasitoids: food web structure along a fertility gradient

Abstract. 1. The ways in which a soil fertility gradient affects three trophic level food webs defined by plants of the family Asteraceae, flower‐head herbivores, and their parasitoids was investigated. It was tested how the fertility gradient alters: (i) the abundance and richness of plants, herbivores, and their parasitoids, (ii) the herbivore–plant ratio, and (iii) the connectance of the plant–herbivore community matrix. 2. From April to May 2000, plants and insects were sampled in 16 Brazilian Cerrado (sensu stricto) sites along a physiognomic gradient varying from open shrublands (cerrado) to closed woodlands (cerradão). Sites were objectively positioned along the physiognomic gradient by a single index, tree density. Sixty‐seven per cent of the variation in tree density among sites was correlated to two principal components of a PCA, representing gradients of soil fertility. 3. Asteraceae abundance, richness, and flower‐head availability were negatively related to tree density due to their preference for sunny environments, despite the surplus of soil nutrients. The abundance and richness of Diptera and Lepidoptera, the most important flower‐head herbivores, were also negatively related to tree density. Parasitoid abundance decreased with tree density; however, the number of parasitoids per hosts was lower in cerrado, suggesting that top‐down forces are not getting stronger in more productive sites, as could be expected. 4. Community allometry analyses showed that the herbivore to plant ratio was independent of community richness and did not respond to tree density. 5. Connectance of the plant–herbivore matrix was dependent on the community matrix size. Proportionally, species‐rich cerrado sites had fewer interactions than their species‐poor counterparts. Nevertheless, after removing the effect of the matrix size, connectance was not related to tree density. 6. Soil fertility, as the primary cause of the cerrado–cerradão physiognomic gradient, strongly affected the abundance and richness of plants, herbivores and their parasitoids; however, it had little effect on important community attributes, such as the herbivore–plant ratio and the connectance of the plant–herbivore matrix.     

Evolutionary potential of Chamaecrista fasciculata in relation to climate change. II. Genetic architecture of three populations reciprocally planted along an environmental gradient in the great plains

Climate change will test the evolutionary potential of populations. Information regarding the genetic architecture within and among populations is essential for prediction of evolutionary outcomes. However, little is known about the distribution of genetic variation for relevant traits in natural populations or alteration of genetic architecture in a changing environment. In this study, pedigreed families from three populations of the annual prairie legume Chamaecrista fasciculata were reciprocally transplanted in three environments across a broad latitudinal range in the Great Plains. The underlying premise of this work is that northern populations will in the future experience climates similar to current-day climates further south. Estimates of narrow-sense heritability ranged from 0.053 to 0.481, suggesting the potential for evolutionary change is possible for most traits. In general, the northern population harbored less genetic variation and had lower heritability for traits than the southern population. This population also experienced large reductions in fitness, as measured by estimated lifetime fecundity, when raised in either the intermediate or the southern climate, whereas the difference between the intermediate and southern population was less extreme. For fecundity, the pattern of cross-environment additive genetic correlations was antagonistic to evolutionary change in four of six cases when native and nonnative sites were compared. Six additional antagonistic positive correlations were found for the rate of phenological development and leaf thickness. Overall, the data suggest that if climate changes as predicted, the northern population will face a severe evolutionary challenge in the future because of low heritabilities, cross-environment genetic correlations antagonistic to selection, and demographic instability due to lower seed production in a hotter and drier climate.     

Climate change shifts population structure and demographics of an alpine herb,Anemone narcissiflora ssp. sachalinensis (Ranunculaceae), along a snowmelt gradient

Alpine ecosystems, characterized by cold climates and short growing seasons, are thought to be most vulnerable to climate change. Warmer temperatures and earlier snowmelt extend the growing season length and increase drought stress for alpine plants, resulting in changes to their distribution. Anemone narcissiflora ssp. sachalinensis is a perennial herb that grows in the alpine snow-meadows of northern Japan. In the last few decades, its distribution has shifted toward later snowmelt habitat in the Taisetsu Mountains of Hokkaido. We recorded demographic data for this species at early, middle and late snowmelt habitats over four years (2009–2012), and constructed transition matrix models to evaluate how demographic parameters and population growth rate vary between local habitats along a snowmelt gradient. The proportion of reproductive plants was low and seed production was limited in the early snowmelt habitat, with drier soil conditions, in comparison to the middle and late snowmelt habitats, with moist soil conditions. Evidence of the transition from small plants to those in the reproductive stage was limited in the early snowmelt habitat, suggesting that growth was inhibited; the local population in this habitat was estimated to be sustained by seed migration from later snowmelt habitats. These results indicate that advancing snowmelt under climate change may decrease the reproductive activity and population growth rate of snow-meadow plants if seed migration from later snowmelt populations is limited, resulting in the extinction of local populations.