Criteria for assessing climate change impacts on ecosystems

There is concern about the potential impacts of climate change on species and ecosystems. To address this concern, a large body of literature has developed in which these impacts are assessed. In this study, criteria for conducting reliable and useful assessments of impacts of future climate are suggested. The major decisions involve: clearly defining an emissions scenario; selecting a climate model; evaluating climate model skill and bias; quantifying General Circulation Model (GCM) between-model variability; selecting an ecosystem model and assessing uncertainty; properly considering transient versus equilibrium responses; including effects of CO(2) on plant response; evaluating implications of simplifying assumptions; and considering animal linkage with vegetation. A sample of the literature was surveyed in light of these criteria. Many of the studies used climate simulations that were >10 years old and not representative of best current models. Future effects of elevated CO(2) on plant drought resistance and productivity were generally included in growth model studies but not in niche (habitat suitability) studies, causing the latter to forecast greater future adverse impacts. Overly simplified spatial representation was frequent and caused the existence of refugia to be underestimated. Few studies compared multiple climate simulations and ecosystem models (including parametric uncertainty), leading to a false impression of precision and potentially arbitrary results due to high between-model variance. No study assessed climate model retrodictive skill or bias. Overall, most current studies fail to meet all of the proposed criteria. Suggestions for improving assessments are provided.     

Conceptual framework for assessment and management of ecosystem impacts of climate change

A conceptual framework is proposed for assessing and managing the ecosystem impacts of climate change. The framework can be used by ecosystem managers to systematically assess the potential adverse impacts of future climate change on ecosystems, and identify best adaptation strategies for alleviating those impacts. The proposed framework: (1) determines the acceptability of the current state of the ecosystem; (2) specifies climate change scenarios; (3) assesses the ecosystem impacts of the scenarios; and (4) identifies the best adaptation strategies for alleviating unacceptable impacts of the climate change scenarios. Concepts and methods employed in the framework include: (1) limits of acceptable change; (2) scenario analysis; (3) simulation; (4) Delphi method; (5) decision making under risk and uncertainty; (6) stochastic dominance; (7) multiple attribute evaluation; (8) Bayesian statistical inference; and (9) adaptive management. Implementation of the framework requires considerable technical, scientific, and other data/information that may not be available at this time, but is likely to become available in the future. It is recommended that a pilot program be initiated to test the proposed framework in a few targeted publicly managed ecosystems for which the requisite ecosystem data/information are available or can be readily obtained. Results of the pilot program would provide insights into the pros and cons of the framework and the conditions under which it is likely to be feasible.     

Effects of elevated nitrogen and exotic plant invasion on soil seed bank composition in Joshua Tree National Park

We investigated the effects of exotic species invasion and 3?years of nitrogen (N) fertilization on the soil seed bank in Joshua Tree National Park, California, USA at four sites along an N deposition gradient. We compared seed bank composition and density in control (no N added) and fertilized (30?kg?N?ha^?1?year^?1) plots to determine if the seed bank would reflect aboveground changes due to N fertilization. Soil samples were collected and germinated in a greenhouse over 2?years. In the field, invasive species cover responded positively to N fertilization. However, we did not observe increased seed density of exotic invasive species in fertilized plots. While no significant differences were detected between treatments within sites, exotic invasive grass seeds overwhelmed the seed bank at all sites. Significant differences between sites were found, which may be due to differences in level of invasion, historic N deposition, and soil surface roughness. Sites experiencing low N deposition had the highest seed bank species richness for both control and fertilized treatments. Aboveground plant density did not correlate well with seed bank density, possibly due to the inherent patchiness of soil seed banks and differential ability of species to form seed banks. This seed bank study provided insight into site-specific impacts on native versus invasive species composition of soil seed banks, as well as magnitude of invasion and restoration potential at invaded sites.     

Contrasting responses of Peromyscus mice of Yosemite National Park to recent climate change

Accurately predicting the response of species to climate change is crucial for the preservation of contemporary species diversity. In the current study, we analyze the response of two congeneric small mammal species (Peromyscus maniculatus and Peromyscus truei) to recent climate change in the region of Yosemite National Park (California, USA). The generalist P. maniculatus did not change its distribution in response to climate change while the specialist P. truei substantially changed its geographic and elevational distribution in the region, expanding into Yosemite. Using molecular genetic techniques we found that a cryptic geographic shift in genetic variation may have occurred within the geographically stable P. maniculatus distribution. Using a combination of morphometric and molecular genetic techniques we confirmed that a P. truei subspecies previously identified as a habitat specialist expanded into new habitat types, suggesting that this subspecies is not in fact a habitat specialist. Instead, we propose that the range of this subspecies is instead limited by climatic variables currently varying in response to contemporary climate change. These results underscore the importance of verifying the natural‐history‐based assumptions used to develop predictive models of species' response to climate change.     

A framework for assessing the vulnerability of species to climate change: a case study of the Australian elapid snakes

Frameworks that provide a system for assessing species according to their vulnerability to climate change can offer considerable guidance to conservation managers who need to allocate limited resources among a large number of taxa. To date, climate change vulnerability assessments have largely been based on projected changes in range size derived from the output of species distribution models (SDMs). A criticism of risk assessments based solely on these models is that information on species ecological and life history traits is lacking. Accordingly, we developed a points-based framework for assessing species vulnerability to climate change that considered species traits together with the projections of SDMs. Applying this method to the Australian elapid snakes (family Elapidae), we determined which species may be particularly susceptible in the future and assessed broad-scale biogeographic patterns in species vulnerability. By offering a more comprehensive and rigorous method for assessing vulnerability than those based solely on SDMs, this framework provides greater justification for resource allocation, and can help guide decisions regarding the most appropriate adaptation strategies.     

Isospora phainopepla n. sp. (Apicomplexa: Eimeriidae) from Phainopepla nitens (Swainson) (Passeriformes: Ptiliogonatidae) in the Joshua Tree National Park,USA

Systematic Parasitology - Isospora phainopepla n. sp. is described from the faeces of Phainopepla nitens (Swainson) collected in Joshua Tree National Park, California, USA. To our knowledge, there...     

Hominid environments at Hadar from paleosol studies in a framework of Ethiopian climate change

The amount and seasonal distribution of paleo-rainfall is a major concern of paleoanthropology because they determine the nature of the vegetation and the structure of the ecosystem, particularly in eastern Africa. The δ¹⁸O and δ¹³C of paleosol carbonates are quantitative proxies of these critical features of the paleoenvironment. The Afar region of Ethiopia lies between the African and Indian summer monsoons, and is prone to profound climate change. In the western Afar, the dominant paleoenvironment of the Hadar Formation during the late Pliocene was a major meandering river's distal low, flat floodplain, on which muds accreted that were continuously transformed into vegetated soils with Bk horizons rich in CaCO₃. The mean δ¹³C of paleosols throughout the Hadar Formation translates to an average vegetative cover across the extensive floodplain of about 30% of the C₄ grasses and 70% of unspecified C₃ plants. The character of the paleosols, such as the one at Locality 333, and their δ¹⁸O_Carbonate argue for a highly seasonal rainfall of about twice today's amount, implying that the C₃ plants were mostly sizeable trees and that the biome for Australopithecus afarensis was a grassy woodland. The amount of grasses abruptly increased in the lower Busidima Formation with its early Homo and artifacts to a more open grassy woodland of ca. 50% grasses. However, this transition in δ¹³C is not mirrored in the δ¹⁸O, which persists at a quite negative average value of −6.4‰ over the entire >2-Myr duration of both formations. This value for the carbonate means that the paleosoil water was a quite negative −4.1‰, a significant 5‰ more negative than our estimate of modern rain at Hadar. We put the negative δ¹⁸O of paleo-Hadar's rainfall into an isotopic framework of the dynamic history of climate change in sub-Saharan northern Africa. There have been two end-member climate regimes: (1) an earlier persistently pluvial Pliocene regime, with its strong summer monsoon, as registered in the Hadar Formation; and (2) the modern cyclical, mostly arid regime that began ca. 1 Myr ago, which has been punctuated by about ten cyclically predictable brief millennia-long pluvial episodes. The best known pluvial of the latter regime is the latest one, the African Humid Period (AHP), just 9.0-6.5 kyr ago, whose δ¹⁸O_Rainfall matches that for paleo-Hadar. The known climatological factors that brought on the AHP are probably the same ones that were persistently present for the Afar of the Pliocene. This dynamic rainfall history undoubtedly has influenced hominid occupation of the keystone Afar area at the gateway out of, and into, Africa.     

Mapping sea level rise impacts to identify climate change adaptation opportunities in the Chesapeake and Delaware Bays,USA

Wetlands Ecology and Management - Salt marshes are at risk globally if they cannot keep pace with sea level rise. Along the United States Mid-Atlantic coast, high marsh has already declined, and is...     

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.     

Impacts of long-term snow climate change on a high-elevation cold desert shrubland, California, USA

Ecological responses to 50-year old manipulations of snow depth and melt timing were assessed using snow fences arrayed across 50 km of a shrub–conifer landscape mosaic in eastern California, USA. We compared how increased, decreased, and ambient snow depth affected patterns of vegetation community composition, fire fuel accumulation, and annual tree ring growth. We also tested the effect of snow depth on soil carbon storage based on total C content under the two co-dominant shrub species (Artemisia tridentata and Purshia tridentata) in comparison with open, intershrub sites. Increased snow depth reduced the cover of the N-fixing shrub P. tridentata but not the water-redistributing shrub A. tridentata. Annual ring growth was greater on +snow plots and lower on ?snow plots for the conifer Pinus jeffreyi but not for Pinus contorta. Graminoid cover and aboveground biomass indicated higher fire fuel accumulation where snow depth was increased. Dead shrub stem biomass was greater regardless of whether snow depth was increased or decreased. Results demonstrate community shifts, altered tree growth, feedbacks on carbon storage, and altered fire fuel accumulation as a result of changes in snow depth and melt timing for this high-elevation, snow-dominated ecotone under future climate scenarios that envision increased or decreased snow depth.     

Projected impacts of climate change on regional capacities for global plant species richness

Climate change represents a major challenge to the maintenance of global biodiversity. To date, the direction and magnitude of net changes in the global distribution of plant diversity remain elusive. We use the empirical multi-variate relationships between contemporary water-energy dynamics and other non-climatic predictor variables to model the regional capacity for plant species richness (CSR) and its projected future changes. We find that across all analysed Intergovernmental Panel on Climate Change emission scenarios, relative changes in CSR increase with increased projected temperature rise. Between now and 2100, global average CSR is projected to remain similar to today (+0.3%) under the optimistic B1/+1.8°C scenario, but to decrease significantly (−9.4%) under the ‘business as usual’ A1FI/+4.0°C scenario. Across all modelled scenarios, the magnitude and direction of CSR change are geographically highly non-uniform. While in most temperate and arctic regions, a CSR increase is expected, the projections indicate a strong decline in most tropical and subtropical regions. Countries least responsible for past and present greenhouse gas emissions are likely to incur disproportionately large future losses in CSR, whereas industrialized countries have projected moderate increases. Independent of direction, we infer that all changes in regional CSR will probably induce on-site species turnover and thereby be a threat to native floras.     

Long-term records of coral calcification across the central Great Barrier Reef: assessing the impacts of river runoff and climate change

Calcification rates are reported for 41 long-lived Porites corals from 7 reefs, in an inshore to offshore transect across the central Great Barrier Reef (GBR). Over multi-decadal timescales, corals in the mid-shelf (1947–2008) and outer reef (1952–2004) regions of the GBR exhibit a significant increase in calcification of 10.9 ± 1.1 % (1.4 ± 0.2 % per decade; ±1 SE) and 11.1 ± 3.9 % (2.1 ± 0.8 % per decade), respectively, while inner-shelf (1930–2008), reefs show a decline of 4.6 ± 1.3 % (0.6 ± 0.2 % per decade). This long-term decline in calcification for the inner GBR is attributed to the persistent ongoing effects of high sediment/nutrients loads from wet season river discharges, compounded by the effects of thermal stress, especially during the 1998 bleaching event. For the recent period (1990–2008), our data show recovery from the 1998 bleaching event, with no significant trend in the rates of calcification (1.1 ± 2.0 %) for the inner reefs, while corals from the mid-shelf central GBR show a decline of 3.3 ± 0.9 %. These results are in marked contrast to the extreme reef-wide declines of 14.2 % reported by De’ath et al. (2009) for the period of 1990–2005. The De’ath et al. (2009) results are, however, found to be compromised by the inclusion of incomplete final years, duplicated records, together with a bias toward inshore reefs strongly affected by the 1998 bleaching. Our new findings nevertheless continue to raise concerns, with the inner-shelf reefs continuing to show long-term declines in calcification consistent with increased disturbance from land-based effects. In contrast, the more ‘pristine’ mid- and outer-shelf reefs appear to be undergoing a transition from increasing to decreasing rates of calcification, possibly reflecting the effects of CO₂-driven climate change. Our study highlights the importance of properly undertaken, regular assessments of coral calcification that are representative of the distinctive cross-shelf environments and discriminate between local disturbances and the global impacts of climate change and ocean acidification.     

Modelling species' range shifts in a changing climate: the impacts of biotic interactions, dispersal distance and the rate of climate change

There is an urgent need for accurate prediction of climate change impacts on species ranges. Current reliance on bioclimatic envelope approaches ignores important biological processes such as interactions and dispersal. Although much debated, it is unclear how such processes might influence range shifting. Using individual-based modelling we show that interspecific interactions and dispersal ability interact with the rate of climate change to determine range-shifting dynamics in a simulated community with two growth forms--mutualists and competitors. Interactions determine spatial arrangements of species prior to the onset of rapid climate change. These lead to space-occupancy effects that limit the rate of expansion of the fast-growing competitors but which can be overcome by increased long-distance dispersal. As the rate of climate change increases, lower levels of long-distance dispersal can drive the mutualists to extinction, demonstrating the potential for subtle process balances, non-linear dynamics and abrupt changes from species coexistence to species loss during climate change.     

The potential impacts of climate change on inshore squid: biology, ecology and fisheries

Squid are important components of many marine ecosystems from the poles to the equator, serving as both important predators and prey. Novel aspects of their growth and reproduction mean that they are likely to play an important role in the changing oceans due to climate change. Virtually every facet of squid life-history examined thus far has revealed an incredible capacity in this group for life-history plasticity. The extremely fast growth rates of individuals and rapid rates of turnover at the population level mean that squid can respond quickly to environmental or ecosystem change. Their ‘life-in-the-fast-lane’ life-style allows them to rapidly exploit ‘vacuums’ created in the ecosystem when predators or competitors are removed. In this way, they function as ‘weeds of the sea’. Elevated temperatures accelerate the life-histories of squid, increasing their growth rates and shortening their life-spans. At first glance, it would be logical to suggest that rising water temperatures associated with climate change (if food supply remains adequate) would be beneficial to inshore squid populations and fisheries—growth rates would increase, life spans would shorten and population turnover would accelerate. However, the response of inshore squid populations to climate change is likely to be extremely complex. The size of hatchlings emerging from the eggs becomes smaller as temperatures increase and hatchling size may have a critical influence on the size-at-age that may be achieved as adults and subsequently, population structure. The influence of higher temperatures on the egg and adult stages may thus be opposing forces on the life-history. The process of climate change will likely result in squids that hatch out smaller and earlier, undergo faster growth over shorter life-spans and mature younger and at a smaller size. Individual squid will require more food per unit body size, require more oxygen for faster metabolisms and have a reduced capacity to cope without food. It is therefore likely that biological, physiological and behavioural changes in squid due to climate change will have far reaching effects.     

Post‐fire tree establishment patterns at the alpine treeline ecotone: Mount Rainier National Park,Washington, USA

Questions: Does tree establishment: (1) occur at a treeline depressed by fire, (2) cause the forest line to ascend upslope, and/or (3) alter landscape heterogeneity? (4) What abiotic and biotic local site conditions are most important in structuring establishment patterns? (5) Does the abiotic setting become more important with increasing upslope distance from the forest line? Location: Western slopes of Mount Rainier, USA. Methods: We performed classification analysis of 1970 satellite imagery and 2003 aerial photography to delineate establishment. Local site conditions were calculated from a LIDAR‐based DEM, ancillary climate data, and 1970 tree locations in a GIS. We used logistic regression on a spatially weighted landscape matrix to rank variables. Results: Considerable establishment after 1970 caused forest line elevation to increase over 150 m in specific locations. Landscape heterogeneity increased with distance from the 1970 forest line. At a broad spatial context, we found establishment was most common near existing trees (0‐50 m) and at low elevations (1250‐1350 m). Slope aspect (W, NW, N, NE, and E), slope angle (40‐60°), and other abiotic factors emerged as important predictors of establishment with increasing upslope distance from the forest line to restricted spatial extents. Conclusions: Favorable climatic conditions likely triggered widespread tree establishment. Readily available seed probably enhanced establishment rates near sexually mature trees, particularly in the less stressful environment at low elevations. The mass effect of nearly ubiquitous establishment in these areas may have obscured the importance of the abiotic setting to restricted spatial extents. Topographic variability apparently produced favorable sites that facilitated opportunistic establishment with increasing upslope distance from the forest line, thereby enabling additional trees to invade the alpine tundra.