Biomedical subjects

Chris D Thomas

Publications and source records attributed to Chris D Thomas.

10 recordsLinked to original sources

PubMed2006

Species richness changes lag behind climate change.

Species-energy theory indicates that recent climate warming should have driven increases in species richness in cool and species-poor parts of the Northern Hemisphere. We confirm that the average species richness of British butterflies has increased since 1970-82, but much more slowly than predicted from changes of climate: on average, only one-third of the predicted increase has taken place. The resultant species assemblages are increasingly dominated by generalist species that were able to respond quickly. The time lag is confirmed by the successful introduction of many species to climatically suitable areas beyond their ranges. Our results imply that it may be decades or centuries before the species richness and composition of biological communities adjusts to the current climate.

Animal Migration↗

PubMed2006

Can occupancy patterns be used to predict distributions in widely separated geographic regions?

Occupancy models, that describe the presence and absence patterns of a species in a given area, are increasingly being used to predict the occurrence of the species in unsurveyed sites, as an aid to conservation planning. In this paper, we consider whether conclusions about local distributions derived from one landscape can be extrapolated to others. We found that habitat patchiness influenced the distribution and abundance of the host-specific moth Wheeleria spilodactylus in a similar way in two landscapes widely separated geographically. In both geographic regions, the spatial location (positive effect of connectivity), and quantity of resource (positive effect of host plant density) increased the likelihood that the moth would be present, consistent with the expectations of metapopulation dynamics. Though some biological attributes of the species appeared to be slightly different, including population density and the timing of the life cycle (phenology), occupancy patterns in one landscape accurately predict occupancy in the other landscape. Our results suggest that it maybe possible to make predictions from one landscape to another, even when the landscapes are widely separated.

Animals↗

PubMed2006

Range retractions and extinction in the face of climate warming.

Until recently, published evidence for the responses of species to climate change had revealed more examples of species expanding than retracting their distributions. However, recent papers on butterflies and frogs now show that population-level and species-level extinctions are occurring. The relative lack of previous information about range retractions and extinctions appears to stem, at least partly, from a failure to survey the distributions of species at sufficiently fine resolution to detect declines, and from a failure to attribute such declines to climate change. The new evidence suggests that climate-driven extinctions and range retractions are already widespread.

Animals↗

PubMed2006

Changing habitat associations of a thermally constrained species, the silver-spotted skipper butterfly, in response to climate warming.

1. The impact of climate change on the distribution, abundance, phenology and ecophysiology of species is already well documented, whereas the influence of climate change on habitat choice and utilization has received little attention. Here we report the changing habitat associations of a thermally constrained grassland butterfly, Hesperia comma, over 20 years. 2. Between 1982 and 2001-2, the optimum percentage of bare ground within habitat used for egg-laying shifted from 41% to 21%. 3. Egg-laying rates are temperature-dependent and females actively adjust microhabitat usage in response to temperature variations; relatively warmer host plants are chosen or oviposition at low ambient temperatures, and cooler host plants at high ambient temperatures. 4. Climate warming has increased the availability of thermally suitable habitat for H. comma at the cool, northern edge of the species' distribution, therefore increasing: (a) egg-laying rate and potentially the realized rate of population increase; (b) effective area of habitat patches as more microhabitats within a given vegetation fragment are now suitable for egg-laying; (c) buffering of populations against environmental variation as eggs are laid within a wider range of microhabitats; and (d) the number of habitat patches in the landscape that are currently available for colonization (including the use of more northerly facing aspects; Thomas et al., Nature, 2001, 411, 577-581). 5. Conservationists often assume the habitat requirements of a species to be constant, and manage habitats to maintain these conditions. For many species, these requirements are likely to change in response to climate warming, and care must be taken not to manage habitats based on outdated prescriptions.

Adaptation, Physiological↗

PubMed2006

Thermal range predicts bird population resilience to extreme high temperatures.

The identification of the characteristics of species that make them susceptible or resilient to climate change has been elusive because non-climatic influences may dominate short- and medium-term changes in population and distribution sizes. Here we studied the 2003 French heat wave, during which other confounding variables remained essentially unchanged, with a correlational approach. We tested the relationship between population resilience and thermal range by analysing the responses of 71 bird species to a 6-month heat wave. Species with small thermal ranges showed the sharpest decreases in population growth rate between 2003 and 2004 in locations with the highest temperature anomalies. Thermal range explained the resilience of birds to the heat wave independently of other potential predictors, although it correlated with nest location and broad habitat type used by species. The geographically deduced thermal range appears to be a reliable predictor of the resilience of these endothermic species to extreme temperatures.

Animals↗

PubMed2005

Prioritizing multiple-use landscapes for conservation: methods for large multi-species planning problems.

Across large parts of the world, wildlife has to coexist with human activity in highly modified and fragmented landscapes. Combining concepts from population viability analysis and spatial reserve design, this study develops efficient quantitative methods for identifying conservation core areas at large, even national or continental scales. The proposed methods emphasize long-term population persistence, are applicable to both fragmented and natural landscape structures, and produce a hierarchical zonation of regional conservation priority. The methods are applied to both observational data for threatened butterflies at the scale of Britain and modelled probability of occurrence surfaces for indicator species in part of Australia. In both cases, priority landscapes important for conservation management are identified.

Algorithms↗

PubMed2004

Spatial patterns in species distributions reveal biodiversity change.

Interpretation of global biodiversity change is hampered by a lack of information on the historical status of most species in most parts of the world. Here we show that declines and increases can be deduced from current species distributions alone, using spatial patterns of occupancy combined with distribution size. Declining species show sparse, fragmented distributions for their distribution size, reflecting the extinction process; expanding species show denser, more aggregated distributions, reflecting colonization. Past distribution size changes for British butterflies were deduced successfully from current distributions, and former distributions had some power to predict future change. What is more, the relationship between distribution pattern and change in British butterflies independently predicted distribution change for butterfly species in Flanders, Belgium, and distribution change in British rare plant species is similarly related to spatial distribution pattern. This link between current distribution patterns and processes of distribution change could be used to assess relative levels of threat facing different species, even for regions and taxa lacking detailed historical and ecological information.

Animals↗

PubMed2004

Changes in dispersal during species' range expansions.

Explanations for rapid species' range expansions have typically been purely ecological, with little attention given to evolutionary processes. We tested predictions for the evolution of dispersal during range expansion using four species of wing-dimorphic bush cricket (Conocephalus discolor, Conocephalus dorsalis, Metrioptera roeselii, and Metrioptera brachyptera). We observed distinct changes in dispersal in the two species with expanding ranges. Recently colonized populations at the range margin showed increased frequencies of dispersive, long-winged (macropterous) individuals, compared with longer-established populations in the range core. This increase in dispersal appeared to be short-lived because 5-10 years after colonization populations showed similar incidences of macroptery to populations in the range core. These changes are consistent with evolutionary change; field patterns persisted when nymphs were reared under controlled environmental conditions, and range margin individuals reared in the laboratory flew farther than range core individuals in a wind tunnel. There was also a reproductive trade-off with dispersal in both females and males, which could explain the rapid reversion to lower rates of dispersal once populations become established. The effect of population density on wing morphology differed between populations from the range core (no significant effect of density) and expanding range margins (negative density dependence), which we propose is part of the mechanism of the changes in dispersal. Transient changes in dispersal are likely to be common in many species undergoing range expansion and can have major population and biogeographic consequences.

Animal Migration↗

PubMed2004

Extinction risk from climate change.

Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.

Animals↗

PubMed2002

Short-term studies underestimate 30-generation changes in a butterfly metapopulation.

Most studies of rare and endangered species are based on work carried out within one generation, or over one to a few generations of the study organism. We report the results of a study that spans 30 generations (years) of the entire natural range of a butterfly race that is endemic to 35 km(2) of north Wales, UK. Short-term studies (surveys in single years and dynamics over 4 years) of this system led to the prediction that the regional distribution would be quite stable, and that colonization and extinction dynamics would be relatively unimportant. However, a longer-term study revealed unexpectedly high levels of population turnover (local extinction and colonization), affecting 18 out of the 20 patches that were occupied at any time during the period. Modelling the system (using the 'incidence function model' (IFM) for metapopulations) also showed higher levels of colonization and extinction with increasing duration of the study. The longer-term dynamics observed in this system can be compared, at a metapopulation level, with the increased levels of variation observed with increasing time that have been observed in single populations. Long-term changes may arise from local changes in the environment that make individual patches more or less suitable for the butterfly, or from unusual colonization or extinction events that take metapopulations into alternative states. One implication is that metapopulation and population viability analyses based on studies that cover only a few animal or plant generations may underestimate extinction threats.

Animals↗