Jane K. Hill

Rapid Range Shifts of Species Associated with High Levels of Climate Warming

A meta-analysis shows that species are shifting their distributions in response to climate change at an accelerating rate. The distributions of many terrestrial organisms are currently shifting in latitude or elevation in response to changing climate. Using a meta-analysis, we estimated that the distributions of species have recently shifted to higher elevations at a median rate of 11.0 meters per decade, and to higher latitudes at a median rate of 16.9 kilometers per decade. These rates are approximately two and three times faster than previously reported. The distances moved by species are greatest in studies showing the highest levels of warming, with average latitudinal shifts being generally sufficient to track temperature changes. However, individual species vary greatly in their rates of change, suggesting that the range shift of each species depends on multiple internal species traits and external drivers of change. Rapid average shifts derive from a wide diversity of responses by individual species.

Rapid responses of British butterflies to opposing forces of climate and habitat change

Habitat degradation and climate change are thought to be altering the distributions and abundances of animals and plants throughout the world, but their combined impacts have not been assessed for any species assemblage. Here we evaluated changes in the distribution sizes and abundances of 46 species of butterflies that approach their northern climatic range margins in Britain—where changes in climate and habitat are opposing forces. These insects might be expected to have responded positively to climate warming over the past 30 years, yet three-quarters of them declined: negative responses to habitat loss have outweighed positive responses to climate warming. Half of the species that were mobile and habitat generalists increased their distribution sites over this period (consistent with a climate explanation), whereas the other generalists and 89% of the habitat specialists declined in distribution size (consistent with habitat limitation). Changes in population abundances closely matched changes in distributions. The dual forces of habitat modification and climate change are likely to cause specialists to decline, leaving biological communities with reduced numbers of species and dominated by mobile and widespread habitat generalists.

Responses of butterflies to twentieth century climate warming : implications for future ranges.

We analyse distribution records for 51 British butterfly species to investigate altitudinal and latitudinal responses to twentieth century climate warming. Species with northern and/or montane distributions have disappeared from low elevation sites and colonized sites at higher elevations during the twentieth century, consistent with a climate explanation. We found no evidence for a systematic shift northwards across all species, even though 11 out of 46 southerly distributed species have expanded in the northern part of their distributions. For a subset of 35 species, we model the role of climate in limiting current European distributions and predict potential future distributions for the period 2070–2099. Most northerly distributed species will have little opportunity to expand northwards and will disappear from areas in the south, resulting in reduced range sizes. Southerly distributed species will have the potential to shift northwards, resulting in similar or increased range sizes. However, 30 out of 35 study species have failed to track recent climate changes because of lack of suitable habitat, so we revised our estimates accordingly for these species and predicted 65% and 24% declines in range sizes for northern and southern species, respectively. These revised estimates are likely to be more realistic predictions of future butterfly range sizes.

Effects of habitat patch size and isolation on dispersal by Hesperia comma butterflies : implications for metapopulation structure

1. Metapopulation dynamics of the silver-spotted skipper butterfly Hesperia comma were studied between 1982 and 1991 along a 25-km stretch of chalk hills on the North Downs, Surrey, UK. Sixty-nine patches of suitable habitat were identified, of which 48 were occupied in 1982. Over the 9-year period, 12 patches were colonized, seven went extinct and nine patches remained vacant. Patches were more likely to be colonized if they were relatively large and close to other large, occupied patches. Local populations in small, isolated patches were more likely to go extinct. 2. Within a 70-ha section of a metapopulation, mark-release-recapture techniques were used in 1994 to investigate the effects of local patch area and isolation on movement of individuals among local patches. 988 butterflies were marked of which 133 moved between patches. 67% of between-patch movements were less than 50 m, although the longest recorded distance moved was 1070 m. Butterflies were most likely to move between large patches that were close together. 3. Metapopulation models have assumed that the distribution of distances moved by migrants follows a negative-exponential function. In our study, this distribution fitted an inverse-power function better than a negative-exponential. The under-estimation of long-distance migration by negative exponentials, compared with inverse power functions, may explain why theoretical models have under-estimated the number of occupied patches in metapopulations of H. comma following natural colonization. 4. Per capita emigration and immigration rates were significantly higher in small patches (area < 0.07 ha) compared with medium-sized (0.33-0.78 ha) or large patches (5.66 ha). However, in absolute numbers, more emigrants came from the largest patch where the source population was the largest. 5. The population system studied here shares attributes of several theoretical types of spatially structured population (patchy population, metapopulation, mainland-island system, non-equilibrium system) depending on the temporal and spatial scale examined. The distribution and dynamics of metapopulations should be regarded as being affected by a variety of behavioural and population processes, and real metapopulations can rarely be characterized as a single theoretical type.

Elevation increases in moth assemblages over 42 years on a tropical mountain

Physiological research suggests that tropical insects are particularly sensitive to temperature, but information on their responses to climate change has been lacking—even though the majority of all terrestrial species are insects and their diversity is concentrated in the tropics. Here, we provide evidence that tropical insect species have already undertaken altitude increases, confirming the global reach of climate change impacts on biodiversity. In 2007, we repeated a historical altitudinal transect, originally carried out in 1965 on Mount Kinabalu in Borneo, sampling 6 moth assemblages between 1,885 and 3,675 m elevation. We estimate that the average altitudes of individuals of 102 montane moth species, in the family Geometridae, increased by a mean of 67 m over the 42 years. Our findings indicate that tropical species are likely to be as sensitive as temperate species to climate warming, and we urge ecologists to seek other historic tropical samples to carry out similar repeat surveys. These observed changes, in combination with the high diversity and thermal sensitivity of insects, suggest that large numbers of tropical insect species could be affected by climate warming. As the highest mountain in one of the most biodiverse regions of the world, Mount Kinabalu is a globally important refuge for terrestrial species that become restricted to high altitudes by climate warming.

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.

Effects of selective logging on tropical forest butterflies on Buru, Indonesia

1. The butterfly fauna of lowland monsoon forest on Buru, Indonesia was compared in unlogged forest and forest that had been selectively logged 5 years previously. 2. Seven variables relating to vegetation structure were measured in each habitat. Tree density and percentage cover of vegetation in the canopy and understorey were significantly higher, and vegetation cover 2 m above the ground was significantly lower, in unlogged forest. There were no differences between sites in the mean heights or girths of trees, but the ranges of both heights and girths were lower in logged forest. Percentage cover of vegetation at ground level was similar at the two sites. 3. Species richness, abundance and evenness of butterflies and an index of taxonomic distinctiveness were all significantly higher in unlogged forest. Two endemic species and a further four species with distributions restricted to Maluku Province were recorded only in unlogged forest. 4. Species abundance data for butterflies at both sites fitted a log-series distribution. Data for unlogged forest also fitted a log-normal distribution, whereas those for logged forest did not. This indicated the presence of a more complex butterfly community in unlogged forest. 5. These results indicate that the distributional pattern of species abundance of tropical butterflies may be used as an indicator of forest disturbance, and that selective logging of tropical forests in SE Asia may be associated with a significant decrease in biodiversity of butterflies, at least during the first 5 years of forest regeneration.

Climate Change and Evolutionary Adaptations at Species' Range Margins

During recent climate warming, many insect species have shifted their ranges to higher latitudes and altitudes. These expansions mirror those that occurred after the Last Glacial Maximum when species expanded from their ice age refugia. Postglacial range expansions have resulted in clines in genetic diversity across present-day distributions, with a reduction in genetic diversity observed in a wide range of insect taxa as one moves from the historical distribution core to the current range margin. Evolutionary increases in dispersal at expanding range boundaries are commonly observed in virtually all insects that have been studied, suggesting a positive feedback between range expansion and the evolution of traits that accelerate range expansion. The ubiquity of this phenomenon suggests that it is likely to be an important determinant of range changes. A better understanding of the extent and speed of adaptation will be crucial to the responses of biodiversity and ecosystems to climate change.

Evolution of flight morphology in a butterfly that has recently expanded its geographic range

Abstract Individuals colonizing unoccupied habitats typically possess characters associated with increased dispersal and, in insects, colonization success has been related to flight morphology. The speckled wood butterfly, Pararge aegeria, has undergone recent major expansions in its distribution: in the north of its range, P. aegeria has colonized many areas in north and east England, and in the south, it was first recorded on Madeira in 1976. We examined morphological traits associated with flight and reproduction in the northern subspecies tircis, and in the southern subspecies aegeria, from sites colonized about 20 years ago in northern England and on Madeira, respectively. Investment in flight was measured as relative wing area and thorax mass, and investment in reproduction as relative abdomen mass. All measurements were from individuals reared in a common environment and there were significant family effects in most of the variables measured. Compared with individuals from sites continuously occupied in recent history, colonizing individuals were larger (adult live mass). In the subspecies tircis, colonizing individuals also had relatively larger thoraxes and lower wing aspect ratios indicating that evolutionary changes in flight morphology may be related to colonization. However, sex by site interactions in analyses of thorax mass and abdomen mass suggest different selection pressures on flight morphology between the sexes in relation to colonization. Overall, the subspecies aegeria was smaller (adult live mass) and had a relatively larger thorax and wings, and smaller abdomen than subspecies tircis. Evolutionary changes in flight morphology and dispersal rate may be important determinants of range expansion, and may affect responses to future climate change.

Flight Orientation Behaviors Promote Optimal Migration Trajectories in High-Flying Insects

Not at the Mercy of the Wind How can insects that migrate at high altitudes on fast-moving winds influence their direction of migration, when wind speeds typically exceed their self-propelled air speeds by a factor of three or four? Using automated vertical-looking entomological radar systems, Chapman et al. (p. 682) show that compass-mediated selection of favorable tailwinds, and partial correction for crosswind drift, are widespread phenomena in migrant insect species. Specialized flight behaviors have decisive influence on the migration pathways achieved by insects. Thus, contrary to popular belief, migrant insects are not at the mercy of the wind. Radar reveals that insects use high-altitude winds and correct for crosswind drift during long-range migrations. Many insects undertake long-range seasonal migrations to exploit temporary breeding sites hundreds or thousands of kilometers apart, but the behavioral adaptations that facilitate these movements remain largely unknown. Using entomological radar, we showed that the ability to select seasonally favorable, high-altitude winds is widespread in large day- and night-flying migrants and that insects adopt optimal flight headings that partially correct for crosswind drift, thus maximizing distances traveled. Trajectory analyses show that these behaviors increase migration distances by 40% and decrease the degree of drift from seasonally optimal directions. These flight behaviors match the sophistication of those seen in migrant birds and help explain how high-flying insects migrate successfully between seasonal habitats.