Brian Huntley

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.

Rapid environmental changes in southern Europe during the last glacial period

Oxygen-isotope records from Greenland ice cores, indicate numerous rapid climate fluctuations during the last glacial period. North Atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice-rafted debris. In contrast, very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents. Here we present high-resolution geochemical, physical and pollen data from lake sediments in Italy and from a Mediterranean sediment core, linked by a common tephrochronology. Our lacustrine sequence extends to the past 102,000 years. Many of its features correlate well with the Greenland ice-core records, demonstrating that the closely coupled ocean–atmosphere system of the Northern Hemisphere during the last glacial extended its influence at least as far as the central Mediterranean region. Numerous vegetation changes were rapid, frequently occurring in less than 200 years, showing that the terrestrial biosphere participated fully in last-glacial climate variability. Earlier than 65,000 years ago, our record shows more climate fluctuations than are apparent in the Greenland ice cores. Together, the multi-proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials, and provide a step towards determining the underlying mechanisms of the centennial–millennial-scale variability.

Reconstructing biomes from palaeoecological data: a general method and its application to European pollen data at 0 and 6 ka

Biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation. The use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological (pollen and plant macrofossil) records provided these records are “biomized”, i.e. assigned to biomes in a consistent way. This article describes a method for the objective biomization of pollen samples based on fuzzy logic. Pollen types (taxa) are assigned to one or more plant functional types (PFTs), then affinity scores are calculated for each biome in turn based on its list of characteristic PFTs. The pollen sample is assigned to the biome to which it has the highest affinity, subject to a tie-breaking rule. Modern pollen data from surface samples, reflecting present vegetation across Europe, are used to validate the method. Pollen data from dated sediment cores are then used to reconstruct European vegetation patterns for 6 ka. The reconstruction shows systematic differences from present that are consistent with previous interpretations. The method has proved robust with respect to human impacts on vegetation, and provides a rational way to interpret combinations of pollen types that do not have present-day analogs. The method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras, and/or lower densities of available modern and fossil pollen samples, than Europe.

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.

July Temperatures in Europe from Pollen Data, 6000 Years Before Present

Mean July temperatures across Europe 6000 years before present were reconstructed from palynological data by the transfer function method. Reconstructed summer temperatures were warmer than those at present over most of Europe with the greatest heating, more than 2�C, in the midcontinent and the far north. This pattern is explained by high summer insolation and a weak zonal insolation gradient 6000 years before present and the effective heating of the landmass relative to ocean and coastal areas. A strong land-sea pressure gradient may in turn have increased westerly air flow into southern Europe, which is consistent with cooler reconstructed summer temperatures in the Mediterranean region, and reduced the environmental lapse rate in the central European mountains.

An indicator of the impact of climatic change on European bird populations.

Rapid climatic change poses a threat to global biodiversity. There is extensive evidence that recent climatic change has affected animal and plant populations, but no indicators exist that summarise impacts over many species and large areas. We use data on long-term population trends of European birds to develop such an indicator. We find a significant relationship between interspecific variation in population trend and the change in potential range extent between the late 20th and late 21st centuries, forecasted by climatic envelope models. Our indicator measures divergence in population trend between bird species predicted by climatic envelope models to be favourably affected by climatic change and those adversely affected. The indicator shows a rapid increase in the past twenty years, coinciding with a period of rapid warming.

Vegetation history and palaeoclimate of the last glacial period at Lago Grande di Monticchio, Southern Italy

A high-resolution palynological study of a 51 m core from Lago Grande di Monticchio, southern Italy, has provided a palaeonvironmental record for the last glacill. A annual lamination based chronology, supported by radiometric and tephrochronological dates, provides an absolute timescale for this record that spans 76,300 years. Correlations are established between the pollen stratigraphy, the GRIP ice core δ18O record and foraminiferal assemblages from Atlantic core V23-81. Both Dansgaard-Oeschger and Heinrich events are reflected by changes in the pollen stratigraphy. Revised dates are estimated for Heinrich events H1–H6. A quantitative palaeoclimate reconstruction based upon the pollen data provides evidence of the climate changes in southern Italy associated with these and other fluctuations during the last glacial.

IMPACTS OF HABITAT FRAGMENTATION AND PATCH SIZE UPON MIGRATION RATES

A spatially explicit model (MIGRATE) was used to investigate the effects of habitat loss and fragmentation on the ability of species to migrate in response to climate change. Illustrative simulations were run using parameters that represent the reproductive and dispersal characteristics of the wind-dispersed tree Tilia cordata (small-leaved lime). Hierarchically structured landscapes with different patch sizes and overall habitat suitability levels were generated at a 1-km resolution for a 200 × 800 km area. Simulated migration rates slowed markedly when habitat availability fell below ∼25% of the landscape area, especially in landscapes composed of fewer larger patches. The implication of these results for the management of landscapes for species conservation is discussed.

Rapid Changes in the Range Limits of Scots Pine 4000 Years Ago

Paleoecological data provide estimates of response rates to past climate changes. Fossil Pinus sylvestris stumps in far northern Scotland demonstrate former presence of pine trees where conventional pollen evidence of pine forests is lacking. Radiocarbon, dendrochronological, and fine temporal-resolution palynological data show that pine forests were present for about four centuries some 4000 years ago; the forests expanded and then retreated rapidly some 70 to 80 kilometers. Despite the rapidity of this response to climate change, it occurred at rates slower by an order of magnitude than those necessary to maintain equilibrium with forecast climate changes attributed to the greenhouse effect.

Weichselian palynostratigraphy, palaeovegetation and palaeoenvironment; the record from Lago Grande di Monticchio, southern Italy

Abstract The palynostratigraphic record from Lago Grande di Monticchio (S. Italy) is presented. An independent sedimentation-rate-based chronology provides an age of 101,530 calendar years BP for the lowermost sediments sampled. This chronology enables assessment of the rapidity of vegetation changes during the last glacial; contrary to widely held views the vegetation showed numerous large magnitude changes in periods of