Abstract
The distribution of arthropod species on a 400 m elevational gradient (equivalent to a temperature decrease of 2.5°C) on Snowdon, North Wales, was examined and compared with the British distribution. Preferred temperature, an indication of optimal body temperature (Tb), and supercooling point (SCP), an indication of cold tolerance, of several species on the gradient were determined experimentally. The alpine beetle species Patrobus assimilis and Nebria rufescens had low preferred Tb, of 5.6 and 7.1°C respectively, whereas the more widespread upland species had higher preferred Tb, between 12.9 and 15.5°C. The SCP of both alpine and widespread beetles were similar, being between -6.9 and -5.8°C. The alpine species, which were smaller, were freeze intolerant, whereas the widespread species, which were larger, were freeze tolerant. On the national scale there was significant correlation between preferred Tb and species elevation, but no correlation with SCP. It is concluded that the alpine species survive on Snowdon because their optimal Tb is close to the ambient temperature at the time of day and year when they are active and because they are able to tolerate winter temperatures, by a combination of cold tolerance and shelter. Although a species' optimal niche will tend to shift upwards as mean temperatures rise with global climatic change, complex microclimatic and biotic factors make changes in distribution difficult to predict.
Highlights
The distribution o f a species within its historical range is usually connected with certain, more or less narrowly defined, habitat conditions (Uvarov, 1931); “moun tain” carabids tend to occur at higher elevations and at northerly latitudes (Luff, 1998)
Despite temperature being only one component o f the environmental factors (weather, food, other organisms and a place in which to live (Andrewartha & Birch, 1954)) which interact with the physiology and behaviour o f a species to determine its distribution, there is evidence that increasing global tem perature is resulting in species shifting northward and to higher elevations (Parmesan, 1996; Parmesan et al, 1999)
This study investigates the involvement o f preferred temperature, i.e. the temperature selected in the laboratory (e.g. Herter, 1926; Thiele, 1964; Thiele & Lehmann, 1967; Laudien, 1973), and cold tolerance, i.e. the ability to survive at low temperature (e.g. Block, 1990; Lee & Denlinger, 1991; Leather et al, 1993; Somme, 1999), in the elevational distribution of selected arthropod species
Summary
The distribution o f a species within its historical range is usually connected with certain, more or less narrowly defined, habitat conditions (Uvarov, 1931); “moun tain” carabids tend to occur at higher elevations and at northerly latitudes (Luff, 1998). The selected 400 m elevational gradient on Snowdon in North Wales is in the alpine zone, i.e. above the timber line; in Britain, because deforestation occurred c. The gradient provides a theoretical mean tem perature difference of 2.5°C between its limits, given a decline o f 0.6°C per 100 m (Mani & Giddings, 1980; Lennon & Turner, 1995). This is similar to the predicted increase in temperature due to global warming in the 100 years (IPCC, 1996). The elevational distribution is compared with the British distribution o f each species, in relation to elevation and temperature
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