Intraspecific variation in habitat availability among ectothermic animals near their climatic limits and their centres of range

Abstract

A promising way of predicting how species' populations may respond to climate warming in the Holarctic is to examine how the same organisms function at lower altitudes or further south in their ranges, where current climates are warmer. Here, we compare how the quantity and distribution of the habitats of four species of ectothermic animal differ in space and time across a heathland landscape under the climates that prevail near their northern edges of range and 300-400 km south, where mean spring and summer temperatures are 2-3°C higher. Both these habitat parameters are key determinants of the size and persistence of animal populations in a region (Dempster & McLean 1998). The quantity (and quality) of habitat determines the carrying capacity of a site for a species or the levels at which populations of interacting species equilibrate, while the juxtaposition and continuity of habitat patches of different sizes influence the extent to which species can track the occurrence of new patches of habitat, and can persist as metapopulations in a landscape. Thomas (1991Thomas ( , 1993Thomas ( , 1995 has suggested that small differences in mean temperatures may have large effects on the availability of habitat for ectotherms in temperate regions because coldblooded animals generally need to raise their body temperatures above a threshold before activity or development becomes possible (Logan et al. 1976) and are often unable to influence this by thermoregulation during certain life-stages, or can do so to only a limited extent within the range of microclimates avail- 2.Habitats both at the northern edge of their ranges and 300-400 km further south for the four species were defined qualitatively from existing sources and then expressed quantitatively in terms of the attributes recorded in the Dorset Heathland Survey. The Survey was then used as a GIS to map the occurrence of the habitats of the four species under two climates and a decade apart. 3. The model predicts that an increase of 2-3°C can result in a large increase in the area of habitat available to these north temperate species, that the length of time that individual patches of successional habitat may be occupied increases and that the distance between habitat patches within the biotope decreases. 4. The warmer conditions should result in a more stable metapopulation structure for P. argus, with fewer metapopulations existing in the landscape but each, on average, containing a greater number of larger and more stable constituent populations. 5. These predictions are of significance to ectothermic species which currently live at the northern limits of their ranges in the British Isles. The reverse effect is likely for species at the southern limits of their ranges. Conservationists who wish to maintain the status quo may be able to reduce some effects of these changes by appropriate habitat management.

Butterfly abundance in a warming climate: patterns in space and time are not congruent

“…Many butterflies occurring towards their cooler range limit shift to inhabit warmer, narrower niches, whereas with core populations sample the landscape more widely (Thomas 1993, Thomas et al 1999, Cowley et al 2001b, Roy and Thomas 2003, Oliver et al 2009). Other studies report gradients in size or melanism in butterflies across latitudes (Dennis and Shreeve 1989, Nylin and Svard 1991, Ayres and Scriber 1994.…”

Ant communities (Hymenoptera: Formicidae) of Flemish (north Belgium) wet heathlands, a declining habitat in Europe

“…obs. ) which reduces the invertebrate diversity (Thomas et al, 1999) in general, and the potential number of sunlit, warm nesting sites for ants in particular (Elmes & Wardlaw, 1982;Thomas, 1995;Thomas et al, 1998). De Boer (1978) found a significantly higher number of ant nests in wet Erica heathland with a relative high Molinia caerulea cover (on average 30%) than in sites with lower Molinia caerulea densities (on average 13%).…”

The effect of temperature and habitat quality on abundance of the Glanville fritillary on the Isle of Wight: implications for conservation management in a warming climate

“…Therefore, within species, individuals can control for variations in temperature by choosing to oviposit on hostplants on different aspects or within vegetation of different heights (Roy & Thomas 2003;Dennis 2010). Furthermore, many butterflies at the northern edge of their range therefore survive by inhabiting earlier (hotter) successional stages of habitats opposed to their conspecifics living within the (warmer) centres of their range (Thomas 1993;Thomas et al 1999), and so the local distribution of higher latitude populations is frequently restricted by warmer microclimates within habitats (Thomas 1995b). …”