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Proc. R. Soc. B (2005) 272, 1257–1263 doi:10.1098/rspb.2005.3074 Published online 9 June 2005

Does habitat fragmentation affect temperature-related life-history traits? A laboratory test with a woodland butterfly
Bengt Karlsson1,* and Hans Van Dyck2,3
Department of Zoology, University of Stockholm, 106 91 Stockholm, Sweden Department of Biology, University of Antwerp, Universiteitsplein 1,2610 Antwerp, Belgium 3 Biodiversity Research Centre, Ecology and Biogeography Unit, Catholic University of Louvain, Croix du Sud 4, 1348 Louvain-la-Neuve, Belgium
2 1

Habitat fragmentation may change local climatic conditions leading to altered selection regimes for lifehistory traits in small ectotherms, including several insects. We investigated temperature-related performance in terms offitness among populations of the woodland butterfly Pararge aegeria (L.) originating from populations of a closed, continuous woodland landscape versus populations of an open, highly fragmented agricultural landscape in central Belgium. Female fecundity and longevity were evaluated in a temperature-gradient experiment. As predicted, females of woodland landscape origin reached higher maximum dailyfecundity and lifetime number of eggs than did agricultural landscape females at low ambient temperatures, but this reversed at high ambient temperature. Egg weight decreased with temperature, and eggs of woodland butterflies were smaller. Contrary to what is generally assumed, remaining thorax mass was a better predictor of lifetime reproductive output than was abdomen mass. Since we used the F2generation from wild-caught females reared under common garden conditions, the observed effects are likely to rely on intrinsic, heritable variation. Our results suggest that differential selection regimes associated with different landscapes intervene by intraspecific variation in the response of a butterfly to variation in ambient temperature, and may thus be helpful when making predictions of futureimpacts on how wild populations respond to environmental conditions under a global change scenario, with increasing temperatures and fragmented landscapes. Keywords: oviposition; fecundity; habitat fragmentation; microclimate; temperature; butterflies

1. INTRODUCTION As patterns of resource distribution change with the process of habitat fragmentation, consequent selective changes in dispersal havebeen the major focus of evolutionary studies within this field (e.g. Travis & Dytham 1999; Thomas 2000; Merckx et al. 2003). However, altered environmental conditions in fragments compared with continuous habitat (Matlack 1993; Malcolm 1998) may also change life-history traits other than dispersal. For insects, temperature and humidity are among the most important factors affecting insectevolutionary strategies (Partridge et al. 1995; Nevo et al. 1998). Variation in life-history traits among differently fragmented landscapes may result from adaptation, but also from constraints when organisms can no longer buffer traits against environmental changes. Therefore, it is not enough to compare survival and fecundity in different landscapes (e.g. Johannessen et al. 2003), but one needs to studyheritable life-history traits in controlled, common environments. To the best of our knowledge, this has only rarely been done. For flying heliothermous insects, changes in thermal profiles with fragmentation may have important consequences for several aspects of their biology, including longevity and reproductive strategies and capacities.
* Author for correspondence(bengt.karlsson@zoologi.su.se). Received 25 November 2004 Accepted 12 February 2005

Microclimatic edge effects are also likely to affect host plant quality ( Jones 1992), which may in turn affect herbivorous insects. Few studies, however, have linked animal responses to microclimate changes within the context of habitat fragmentation (Meyer & Sisk 2001). We use Pararge aegeria (L.) as a model to test for differences in...
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