Quantifying the activity levels and behavioural responses of butterfly species to habitat boundaries

Abstract

1. The ability of species' to undergo climate‐driven range shifts across fragmented landscapes depends on their dispersal ability as well as the structure of the landscape. For species' range shifts to occur, individuals must first leave suitable habitat to seek new habitat; this is likely to depend on the rate of movement of individuals within habitat and the likelihood that a boundary is crossed, once it is encountered. For three species of butterfly with contrasting histories of recent range expansion, we examined the propensity of individuals to move within a habitat and their responses to habitat boundaries.2. We quantified the extent to which Plebejus argus (Linnaeus) (a declining habitat specialist), Aricia agestis (Schiffermuller) (an expanding generalist) and Polymmatus icarus (Rottemburg) (a geographically ubiquitous generalist) crossed habitat boundaries into unsuitable habitat and moved within suitable habitat. The observed movement was then related to individual and environmental conditions.3. Species differed in their activity levels in accordance within their recent distribution patterns (P. icarus > A. agestis > P. argus). Our results for P. argus suggest that movement may be motivated by nectar‐seeking, and that males generally move more than females. All three species tended to avoid crossing habitat boundaries; however the proportion of individuals crossing habitat boundaries did not differ significantly among species.4. We conclude that levels of activity within a habitat, which will affect the frequency with which individuals encounter habitat boundaries, rather than behavioural responses to the boundaries, may be important drivers of distribution change.