British butterflies differ in micro-temperature and habitat preferences, and in their ability to buffer body temperature against changes in air temperature – consequences for reserve management

Abstract

The ecological impacts of global warming are clear, with changes in species’ ranges, interactions between species, and species’ declines observed and predicted to continue. A key factor exacerbating these impacts is human-induced habitat loss and fragmentation, which reduce species’ ability to migrate and respond to change. Conservation action to increase reserve connectivity and size, and create habitat in more favourable climatic areas, can protect species from some impacts of warming.

Another option for climate change mitigation is within-reserve habitat management. This includes creating more varied topography and vegetation structure, and refuges of suitable microclimate within reserves that buffer species against regional warming [1], or facilitate colonisation of new sites as populations track climate change [2]. Butterfly species are able to alter their distribution and activity in response to local temperatures, demonstrating the potential of such management to assist their conservation [3].

However, to understand the potential for habitat management to facilitate species’ responses to climate change, and to understand the ecological landscape butterflies are faced with, we must first establish species’ thermal and habitat preferences, and their ability to tolerate, or otherwise, deviations from their thermal optima.

We searched five calcareous grassland reserves in Bedfordshire, UK, managed by the Bedfordshire, Cambridgeshire and Northamptonshire Wildlife Trust, on over 40 days between April and September, recording the species and behaviour of every butterfly seen. Information on the habitat type, slope and aspect of the location in which each butterfly was observed were also recorded, as well as local air temperature. A subset of individuals were caught and their thoracic temperature taken using a fine thermocouple, along with measurements of wing length, sex and condition.

Butterfly species differed in their habitat preferences, and in the ambient temperatures found in their microsites. Moreover, species differed in their ability to buffer their body temperature against changes in air temperature. Species such as large white and large skipper showed greater thermoregulatory ability, whilst others such as dingy skipper and Duke of Burgundy appeared less able to thermoregulate.

Our results suggest that species will differ in their ability to cross microclimatic boundaries in order to colonise new sites as they become more climatically suitable, and therefore that species will be differentially affected by habitat management strategies and climate-change induced temperature shifts. Whilst some may respond quickly to relatively broad management regimes, others will require a finer-tuned management strategy. We are conducting work to test this, and will further present preliminary results.

1 Bramer et al. (in press) Adv. Ecol. Res. 58 2 Ausden 2014. Environ. Manage. 54, 685–698 3 Turner et al. 2008. J. Insect Conserv. 13, 475–486