The thermal ecology of butterflies in a changing climate

Abstract

Many organisms inhabit microclimates that are very different from the conditions measured by standardised weather stations. Yet despite this, most conventional approaches in climate ecology still rely on statistically relating species’ responses to spatially-coarse and seasonably-aggregated climate variables derived from weather stations. In recent years, however, advances in remote sensing and biophysical modelling, have revolutionised our ability to estimate microclimate conditions across landscapes. This thesis capitalises on these new developments to investigate how microclimate and behaviour alter predictions about the responses of butterflies to climate change. In Chapter 1, I review the remote sensing literature to highlight new ways in which advances in remote sensing are providing novel methods for studying insect microclimate ecology. In Chapter 2, I apply a newly developed microclimate model to demonstrate the importance of microclimate in driving species’ distributions at fine spatial scales, and highlight three mechanisms by which microclimate conditions are decoupled from macroclimate. In Chapter 3, I develop a mechanistic biophysical model for predicting butterfly body temperature. Using this model, I predict the range of hourly body temperatures that a common blue (Polyommatus icarus) butterfly can achieve across an area of grassland in Cornwall, United Kingdom over the course of a year. I demonstrate that through behavioural thermoregulation, a butterfly is able to decouple its body temperature from ambient conditions, achieving a range of body temperatures that exceed the magnitude of climate change expected over the next 50 years. In Chapter 4, I apply the microclimate and butterfly biophysical models to the Sierra de Gredos in central Spain under both historical and future climate scenarios. I demonstrate that behavioural thermoregulation has the potential to offset 50 years’ worth of climate change under a high emissions scenario (RCP8.5). Overall, this thesis demonstrates the importance of microclimate and behaviour in mediating species’ responses to climate, and emphasises the need for using biophysically-relevant measures of temperature for making accurate predictions under future climates. I suggest that there may be overlooked potential to conserve species in situ under climate change.