The effects of habitat management and climate change on the Lulworth Skipper butterfly

The interacting effects of habitat loss and climate change are the major threats to biodiversity. Understanding how these drivers act synergistically to affect species is critical for predicting responses and informing effective conservation strategies, but important questions remain about where climate-driven range retractions will occur across species ranges and how to conserve these vulnerable populations. A conservation framework that identifies at-risk populations and sets out the management actions which reduce their exposure to climate extremes would support more effective decision-making, but limited evidence on how to carry out actions in real landscapes remains a barrier to implementation. In this thesis I explore how habitat loss and climate change interact to affect species and then develop a conservation framework to support species conservation under the pressures of climate change and habitat loss. I use the Lulworth Skipper butterfly Thymelicus acteon as an example of a range-restricted grassland butterfly dependent on mid-successional habitat, to address key knowledge gaps within the framework. In Chapter 2 I review primary literature and find that trailing edges can occur throughout species ranges as environmental heterogeneity results in spatial variation in climate. I show that the interaction of climate variability with habitat quality affects species fitness, survival and reproduction, creating localised extinction hotspots and climatically resilient microrefugial landscapes. I then review evidence to inform a conservation framework that identifies and sets out management for vulnerable populations. The T. acteon study system is then used to address knowledge gaps within this framework. Firstly, in Chapter 3, I use a mechanistic microclimate model to quantify how changes in vegetation structure and terrain influence vertical variation in leaf and air temperatures within grassland at scales relevant to small organisms. I show that microclimates within grasslands are complex and discuss the outputs in the context of thermoregulation opportunities, exposure to extremes and the extent to which grassland management could help species cope with climate change. Secondly, in Chapter 4 I parameterise and run a metapopulation model for T. acteon and show how habitat quality can help to overcome constraints imposed by physical components of habitat patch area and spatial location on relative rates of colonisation and local extinction. I show that the scaling-up of local habitat management can play a key role in maintaining metapopulation resilience and facilitating range recovery. Lastly, in Chapter 5, I conduct a factorial experimental management trial to understand effects of cutting and rotovation on habitat suitability and occupancy of T. acteon a mid-successional habitat specialist sensitive to management intensity. I found that habitat recovers sooner on cut plots, but larval occupancy increases more rapidly on rotovated plots. I discuss how these interventions could be utilised to manage habitats for mid-successional grassland species such as T. acteon. My thesis has implications for understanding biological responses to the interacting effects of climate change and habitat loss and in guiding climate-adaptive conservation. Beyond this, the thesis also advances practical knowledge of the habitat requirements, metapopulation dynamics, management strategies, and microclimate preferences of T. acteon.<p></p>