Curtis, R; (2012) The importance of resources in determining butterfly population abundance at multiple scales. Doctoral thesis , UCL (University College London).

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Abstract

Long term monitoring has revealed that butterfly populations vary dramatically between years, among sites and across species. This PhD investigates the importance of biotic and abiotic resources in determining butterfly abundance at multiple scales, using long term data from intensive studies on the Glanville fritillary and from the extensive UK Butterfly Monitoring Scheme. The most important resource at local scales is the ‘suitability’ of the larval hostplant: only plants within a certain temperature range are likely to be utilised for oviposition. Laying eggs on warmer plants maximises the probability of successful larval development within restricted seasonal temperature constraints. Analysis of Glanville fritillary population time-series reveals that populations are more abundant in those habitat types providing suitable microclimates for larval development, and in years following warm spring temperatures (i.e. during oviposition). These factors were also important when comparing abundance across sites, as were patch area and isolation. This landscape-scale analysis also revealed a significant negative interaction between habitat quality and temperature, suggesting that microsites for oviposition are less restricted in warm than cool years. Across regional scales (southeast England), the availability of both host and nectar plants are important in determining butterfly abundance, both across and within species. However, hostplant availability is a stronger predictor of abundance than nectar, and is most pronounced on sites with a northerly aspect. Trait analysis revealed that species with restricted diets, low mobility and habitat specialism are most sensitive to variation in foodplant availability. Taken together, the results suggest that many UK butterfly species are limited at small scales by the availability of hostplants in warm microclimates, but at large scales by dispersal limitation and climatic tolerance. Site management can therefore increase the abundance of key species of conservation concern by creating thermally diverse habitats and maximising the biomass of their hostplants.

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