Dispersal and population persistence of a threatened butterfly in the face of habitat fragmentation and environmental change

Blomfield, Alex and Wilby, Andy and Menendez Martinez, Rosa (2022) Dispersal and population persistence of a threatened butterfly in the face of habitat fragmentation and environmental change. PhD thesis, Lancaster University.

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Abstract

Butterflies are sensitive indicators, showing vulnerability to habitat and environmental change. The ecological requirements of Lepidoptera are relatively well documented, but in addition to the provision of adult and larval resources, species persistence in fragmented landscapes is influenced by the spatial configuration of habitat patches. This thesis aimed to assess population persistence and dispersal of the pearl-bordered fritillary, Boloria euphrosyne, a threatened butterfly in the UK. While the drivers of population decline in B. euphrosyne are likely multifactorial, site connectivity, climate and nitrogen deposition were shown to be important regulators of abundance and extinction risk. Notably, analysis of population abundance at sites across England suggested that the impacts of nitrogen deposition and elevated rainfall may be dependent on habitat type, with wooded sites likely to be most vulnerable. Population synchrony was used to investigate the implications of site connectivity on extinction risk and is suggested to be an effective indicator of functional connectivity between local populations. Population size, structure and mobility was also assessed directly, by mark-release-recapture, in the Morecambe Bay region, in north-west England. In addition, morphology was trialled as a proxy for mobility. Wing aspect ratio and wing loading were shown to be significantly related to the distance moved in individuals that were recaptured only once. Wing aspect ratio was positively correlated with the number of times an individual was recaptured, this may indicate sampling bias, but also suggests intraspecific variation in flight capacity. Comparisons between historical specimens and butterflies from current populations highlighted morphological changes including declines in thorax size and wing loading. Current populations in Morecambe Bay have become increasingly isolated and these morphological changes suggest altered flight capacity as a possible response. Overall, this thesis demonstrates that site isolation has consequences for population persistence and dispersal, including potential effects on extinction risk and flight capacity.