Conservation biology of the marsh fritillary butterfly Euphydryas aurinia

Abstract

The conservation biology of Euphydryas aurinia was investigated, analysing its metapopulation dynamics, interactions with parasitoids and the efficacy of habitat restoration. Euphydryas aurinia has undergone a widespread national decline in recent years. This decline is quantified at a 10km scale. The distribution in 2020 was predicted for E. aurinia from the 1995-99 distribution, assuming that the current causes and pattern of decline continued. The predicted distribution in 2020 represented a 48% loss in 10km grid square records, with only the core regions surviving. The distribution and persistence of the butterfly was quantified at a regional scale in one, intensively studied area (25km by 25km) in Dorset (England, UK). The metapopulation approach was useful in understanding the occupancy pattern and persistence of E. aurinia within this landscape. The probability of patch occupancy increased with patch connectivity (isolated patches were less likely to be occupied), vegetation height and resource area (patch area multiplied by host plant cover). Such a pattern was consistent with the interpretation that the butterfly persists as a metapopulation. This supported the use of the Incidence Function Model, as a tool to explore the possible fate of E. aurinia in fragmented landscapes in Dorset and in five pairs of independent networks across the species' range in England and Wales. The threshold network area was predicted to be 7 iha, to achieve a 95% probability of persistence for 100 years, for a network within a 4km by 4km area. However, this figure may actually be an underestimate of the area required, if extinction debt is a reality. Parasitoid attack, principally by Cotesia bignellii, appears to have an effect on the population dynamics of E. aurinia and may help to explain the requirement of E. aurinia for large habitat patches. This preliminary work suggests that the parasitoid also has a metapopulation structure and that it is of equal conservation concern. At a local scale the results suggest that the parasitoid and host may have a shifling disiribution, with the butterfly 'escaping' parasitism in some areas. Habitat restoration and re-creation will be necessary in many networks with insufficient habitat area. Experimental investigation into methods of habitat restoration showed that unsuitable but potential habitat may be restored through cutting twice a year in combination with grazing. Habitat re-creation has been shown to be feasible for agriculturally improved sites, but may be more difficult to achieve due to the higher nutrient status and the competitive interaction of other species with the host plant Succisa pratensis