Effectiveness of Existing Reserves in the Long‐Term Protection of a Regionally Rare Butterfly

Abstract

Abstract: The importance of unprotected habitats for the persistence of species in reserve networks is likely to be high for species living in highly fragmented habitat in which regional persistence depends on metapopulation processes. The dingy skipper butterfly (Erynnis tages) is a regionally rare declining species in Britain. In the Creuddyn Peninsula (North Wales), it inhabits patches of its host plant, Lotus corniculatus L., growing in lightly grazed areas in sheltered microhabitats, and its regional distribution is dominated by metapopulation processes. In this area, 16 (61%) out of 26.20 ha of dingy skipper habitat are located in reserves. The remaining unprotected habitat is mostly located in wasteland areas vulnerable to urban development. Using a metapopulation model, the incidence function model, I evaluated the extent to which the persistence of the dingy skipper in the landscape could be guaranteed with the existing reserve network. According to model projections, the dynamics within the reserve system were relatively stable when the unprotected habitat remained, with a maximum of 4% simulation replicates going extinct in a 100‐year time frame. When unprotected habitat was completely removed, however, the dynamics in the reserve network became markedly unstable, with an increased extinction risk ranging from 15 to 36%. We calculated a relatively simple measure of “patch importance,” the colonization potential, for each patch. The incidence function model predicted that for low and medium levels of regional stochasticity (σ value from 0 to 0.2), protecting only a relatively small number (four to six) of large and well‐connected patches (high colonization potential) in addition to the existing reserves would be enough to decrease notably the extinction risk of the dingy skipper metapopulation. The number of patches needed to be increased (11 patches) for high levels of regional stochasticity (σ= 0.3). My results suggest that long‐term persistence of a regionally rare butterfly in a reserve network may depend on the presence of unprotected habitat. For a more realistic estimate of the efficiency of reserves for protecting rare species, conservation biologists should consider incorporating metapopulation dynamics in their evaluations of persistence in existing reserves.