Revisiting urban refuges: changes of butterfly and burnet fauna in Prague reserves over three decades

摘要

We studied changes in the composition of butterfly and burnet fauna in 25 reserves of xeric grasslands within the city Prague, Czech Republic, based on a recent repetition of a survey conducted three decades ago. The past and recent survey detected 91 and 84 species, 12 species were lost and four were gained between the surveys. There was no significant change in mean numbers of species per reserve or in mean species incidences, even if the categories of the habitat association, mobility and body size were analysed separately. Contrary to these comparisons, ordination analyses indicated a significant shift in species composition in individual reserves. Species of short-sward xeric grasslands tended to be associated with the past survey, whereas species of taller grasslands and xeric scrub were associated with recent survey. These shifts were more prominent in large reserves with high proportion of natural (as opposed to urban) perimeter, connected with other reserves, having diverse topography and high plant and biotope richness. We interpret this by gradual successional changes which affect the reserves despite conservation management. Despite these changes, butterfly losses were lower than in comparable surveys recently conducted elsewhere in Central Europe, partly because major losses occurred long before the 1980s survey and partly owing to a high heterogeneity of the urban landscape surrounding the reserves.