Change of species set and abundance along a short time gradient: The impact of weather conditions on the conservation of butterflies.

Abstract

In a species-poor region of a low-mountain area of Nordrhein-Westfalen (Germany) a butterfly monitoring scheme that was started in 1989-1991 and repeated in 1997 revealed changes in the species set and the frequency (abundance) of several species. In line with previous studies the impact of weather conditions on butterfly occurrence and frequency is discussed. As regards the nine-year period from 1987-1995 weather conditions in the study area have become more favourable since 1989. An increase in the average monthly temperatures and the monthly amount of sunshine and a decrease in monthly rainfall was mainly recorded between 1989 and 1992. The increase was observed during the main flight period (April to September) as well as between October and March (possibly relevant for juvenile stages of several species). Several xerothermophilous species never before recorded in the study area were found to have immigrated. Other species which had vanished during the last thirty years have notably recovered, although landscape structure and habitat conditions have remained basically unchanged. - The importance of favourable weather conditions for the immigration and recovery of rare or endangered species is discussed and compared to the effects of conservation management.

Keywords

Butterfly monitoring, species set, impact of weather conditions, Germany, nature conservation.