role of weather-related habitat use on the impact of the European speckled wood Pararge aegeria on the endemic Pararge xiphia on the island of Madeira

Habitat use and microclimatic constraints on the activity of the endemic Madeiran speckled wood butterfly and European speckled wood were studied in September 1989 and April 1990. The endemic species is the most closely associated with laurel forest and the recently established European speckled wood with pine and eucalyptus forest. The relative abundances of the two species in different sites changes with season, with the endemic species being relatively more common in low level sites in April at the end of the cool season, than in September at the end of the warm summer period. It is suggested that changes of abundance in different locations are related to the thermal biology of the two species. The endemic speckled wood is active at lower air temperature than the European species, and the cool winter period may facilitate occupation of open sunny sites. The activity of the endemic speckled wood is less constrained by cool and dull conditions than is that of the European species, which requires higher temperatures for activity. It is proposed that the activity and behavioural repertoire of the endemic is most suited to climatic conditions in, and structural features of, laurel forest. The European species is most suited for activity in open woodland and agricultural habitats. Interactions between adults of the two species do not indicate direct competition. Changes in the distribution of the two species can be linked to probable changes of habitat on the island of Madeira.