Libellen op Noord-Brabantse vennen; een aanzet tot een synecologische analyse van het databestand libellenwaarnemingen

Shallow soft-water lakes are one of the most Odonata rich habitats in the Netherlands. Different types of shallow soft-water lake ecosystems are distinguished. To test whether the Odonata species composition of those waters reflect this classification, a comparison was made of observations of adults at 13 shallow soft-water lakes in the province of Noord-Brabant, which is situated on sandy soils in the southern part of the Netherlands. Information about the species composition was gathered using the database of Odonata observations of the Netherlands, considering the period 1990- 2003, the months may-august. TWINSPAN was used to analyse the species composition data. Because observations from the database are used, there is a lot of uncertainty regarding investigated area, search time, number of individuals. Therefore, only present/absent data were used. Despite this drastic transformation, the analysis shows that the species composition of shallow soft-water lakes fed by rain water differs from lakes which are fed by both rain water and buffered ground water. The lakes fed by buffered ground water were characterised by Aeshna grandis, Aeshna mixta, Aeshna cyanea, Erythromma najas, Brachytron pratense and Cordulia aenea. The lakes fed by rainwater were characterised by Lestes dryas and Libellula depressa.