Flower abundance and vegetation height as predictors for nectar-feeding insect occurrence in Swedish semi-natural grasslands

Abstract

With steadily shrinking areas of species-rich semi-natural grasslands in Europe, the management of the remaining fragments becomes ever more crucial for the preservation of key elements of biodiversity in the agricultural landscape. Detailed knowledge about species-wise, as well as group-wise, relationships can provide guidelines for conservation management and a basis for predictions about different management scenarios. In the present study, we related the occurrence of species of bumblebees (N=12), butterflies (31) and day-flying moths (4) and their total richness in 424 sites in southern Sweden to three grass sward attributes, (i) flower abundance, (ii) height of the grass sward and (iii) within-site variation in height of vegetation. The abundance of nectar-bearing flowers proved overall the best predictor of richness and in most of the occurrence-based species-wise models. However, both high grass sward height and high variation in grass sward height contributed significantly to species richness and occurrence of individual species. There was a tendency for bumblebees to respond less positively to flower abundance and vegetation height than butterflies and moths. One expectation was that grassland specialists, red-listed species, or species decreasing in other part of Europe, would be more responsive to tall vegetation or flower abundance but there was no support for this in the data. Hence, management strategies that promote common species will also benefit all, or most of, the rare ones as well.