Effect of habitat diversity on flower-visiting insects varies across season and spatial scale in a highly fragmented landscape
Landscape fragmentation involves a reduction in the overall amount of original habitat and in the connectivity of the remaining habitats. Consequently, it results in a reduction of the availability of the resources that species need to survive and reproduce. The variety and the extent of resources in an environment is particularly relevant for flower-visiting insects. The purpose of this study was to examine the diversity of multiple groups of flower-visiting insects in highly fragmented agricultural landscapes. We worked on two groups of dipterans (tachinid flies and hoverflies) and three groups of hymenopterans (ichneumonid, spheciform and cuckoo wasps). These groups have been largely overlooked in ecological research. The study was conducted in a highly fragmented landscape dominated by intensively farmed crop fields, with several remnant patches of semi-natural forests and grasslands interspersed into the agricultural land. We selected 18 patches with statistically uncorrelated gradients in (i) habitat area and (ii) habitat diversity. The effects of the explanatory variables were analyzed at three spatial scales (landscape, patch and micro-scale) separately by season (spring, summer and fall). We identify habitat diversity, instead of other variables as habitat area or connectivity, as the main driver of flower-visiting species richness and abundance. The intensity and direction of habitat diversity on flower-visiting insects changes over scales and seasons.