Influence of landscape structure and land use on Merodon and Cheilosia (Diptera: Syrphidae): contrasting responses of two genera

Recent advances in landscape ecology have revealed the importance of landscape structure on insect species diversity and composition. We investigated how landscape structure and land use influence species compositions of Cheilosia and Merodon (Diptera: Syrphidae); two phytophagus genera of hoverflies. Our study shows that Shannon’s Diversity Index, Connectance Index, Grazing Intensity, Mean Fractal Dimension Index and Percentage of Agricultural Patches explained 38.6% of the variance in species composition at a 2 km scale, with the total ordination being significant (P = 0.04, Monte Carlo test, 499 permutations). Merodon and Cheilosia species differ in their responses to land-use change and connectivity, with the latter genus being positively correlated with connectivity and negatively correlated with all other variables. We conclude that connectivity is the primary factor affecting Cheilosia, while most Merodon species demonstrated greater resistance to changes in human-modified ecosystems. Our results suggest that different management efforts, focused on land-use intensity (grazing) or connectivity, seem to be appropriate when trying to conserve these taxa.