Räumlich-zeitliche Auswirkungen der Landnuzung auf die Diversität von Bienen und Wespen.

Abstract

Anthropogenic land use changes may have major consequences for global biodiversity and the functioning and stability of ecosystem processes. However, species diversity is determined by a suite of factors that may affect species differently across habitats and at different spatial and temporal scales. We used standardised nesting resources for reproducing communities of cavity-nesting bees and wasps (Hymenoptera: Aculeata), within 48 plots of five habitat types in coastal Ecuador. These habitats comprised a gradient of decreasing agricultural intensity from rice and pasture to coffee agroforests, unmanaged abandoned agroforests and forest.1) High soil heterogeneity led to a domino effect of increased diversity across three trophic levels (herbaceous plants, cavity-nesting bees and wasps, and their natural enemies) in three different habitat types. 2) Land use affected diversity of cavity-nesting Hymenoptera differently at different spatiotemporal scales, with the strongest effects being at the lowest (alpha diversity) scale of subplot diversity per month. 3) Overall, spatial and temporal turnover (beta diversity) explained 38.6% and 23.1%, respectively, of partitioned regional species richness. Beta diversity between plots and especially through time, was significantly higher in the more natural habitats abandoned coffee and forest. 4) Parasitism rates increased with increasing diversity of natural enemies and their hosts, exceeding the effects of increased enemy abundance alone. Temporal variability in parasitism was lower in plots with high mean natural enemy diversity and higher in plots with temporally variable host and natural enemy diversity. 5) The slope of the natural enemy diversity/parasitism rate function increased in systems with more heterogeneous host distributions, indicating that niche complementarity is more likely to lead to a positive diversity/function effect in heterogeneous habitats.Biodiversity of a variety of taxa may be enhanced in managed systems by maintaining high habitat heterogeneity. However, the effects of land use on species richness may be highly dependent on spatial and temporal scale, and we emphasise caution in the interpretation of studies conducted at only one scale. Conservation strategies need to take a landscape scale approach, in order to maximise beta diversity (species turnover) within and between fields, and between habitat types. Maintaining high diversity may also have great benefits for biological pest control, through higher rates of parasitism, and stability of parasitism rates through time.