Promoting diverse communities of wild bees and hoverflies requires a landscape approach to managing meadows

Abstract

There is ongoing concern regarding the observed decline in pollinator populations. Managing agricultural landscapes through agri-environment schemes (AES) supports biodiversity and could counteract pollinator population declines. We investigated whether alterations to current AES grassland mowing regimes would increase the abundance and species richness of wild bees and hoverflies. Furthermore, we investigated the response of different feeding and nesting guilds of wild bees and hoverflies, respectively, to these regimes. The three experimental mowing regimes were: (i) first cut not before 15 June, before the beginning of summer (Swiss AES management, control meadows); (ii) first cut delayed until 15 July (delayed meadows); (iii) as for control meadows but leaving 10-20% uncut as a refuge (refuge meadows). The rationale behind the delayed and refuge mowing regimes was extending the availability of floral resources for pollinators, while also providing refugia for species that may be directly impacted by mowing. Hoverflies and wild bees were collected in 2014 and 2015, respectively, using pan-trapping and sweep-netting, once before and once after the first cut. The two collecting methods showed contrasting results. While there was no difference in the abundance or richness of wild bees between the meadows when using pan traps, following the first cut, sweep-netting resulted in a higher abundance and richness of wild bees in delayed and refuge meadows compared to control meadows. Pan-trapping detected a higher abundance of hoverflies in delayed compared to refuge meadows, whereas sweep-netting detected a higher abundance in delayed and refuge compared to control meadows, after the first cut. Saprophagous hoverflies were more abundant in the control and delayed than refuge meadows following the first cut, when sampled with pan traps. Predatory hoverflies were more abundant and species rich in delayed and refuge compared to control meadows following the first cut, when sampled by sweep-netting. Our study demonstrates that simple alterations to a common AES grassland mowing regime can enhance populations 3 of pollinators and natural enemies of crop pests. Furthermore, the contrasting response of the life-history guilds indicates that promoting heterogeneous management practices within the landscape is important for supporting diverse communities, and maintaining key ecosystem services such as pollination and biocontrol.

Larval and phenological traits predict insect community response to mowing regime manipulations

“…Analyses separated between the methods and on the effects after the first cut can be found in Meyer et al. ().…”

“…and 2015, respectively. Both groups were collected using two complementary methods (Grundel et al 2011): colored pan traps and sweep netting (see Meyer et al 2017 for more details on the methodology). Briefly, in the center of each meadow, three sets of three pan traps (yellow, white, and blue) were attached to wooden poles and arranged in a triangular pattern.…”

“…For this analysis, the data of both trapping methods were pooled. Analyses separated between the methods and on the effects after the first cut can be found in Meyer et al (2017).…”

Influence of abandonment on syrphid assemblages in mountainous meadows

“…Later drop1 function takes the likelihood of full model. The presence of overdispersion was checked by adding observation level as a random factor in the model (Meyer, Unternährer, Arlettaz, Humbert, & Menz, ). We also analyzed the interaction between management and different explanatory variables.…”

Hoverfly Communities in Semi-Natural Grasslands, and their Role in Pollination

“…Pollinator populations can operate on a scale larger than the average English farm (145ha) (McKenzie et al 2013). Given that larger patches of habitat can support a higher species-richness of hoverflies compared to smaller areas (Ouin et al 2006;Ockinger et al 2012), a pattern that has been replicated in other arthropod groups (Debinski & Holt 2000;Rosch et al 2013;Slade et al 2013), a more strategic landscape approach to pollinator conservation may be more effective (Meyer et al 2017).…”