Linking life history traits to pollinator loss in fragmented calcareous grasslands

Birgit Jauker,Frank Jauker,Ingolf Steffan-Dewenter,Jochen Krauss

doi:10.1007/s10980-012-9820-6

Birgit Jauker, Frank Jauker + Show 2 more

Open Access

https://doi.org/10.1007/s10980-012-9820-6

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Abstract

AbstractTo gain insight into the drivers of pollinator loss, a holistic approach to land-use change including habitat size, isolation, habitat quality and the surrounding landscape matrix is necessary. Moreover, species’ responses to land-use change may differ depending on their life history traits such as dispersal ability, trophic level, or sociality. We assessed species richness and life history traits of wild bees in 32 calcareous grasslands in central Germany that differ in size, connectivity, resource availability and landscape context. Declining habitat area and, to a lesser degree, reduced diversity of the surrounding landscape were the key factors negatively influencing species richness. In the community-wide analysis, small body size and solitary reproduction were traits that made species particularly vulnerable to habitat loss. Contrary to our expectations, cleptoparasitic species were not more affected by reduced habitat area and landscape diversity than nest-building species. We performed further detailed trait analyses within the family Halictidae to prevent possible confounding effects due to trait correlations across families. Here, social as opposed to solitary species were more affected by habitat loss. We conclude that the opposite pattern observed for all social bees was mainly caused by large-sized social bumblebee species with high mobility and large foraging distances. Our results demonstrate the risks of concealed trait interference when analyzing community-wide patterns of life history traits. As a consequence, conservation requirements of small social bee species might be overlooked by generalizations from community responses.

Highlights

Bees are the most important group of pollinators in many parts of the world (LaSalle and Gauld 1993) ensuring the pollination of wild plants (Burd 1994) and agricultural crops (Klein et al 2007)
A hierarchical partitioning model (Table 1) revealed that habitat area was the key factor in determining species richness of bees
When we analyzed the effects of surrounding landscape diversity on bee species richness at twelve different spatial scales, we found the most significant correlations at the smallest scale of radius 250 m (Fig. 2)

Summary

Introduction

Bees are the most important group of pollinators in many parts of the world (LaSalle and Gauld 1993) ensuring the pollination of wild plants (Burd 1994) and agricultural crops (Klein et al 2007). There is growing evidence for an ongoing decline of bee species richness in recent decades (Biesmeijer et al 2006) As this decline is mirrored by an increasing dependency of world crops on pollination services, the conservation of pollinators will become increasingly important in the near future (Aizen et al 2009). One of the most detrimental factors affecting pollinator communities is the overall loss of suitable habitat and the resulting fragmentation into smaller and more isolated habitat patches (Fahrig 2003; Winfree et al 2009) Populations in these small, isolated fragments suffer from increased extinction risks and decreased immigration rates compared to those in large, connected fragments (Hanski 1999; Kuussaari et al 2009) resulting in reduced species richness in small, isolated fragments (Hendrickx et al 2009; Bruckmann et al 2010). Main drivers of these species-area relationships are decreasing microhabitat diversity and lower resource availability (Rosenzweig 1995; Ricklefs and Lovette 1999)

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