Contrasting responses of bee communities to coffee flowering at different spatial scales.
Veddeler, Dorthe*,1, Klein, Alexandra-Maria1, Tscharntke, Teja1, 1 University of Goettingen, Goettingen, Lower Saxony, Germany
ABSTRACT- An understanding of the factors driving communities of flower-visiting bees is important, since bees as pollen vectors greatly contribute to ecosystem functioning. Floral resource availability is known to influence bees′ foraging behaviour, but little is known how it affects bee communities on different spatial scales. We studied density and species richness of flower-visiting bees in relation to floral resource availability, provided by coffee, in 22 traditional agroforestry systems on a field, a shrub, and a branch scale, and evaluated additional factors by which bee communities were influenced. On a field scale, mean bee density per shrub increased with decreasing proportion of flowering coffee shrubs per site, showing a dilution effect. Conversely, on a shrub and branch scales bee density per shrub, or shrub part, increased with increasing number of inflorescences, showing a concentration effect. Additionally, bee density per shrub was higher on those that were only partly, rather than totally surrounded by other flowering coffee shrubs. Species richness of flower-visiting bees was positively affected by high resource availability on a shrub and a branch scale, expressed by a high number of inflorescences, but was not related to the proportion of flowering shrubs regarding the field scale. Furthermore species richness was positively related to a high diversity of shade trees on a field scale, while on a shrub scale more species preferred sunny and half-shaded coffee shrubs to shaded ones. Our results show contrasting responses of the community of flower-visiting bees to floral resource availability, depending on the spatial scale considered. We conclude that patterns of flower-visiting bee communities of only one spatial scale can not be generalized, since the number of pollinators may be limited on a field scale, but not on smaller scales. From an applied perspective flower visitation by a diverse and abundant bee community should be enhanced by a diverse and gappy canopy, preventing full shade, and successively rather than synchronously flowering coffee shrubs enabling concentration rather than dilution effects of the bees′ flower visitation.
Key words: bee communities,
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