ORIGINAL ARTICLE Farming with native bees (Apis mellifera subsp. capensis Esch.) has varied effects on nectar-feeding bird communities in South African fynbos vegetation Sjirk Geerts • Anton Pauw Received: 9 March 2010 / Accepted: 29 August 2010 / Published online: 17 September 2010 Ó The Society of Population Ecology and Springer 2010 Abstract Outside their natural range, honeybees (Apis mellifera) are known to have detrimental effects on indig- enous pollinators through exploitative or interference competition, but little is known about the effect of honeybee farming in areas where honeybees occur naturally. In the Cape Floristic Region of South Africa, where honeybees are indigenous, managed hives potentially elevate the abun- dance of honeybees far above natural levels, but impacts on other floral resource-dependent species have not been studied. Here we use experimental manipulation of honey- bee density to test whether honeybee farming affects nectar-feeding birds. We selected the common sugarbush (Protea repens), utilized by both birds and bees, and ana- lysed the time (before/after) by treatment (control/experi- ment) interaction to explore changes in bee abundance, nectar availability and bird abundance at three sites. Hive addition increased honeybee abundance in inflorescences of P. repens above expected levels. Despite experimental increase in honeybee numbers, there is no reduction in nectar sugar availability relative to the control areas. Where honeybee density was highest, sugarbird (Promerops cafer) numbers declined relative to expected, but sunbirds (Nec- tarinidae) were not affected at any of the sites. We conclude that stocking rates of more than one honey bee per P. repens inflorescence have detrimental effects on bird abundance due to interference, rather than resource competition. Keywords Biodiversity conservation Á Competition Á Ecosystem services Á Pollination Á Sugarbirds Á Sunbirds Introduction Honeybees (Apis mellifera) are invasive aliens in many parts of the world, where they disrupt native pollination mutualisms and have a negative impact on native pollinators (reviewed in Huryn 1997; Goulson 2003; Paini 2004; Traveset and Richardson 2006). Honeybees are extreme generalist floral visitors, and their impact is felt throughout the pollination network. Many studies, however, have focused on impacts on nectar-feeding birds (Paton 1993). Outside their natural range, honeybees decrease flower visitation in native nectar-feeding birds through exploitative competition by reducing nectar availability, or more directly through interference competi- tion (McDade and Kinsman 1980; Paton 1993; Gross and Mackay 1998; Hansen et al. 2002; Mallick and Driessen 2009). In contrast to the wealth of knowledge about the impacts of honeybees in areas where they are alien, little is known about the potential effect of honeybee farming on pollinators (and bird pollinators in particular) where honeybees are native (but see Brand 2009). Although nectar- feeding birds and honey bees has co-existed for a long time in the native range, the potential for impacts exists because honeybee farming elevates the traditionally low abundance of honeybees far above natural levels by supplying additional nest sites. This artificially elevated abundance is expected to negatively effect the traditional interactions with other floral visitors through exploitative (decreasing the shared resource, nectar) or interference competition. The Cape honeybee, Apis mellifera subsp. capensis Eschscholtz, is endemic to the Cape Floristic region. In this region, its abundance might historically have been limited Electronic supplementary material The online version of this article (doi:10.1007/s10144-010-0245-2) contains supplementary material, which is available to authorized users. S. Geerts (&) Á A. Pauw Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa e-mail: sjirk@sun.ac.za 123 Popul Ecol (2011) 53:333–339 DOI 10.1007/s10144-010-0245-2