The Abundance and Pollen Foraging Behaviour of Bumble Bees in Relation to Population Size of Whortleberry (Vaccinium uliginosum)

Abstract

Habitat fragmentation can have severe effects on plant pollinator interactions, for example changing the foraging behaviour of pollinators. To date, the impact of plant population size on pollen collection by pollinators has not yet been investigated. From 2008 to 2010, we monitored nine bumble bee species (Bombus campestris, Bombus hortorum s.l., Bombus hypnorum, Bombus lapidarius, Bombus pascuorum, Bombus pratorum, Bombus soroensis, Bombus terrestris s.l., Bombus vestalis s.l.) on Vaccinium uliginosum (Ericaceae) in up to nine populations in Belgium ranging in size from 80 m2 to over 3.1 ha. Bumble bee abundance declined with decreasing plant population size, and especially the proportion of individuals of large bumble bee species diminished in smaller populations. The most remarkable and novel observation was that bumble bees seemed to switch foraging behaviour according to population size: while they collected both pollen and nectar in large populations, they largely neglected pollen collection in small populations. This pattern was due to large bumble bee species, which seem thus to be more likely to suffer from pollen shortages in smaller habitat fragments. Comparing pollen loads of bumble bees we found that fidelity to V. uliginosum pollen did not depend on plant population size but rather on the extent shrub cover and/or openness of the site. Bumble bees collected pollen only from three plant species (V. uliginosum, Sorbus aucuparia and Cytisus scoparius). We also did not discover any pollination limitation of V. uliginosum in small populations. We conclude that habitat fragmentation might not immediately threaten the pollination of V. uliginosum, nevertheless, it provides important nectar and pollen resources for bumble bees and declining populations of this plant could have negative effects for its pollinators. The finding that large bumble bee species abandon pollen collection when plant populations become small is of interest when considering plant and bumble bee conservation.

Early spring floral foraging resources for pollinators in wet heathlands in Belgium

“…Unlike other Salix species (Füssel 2007 mart 1993;MacKenzie and Eickwort 1996;Javorek et al 2002;Mayer et al 2012) bumblebees were the main visitors of V. myrtillus. Andrena species were also caught on V. myrtillus flowers.…”

“…Because of their economic importance, much of the research on habitat use by pollinators has been carried out in agricultural ecosystems (Osborne et al 1999;Persson and Smith 2013); nevertheless, work has also been carried out in semi-natural and natural ecosystems (Lack 1982;Petanidou and Ellis 1993;Carvell 2002;Potts et al 2003). Among semi-natural ecosystems, less attention has been paid to heathland ecosystems (but see Descamps et al 2015;Forup et al 2007;Kaiser-Bunbury et al 2009;Mayer et al 2012).…”

Variability of bumblebee communities (Apidae, Bombini) in urban green areas

“…It was confirmed that populations which cannot freely move between habitats are forced to inbreed, and this leads to a decrease in the condition of the whole population (Krebs 2009). Habitat fragmentation may cause a situation where too small sites with food plants will not be attractive for some bumblebee species (Mayer et al 2012).…”

Climatic Risk and Distribution Atlas of European Bumblebees

“…Several hypotheses have been proposed to explain this global decline such as (i) habitat fragmentation (Williams, 1982;Williams & Osborne, 2009;Darvill et al, 2010;Mayer et al, 2012;Hatten et al, 2013), (ii) shortage of flower resources (Peters, 1972;Williams, 1989;Rasmont & Mersch, 1988;Rasmont et al, 1993Goulson et al, 2005Goulson et al, , 2008a, (iii) killing by car traffic (Donath, 1986), (iv) overgrazing of bumblebee habitat by cattle (Özbek, 1995;Xie et al, 2008), (vi) parasites and pathogens resulting from spillover from domesticated species Arbetman et al, 2013), (vii) urbanization (Ahrné et al, 2009;Martins et al, 2013), or (viii) vegetation displacement due to nitrogen deposition (Rasmont, 2008). Pesticides have most likely also played a role because of their extreme toxicity for some bumblebee species (e.g.…”