The Competition Box: A Graphical Aid to Forecasting Pollinator Performance

Increased density of honeybee colonies affects foraging bumblebees

“…Interspecific competition is assumed to be a major factor in structuring foraging communities on flowers (Schaffer et al, 1979;Pleasants, 1981;Zimmermann and Pleasants, 1982;Schoener, 1987;Westrich, 1989;Corbet et al, 1995). However, the mechanisms underlying these interactions are difficult to test in the field.…”

“…Many studies on resource overlap and possible competition with native wild bees have been carried out in regions where honeybees had been introduced (Buchmann, 1996;Buchmann and Nabhan, 1996;Sudgen et al, 1996;Butz Huryn, 1997). Though honeybees are native to Europe, extraordinarily Corresponding author: K. Walther-Hellwig, walther-hellwig@web.de * Manuscript editor: Jacqueline Pierre high local densities may adversely impact species richness and abundance of wild bees (Westrich, 1989;Evertz, 1995;Corbet et al, 1995;Steffan-Dewenter and Tscharntke, 2000;Steffan-Dewenter and Kuhn, 2003).…”

“…Some mechanisms for avoiding intra-genus competition have been described for coexisting bumblebee species (abundant vs. rare, shorter-tongued vs. longer-tongued; Inouye, 1978;Hanski, 1982;Thomson et al, 1987;Prys-Jones and Corbet, 1991;Inoue and Kato, 1992;Goulson, 2003). Thus, evidence suggests that increased honeybee density differently affects various bumblebee species (Pleasants, 1981;Corbet et al, 1995). To obtain a deeper insight into the underlying mechanisms, investigations must be carried out that explicitly take into account species-specific differences in proboscis length and in foraging strategies.…”

“…If increased honeybee densities could be achieved by increasing the number of colonies, we assumed we would observe a "temporal avoidance strategy" (i.e. bumblebees forage earlier in the morning or later in the evening, Corbet et al, 1993Corbet et al, , 1995Williams and Christian, 1991). We further assumed that spatial displacement from the mass resource Phacelia tanacetifolia due to exploitative competition should mainly affect short-tongued and abundant species of the B. terrestris-group that have a foraging strategy similar to that of honeybees.…”

“…We further assumed that spatial displacement from the mass resource Phacelia tanacetifolia due to exploitative competition should mainly affect short-tongued and abundant species of the B. terrestris-group that have a foraging strategy similar to that of honeybees. Shorttongued honeybees may have an advantage over long-tongued bumblebees when nectar depletion exceeds nectar secretion (Corbet et al, 1995). Second, we tested whether honeybees exploited small patches of wild flowers when a mass resource like Phacelia tanacetifolia is available since honeybees are assumed to concentrate on the most profitable resources (Seeley, 1995;Beekmann and Ratnieks, 2000).…”