Resource availability, competitor abundance and specialization affect competition among bumblebees

The strength of interspecific and intraspecific competition depends on
resource availability, competitor abundance, and specialization. Most
studies are conducted with single species pairs, constraining our
understanding of what drives competition in multispecies communities. We
investigated the effect of floral density, competitor abundance, flowering
period, and trait specialization (proboscis length) on the potential for
interspecific and intraspecific competition between seven common bumblebee
species in the Hengduan Mountains of southwest China. We estimated the
potential for interspecific and intraspecific competition using resource
partitioning indices in plant-bumblebee networks (Müller’s index) over
five consecutive years, quantifying changes in floral densities and
bumblebee abundance throughout the season. The potential for interspecific
competition increased with bumblebee abundance, particularly when floral
density was low later in the season. On the other hand, the potential for
intraspecific competition increased with abundance of focal bumblebee
species and for specialized long-tongued bumblebees, especially when
floral density was low. This suggests that resource scarcity regulates
species coexistence by limiting abundant species dominance via
interspecific competition and intraspecific competition. Our results
indicate the importance of intraspecific competition and specialization in
maintaining diversity in multispecies communities.