Diet breadth, coexistence and rarity in bumblebees

Abstract

Factors that determine the relative abundance of bumblebee species remain poorly understood, rendering management of rare and declining species difficult. Studies of bumblebee communities in the Americas suggest that there are strong competitive interactions between species with similar length tongues, and that this competition determines the relative abundance of species. In contrast, in Europe it is common to observe several short-tongued species coexisting with little or no evidence for competition shaping community structure. In this study we examine patterns of abundance and distribution in one of the most diverse bumblebee communities in Europe, found in the mountains of southern Poland. We quantify forage use when collecting nectar and pollen for 23 bumblebee species, and examine patterns of co-occurrence and niche overlap to determine whether there is evidence for inter-specific competition. We also test whether rarity can be explained by diet breadth. Up to 16 species were found coexisting within single sites, with species richness peaking in mountain pasture at ~1000m altitude.Results concur with previous studies indicating that the majority of pollen collected by bumblebees is from Fabaceae, but that some bee species (e.g. B. ruderatus) are much more heavily dependent on Fabaceae than others (e.g. B. lucorum). Those species that forage primarily on Fabaceae tended to have long tongues. In common with studies in the UK, diet breadth was correlated with abundance: rarer species tended to visit fewer flower species, after correcting for differences in sample size. No evidence was found for similarity in tongue length or dietary overlap influencing the likelihood of co-occurrence of species. However, the most abundant species (which co-occurred at most sites) occupied distinct dietary niche space. While species with tongues of similar length tended, overall, to have higher dietary niche overlap, among the group of abundant short-tongued species that commonly co-occurred there was marked dietary differentiation which may explain their coexistence.

Plant diversity and composition compensate for negative effects of urbanization on foraging bumble bees

“…The strong preference of bumble bees for Fabaceae also agrees with results from previous studies (Goulson and Darvill 2004;Goulson et al 2005Goulson et al , 2008aConnop et al 2010;Redpath et al 2010). Fabaceae seem thus to be highly important for bumble bees, especially for longer-tongued species, such as B. hortorum (19 visits to Fabaceae in this study, 47.5 %), B. lapidarius (68 visits, 52.3 %), and B. pascuorum (76 visits, 32.2 %).…”

“…Note that all bumble bees observed in our study belong to species commonly found in and outside of cities (Goulson et al 2005(Goulson et al , 2008a; Banaszak-Cibicka and Żmihorski 2012), while typically rare species, such as B. sylvarum L. or B. humilis Illiger, were not observed in our study. Consequently, there are most likely Bwinners and losersô f urbanization (Banaszak-Cibicka and Żmihorski 2012).…”

“…Especially the Kurpark and Pferdeteich were further surrounded by additional gardens (see Table SI), which are known to attract and support insects (Samnegård et al 2011). Another reason for the high abundance of bumble bees at these sites could be the comparatively high abundance of Fabaceae and Lamiaceae (see Tables SI and SII), which are known to be preferentially visited by bumble bees (Goulson et al 2008a;Sikora and Kelm 2012). We also found high numbers of bumble bees on study plots in the city center of Lüneburg, e.g., 15 B. terrestris and 12 B. pascuorum in the Rathaus garden (with 65 % of concrete in the surrounding) at 1 day in August, demonstrating that bumble bees are able to forage even at very isolated patches in the city center, Figure 3.…”

The most effective pollinator revisited: pollen dynamics in a spring-flowering herb

“…), Bombus lapidarius (L.), B. ruderarius (Müller), B. terrestris (L.)]. Bombus species recorded during the experiment represented two tongue-length classes (shorttongued B. terrestris and B. lapidarius and medium-tongued B. ruderarius; Goulson et al 2008b), and we, however, observed no significant differences in performance among these species and therefore in subsequent analyses treat them together as one functional group. Bumblebees made over 81 % of the visits, Andrena made 13 % and A. plumipes 6 % (the latter, for simplicity, hereafter referred to as Anthophora).…”

Revealing the hidden niches of cryptic bumblebees in Great Britain: Implications for conservation

“…Consequently, the only reliable information we have on the ecology of these three species comes from Murray et al (2008) and Stanley et al (2013) who used molecular methods to study the lucorum complex in Ireland and Waters et al (2010) who studied them in the Western Isles of Scotland. Niche-partitioning might be expected between these species (Goulson et al, 2008b) and indeed some ecological differences have been suggested. Specifically, Waters et al (2010) found that B. magnus appeared to be strongly associated with the heathland forage plant Calluna vulgaris.…”