Species richness of cuckoo bumblebees is determined by the geographical range area of the host bumblebee

Abstract

The geographical range area of host hypothesis predicts that regionally widespread host species are able to support higher local parasite species richness. In this study, we investigated the macro‐ecological patterns in cuckoo bumblebee species richness in relation to the geographical range area of their bumblebee hosts (Hymenoptera: Apidae: Bombini). The cuckoo bumblebees live in naturally fragmented environments composed of host bumblebee colonies upon which they are exclusively dependent. We collected data on all 11 known cuckoo bumblebee species that are classified as parasites (obligate workerless social parasites) – and all 69 known bumblebee species in Europe. Whereas some bumblebee hosts harbour several cuckoo bumblebee species, most are cuckoo free (78%). Bumblebees with a large geographical range area hosted more cuckoo bumblebee species than host species with a narrow range area. The geographical range area of cuckoo bumblebee species increased with increasing combined range area of all hosts, but it was smaller than combined range area of all hosts. We found support for the hypothesis that the geographical range area of the host bumblebee species has an effect on the species richness of cuckoo bumblebees. If the range area of the host bumblebee species decreases, cuckoo bumblebees may become vulnerable to extinction.

Differential effects of farming practice on cuckoo bumblebee communities in relation to their hosts

“…Obligate brood parasites such as cuckoo bumblebees, are entirely dependent on their hosts for reproduction, thus the host can be considered a resource (Steffan-Dewenter and Schiele, 2008;Suhonen et al, 2016). Therefore, elements of their community structure are likely to be driven by those of their host (Murray et al, 2009;Suhonen et al, 2015;Suhonen et al, 2016). Therefore, we also predicted that cuckoo bumblebee community metrics would be driven by the community metrics of their hosts.…”

“…As such, further research is needed to fully understand their ecology (Lhomme and Hines, 2018) and evidence suggests that they are even more at risk of extinction than their hosts (Suhonen et al, 2015). Whilst the ecology and community metrics of hosts will affect cuckoo community metrics due to their reproductive dependency on their host (Suhonen et al, 2016), the results suggest that perhaps cuckoos can respond differently from their hosts to environmental factors, such as farming practice. Differential effects of farming practices have previously been found among groups within the bee superfamily, for example among honeybees, bumblebees and solitary bees (Le Féon et al, 2010;Holzschuh et al, 2008) and are even found within the Bombus genus (Rundlöf et al, 2008).…”

“…Despite a lower abundance of hosts on conventional farms, cuckoo bumblebees were equally as abundant on organic farms as they were on conventional farms. This was not expected, since for obligate parasites such as cuckoo bumblebees, the host can be considered a resource (Suhonen et al, 2016), hence elements of their community structure are likely driven by those of their host (Murray et al, 2009;Suhonen et al, 2015;Suhonen et al, 2016).…”

“…Firstly, we predicted that species richness, diversity, and abundance of hosts, and cuckoos, will be higher on organic farms than on conventional farms. Obligate brood parasites such as cuckoo bumblebees, are entirely dependent on their hosts for reproduction, thus the host can be considered a resource (Steffan-Dewenter and Schiele, 2008;Suhonen et al, 2016). Therefore, elements of their community structure are likely to be driven by those of their host (Murray et al, 2009;Suhonen et al, 2015;Suhonen et al, 2016).…”

Brood parasitism in eusocial insects (Hymenoptera): role of host geographical range size and phylogeny

“…According to the resource distribution hypothesis [10,11], widespread species are able to support a higher parasite diversity than are species with more restricted geographical ranges. Large GRS and large population size of host species have often been shown to correlate with high parasite prevalence and diversity [12 -16], so that rare hosts tend to have fewer [8] or no [15] parasite species. However, it is poorly known how GRS and phylogenetic relationships among actual and potential host species affect the probability of host switching by parasites [9].…”