Don't eat where you sleep: unexpected diversity of food web for beetles feeding on mosses

Abstract

Abstract Bryophytes represent favourable habitats for many arthropods, but their utilisation as a food source is marginal. While one of the largest monophyletic groups that represent obligatory bryophyte consumers are the Byrrhidae, host ranges for species in this group of beetles remain largely unknown due to their cryptic appearance and rarity. The occasional notes of ‘associated’ moss species that do exist are related to where Byrrhidae were found and not to diet analysis. Because the majority of Byrrhidae are stenobionts with limited dispersal, the assumption that associated moss species are also used as food is a useful hypothesis. To test this hypothesis, 328 individuals were sampled from the species: Cytilus sericeus, Byrrhus fasciatus, Byrrhus pilula, and Byrrhus glabratus. Mosses from both the stomachs and the immediate microhabitats of beetles were determined with the aim of (i) identifying their host range and (ii) testing whether the moss species from microhabitats in which beetles were collected were also found in their stomachs. Almost 40 bryophyte species were found in beetle stomachs and accumulation curves for all beetle species failed to achieve asymptotes, together showing that all species are highly polyphagous. Although a strong general correlation existed between moss consumption and occupation, discrepancies were present at the individual level with there being considerably higher moss species richness in beetle stomachs than in their immediate microhabitats. Our results question the assumption that bryophyte occupancy and consumption can be used interchangeably when studying host use in these insects.