Do threatened beetle larvae compete with other beetles sharing the same hollow trees?

Details

Researchers investigated interactions between larvae of Osmoderma eremita (Scopoli, 1763), described as one of the most charismatic and threatened saproxylic beetles, and other flower chafer species (Coleoptera: Scarabaeidae). In an observational field sampling study during August 2010, they sampled wood mould—the loose material inside tree cavities—from 151 living hollow trees in two Mediterranean woodlands.

Multi-species occupancy models estimated low occupancy probabilities for both O. eremita (ψ ± SE = 0.36 ± 0.13) and other flower chafer species (0.42 ± 0.06). The groups showed similar microhabitat requirements without competing.

In cavities containing larvae of both groups, the probability of detecting O. eremita by sieving 2 l of wood mould was not affected by whether other flower chafer larvae occurred in that same sample; the reverse was also true. Unexpectedly, however, O. eremita larvae were more likely to be detected when other flower chafer larvae occurred in the cavity.

Model selection statistics strongly supported an increase in the probability of detecting larvae as the sampled volume of wood mould increased, especially for O. eremita.

Wood mould sampling proved reliable for detecting the presence of O. eremita larvae. However, further studies are needed to investigate the potential damage this procedure may cause to the fragile microhabitat of tree cavities.

To preserve populations of O. eremita and other flower chafers, the authors recommend management focused on increasing the density of hollow trees and the volume of tree cavities, by favouring natural tree ageing and creating artificial habitats in living trees.