Settling in or passing through: differentiating between wood‐boring beetle visitation and colonization after a dead wood pulse

Abstract

To determine the effect of resource pulses on animal communities, it is important to differentiate the species colonizing the resource substrate from the ones simply moving through the system. In a manipulative field study, we surveyed the response of wood‐boring beetles (Coleoptera) to the small debris produced by commercial thinning operations in white spruce plantations using two methods. First, we sampled the wood‐boring beetles visiting the plantations using flight intercept traps. Then, at the end of the resource pulse in fresh woody debris, we documented the abundance of beetle emergence holes on vertical and horizontal woody debris, which indicate wood‐boring beetle colonization. Results demonstrated that the small horizontal debris generated by commercial thinning were used by saproxylic beetles but were not a preferred resource for colonization, by contrast with vertical dead wood. Only small‐body beetles colonized the horizontal debris and most debris were not colonized. Vertical dead wood, even if present in relatively small quantity when compared to horizontal dead wood, was a major determinant of beetle colonization and community composition. Biomass removal was shown to have a strong detrimental impact on beetle colonization rates. Based on these results, we suggest that most of the saproxylic species trapped after commercial thinning operations were attracted in response to the initial pulse of resource but did not actually colonize the debris from thinning. Thus, we stress the importance of distinguishing between species visitation and colonization following a resource pulse when sampling relies on indirect trapping methods.

Size matters: When resource accessibility by ecosystem engineering elicits wood‐boring beetle demographic responses

“…Here, no general trends regarding the distance from the pond nor control sites have been identified (Figure 3), which highlights a more diffused effect of beaver activity compared with the actual colonization (see Gandiaga et al, 2018, for a discussion on visitation vs. colonization). The results of the present study together with our previous work in the same study system (Mourant et al, 2017) give a complementary view of the disturbance impacts at different time intervals, ranging from the initial pulse up to 44 years later.…”

“…Placing the traps between the trees rather than against the trunk of a given tree species allowed for the sampling of all saproxylic beetles and not only that of the beetles attracted to a given host species. While window traps baited with ethanol are more efficient to trap saproxylic beetles than unbaited traps in terms of abundance and richness (Bouget et al., 2009), previous work has shown that these traps are highly sensible to detect localized changes in the resource (Gandiaga et al., 2018; Thibault & Moreau, 2016b) and that their efficiency does not vary with forest stand type (Bouget et al., 2009).…”