Towards a better understanding of the effect of anthropogenic habitat disturbance on the invasion success of non-native species: slugs in eastern Canadian forests

The disturbance hypothesis postulates that habitat disturbance favours the invasion success of non-native species. Its unspecific formulation has led invasion biologists to evaluate either the effect of the occurrence of a disturbance or its characteristics (e.g., its intensity) on the invasion success of non-native species. However, the hypothesis is unclear about these two effects, which might explain why studies offer ambivalent support for this hypothesis. Our objective was to determine the effects of the occurrence of an anthropogenic disturbance (i.e., logging), its intensity, and the time since its occurrence on the invasion success (i.e., abundance) of the non-native slug species complex Arion subfuscus s.l. (hereafter Arion). We used pitfall trapping in stands located in two boreal and two temperate forest ecosystems in eastern Canada. We sampled unlogged and logged stands that differ in harvesting intensity (from partial to complete removal of standing live trees and downed biomass) and time since logging (from 1 to 66 years). Our results revealed a positive effect of logging occurrence on Arion abundance in only one of the four study sites, whereas it had a negative or no effect at the three other study sites. Our results also showed that Arion abundance decreased with increased biomass removal intensity and usually increased with time-since-logging. Given the varying response of non-native species to logging and its characteristics, future studies should aim to reformulate the disturbance hypothesis to make more specific predictions of the conditions under which habitat disturbance promotes the invasion success of non-native species.

Automated summary

The disturbance hypothesis suggests that habitat disturbance promotes the invasion success of non-native species. This study aimed to investigate the effects of anthropogenic disturbance (logging) occurrence, intensity, and time since logging on the invasion success of the non-native slug species complex Arion subfuscus s.l. The results showed that logging occurrence had a positive effect on Arion abundance in only one of the study sites, while having a negative or no effect in the other sites. Additionally, Arion abundance decreased with increased biomass removal intensity and generally increased with time-since-logging. Future studies should aim to reformulate the disturbance hypothesis to make more specific predictions about the conditions under which habitat disturbance promotes the invasion success of non-native species.