Forest Tent Caterpillar Outbreaks Drive Change in Ant Communities in Boreal Forests

Abstract

Insect outbreaks are major drivers of natural disturbances in forest ecosystems. Outbreaks can have both direct and indirect effects on the composition of soil arthropod communities through canopy opening, nutrient addition and predator-prey interactions. In this study, we aimed to understand the effects of forest tent caterpillar (Malacosoma disstria; FTC) outbreaks through cascading effects on ant communities in both temperate and boreal forests in Canada. Pitfall traps and Berlese funnels were used to compare the ant communities, as well as the surrounding arthropod communities, between control and outbreak sites in boreal and temperate forests (in Quebec, Canada). Using the Sørensen dissimilarity index, we determined the alpha and beta diversity of the ant community. Other arthropods collected in the traps were counted to evaluate the richness and abundance of potential prey for the ants and other potential predators of the FTC. We used an indicator species analysis to examine the species associated with sites defoliated by the outbreak. In the boreal forest, we found that FTC outbreaks caused decreases in species richness and increases in the evenness of ant communities in defoliated sites. In the boreal forest sites, species composition varied significantly between control and outbreak sites. This pattern was driven in part by the presence of other predators. A similar, but weaker pattern was observed in the temperate forest. We saw no changes in the beta diversity in the boreal forest, but did see a significant decrease in the temperate forest between the outbreak sites and the control sites. Ant species in the boreal forest tended to exhibit a more marked preference for either control or previously defoliated sites than species in the temperate forest. Our study showed that disturbances such as insect outbreaks can drive changes in the ant community. While we saw small effects of outbreaks, manipulation experiments using resource addition could help us validate the mechanisms behind these relationships.

Soil Springtail Communities Are Resilient to Forest Tent Caterpillar Defoliation in Quebec Mixed Hardwood Forests

“…Our results did not support our first hypothesis that abundance or diversity of springtail communities would be altered following the forest tent caterpillar outbreak (Figure 1). This result contrasts to the observed reduction in microbial abundance following defoliation [68], as well as a reduction in species richness and an increase in evenness of ant communities following defoliation [68,75] in the same stands and years. However, Shannon diversity showed a tendency toward lower diversity with defoliation history in 2019, which is a reminder that interannual seasonal variation can modulate community structure (Figure 1).…”

“…Our exploration of whether springtail species composition correlated with other local environmental variables yielded mixed results. Neither top-down food web control estimated by the inclusion of predator abundances [75] nor soil resources estimated by glucose-induced soil microbial biomass [69] showed a significant correlation to species composition. However, sites with a defoliation history showed a trend of lower C, P, Mg, and Mn concentrations (Table S4) and Anurophorus sp1 and Folsomia nivalis were negatively correlated with these soil nutrients (Figure 3).…”

The diversity of soil insects in rice field ecosystems

“…(Despland & Lessard, 2022) or tent caterpillars (Malacosoma spp.) (Caron et al, 2023). In addition, this species is also a structural pest that can cause severe can cause more damage by dig deep into wood to create or expand nesting locations (Aronson et al, 2015;Anjos et al, 2017).…”