Interactive effects and feedbacks between soil biodiversity and global change
The global trend of biodiversity loss due to habitat fragmentation and climate change has consequences on the functioning of natural ecosystems. Responses to these changes at the community level are poorly understood, as are the impacts of community disassembly on ecosystem-level processes. We examined how habitat connectivity can mitigate the ecosystem-level effects of habitat fragmentation through facilitating species movement, as well as mitigate species loss under climate change using laboratory and field-based experiments in a model soil system.
In the lab experiment, isolation led to the extinction of large-bodied apex predators, subsequently followed by increases in prey species abundance. This trophic cascade was associated with significantly altered carbon and nitrogen fluxes in fragmented treatments. The ecosystem impacts were characteristic of a function debt because they persisted for several generations after the initial loss of connectivity. Local extinctions and disruption of ecosystem processes were mitigated, and even reversed, by the presence of corridors in the connected metacommunities, although these beneficial effects were unexpectedly delayed. We hypothesized that corridors maintained grazer movement between fragments, which enhanced microbial activity, and decomposition in comparison to isolated fragments. Our results indicate that knowledge of habitat connectivity and spatial processes is essential to understand the magnitude and timing of ecosystem perturbation in fragmented landscapes. In the field, the outcome of community disassembly under alterations in temperature and moisture was mediated by the correlation between our environmental factors and species traits, particularly body size. Minor increases in summer temperatures maintained greater species richness, whereas drought stress had a significant negative effect on community-level abundance and richness. These effects were reflected in modifications to the community-wide body-size spectra. Habitat connectivity alleviated biodiversity loss in the larger-bodied species of the most abundant taxonomic group, but did not fully mitigate the effects of drought. The most striking result of this experiment was an overall contraction of the food web among persistent species under drought stress (i.e. those not extirpated by environmental change). These results suggest that major changes in soil faunal community structure are likely to occur in response to common forms of global change. Moreover, the contraction in trophic structure even amongst tolerant species suggests that ecosystem function within soil systems can be altered by environmental change.