Little bugs in the big city: Investigation of litter invertebrates along an urbanization gradient

Background/Question/Methods   The effects of increased urbanization and land modification by humans on ecological processes is an area of study growing in importance as human populations and, consequently, urban areas increase. With much of our past ecological knowledge originating from rural or agricultural settings, a relative gap in understanding of urban ecological processes has formed. The diversity and abundance of forest floor litter invertebrates allows them to serve as effective indicator species for investigating how urbanization affects terrestrial ecosystems. In this study, we inspected the abundance and composition of orders of litter invertebrates between more and less urban sites, as well as across an array of environmental conditions (soil temperature, litter depth, canopy density, and moisture levels). Seattle University's campus provided a site that was considered heavily urban, followed by Volunteer Park (moderate urban), Seward Park (low urban), and Cougar Mountain Regional Wildland Park (no urban, or rural).

Results/Conclusions   Results showed significantly higher total abundance (p < 0.01), richness (p < 0.01), and evenness (p < 0.01) of invertebrate orders as well as lower soil temperature (p < 0.001) and higher soil moisture levels (p < 0.001) at the least urban area. Additionally, individual orders varied in their responses to the environmental variables measured (e.g. Spiders, p = 0.009; Pseudo-Scorpions, p = 0.01), potentially helping to explain the observed community-level patterns. This work aims to capture how a gradient of urbanization, through multiple sites, provides a model to discern the effects of urbanization on terrestrial ecosystems. Current work uses terrariums to investigate effects of litter invertebrate community composition and diversity on decomposition rates to determine how urbanization affects an essential function of terrestrial ecosystems.