Urbanization and plant invasion alter the structure of litter microarthropod communities

Abstract

1. Anthropogenic activity underpins the creation of urban ecosystems, often with introduced or invasive species playing a large role in structuring ecological communities. While the effects of urbanization on charismatic taxa such as birds, bees or butterflies have received much attention, the impacts on small and inconspicuous organisms remain poorly understood. 2. Here, we assess how the community structure of leaf litter-inhabiting microarthropods in city parks varies along an urbanization gradient in Toronto, Canada. At each park, we established paired forest understorey plots which were either dominated by native vegetation or dog-strangling vine Vincetoxicum rossicum, an invasive species that is spreading throughout northeastern North America and abundant in urban areas. We compared microarthropod richness, abundance and diversity in ecological traits between invaded and non-invaded plots as well as compositional dissimilarities among plots across the urbanization gradient. 3. We recorded 123 genera and found (a) there was a negative effect of urbanization on microarthropod richness and abundance but only in invaded plots; (b) richness and abundance increased continuously with urbanization in non-invaded plots, but peaked at intermediate urbanization levels in invaded plots and (c) there was significant turnover with increasing urbanization, with distinct communities represented in highly urbanized areas compared to less urbanized areas, regardless of whether invaded. We also found litter microarthropod richness and abundance increased with soil ammonium and decreased with nitrate. These trends were especially strong for fungivorous microarthropods; however, there was no relationship between soil nutrients and urbanization or invasion. 4. Urbanization and biological invasion drive biodiversity change, and there is a need to disentangle these effects on ecological communities and related ecosystem processes. We show microarthropod communities change with urbanization, with the effects of invasion most prominent in non-urban areas. Here, there is high richness and abundance but low ecological trait diversity, possibly because certain feeding traits are excluded and others overrepresented.

Saproxylic insects and fungi in deciduous forests along a rural–urban gradient

“…We also recorded a shift in total beetle species composition along the urbanization gradient. This result parallels the findings of some studies showing that urbanization changes the species composition of nonsaproxylic carabid beetles (Niemelä & Kotze, 2009) and that of staphylind beetles (Magura et al., 2013) and of microarthropod litter communities in urban forests (Malloch et al., 2020), and thus may reduce the functional diversity of the beetle community (Hagge et al., 2019).…”

Urban forest invertebrates: how they shape and respond to the urban environment

“…The high proportion of non-native plant species in urban areas results in novel resources available to urban forest invertebrates and may influence trophic and non-trophic interactions in these ecosystems (Valentine et al 2020). For instance, non-native trees as sources of organic matter for invertebrates have the potential to influence the community assembly of collembolans (Raymond- Leonard et al 2018) and mites (Malloch et al 2020), and ultimately, litter decomposition rates (Makkonen et al 2012; but see Finerty et al 2016).…”

“…Often, changes in vegetation structure occur as a result of development, management (e.g., mowing), or through invasive species proliferation in city parks (Kühn and Klotz 2006;Cadotte et al 2017). The latter has been shown to result in a decline in soil micro-invertebrate richness and abundance along an urbanization gradient in Toronto, Canada (Malloch et al 2020). However, the invasion of urban forests by exotic tree species can accelerate species turnover without decreasing invertebrate richness or abundance (Buchholz et al 2015).…”

Urbanization and urban habitat fragmentation do not compromise soil food web complexity and conservation value

“…Soil and litter layer perform a wide range of ecosystem functions and services, for example providing refugia for wildlife, regulating microclimate, and nutrient cycling and sequestering carbon (Wang & Tong 2012;Malloch et al 2020). Soils in urban areas often are artificially formed, e.g.…”

“…Further, litter materials forming an important food resource for soil food webs often are removed in urban greenspaces (Milano et al 2017;Kotze et al 2022). These changes likely result in soil arthropod communities diverging from surrounding natural systems (Malloch et al 2020).…”