Urbanization effect of homogenization on ground-dwelling arachnids’ diversity in natural forest and peatland remnants

Abstract

Continuous large forests intermingled with small patches of open ecosystems (e.g. peatlands) are typical in temperate mountain regions. They are usually removed when cities are installed, but patches remain inside. Moreover, the constant growth of cities threatens the surrounding natural landscapes. Urbanization and land-use change generates degradation of natural habitats, and loss of biodiversity and ecosystem services. In this context, we assessed arachnid diversity in non-urban, peri-urban and urban forests and peatlands in Ushuaia city (Argentina) to evaluate the effect of urbanization in these habitats. We evaluated spider abundance, richness, Exponential of Shannon Entropy (Exp(H)), Simpson Diversity (D), similarity indices and composition. Also, we explored the association between spider assemblage, urbanization categories in each habitat type and local characteristics. We installed 115 pitfall traps, and collected 2589 individuals identified in 50 species from 14 families (including Opiliones and pseudoscorpions). Urbanization had significant effects on abundance and D in both habitat types, with higher abundances in non-urban than urban and peri-urban, and higher D in peri-urban than no-urban and intermediate values in urban. Meanwhile, richness, Exp(H) and D differed between habitats, with consistent higher values in peatlands than forests. At species level, composition was different among urbanization categories, with some species lost (species that only occur in non-urban category) and gains (species that only occur in urban and peri-urban categories). In both habitats, spider assemblages of urbanizations were better correlated with vascular plant cover, with woody debris + litter cover most significantly and positively related to spiders in non-urban forests, and bryophyte cover more related to spiders in non-urban peatlands. We conclude that urban forest fragments and peatlands were able to conserve some of the arachnid diversity characteristic of natural habitats, but homogenization mediated by urbanization exists, which could affect arachnid community functions and conservation. Implication for insect conservation Our results show that urbanized habitats must undergo long-term monitoring, because although certain species are preserved, some specialists were present only in natural remnants, while others showed an affinity with urbanized habitats only. The species replaced due to possible inter-specific competition, niche modification, or both can lead to the impoverishment of the arachnid fauna. Therefore, urban planning should consider strategies to preserve and restore these semi-natural habitats to promote the conservation of these natural predators.