Impact of urbanization on the taxonomic and functional diversity of spider assemblages in Guwahati City, Assam, India

Abstract

The homogenous nature of the urban environment rapidly alters community dynamics of extant flora and fauna due to short-term spatial and temporal factors. However, such impacts of urbanization are mostly investigated in terms of taxonomic diversity, while its impact on functional diversity remains poorly understood. Whereas taxonomic information is limited to the identity of species, functional traits determine the relationship between species identity and ecosystem functioning. Studies investigating the role of urbanization in altering these ecological parameters have mostly focused on avian communities or plant species, while arthropods such as spiders which are integral components of urban households have largely been overlooked. This study aims to understand the impact of urbanization on both taxonomic diversity and functional diversity of spider assemblages across an urban-semi-urban-forest gradient in Guwahati, a rapidly growing city in northeast India. We surveyed spiders at 13 sites representing four habitat types (urban, urban parks, semi-urban, and forests) using belt transects, and also recorded functional traits relating to key life history processes. Spider species composition differed significantly between various habitats. The taxonomic diversity of spiders was highest in forests and lowest in urban parks. The turnover component was the major contributor to changing the beta diversity of spiders. Reduced diversity in urban regions was likely due to the dominance of a few synanthropic species. Generalised linear mixed-effects model analysis indicated that the habitat types significantly impacted spider abundance. Functional richness was maximum in forests (Fric = 23.43) and minimum in urban habitats (Fric = 12.98), while functional divergence was maximum in urban sites (Fdiv = 0.79). Our study demonstrates that urban land-use change can alter the structure and functioning of the spider community.