Does a Rural-Urban Gradient Affect Beetle Assemblages in an Arid Ecosystem?

Urbanization affects all elements of the pre-urban environment, including soils, hydrology, vegetation, and microclimate. Recently, Saudi Arabia has experienced rapid urbanization and growth. Thus, the country's biodiversity has been threatened. In the Riyadh region, beetle assemblages were assessed along a rural-suburban-urban gradient. A total of 2791 individuals from 94 species belonging to seven families were collected at 15 sites along three different gradients of urbanization in Wadi Hanifa, which runs for a length of 120 km from northwest to southeast. Tenebrionidae dominated abundance (60.1%) and richness (38%). Beetle abundance, evenness, and diversity were not different among habitats; however, species richness was higher in rural habitats. Detrended correspondence "DCA" and canonical correspondence "CCA" analyses showed distinct differences among sites along gradients. Urbanization intensity, soil variables, and land cover were significantly correlated with CCA axis 1, while elevation and flora were significantly correlated with CCA axis 2. The most critical operating environmental variables in Wadi Hanifa were buildings, elevation, soil organic carbon, litter cover, and litter depth, as well as plant species such as Launaea capitata, Lycium shawii, Alhagi graecorum, and Heliotropium currasavicum. Ten species in our study were associated with urban habitats, six with suburban habitats, and seven with rural habitats. Consequently, expanding urban areas may negatively affect the richness and composition of beetles and may result in the loss of some native species.