Interactive effects of keystone rodents on the structure of desert grassland arthropod communities

Abstract

Certain species play particularly large roles in ecosystems, and are often referred to as keystones. However, little is known about the interactive effects of these species where they co‐occur. Prairie dogs (Cynomys spp.) and banner‐tailed kangaroo rats Dipodomys spectabilis are commonly considered keystone species of grassland ecosystems, creating a mosaic of unique habitats on the landscape through ecosystem engineering and herbivory. We examined the separate and interactive effects of these species on the structure of grassland arthropod communities. We conducted a cross‐site study at two locations in the northern Chihuahuan Desert, and evaluated the impacts of these rodents on ground‐dwelling arthropod and grasshopper communities in areas where prairie dogs and kangaroo rats co‐occurred compared to areas where each rodent species occurred alone. Our results demonstrate that prairie dogs (C. gunnisoni and C. ludovicianus) and banner‐tailed kangaroo rats had keystone‐level impacts on arthropod communities both separately and interactively. Their burrow systems provided important habitats for multiple trophic and taxonomic groups of arthropods, and increased overall arthropod abundance and species richness. Many arthropods also were attracted to the aboveground habitats around the mounds and across the landscapes where the rodents occurred. Detritivores, predators, ants, grasshoppers, and rare rodent burrow inhabitants were especially associated with prairie dog and kangaroo rat activity. The impacts of prairie dogs and kangaroo rats were unique, and the habitats they created supported different assemblages of arthropods. Where both rodent species co‐occurred, there was greater heterogeneity and arthropod diversity on the landscape. Our results suggest that the interaction of multiple keystones, especially those with engineering roles, results in unique and more diverse communities in time and space.