Testing the niche reduction hypothesis for a fossorial rodent (Geomys bursarius) experiencing agricultural intensification.

Abstract

Habitat loss and fragmentation from conversion to agriculture are known threats to grassland species. However, continued agricultural intensification may further reduce a species distribution and realized niche. Here, we create species distribution models (SDMs) for the plains pocket gopher (Geomys bursarius), an ecosystem engineer in grasslands, for historic and contemporary eras in a dynamic agroecosystem and test the "niche reduction hypothesis." We compare SDMs created from gopher occurrences from the historic era (~1950s, pre-agricultural intensification) and the contemporary era (post-agricultural intensification) and assess model transferability. We evaluate shifts in environmental relationships, changes in limiting factors, and an overall decline in niche hypervolume. SDMs were nontransferable between the historic and contemporary eras. Environmental drivers of gopher distribution shifted from elevation, precipitation, and land cover in the 1950s to land cover, soil texture, and soil drainage presently. There also were shifts in environmental associations with gophers now occurring at lower elevations, in sandier soils, and less often in agriculture. Dominant limiting factors of gophers shifted from precipitation to land cover. Gophers were not detected at historic locations during recent resurveys. Contemporary niche hypervolume was reduced compared with the historic niche hypervolume. We found support for the niche reduction hypothesis for a fossorial, grassland species. Further application of the niche reduction hypothesis in landscapes experiencing agricultural intensification is warranted. Understanding niche reduction allows for conservation efforts that promote continued persistence in the contemporary niche while also identifying areas to restore within the historic niche.