Foraging Efficiencies of Competing Rodents: Why Do Gerbils Exhibit Shared-Preference Habitat Selection?

Abstract

Two coexisting gerbil species, Gerbillus allenbyi (26 g) andG. pyramidum (40 g), exhibit shared-preference optimal habitat selection. In a mosaic of stabilized sands and semistabilized dunes, both species primarily prefer the semistabilized-dune habitat. We hypothesized that foraging benefit, due to the lower amount of loess in the semistabilized dunes, is the underlying cause for this preference. We tested this by measuring foraging efficiencies (giving-up density of seeds) in both manipulated foraging substrates (sand and loess) and natural habitats (semistabilized dunes, stabilized sands, and loess plateau). We also compared harvest rates on sand and loess. We used the loess substrate and loess plateau habitat to exaggerate the effect of loess on the gerbils' foraging behavior. Regarding foraging substrate, gerbils had significantly higher foraging efficiencies on sand in the field. They also had significantly higher harvest rates on sand in the laboratory. Regarding habitats, both species were more efficient in semistabilized dunes than in stabilized sands or loess plateau. Additional results suggested that the area surrounding a foraging patch had an important role in predator avoidance. We concluded that the semistabilized-dune habitat allowed gerbils to forage more efficiently in a patch, because it is easier to dig for seeds in the sandy substrate found there, and because gerbils enjoyed lower predatory risk traveling to and from the seed patch. The results supported the hypothesis that foraging benefit is the basis of the shared-preference habitat selection of the gerbil species