Spatial Overlap and Dietary Selection of Native Rice Rats and Exotic Black Rats

Abstract

The silver rice rat (Oryzomys argentatus), a rare endemic rodent, and the black rat (Rattus rattus), an exotic species, have coexisted for <500 years in the Florida Keys. Determination of fine8 scale movements and behavior, by use of neck-attached fluorescent dust dispensers, revealed the degree of overlap in use of space, and some food resources, in free-ranging animals. Food selection tests were conducted in the laboratory. Significant differences in vegetation association, behavior, arboreality, and diet were found. From estimates of spatial niche overlap based on four indices I suggested the differences were biologically insignificant; the average value of four estimators on the habitat-choice resource axis was 89%, higher than reported for 47 of 48 pair-wise comparisons of native rodent species. I suggest that silver rice rat populations may be jeopardized by the presence of black rats whose invasion was reported to have caused oryzomine extinctions in the Galapagos and Antilles islands.

Review of negative effects of introduced rodents on small mammals on islands

“…Clark 1984;Goodyear 1992;Carleton and Olson 1999). In support of such conjecture, I have reviewed some compelling circumstantial, correlative and experimental evidence.…”

“…While niche overlap between introduced rodents and insular small mammals has been identified by studies of resource and microhabitat use (Goodyear 1992;Goodman 1995;Gregory 2006;Harris et al 2006) further investigation is required before resource competition can be confirmed. In contrast to our lack of knowledge regarding the importance of interspecific competition between introduced rodents and native small mammals, a great deal is known about small mammal interactions in natural communities.…”

Variation in Peccary Populations: Landscape Composition or Competition by an Invader?

“…observable effects on terrestrial ecosystems. Predation by the brown tree snake (Boiga irregularis) was implicated in the extinction of several species of birds on Guam (Savidge 1987), and the introduction of the black rat (Rattus rattus) was associated with the extinction or decline of several native rodent species (Thornton 1971, Woods 1989, Goodyear 1992. Introduced land animals produce other large-scale effects, such as destruction of habitat, vectoring of diseases, and alteration of ecosystem processes.…”

Variation in Peccary Populations: Landscape Composition or Competition by an Invader?

“…Predation by the brown tree snake (Boiga irregularis) was implicated in the extinction of several species of birds on Guam (Savidge 1987), and the introduction of the black rat (Rattus rattus) was associated with the extinction or decline of several native rodent species (Thornton 1971, Woods 1989, Goodyear 1992. Predation by the brown tree snake (Boiga irregularis) was implicated in the extinction of several species of birds on Guam (Savidge 1987), and the introduction of the black rat (Rattus rattus) was associated with the extinction or decline of several native rodent species (Thornton 1971, Woods 1989, Goodyear 1992.…”