Effect of Habitat Quality on Distributions of Three Sympatric Species of Desert Rodents

Congdon, J

Field data on species dominance were obtained by baiting an area with wild bird seed to maximize rodent densities. Observations were then made on interspecific encounters from a platform using battery-powered red lights for illumination. In 11 interspecific encounters between kangaroo rats, D. merriami would retreat from the larger D. deserti. Retreat always began before any physical contact took place and the dominant individual showed little or no interest in pursuit. In four encounters with either of the kangaroo rat species, P. longimembris always retreated with no interest in pursuit being shown by the kangaroo rats. Individuals of each species were trapped and exposed to each other in the laboratory to gather supportive evidence on species dominance. Each encounter took place during early evening in a 1.0 by 1.8 meter (m) cage illuminated by a dim red light and center divided with plywood. A single individual of each of two species was placed in opposite ends of the divided cage and allowed five minutes to adjust before the divider was removed. All actions and postures were noted for ten minutes, or less if fighting seriously endangered one of the individuals. Five trials of each of the four combinations of species were tested. Both field and laboratory observations showed that D. deserti was by far the most aggressive species and the dominant rodent. D. merriami, the subordinate kangaroo rat, was dominant in all encounters with P. longimembris. Results of these observations were used to supplement distribution data obtained from the trap grid.

Effect of Habitat Quality on Distributions of Three Sympatric Species of Desert Rodents

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