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Species that occupy the same area and use the same resources must either compete with each other or find ways to minimize competition. For rodents, 1 important resource is nesting sites. In this study I present data from direct behavioral observations in the succulent karoo of South Africa that show aggressive interactions between bush karoo rats (Otomys unisulcatus) and striped mice (Rhabdomys pumilio). Because both species nest in shrubs, the potential exists for interspecific competition for nesting sites. Because of a severe drought in 2003, the bush karoo rat became locally extirpated. As a result, striped mice nested significantly more often in shrubs that contained bush karoo rat nests than in 2001 and 2002, when the population density of bush karoo rats was high. Furthermore, I observed that striped mice never nested in the shrub Lycium cinerum, the favorite nesting site of bush karoo rats, when bush karoo rats were present, but regularly used these nesting sites after bush karoo rats became extirpated. I conclude that striped mice and bush karoo rats compete actively for access to preferred nesting sites in the succulent karoo.
Key words: interspecific competition, nest, Otomys unisulcatus, Rhabdomys pumilio, succulent karoo
Reproductive success of animals is restricted by their access to important resources such as food, mating partners, and shelter. Shelters provide protection against predators and harsh environmental conditions such as extreme temperatures, wind, and rain. Thus, shelters offer safe sleeping and nesting sites. If these are of limited supply, competition for this resource will occur. For example, intraspecific competition for nesting sites is common in fish (Draud and Lynch 2002; Kroon et al. 2000), and the same has been reported for small mammals (Dooley and Dueser 1996; Radespiel et al. 2003).
Territoriality to defend space against members of the same species also functions to defend nesting sites within territories (Schradin 2004; Stamps 1994). However, suitable nesting sites might not only be used by conspecifics, but also by other species that occur sympatrically. For example, in mouse lemurs, sympatric species can avoid competition by choosing different categories of sleeping sites (Radespiel et al. 2003). Nest-site selection also can be dependent on the presence of other species. For example, the white-footed mouse (Peromyscus leucopus) prefers to nest in trees, as does...