Competition in an invaded rodent community reveals black rats as a threat to native bush rats in littoral rainforest of south‐eastern Australia

Abstract

Summary1. Interspecific competition is a recognized but under-studied mechanism by which invasive species affect native fauna. 2. We experimentally reduced populations of the introduced black rat Rattus rattus in relatively undisturbed littoral rainforest in south-eastern Australia to test its competitive impact on populations of the native bush rat Rattus fuscipes. 3. Removal of R. rattus resulted in significant and sustained increases in populations of the native rodent due to immigration, juvenile recruitment and increases in residency of females. Native juveniles were particularly vulnerable to R. rattus, being largely absent from untreated populations despite indications of breeding in females, but responding rapidly to their removal. 4. The absence of changes in body condition and reproduction of adult R. fuscipes with long-term removal of R. rattus suggests that direct interference by R. rattus rather than competition for resources best explains the low densities and poor juvenile recruitment of R. fuscipes. 5. The behavioural dominance of R. rattus was not due to an inherent competitive ability because they did not re-establish post-removal as expected if competition was asymmetrical. Instead, competitive dominance seemingly shifted to R. fuscipes with changes in residency status of populations. Improved survivorship among native females reveals that they were particularly important in establishing resident populations following removal of R. rattus. 6. Synthesis and applications. These findings identify R. rattus as a significant competitive threat to native R. fuscipes. Removal of invasive rodents and active conservation of common native species is recommended to forest managers based on the potential for R. fuscipes to prevent re-invasion subsequent to pest control efforts and maintain invasion resistance.

Differential population responses of native and alien rodents to an invasive predator, habitat alteration and plant masting

“…The predatory impact of the black rat on Amami Island is also unlikely to be a major limiting factor on endemic rat populations. As for interspecific competition, many pre-post eradication surveys revealed a competitive impact of black rats on island-endemic small mammals [64,65], but we found no such evidence. Dietary segregation, spatial segregation [66] and temporal resource variation [67,68] may explain the lack of competitive interactions among rodent species.…”

Dietary niche differentiation among three species of invasive rodents (Rattus rattus, R. exulans, Mus musculus)

“…Much evidence points to the largest of the three rodents, the black rat, as the dominant competitor of the three species studied (Yom-tov et al 1999;Russell and Clout 2004;Shiels 2010). Stokes et al (2009) in Australia, and Harris and Macdonald (2007) in the Galápagos Islands, demonstrated that native rats (R. fuscipes and Nesoryzomys swarthi, respectively) suffered from interference competition rather than resource competition with the larger, non-native black rats. Furthermore, removal of black rats can result in population increases in coexisting rodents such as house mice (Harper and Cabrera 2010;Ruscoe et al 2011).…”

Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus,the Black Rat (Rodentia: Muridae)

“…rats), one from New Zealand (Mystacina robusta bat), and one from the Marías Islands in Mexico (Oryzomys nelsoni rat). Stokes et al (2009) in Australia, and Harris and Macdonald (2007) in the Galápagos demonstrated that native rats (Rattus fuscipes and Nesoryzomys swarthi, respectively) suffered from interference competition with nonnative R. rattus. Furthermore, removal of R. rattus can result in population increases in coexisting nonnative rodents on Pacific islands, which has been observed with M. musculus in New Zealand (Ruscoe et al 2011) and in the Galápagos (Harper and Cabrera 2010).…”