Commensal black rats Rattus rattus select wild vegetation over urbanised habitats

Abstract

Human commensal species are thought to depend so closely on resources provided by humans that they are effectively ‘natives' of urban environments. However, while their adaptations to urban existence are well understood, their ecology and habitat choices have not been closely examined. This study investigated the habitat preferences of the archetypal commensal species, the invasive black rat Rattus rattus, at the urban–bushland interface in Sydney, Australia, and modelled the results using isodar analysis. Unexpectedly, we found evidence that rats perceived bushland as a more resource‐rich habitat compared to urban areas, resulting in higher rat abundance in bushland areas. Resultant spillover of commensal species into native vegetation may pose acute ecological risks in the future, yet management of commensal pests remains focused on urban areas. Ultimately, these findings highlight the complex nature of commensal ecology, suggesting that adaptation to human coexistence does not necessarily lead to a preference for human‐modified landscapes. We suggest that inter‐specific interactions with competitors, or the lack thereof, likely modulate the habitat preferences of commensals.

The ratting of North America: A 350-year retrospective on Rattus species compositions and competition

“…In that context, the differing δ 15 N values of brown and black rats appear to represent a fundamental difference in the preferred niche of these taxa in urbanizing spaces. While quantitative urban dietary comparisons (isotopic or otherwise) for sympatric black and brown rats continue to be rare, a preference for use of more vegetation-based, less urban food resource areas has recently been observed along an urban-to-bushland spectrum for black rats in an Australian urban center [( 57 ); also see ( 58 )], suggesting that our spatiotemporally broader scale archaeological observations do have contemporary and potentially wider-spread analogs today.…”

Older urban rats are infected with the zoonotic nematode Angiostrongylus cantonensis

“…Although rat species was not significant in our model, a higher proportion of R. rattus were infected. Despite both species of rat being generalist omnivores, perhaps (i) R. rattus preference for wild vegetation ( Cox et al, 2000 ; Adams et al, 2023 ) and (ii) aggressive competition from highly urban R. norvegicus ( King et al, 2011 ) would drive R. rattus in Sydney to denser natural habitats (such as parks and gardens) where gastropods as a food source are abundant.…”

Underestimating the underdog: Camera trap observations of full‐contact combat between quenda (Isoodon fusciventer) and black rats (Rattus rattus)

“…It is of note that black rats, although regarded as urban exploiters, are found in higher numbers in resource‐rich urban bushlands than in urban gardens (Adams et al., 2023) and therefore, residential gardens may act as refugia where quendas can successfully reproduce and re‐populate neighbouring urban bushlands where quenda populations might experience more predation. Overall, the presence of quendas in urban backyards and in nearby remnant bushlands indicates their ability to persist in such habitats, but this may be impeded by the presence of black rats.…”