Commensal black rats Rattus rattus select wild vegetation over urbanised habitats

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.

Automated summary

Human commensal species are considered to be 'natives' of urban environments, but their habitat choices have not been well examined. This study found that the invasive black rat Rattus rattus prefers bushland as a habitat, which may pose ecological risks. These findings highlight the complexity of commensal ecology.