Life in the big smoke: terrestrial vertebrate assemblages and their drivers along an urbanisation gradient in Sydney, Australia

Abstract

Context. Urban areas are rapidly expanding, increasing anthropogenic pressure on global biodiversity. There are many threats associated with urbanisation,such as habitat loss and the spread of invasive species. Thus, to effectively manage urban greenspaces for native species, we need to understand species assemblages, and the factors that influence their diversity. Aims. We assessed how assemblages of terrestrial vertebrate species differ across urbanisation levels in northern Sydney, Australia, and whether habitat characteristics influenced them. We also investigated the role of invasive species in these areas by comparing daily activity patterns between invasive and native species. Methods. Nine forest (dry sclerophyll) patches, surrounded by three urbanisation levels (high-urban, mid-urban and low-urban), each with five motion-sensor cameras, were used to survey terrestrial fauna in northern Sydney from May to July 2023. Five vegetation variables and eight spatial variables were also recorded at each patch. Key results. There were differences in terrestrial vertebrate assemblages across the three urbanisation levels, with more invasive species, including red foxes (Vulpes vulpes) and black rats (Rattus rattus), in high-urban areas. We also found native species assemblages (particularly superb lyrebirds, Menura novaehollandiae; long-nosed bandicoots, Perameles nasuta; and bush rats, Rattus fuscipes) to differ with tall and low shrub cover, whereas invasive species did not differ. Furthermore, mean activity peaks did not differ between red foxes and a critical weight range (CWR) mammal was recorded in high-urban sites. Last, we observed a significant negative relationship between invasive species richness and native species diversity. Conclusions. Urbanisation has a strong effect on the assemblages, activity and interactions of native and invasive terrestrial vertebrate species in Sydney. Whereas remnant patches may support native species, the prevalence of invasive fauna in areas that are more highly urbanised may compound other factors affecting biodiversity. Implications. This study has provided a baseline understanding of urban terrestrial vertebrate assemblages in northern Sydney, and has shown that mid-urban areas may be good candidates for reintroduction sites. Our findings can be used to guide management actions to support the conservation or re-establishment of native species in the region or other urban areas.