Street fighters: bite force, injury rates, and density of urban Australian water dragons (Intellagama lesueurii)

In an increasingly urbanized world it is imperative that we understand how wildlife responds to this novel anthropogenic landscape, both at the individual- and population-level. Urbanization generally reduces biodiversity, but can also favour particular species and increase their abundance relative to wild populations. When population density increases, so too does the frequency and cost of social interactions. We studied Australian water dragons (Intellagama lesueurii), a species common in urban, semi-natural and natural areas, to firstly test the prediction that urban populations occur at higher densities, and then determine the consequences of urbanization for combat rates (quantified using wounding) and bite force. We established that urban populations are denser than ones from semi-natural and natural habitats. We also recorded significantly more wounds in females from urban populations than females from both natural and semi-natural populations. Urban males also had significantly higher incidence of wounding than males from natural populations. We did not find a difference in male or female bite force among any populations across the urban-natural gradient. Overall, we found evidence that urbanization results in a higher population density of water dragons and more frequent conspecific combat, but this was not associated with an increase in bite force. These finding suggests that there may be a physiological cost to living in urban habitats related to increased contest rates and wounding.