You can't bask with us: Does urbanization affect response to invasive and native competitors in lizards?

Urbanization impacts biodiversity, changing the breadth and depth of species interactions. Urban animals may experience more intraspecific interactions and fewer interspecific interactions than nonurban animals due to reduced biodiversity in urban areas. Interspecific interactions in urban areas may be with novel competitors as invasive species are commonly associated with urbanization. Here, we tested whether urbanization affects animal responses to inter- and intraspecific competitors by quantifying physiological and behavioural traits of male western fence lizards, Sceloporus occidentalis , when exposed to potential competitors. We filmed fence lizard behaviour both when individuals were alone and when they were paired with either a nonurban or an urban unfamiliar conspecific competitor, or with a novel heterospecific competitor (a non-native Italian wall lizard, Podarcis siculus ) . We also quantified stress responses (corticosterone concentrations, CORT) from blood samples. Overall, urbanization did not impact fence lizard responses to competitors. Instead, we found that regardless of habitat, lizards were the most stressed and exhibited the most visual displays and aggressive behaviours when encountering a conspecific. Lizards also reduced usage of the basking site in heterospecific trials, suggesting potential responses to novelty, body size differences or exploitation competition by Italian wall lizards. Lastly, urban lizards exhibited more information-seeking behaviours and higher body temperatures than their nonurban counterparts, which could be associated with different risks and thermal environments, respectively, between urban and nonurban habitats. Collectively, our findings suggest that urbanization does not strongly affect responses to competitors, contrary to expectations based on differences in population density and biodiversity between urban and nonurban environments. • We examined lizards' inter- and intraspecific responses to urban vs nonurban competitors. • Lizards with conspecific competitors showed more aggression and higher CORT levels. • Native lizards basked less in the presence of an invasive heterospecific competitor. • Urban lizards displayed more information-seeking behaviours. • Urban lizards also had higher body temperatures than nonurban lizards.