Abstract: Invasive plants substantially modify habitats, which may lead to changes in animal behavior. Behavior is important to understand because it affects survival, reproduction, and can govern species interactions. Although behavior is clearly sensitive to the environment in which an animal lives, behavior is also likely to depend upon individual state, with important differences in behavior likely arising due to the sex or reproductive status of an individual. Although invasive plants can affect animal behavior, we know less about how individual state might modify behavior in invaded habitats. This knowledge gap is critical because it affects our ability to predict how invasions will ultimately affect individual fitness as well as interactions that are mediated by behavior. We experimentally manipulated the presence of invasive shrubs (Rhamnus cathartica) to determine if plant invasions generate changes in an individual’s expression of antipredator behavior in white-footed mice, Peromyscus leucopus, of varying sex and reproductive state. We live-trapped adult individuals within invaded habitats, uninvaded habitats, and habitats with invasive shrubs removed. Captured individuals each underwent two standardized behavioral assays to measure a suite of antipredator behaviors – an emergence test examine to the probability of leaving a protective refuge and an open field test to examine risky exploratory behavior within a novel environment. We find that the presence of invasive shrubs reduced the expression of antipredator behavioral traits regardless of sex and the reproductive state of an individual. However, when invasive shrubs were absent (uninvaded sites) or removed, an individual’s sex and reproductive state had independent and interactive effects on antipredator behavior. Our findings suggest that plant invasions reduce perceived predation risk for rodents leading to an increased probability of emergence and expression of risky exploratory behaviors. Furthermore, the effect of sex and reproductive status may consistently predict the magnitude of antipredator behavior when invasive shrubs are absent or removed, but not when present. Individuals living within habitats invaded by plants may be more likely to exhibit bolder behaviors, less responsive to the effects of predation risk, and more willing to explore risky environments relative to their counterparts in uninvaded habitats. These significant differences in individual risk-taking behavior suggest that plant invasions have the potential to fundamentally alter not only the fitness of individuals but also the nature of small-mammal interactions within invaded habitats.
