While the direct effects of non-native species as predators and competitors have been widely studied, the indirect effects of invasive species as novel prey on freshwater food webs are relatively unexplored despite their importance on long-term community dynamics. One type of indirect effect that can negatively impact native species arises through apparent competition, indirect competition mediated by a mutual predator. Recently, more attention has been given to such indirect relationships, yet few explore trait-mediated effects (behavior, morphology). Given their ability to influence interactions prior to emergence of density effects, these trait-mediated effects may be important drivers in community response to invasion. In Ohio, the invasive rusty crayfish (Orconectes rusticus) has been implicated as a contributing factor in the decline of native Sanborn’s crayfish (Orconectes sanbornii). This study sought to evaluate the indirect effects of the invasive rusty crayfish on native Sanborn’s crayfish through simulated apparent competition. Laboratory manipulation was used to explore the behavioral effects upon O. sanbornii and O. rusticusindividuals in response to competition, simulated predation risk and the interaction of competition and predation. Trials were video recorded and repeated over five consecutive days. Zero-and-one, beta regression was used to analyze results.
Results/Conclusions
Significant effects were observed resulting from predation risk and competition. These effects additionally interacted with species identity, indicating significant differences in the way native O. sanbornii behaviorally responded to treatments compared to invasive O. rusticus. O. sanbornii utilized refuge less than O. rusticus, however, following simulated attack refuge use significantly increased. O. rusticus demonstrated decreased refuge use prior to attack, followed by a return to control levels afterward, suggesting a possible carry-over effect across each day. Competition increased refuge use for both species at all risk levels. Activity decreased in response to elevated predation risk following simulated attack, however there is no evidence of a carry-over effect. The significance of the response varied between species, with a reduced effect on O. rusticus. Additionally, there were differences in how active time was utilized by each species. Predation risk decreased time spent foraging. However, this effect was more significant on O. sanbornii. Our results suggest species level differences between a native prey and its invasive competitor in response to elevated risk of predation and competition, providing a mechanism by which behavior may affect response to invasion. Future research should consider trait-mediated effects of indirect interactions, such as apparent competition, when exploring response to biological invasion.