Scale dependence of sex‐specific movement in a small‐bodied stream fish

Abstract

Abstract Animal movement at localised scales is often modulated by competing pressures such as avoiding predators while acquiring resources and mates. The relative magnitude of these trade‐offs may affect males and females differently, often resulting in sex‐specific differences in movement. Sex‐biases in movement have been linked to mating systems (e.g. monogamy or polygamy) in birds and mammals; however, this relationship has received less attention among fishes. Using passive integrated transponder tags and a series of stationary antennas, we evaluated the movement dynamics of a small‐bodied, sexually dimorphic stream fish Fundulus olivaceus over a 30‐day period in a fourth‐order tributary to the Pascagoula River in Mississippi (U.S.A.). We documented dissimilar sex‐specific movement behaviours at different spatial scales that were likely to be facilitated by differential resource demands and competitive pressures. Females exhibited an increased propensity to engage in longer, exploratory moves (>30 m); whereas most males remained active within an established territory, making few long‐distance longitudinal movements. Local activity levels (proportion of individuals moving) were positively related to density (manipulated during the study), and density was found to affect the magnitude of sex‐specific movement. In contrast to females, males increased local activity and movement distance at the reduced density, presumably to expand territory size or mate‐searching behaviours, suggesting local mate competition may suppress the movement distance of males. Despite some evidence substantiating a relationship between movement and mating system, our results suggest that the documented sex‐specific differences may be related to traits that co‐evolve with mating systems, rather than the mating system per se. Our findings also highlight the importance of spatial scale when evaluating patterns of sex‐biased movement tendencies.