Mechanisms of Movement Patterns: Physiology and Sex Influence Gopher Tortoise (Gopherus polyphemus) Movement

A central topic in spatial ecology is identifying what determines animal movement patterns, including both exogenous and endogenous factors. Given that there are different sex-based selection pressures in mating and reproduction, movement patterns often vary between males and females in predictable manners; males of polygynous species typically move more than females to maximize mating opportunities. In female polygynous animals, selection is generally thought to favor movement patterns with smaller home ranges and high spatial site fidelity. Physiology may also constrain movement patterns in a way that can obscure sex-specific selection. We used GPS loggers and physiological assays to study Gopher Tortoise (Gopherus polyphemus) movement patterns to determine how movement patterns depend on physiology (as measured by the baseline and the change in plasma lactate concentration in response to standardized exercise challenge and body condition) and movement strategy (total distance traveled over the course of the study, daily distance traveled, maximum daily displacement, home range area, burrow use) by sex. Total distance traveled was positively related to body condition and negatively related to baseline lactate concentration (which is an inverse metric of aerobic fitness). Thus, total distance traveled was physiologically constrained. Change in plasma lactate concentration, however, was not related to any of the space usage parameters. Home range area and burrow use were not related to any physiological metrics. There was not a significant difference in total distance traveled nor daily distance traveled between male and female Gopher Tortoises, but males had larger maximum daily displacements than females. Males also had larger home range areas. Male and female Gopher Tortoises thus used different movement strategies that may have maximized fitness consistent with different selection pressures by sex in a scramble competition mating system.