Does the activity budget hypothesis explain sexual segregation in ungulates?

The activity budget hypothesis proposes that the main force driving sexual segregation is the difference in activity between males and females. Recently, a model was developed to demonstrate explicitly that such differences in activity could, in theory, produce sexual segregation (Ruckstuhl & Kokko 2002, Animal Behaviour, 64, 909-914). The question remains whether realistic parameter values can also generate significant sexual segregation. Using this model and data on the body size dimorphism for 144 ungulate species, we compared the sexual segregation predicted by the model with expectations based on field observations. The results do not support the activity budget hypothesis as the main factor explaining sexual segregation. We investigated activity synchronization, the animal movement rule and transient spatial distributions in further detail. Introducing activity synchronization into the model slightly increases the ability of the activity budget to generate sexual segregation. Changing an animal's movement rule has a strong effect; movement rules that are independent of activity generate no long-term segregation. Finally, changes in a population's home range allow activity budget differences to generate transient sexual segregation. This method of generating sexual segregation is not sensitive to the animal movement rule and is potentially an important mechanism by which activity budgets can generate sexual segregation.