Temporal variability in sexual selection acting on reproductive tactics and body size in male snakes.

Although the selective forces responsible for the evolution of mating systems and sexual size dimorphism have been the subjects of intensive research, most studies rely on data from only one or a few years (e.g., Clutton-Brock 1988). Temporal variation in the importance of alternative reproductive tactics, or in consequent selective pressures on behavior or morphology, has not been documented from long-term studies. Nonetheless, the magnitude of such variation and the factors responsible for it are of central importance to any attempt to infer long-term evolutionary pressures from short-term data on the direction and intensity of selection. Previous authors have suggested, on the basis of variation in sex ratios within a single breeding season (Arak 1983; Verrell 1983) or interspecific