Habitat scale, female cannibalism, and male reproductive success in three-spined sticklebacks <i>(Gasterosteus aculeatus)</i>

Abstract

We studied the effects of habitat scale (pool size) on the risk of egg cannibalism and the breeding behavior of three-spined sticklebacks (Gasterosteus aculeatus). Laboratory experiments showed that in pools with similar population density, a larger fraction of males nested in pools of 4.8-m2 surface area than in 15-m2 pools. Breeding males in the 4.8-m2 pools also had bigger territories, obtained more eggs, and were more aggressive toward intruders than those in the 15-m2 pools. The numbers of raids attempted on nests were similar in the two pool sizes. However, raiding-shoal sizes were larger, and hence individuals in these larger shoals were more succesful at overwhelming male territorial defenses in the 15-m2 pools than in the 4.8-m2 pools. At the field site, a salt marsh containing hundreds of tide pools of different sizes, sticklebacks settled at similar densities in small (<30 m2 surface area) and large (>355 m2) pools. This resulted in significantly more fish being present in large pools than in small pools, a concomitant increase in the amount of nest raiding, and a decrease in individual male reproductive success in large compared to small pools. A photogrammetry analysis of the salt-marsh pools suggests that the majority of fish breeding at the site will be subjected to a high risk of cannibalism because most fish nest in large pools. We conclude that spatial scale has a major influence on this species' breeding behavior and reproductive success.