Egg cannibalism and the reproductive strategies of threespine sticklebacks (Gasterosteus aculeatus) in a coastal British Columbia lake

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Abstract
Patterns of egg eating and their association with differences in sex, size, abundance, and reproductive status of free-ranging sticklebacks from Kennedy Lake, British Columbia, were examined as a means of identifying the relative importance of filial cannibalism or heterocannibalism as the source of eggs in the diet. Egg cannibalism was a common event: 23.0 and 11.2% of the sticklebacks examined in 1982 and 1985, respectively, had engaged in egg eating. Eggs were a substantial part of the overall diet of the stickleback population during two breeding seasons: 27.4% of the diet of all fish by weight in 1982, 32.8% on the diet by volume in 1985. Our results do not support Rohwer''s contention that filial cannibalism is the source of most eggs in stickleback diets. Ten out of 11 predictions based on the filial cannibalism hypothesis were rejected, whereas the 11th was compatible with either the filial cannibalism hypothesis or the alternative heterocannibalism hypothesis. We conclude that heterocannibalism, not filial cannibalism, is the major source of eggs in the diet of Kennedy Lake sticklebacks. We suggest that nest raiding and egg cannibalism may minimize time spent foraging and maximize time spent on activities that increase the probability of initiating and successfully completing one or more reproductive cycles. Although the benefits of nest raiding and cannibalism are most obvious for populations breeding under conditions where food supplies clearly limit their potential reproductive output, the benefits may still apply even under conditions where alternative prey sources appear to be abundant.