Consequências do tamanho e do sexo sobre os hábitos alimentares da sucuri-amarela (Eunectes notaeus)

Abstract

The study of food habits may help to predict the consequences of ontogeny and sexual dimorphism in resource use, which can be a major factor modelling niche hypervolume. Whereas sex-related food habits changes are expected in highly dimorphic species, ontogeny can be a major factor in determining the degree of resource use variation within a species. 2. In this study we use a highly dimorphic predator with indeterminate growth, the Yellow Anaconda (Eunectes notaeus), to study the implications of sex and size on food habits. This was done under an official management plan of these snakes in Argentina, which allows collecting large sample size. 3. We tested the consequences of sex-related size-dimorphism over two foraging metrics: prey size and feeding frequency. Similarly, to test the consequences of ontogeny on trophic niche metrics, we related changes in feeding frequency and maximum prey size to increase in anacondas’ body size. 4. While females (the larger sex) did eat larger prey compared to males, this effect disappeared when we added the effect of body size. Females ate more frequently than males, even when body size effect was added. Body size positively affected maximum prey size, and as expected from foraging theory, did not increase minimum prey size. Feeding frequency did not suffer an effect of ontogeny.3 5. Our results indicate that variations in resource use as a product of sex-based differences in size are negligible in anacondas. Although females feed more frequently, this can be an effect of greater energetic costs of reproduction. Higher reproductive success for larger females seems a better explanation for sexual dimorphism in anacondas. Ontogeny, by its time, has a positive effect of maximum prey size, and this can be considered general, as it was already demonstrated for several other species which express indeterminate growth. Finally, knowledge on sex-based changes in resource use will benefit from well-defined quantitative research on diet and other resources use, which can be relevant in learning if they are consequences rather than causes for sexual dimorphism.