THE ONTOGENY OF PISCIVORY AND ITS ECOLOGICAL CONSEQUENCES

In this study, we review the wealth of ecological information availabl e for 27 species of freshwater piscivores from Europe and North Americ a and examine the factors that determine variation in the diet ontogen y of piscivores and consider some of the ecological consequences of th is variation. Focusing on interspecific variation, we found that speci es that were born larger and had larger mouth gapes became piscivorous at younger ages and at smaller sizes. However, there was no relations hip between time of spawning (measured by average spawning temperature ) and size at age 1 or size when becoming piscivorous. Species that be came piscivorous at smaller sizes were also larger by age 1, and size differences expressed by piscivores in their first year of life tended to carry over to later ages. Not surprisingly, maximum and mean prey size eaten increased with predator size in all species. However, while piscivore species differed in morphologies and feeding efficiencies, prey sizes in the diets were remarkable similar for piscivores of simi lar body length. These data suggest that most of the variation found i n the sizes of prey eaten by piscivores is due to differences in pisci vore body size.