The ontogeny of piscivory and its ecological consequences

In this study, we review the wealth of ecological information available for 27 species of freshwater piscivores from Europe and North America and examine the factors that determine variation in the diet ontogeny of piscivores and consider some of the ecological consequences of this variation. Focusing on interspecific variation, we found that species that were born larger and had larger mouth gapes became piscivorous at younger ages and at smaller sizes. However, there was no relationship between time of spawning (measured by average spawning temperature) and size at age 1 or size when becoming piscivorous. Species that became 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 similar body length. These data suggest that most of the variation found in the sizes of prey eaten by piscivores is due to differences in piscivore body size.