Reciprocal Oscillations in Densities of Larval Fish and Potential Predators: A Reflection of Present or Past Predation?

Abstract

Reciprocity in time series data on the abundance of potentially interacting species has been one basis of empirical support for existing predator–prey theory. Evidence of this type has frequently been used to support the belief that predation by macroinvertebrates is one of the major causes of mortality among the early life stages of marine fishes. We question the validity of this generalization. We observed statistically significant inverse correlations between the abundance of macroinvertebrate predators and coastal ichthyoplankton in coastal Newfoundland both at the same site between years and at different sites in the same year. This correlation was shown to result not from a causal predator–prey interaction, but from occupation by the larvae and the macroinvertebrates of discrete water masses whose presence in the coastal area oscillates temporally in response to changes in wind conditions. Reevaluation of previously published reciprocal oscillations in the abundance of larval fish and potential predators, which had been cited as evidence of predatory regulation of larvae numbers, showed that in all cases available physical data suggest that these correlations too may have been spurious. We suggest that historical temporal variations in predator abundance may have served as a template for the evolution of adaptive strategies on the part of larval fishes which effectively isolate them from potential predators in either the temporal or spatial dimension. Our analyses suggest that such adaptations involve active behavioral responses to reliable physical and/or biological signals indicative of the existence of ecological "safe sites."