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Keywords:

  • Behaviour;
  • bottom-up;
  • competition;
  • predation;
  • recruitment;
  • reproduction;
  • top-down

Abstract

Generalizations describing how top-down and bottom-up processes jointly influence the production of offspring (recruitment) and the number of reproducing adults are lacking. This is a deficiency because (1) it is widely recognized that both top-down and bottom-up processes are common in ecosystems; and (2) the relationship between the number of individuals recruiting and number of reproductively active individuals present in that population is of fundamental importance in all branches of ecology. Here we derive a model to consider the joint effects of top-down and bottom-up forcing in any ecosystem. In general, during the lifetime of a cohort, bottom-up effects are likely to limit recruitment over longer periods of time than top-down effects. Top-down effects are likely to be most important early in the life history when potential recruits are small in size, and such effects will be more recognizable in small cohorts comprised of slowly growing individuals.