Population Dynamics Based on Size or Age? A Reef-Coral Analysis

Abstract

Much of the variability in the dynamics of individuals in a population is due to differences in age or size. We simultaneously classified colonies of three coral taxa into age and size classes and found that virtually every size class contained colonies that were both young and old. Rates of growth and survival of colonies were measured in order to examine, for the first time for an animal population, the influence of age on growth and survival regardless of size, and vice versa. Size effects were stronger, but the age of the colony also had a significant impact on growth rates of the colony in two of the three taxa. Age effects independent of size were also found. Specifically, old small colonies died more often and grew more slowly than younger corals of the same size. Although biologists have traditionally viewed size and age as alternative ways of classifying populations, models based on simultaneous analyses of size and age may provide greater insight into the dynamics of organisms with highly variable rates of development.