Date of Award

Spring 2001

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Ecological Sciences

Committee Director

Mark J. Butler IV

Committee Member

Fred C. Dobbs

Committee Member

Cynthia M. Jones


The target-area hypothesis, based on the theory of island biogeography, predicts that larger islands are more effective at intercepting passive immigrants. Most marine invertebrates have meroplanktonic larvae and open population dynamics, so immigration to populations in isolated benthic habitats is primarily by pelagic larval recruits. Thus, recruitment to isolated habitat “islands” may be more continuous and predictable on large islands than on small ones. Consequently, populations on large islands should not only be larger than those on small islands, but should also have more evenly distributed size structures. These differences in size structure among populations in isolated habitats of differing size could have profound impacts on the local reproductive success of species if mating is size-dependent or if fecundity is related to male or female size.

I used laboratory experiments and field observations to test these predictions of the target-area hypothesis by determining if patch reef size influences the size structure and reproductive success of isolated populations of the spotted spiny lobster, Panulirus guttatus in the Florida Keys, Florida (USA). In chapter I, I provide a general introduction to the problem. Chapter II describes how growth and size-at-maturity of P. guttatus in isolated populations on coral patch reefs may be impacted by trade-offs with predation, food limitation and reproduction. In Chapter III, I explore the mating dynamics of P. guttatus as a function of different population size structure distributions that might occur on small and large patch reefs. Finally, in Chapter IV I examine the population size, size structure, and reproductive success of P. guttatus on patch reefs of varying size. Chapter V is a synopsis of these studies.

I found that the growth of P. guttatus declined significantly with the onset of reproductive activity. Although this species matures at a small size, its age-at-maturity is similar to other spiny lobster species in comparable environments. Male P. guttatus compete for mates, but it is female choice that establishes the size assortative mating system I observed in this species. Fecundity is positively related to both male and female size, which suggests that fertilization success may at times be limited by sperm availability.

The abundance of P. guttatus increased with reef size and population size structure was more evenly distributed on larger reefs, as predicted by the target-area hypothesis. Total reproductive output for local populations increased significantly with reef size, but more importantly reproductive output (i.e., success) was significantly more variable on small reefs. For isolated populations with limited immigration and size-dependent fecundity, population size, size structure, and reproductive output are impacted by the size of habitat patches on which they are resident.