Date of Award

Fall 1999

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Mark Butler, IV

Committee Member

Simon Thorrold

Committee Member

Kent Carpenter

Call Number for Print

Special Collections LD4331.B46 S342


There has been a considerable amount of research devoted to exploring the relationship between predators and prey, but many of these studies fail to address how predation can vary over spatial and temporal scales. The tendency of ecologists to model predation as a static entity often masks its capacity for creating distinctive effects in prey populations and communities. Most predation studies also focus on the effect of a single species of predator on a prey population, an unrealistic situation in nature. In the Florida Keys, juvenile spiny lobsters are subjected to two general classes of predators: i) "resident" predators such as groupers and octopus, and ii) "transient" predators such as sharks and large teleost fish. The purpose of this study was to compare the impact of a resident predator (red grouper; Epinephelus morio) to a suite of transient predators on juvenile spiny lobster population structure and dynamics. The Jolly-Seber mark-recapture protocol, modified for Jackson's method, was run at 12 paired grouper and transient predator field sites to estimate emigration, immigration, and mortality. In a separate experiment, I tethered lobsters at increasing distances from a grouper's den to estimate of the relative vulnerability of different sizes of lobster and grouper foraging distances. Tethering results indicate that red grouper exhibit localized foraging, and when at sizes >45 cm total length, they are capable of consuming lobsters at least as large as 33 mm carapace length (CL). Mark-recapture sites containing grouper had significantly fewer juvenile lobsters < 35 mm CL than transient predator sites, implying either that resident groupers effectively reduce the densities of small lobsters, or that small lobsters avoid areas harboring grouper. However, size-specific survival was not affected by predator treatment, as measured using Jackson's method. In addition, the presence of resident grouper also did not affect size-specific lobster emigration, immigration, or on-site movement. The disparity between population structure and size-specific survival and movement may be due to low densities of lobsters on field sites and/or low recapture rates, which resulted in weak estimates of movement and survival.


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