Date of Award

8-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Biological Sciences

Advisor

Childress, Michael J

Committee Member

Ptacek , Margaret B

Committee Member

Kosinski , Robert J

Abstract

Traditional studies of predator-prey interactions have primarily focused on direct consumption as the most important effect on prey. Recent studies, however, have illustrated that nonlethal, risk effects may have an even greater impact. In this study, I evaluated the role of direct consumption and risk effects of the Caribbean reef octopus, Octopus briareus, on multiple species of crab and spiny lobster prey in Florida Bay, Florida. I conducted 13 monthly censuses of 8 nearshore field sites and observed the density and distribution of octopuses, crabs and lobsters. I found a significant negative correlation between the density of octopus predators and crabs, but not with lobsters. A manipulative tethering study found no correlation between crab mortality and the density of octopuses. To examine risk effects, I also quantified traits of individual octopuses, such as size, sex, and behavioral temperament (boldness). Average octopus weight was negatively correlated with crab density, but not lobster density. I also analyzed the frequency of crab and lobster prey co-denning with each octopus in shelter blocks. Shelter block use was significantly reduced for both lobsters and crabs when a resident octopus was present. Neither size nor boldness of the octopus, however, influenced the frequency of co-denning. Finally, to examine if octopus behavioral temperaments were due to adaptive phenotypic plasticity or a fixed behavioral syndrome, I captured a subset of octopuses for further behavioral observations in the laboratory. I found repeatability of behavior within individuals in response to boldness tests in the field and in the laboratory, but no correlations in temperament across situations (boldness in the field vs. boldness in the laboratory) or contexts (boldness in the field vs. activity in the laboratory). My results suggest that (1) direct consumption effects are more important on crabs than on spiny lobsters but may be relatively weak overall, (2) octopus risk effects influence den use of both lobsters and crabs, reducing availability of protective shelters and increasing risk of predation from other predators, and (3) octopuses have consistent behavioral temperaments that are expressed variably in each new situation and context. I found no significant relationship between the temperament of octopuses and co-denning of either prey species, suggesting prey limitations in assessing risk effects associated with predators of varying boldness.

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