Identifying population sinks in the upper Florida Keys: A demographic modeling approach.
Chockley, Brandon*,1, 2, St. Mary, Colette1, Osenberg, Craig1, 1 University of Florida, Gainesville, Florida, USA2 Lewis and Clark College, Portland, Oregon, USA
ABSTRACT- In this talk, we detail a demographic model that was developed to identify sink populations of the banded coral shrimp, Stenopus hispidus, in the upper Florida Keys. Field studies identified variable size-structures between inshore and offshore reefs, where smaller, typically immature, shrimp dominated offshore reefs, while larger, mature shrimp, dominated inshore reefs. By using artificial reefs, we showed that settlement to the offshore reefs was much higher than that to those inshore. Using an extensive tagging study, we documented size-selective mortality, which was consistent between the offshore and inshore reefs. Smaller individuals experienced higher rates of mortality than did larger individuals. Post-settlement movement was found to be minimal, with no evidence of long distance movement between offshore and inshore reefs. Finally, growth in the offshore reefs was much slower than that in the inshore reefs. These studies indicated that the offshore reefs may be dominated by smaller shrimp because settlers rarely reach larger sizes, due to lower growth rates and increased periods of vulnerability to high mortality and may be acting as population sinks. To investigate this hypothesis, we developed a demographic model that utilized the estimated parameters for size-specific molt frequency and mortality, and region-specific settlement and growth rates for 10,000 settlers over a span of 200 weeks. The model allowed us to follow individual settlers through time, while keeping track of weekly sizes, pairing and reproductive events, and size at mortality. Preliminary results indicated that only a single individual reached sexual maturity in the offshore region, while 42 individuals reached maturity in the inshore region. In addition, 5 mating pairs were formed in the inshore reefs, resulting in a total of 10 mating events and an estimated reproductive output of approximately 5,842 larvae. Results from the model indicate that the offshore region is, in fact, acting as a population sink.
Key words: demographic modeling, population sinks, stenopus hispidus
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