Factors influencing movement probabilities of Florida tree snails Liguus fasciatus (Muller) in Big Cypress National Preserve following Hurricane Andrew

Bennetts, Robert; Sparks, Steven; Jansen, Deborah

Beginning in 1993, approximately one year after Hurricane Andrew, we marked 2,547 Florida tree snails (Liguus fasciatus) during six sampling (mark-resighting) occasions twice per year over a three-year period. During each sampling occasion, we conducted a search for all tree snails within 16 sample plots on eight hammocks (tree islands) and for an extended radius of approximately 20 m around each plot. We individually marked all trees > 5 em dbh within each plot and all trees within the extended radius in which a marked snail was found. Because the host tree for each marked animal was known, inter-tree movements could be directly measured as the proportion of animals found on different host trees at times t and t + 1 . We observed 533 marked snails during two or more consecutive sampling occasions. Of these, 414(77. 7%) snails had moved from one host tree to another between sampling occasions. Based on a conditional logistic regression model, movement probabilities were influenced by whether or not the snail's host tree had been Lysiloma at time t, the diameter of the host tree at time t, and interactions among these and with year. Overall, snails had a lower probability of moving from one tree to another if their host tree had been Lysi/oma and if they were on larger host trees. We found no evidence that movement probabilities were influenced by the snail's subspecies, age, hammock size class, or by the season. An effect of latitudinal gradient or proportion of host-trees damaged was not retained in our final model. However, a preliminary univariate analysis did indicate a difference in movement probabilities between our northernmost hammocks, which had relatively little hurricane damage, and the southern hammocks, which had extensive damage.

Factors influencing movement probabilities of Florida tree snails Liguus fasciatus (Muller) in Big Cypress National Preserve following Hurricane Andrew

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