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The Likely Cause of Extinction of the Tree Snail Orthalicus Reses Reses (Say)

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The Likely Cause of Extinction of the Tree Snail Orthalicus Reses Reses (Say) University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Cooperative Fish & Wildlife Research Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications Unit 2001 The Likely Cause of Extinction of the Tree Snail Orthalicus Reses Reses (Say) E.A. Forys Eckerd College A. Quistorff Eckerd College Craig R. Allen University of Nebraska-Lincoln, [email protected] D.P. Wojcik United States Department of Agriculture Follow this and additional works at: https://digitalcommons.unl.edu/ncfwrustaff Part of the Other Environmental Sciences Commons Forys, E.A.; Quistorff, A.; Allen, Craig R.; and Wojcik, D.P., "The Likely Cause of Extinction of the Tree Snail Orthalicus Reses Reses (Say)" (2001). Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications. 6. https://digitalcommons.unl.edu/ncfwrustaff/6 This Article is brought to you for free and open access by the Nebraska Cooperative Fish & Wildlife Research Unit at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Published in Journal of Molluscan Studies 67 (2001), pp. 369-376. THE LIKELY CAUSE OF EXTINCTION OF THE TREE SNAIL ORTHALICUS RESES RESES (SA Y) E.A. FORYS,I A. QUISTORFF,I C.R. ALLEN,2 AND D.P. WOJCIK3 JEnvironmental Studies, Natural Science Collegium, Eckerd College, 4200 54 ,h Avenue South, St. Petersburg, Florida 33711, US A., email forysea@eckerdedu 2 US Geological Survey, Biological Resources Division, South Carolina Cooperative Fish and Wildlife Research Unit, Clemson University, Clemson, SC29634, USA. 3 United States Department of Agriculture, ARS, CM A VE, Gainesville, FL, 32604, USA. (Received 30 June 2000; accepted 19 February 200 I) ABSTRACT The Stock Island tree snail, Orthalicus reses reses, went extinct in its native range in the Florida Keys in 1992. Fortunately, 0. r. reses has been introduced elsewhere and further reintroductions are currently planned. Before these reintroductions are implemented, it is important to try and determine which factors were most likely to have caused the decline and extinction. While habitat destruction was prob­ ably the ultimate reason why there were so few tree snails, it is likely that an interaction of habitat frag­ mentation and the invasion of an exotic predator caused the final decline that lead to the extinction in 1992. We examined the last 93 0. r. reses shells to infer cause of death. In addition, using surrogate Florida tree snails, Liguusfasciatus, we conducted experiments on two previously unstudied causes of mortality: predation by red imported fire ants, Solenopsis invicta, and mortality from falls caused by wind. We found that the majority of the last 0. r. reses shells were intact, indicating that mammalian and bird predation were not the greatest causes of mortality. Mortality caused by wind knocking tree snails onto the rocky hammock substrate appeared to be a potential source of mortality, but few of the tree snails exhibited signs of breakage. Mortality from fire ants appears to be one of the most likely causes of the recent decline and extinction of 0. r. reses. Experiments indicated that in a semi-natural enclosure, fire ants were capable of killing all ages of L.fasciatus, even during aestivation. Fire ants are currently found throughout the last known habitat of 0. r. reses and were first discovered in this area at the time of the decline. INTRODUCTION and the last 93 shells were collected soon after death and preserved. In 1992, in the wake of a large hurricane, the last few Orthalicus r. reses is a tree snail that has a large (up to Stock Island tree snails, Orthalicus reses reses (Say), 7.5 cm length) white to buff conical shell with narrow, were removed for a captive-breeding project from a flame-like purple-brown axial stripes (Binney, 1885). 3 ha forest patch in the Lower Keys of Florida. Despite Historically it occurred in hardwood hammocks (trop­ several intense searches conducted over the next several ical evergreen forests) throughout Stock Island and years, no additional snails were found, indicating that Key West (Fig. 1). Relatively little is known about the this subspecies has gone extinct in its historic range. natural history or ecology of this tree snail, however, Fortunately, the snail had been reintroduced outside they are most active immediately following rains this range and there are several small remaining popu­ during the wet season (May- October) and aestivate for lations. In addition, individuals have been found in a much of the dry season (November- April). residential yard in Key West, although it is possible In addition, research on reproduction indicates that that this population was recently introduced (U.S. Fish 0. r. reses is hermaphroditic and mates during the wet and Wildlife Service, 1999). Currently, debate exists as season. Eggs are laid in a shallow hole in the ground to whether to reintroduce the snails to several remain­ beneath a tree, approximately two weeks after copula­ ing patches of hardwood forests in their native range. tion and young emerge during rainy periods at the end Before such a reintroduction occurs, it is important to of the dry season (Deisler, 1987). Throughout its life it determine why 0. r. reses went extinct. Unlike many feeds on epiphytic lichens, fungi, and algae on tree extinctions of small, secretive organisms, the decline of surfaces. this subspecies has been relatively well documented In museum collections, the last 0. r. reses was 1. Moll. Stud (2001 ), 67,369- 376 © The Malacological Society ofLondon 2001 This article is a U.S. government work, and is not subject to copyright in the United States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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