Green Iguana Proliferation in the Key West National Wildlife Refuge: a Hurricane By-Product and a Threat to the Imperiled Miami Blue Butterfly?
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Green Iguana Proliferation in the Key West National Wildlife Refuge: A Hurricane By-product and a Threat to the Imperiled Miami Blue Butterfly? Tom Wilmers, Florida Keys National Wildlife Refuges, Big Pine Key, FL 33043 Introduction No panacea: some imperfect measures: A neotropical folivore, the green iguana (Iguana iguana) • Wait for another hurricane of Wilma’s magnitude is exotic to southern Florida, where it has few known Conclusions --live vegetation will be limited and iguana numbers likely predators (Kryskyo et al. 2007) and limiting factors are greatlyYou reduced, can, of course,concentrating start your survivors conclusions and in increasing column #3 theif poorly understood. At high densities (see Meshaka et al. effectivenessyour results of intensive section is trapping“data light.” and nest destruction 2007), this reptile may threaten native wildlife (Smith et • Trap nestingConclusions females should February not be-March mere reminders of your al. 2006), including the imperiled Miami blue butterfly • Find andresults. destroy Instead, nests you want to guide the reader through what (Cyclargus thomasi bethunebakeri) (FFWCC 2010). • Collectyou stomach have concluded contentsfrom from the results. 50 trapped What isiguanas the broader to Gravid female iguanas shun densely shaded areas for determinesignificance? if blackbead Would isanyone commonly be mildly eaten surprised? Why nesting and move to more open settings to nest (Bock should anyone care? This section should refer back, Figures 1,2. The absence (left) and abundance (right) of and Rand 1989). Thus, hurricanes may create or explicitly, to the “burning issue” mentioned in the iguana nesting habitat on Boca Grande Key before and 1 maintain clearings favorable for iguana nesting. Here I introduction. If you didn’t mention a burning issue in the month after Hurricane Wilma. Notice the lone palm tree. suggest that Hurricane Wilma, the most severe Florida introduction, go back and fix that -- your poster should have Keys hurricane since 1965 (Kasper 2007), was a made a good case for why this experiment was worthwhile. catalyst for iguana proliferation. Until my study, the distribution of this reptile and its sympatry with the Miami blue in the Key West National Wildlife Refuge Distribution of green iguanas in the Key West National Wildlife (KWNWWR) were unknown. Refuge, 2011. Yellow markers indicate islands where iguana burrows were found. Methods • Searched for iguana burrows and tracks on 14 Green Iguanas and the Miami blue butterfly islands, 12 with uplands, in the KWNWR during the In the KWNWR, the Miami blue lays eggs only on blackbead In the KWNWR, the Miami blue (left), one of the rarest iguana nesting season (Feb-March) East Man Key 2 months (left) after Hurricane Wilma and the (Pithecellobium keyense) leaves and buds (Cannon et al. 2010). In butterflies in the world, lays eggs (right) only on • Trapped (42 trap nights) iguanas on 1 island in the same area 5 years later (right). Today, iguana nesting in the their native range, green iguanas eat a variety of plants but may blackbead leaves or buds. Iguana consumption of Marquesas Keys KWNWR is limited largely to remnant clearings created by consume whatever plant is most abundant and common (Rand et al. blackbead is unconfirmed but merits investigation. • Necropsied captured females to obtain clutch sizes this hurricane. 1990). Blackbead is the most common woody plant on 6 of the 8 factor for the reptile’s proliferation in the KWNWR. With few uplands that harbor the Miami blue (Wilmers pers obs.). Whether Literature Cited •Results known iguana predators in Florida (Smith et al. 2006), as the green iguana eat blackbead leaves is unconfirmed and merits Bock, B.C. and A.S. Rand. 1989. Factors influencing nesting synchrony • Iguanas present on 12 islands distributed over 28 vegetation grew after the hurricane the abundance of suitable investigation. If it does eat blackbead, Miami blue eggs and larvae nesting areas likely allowed the iguana population to grow and hatching success at a green iguana aggregation in Panama. Copeia linear km would be consumed. Miami blue numbers greatly fluctuate (Cannon 1989 (4): 978-986. • All iguana burrows were in remnants of once- large exponentially. et al. 2010) and at low numbers, iguana consumption of the clearings created by Hurricane Wilma Cannon, P., T. Wilmers, and K. Lyons. 2010. Discovery of the imperiled butterfly’s eggs could lead to extirpation on one or more of the 8 Miami Blue Butterfly on islands in the Florida Keys National Wildlife • Burrow density varied greatly among islands: highest The green iguana’s origin in the KWNWR is unknown, but given islands that harbor the butterfly. The iguana population may Refuges, Monroe County. Southeastern Naturalist 9: 847-953. on east Man Key (31 burrows in < 0.2 upland ha) their now wide distribution, it is untenable that they arrived at all increase unchecked in KWNWR until some a limiting factor is islands as waifs transported by the hurricane. Instead, as their Florida Fish and Wildlife Conservation Commission 2010. Miami blue • Largest number of burrows (n = 62) on Long Beach reached. Of great concern is a future hurricane of Wilma’s butterfly management plan. FFWCC, Tallahassee, FL. 41 pp. (Marquesas) despite only a partial search population expanded in the KWNWR, individuals from a source magnitude once again killing most of the blackbead, concentrating Kasper, K.N. 2007. Hurricane Wilma in the Florida Keys. National • Gravid females (n=3) averaged 55.6 eggs (range = population likely swam to other islands, as occurs in their native the butterfly and the reptile in the small patches that remain. The range (see Bock and Rand 1998). Oceanic and Atmospheric Administration (NOAA)/National Weather 42-61) number and severity of hurricanes is expected to increase due to Service (NWS) Weather Forecast Office (WFO) Key West, Florida. • Iguanas were syntopic with the Miami blue and global warming (Webster et al. 2006). Krysko,K.M., E.M. Enge, J.C. Donlan, and E.M Golden. 2007. nested in all 8 areas harboring the butterfly Distribution, natural history and impacts of the introduced green iguana Why iguana eradication is likely an exercise in futility: (Iguana iguana) in Florida. Iguana 14:142-151. • The size and remoteness of the occupied areas Discussion Meshaka, W.E., H.T. Smith, E. G., and J.A. Moore. 2007. Green iguanas • Iguanas swim well and move between islands. (Iguana iguana): The unintended consequence of sound wildlife In the KWNWR, Hurricane Wilma transformed what had • The largest island in the Marquesas is > 8 km long and thus is a management practices in a south Florida park. Herpetological once been a densely vegetated setting with little suitable reservoir for replenishment of animals removed from smaller Conservation and Biology 2:149-156. iguana nesting habitat (Fig. 1) into an open landscape islands Rand, S.A. B. Dugan, and D. Vianda. The diet of a generalized folivore, (Fig. 2) with an abundance of it. More than 5 years after • The reptile’s high reproductive rate and a lack of native predators Iguana iguana in Panama. J. Herpetology 26:211-224. the storm virtually all iguana burrows were found in • Trapping constraints: 1. inability to capture most age classes; 2. Smith, H.T., W.E. Meshaka, and R. Engeman. 2006. Raccoon predation remnants of clearings known to have been created by The captured gravid females (left) were large. Mean clutch trap-shyness; 3. state law mandates checking traps every 24 size was 55.6 eggs. Green iguana burrows (right) on east as a potential limiting factor in the success of the green iguana in Hurricane Wilma (Wilmers pers obs.), suggesting that hours but vagaries of weather preclude this; 4. dense, dead southern Florida. Journal of Kansas Herpetology 20:7-8. this hurricane was and continues to be an important Man Key. vegetation is mixed with live vegetation in the coastal strand; 5. Webster, P. J., G. J. Holland, J. A. Curry, and H.-R. Chang. 2006. enormous manpower needed even if traps were effective. Changes in tropical cyclone number, duration, and intensity in a warming environment. Science 16 :1844-1846. .