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