The Effects of the Cuban Treefrog (Osteopilus septentrionalis) on Native
Treefrog Populations within Everglades National Park
Kenneth G. Rice
U.S. Geological Survey, Center for Water and Restoration Studies, Ft. Lauderdale
FL
J. Hardin Waddle
U.S. Geological Survey, Big Cypress Field Station, Ochopee FL
Marquette E. Crockett and Amber D. Dove
USGS Florida Cooperative Fish and Wildlife Research Unit, Everglades Field
Station, Homestead FL
Native amphibian fauna throughout South Florida is currently threatened by the
presence of an exotic competitor, the Cuban treefrog (Osteopilus septentrionalis)
(fig. 1). First reported in the Florida Keys (Barbour, 1931), Cuban treefrogs
expanded their range and were present in Everglades National Park as early as the
1950’s (Meshaka 2001). Cuban treefrogs compete with native treefrogs for
breeding space and food sources.
Figure 1: Cuban Treefrog
(Osteopilus septentrionalis)
in Everglades National Park
In addition, Cuban treefrogs and their tadpoles are carnivorous and prey upon
other frog species (Meshaka 2001; Babbitt and Meshaka 2000). Despite anecdotal
evidence, no study has shown the extent to which Cuban treefrogs reduce
populations of native hylids in natural areas. The goal of this study is to examine
the direct effect Cuban treefrogs have on native treefrog populations within
Everglades National Park. Native treefrogs studied included the Green (Hyla
cinerea; Hci), and Squirrel (Hyla squirella; Hsq).
Population estimates for treefrogs were obtained through a mark-recapture study
using PVC refugia. Five study plots were selected within Everglades National
Park (2 mangrove and 3 pine rockland sites). Two of these sites are near disturbed
areas, while all others are fairly remote. After initial population estimates were
obtained, Cuban treefrogs were removed from sites to examine the recovery of
native populations. Additionally, predation of hylids by Cuban treefrogs was
quantified through stomach content analysis of removed animals.
To date, approximately 2,200 individual frogs have been included in this study.
Preliminary results indicate Cuban treefrogs are more numerous in plots 501 and
101, which are located near disturbed areas, while remote sites contained larger
populations of native species (fig. 2). Initial results indicate that native
populations significantly increase as Cuban treefrogs are removed. The largest
population increases occurred at sites where Cuban treefrogs were originally most
dense (table 1). Preliminary analysis of stomach contents suggest that predation
on hylid treefrogs is higher in mangrove than pine rockland sites.
800
700
600
500
Ose
Native
400
300
200
100
0
101
501
Shark
LPK-W
LPK-E
Figure 2: Total captures of Cuban (Ose) and native treefrogs in study plots
within Everglades National Park from November 2000 to November 2002
Table 1: Mean number of captures per visit of Cuban (Ose), Green (Hci) and
Squirrel (Hsq) treefrogs before and after removal of Cuban treefrogs in sites
101 and 501 (* statistically significant)
N (NUMBER
VISITS)
PREREMOVAL
N (NUMBER
VISITS)
POSTREMOVAL
501-Ose
30
8
28.100 (± 5.497)
30.375 (± 5.928)
501-Hci *
30
8
1.533 (±0.328)*
19.500 (± 6.743)*
501-Hsq *
30
8
0.267 (± 0.117)*
1.500 (±0.886)*
101-Ose
29
7
15.414 (±3.260)
13.714 (±2.476)
101-Hci
29
7
1.517 (±0.411)
0.143 (±0.143)
101-Hsq *
29
7
0.379 (±0.104)*
3.571 (±1.343)*
SITE AND
SPECIES
MEAN
CAPTURES
PRE-REMOVAL
MEAN
CAPTURES
POST-REMOVAL
To adequately monitor the effects of Cuban treefrogs on native populations, this
study will continue until Fall 2003. After completion, the results of this study
may be used to identify factors that facilitate or obstruct dispersal of Cuban
treefrogs into natural areas. In addition, this information will be incorporated into
an ArcInfo model of the potential spread and impact of Cuban treefrogs on native
species in protected areas. Data will be available to cooperating agencies and the
public.
Literature Cited
Babbit, K.J. and W.E. Meshaka. 2000. Benefits of eating conspecifics: Effects of
background diet on survival and metamorphosis in the Cuban treefrog (Osteopilus
septentrionalis). Copeia 2000(2): 469-474.
Barbour, T. 1931. Another introduced frog in North America. Copeia 1931(3):
140.
Meshaka, W.E. 2001. The Cuban Treefrog in Florida – Life History of a
Successful Colonizing Species. University Press of Florida.
Marquette E. Crockett, USGS - Florida Cooperative Fish and Wildlife Research
Unit, Everglades Field Station, 4001 SR 9336, Homestead FL 33314
Phone: 305-242-7800 x7333, FAX: 305-242-7834
marquettecrockett@hotmail.com