Importance of Isolated Wetlands to Vertebrates in Florida
Office of Environmental Services, Vero Beach
Florida Game and Fresh Water Fish Commission
Wetlands, with their combination of plant and water regimes,
support a great variety of flora and fauna and contain the most
productive wildlife habitat of all land forms (Toburen and Windell,
1977). Section 373.414 Florida Statutes (1986), requires the five
Florida water management districts to adopt a rule, by March 31, 1987,
establishing specific perr:itting criteria for isolated wetlands,
including size thresholds below which impacts on fish a:d wildlife and
their habitats will not be considered. The isolated wetlandss under
consideration do not fall under the jurisdiction of the Department of
Environmental Regulation for the purposes of regulation of dredginii and
Small, isolated wetlands, whether managed individually or as
components of clusters or complexes linked by sheet flow, increase
habitat heterogeneity and provide more edge (Brown and Dinsmore, 1986).
Because of their physical diversity (i.e. marshes, ponds, cypress heads,
hardwood swamps) and juxtaposition with an array of important upland
habitats, these wetlands provide some or all of the habitat requirements
for not only wetland species, but upland wildlife as well (Schitoskey
and Linder, 1978).
Small, isolated wetlands provide water, food, and cover for a
diversity of herpetofauna, waterfowl, marsh birds, wading birds, and
small mammals. Many species of upland wildlife use wetlands for
foraging or as escape cover, including white-tailed deer, opossum, and
eastern cottontail, while the presence of prey such as deer, waterfowl,
and marsh rabbits attracts a host of predators including carnivores,
raptors, and snakes (Schitoskey and Linder 1978).
At least 190 species of vertebrates, excluding fishes, may depend
on Florida's small, isolated, often ephemeral wetlands according to
their availability and geography, during one or more seasons of the year
(Table 1). Species listed by the Commission as endangered (E),
threatened (T), or of special concern (SSC) comprise over 5% (11 of 190)
of this total. Because man continues to usurp upland habitats at an
alarming rate, wetlands are becoming more and more important as breeding
habitat for many of these species (70%, 133 of 190).
Fish species composition and density is influenced by the duration
and depth of standing water, and the relationship of the wetland to a
permanent body of water. For example, the mosquitofish could be found
in a very shallow, temporary wetland if the wetland was connected by
sheet flow to a canal, deep marsh, or farm pond. A wetland with
permanent standing water has a high probability of maintaining a viable,
diverse fish population, regardless of its size.
At least 108 species of birds use small, isolated wetlands,
including 8 (7.4%) listed as E, T, or SSC by the Commission. These
avifauna utilize, and at certain times depend on, isolated wetlands as
small as 1/2-acre, including the wood stork (E) and Florida sandhill
crane (T) (S. Nesbitt, pers. comm.). The location, rather than size, of
the wetland in relation to other habitat types may be the most critical
factor determining its utilization by cranes (S. Nesbitt, pers. comm.).
Thus, juxtaposition of small, isolated wetlands to other important,
disimilar habitats as well as other isolated wetlands is attractive to
an array of avian species for nesting, foraging, loafing, roosting, and
Small wetlands interspersed with improved pastures are extremely
attractive to sandhill cranes, especially in south Florida where one
study documented 23 of 58 (40%) active nests in isolated wetlands less
than 5 acres in size (M. Bishop, pers. commn.).
Many species of dabbling ducks which nest on small prairie
potholes, winter on small, isolated marshes, ponds, and strip pits
(Bellrose 1980). In addition, many species of marsh birds such as rails
and gallinules prefer wetlands as small as 1/2-acre; sufficient sedge
aud cattail edge seem to be more important than large size (Berger 1951,
In some ways, the biological importance of isolated wetlands to
amphibians is directly proportional to their degree of isolation (P.
Moler, pers. comm.). The presence of small lakes, ponds, marshes, and
swamps are particularly critical for the survival of at least 17 species
of Florida amphibians. Aquatic species, such as the two-toed amphiuma,
dwarf siren and greater siren, and many ranid frogs require permanent
water habitats, while hylid frogs and some salamanders require
seasonally flooded, ephemeral wetlands adjacent to uplands (Kautz 1984).
The presence of a diversity of small wetland types scattered throughout
the landscape is especially valuable to the production of these
Lrimnutive vertebrates that are essential components of food chains of
L;iger animals (Kautz 1984).
SMany species of amphibians are restricted to small, isolated,
ephemeral wetlands for breeding (P. Moler, pers. comm.). While many
amphibians utilize a wide range of different sized wetlands, at least 13
(43%) depend on these small wetlands, even when larger, permanent waters
are available (Table 1).
In summary, isolated wetlands provide essential habitat for several
vertebrates with specific habitat requirements, but are utilized by a
grcat variety of species with more generalized food and cover
requirements. Indications are that wetland habitat proximity,
physiography, and seasonality are more important factors governing
wildlife use than wetland size.
Bellrose, F.C. 1980. Ducks, geese, and swans of North America.
Stackpole Books, Harrisburg, Pa.
Brown, M. and J. J. Dinsmore. 1986. Implications of marsh size and
isolation for marsh bird management. J. Wildl. Mgmt.
Sanderson, G. C. 1977. Management of migratory shore and upland game
birds in North America. The Internat. Assoc. of Fish and Wildl.
Kautz, R. S. 1984. Criteria for evaluating impacts of development on
wildlife habitats. Proc. Annu. Conf. Southeast. Assoc. Fish and
Wildl. Agencies 38:121-136.
Schitosky, F. and Linder, R. L. 1978. Use of wetlands by upland
wildlife, in Wetland functions and values: the state of our
understanding. Ed. Greeson, Clark, and Clark.
Toburen, C. D. and J. T. Windell. 1977. Study plan for the lower
' Gunnison River basin wetland inventory and evaluation. U.S.D.A.,
Soil Conservation Service, 14 pp.