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Effective Management for Frogs and Toads on Florida's Ranches 1
Kimberly J. Babbitt and George W. Tanner2In this document we explain how cattle ranchers can maintain and/or provide habitat for Florida's frog and toad species within the context of a successful ranching operation.
Background
Florida boasts 28 species of frogs, each with their own particular requirements. Body sizes of frogs in Florida range from the familiar bullfrog that can reach 8 inches in length-to the little grass frog which, at less than an inch long, is the smallest frog in North America.Florida's warm, humid climate and the variety of habitat types found within the state are some of the reasons for its large number of species of frogs and toads. Another key feature is the abundant number and type of aquatic environments. Of particular importance to frogs and toads are wetland habitats.
Biology of Frogs and Toads
Frogs and toads are amphibians, which literally means "double life" in ancient Greek. The designation "amphibian" is appropriate for most frogs and toads because they have two distinct stages: an aquatic larval stage known as a tadpole and an adult terrestrial stage.With the exception of one introduced species, all frogs and toads living in Florida lay eggs in water. The eggs develop into tadpoles which have more of a fish-like, than frog-like, appearance. After a period of growth and development, tadpoles undergo a complex and rapid metamorphosis (change in form) where they take on the body form and appearance of a typical adult.
In addition to their differing appearances, tadpoles and adults also have very different food and habitat requirements. In the aquatic environment most tadpoles eat algae and bacteria. After metamorphosis, frogs mainly eat insects. All tadpoles require an aquatic environment for development. Some species, such as the pig frog, remain semi-aquatic as adults; however, many species are very terrestrial, living in pastures and forests, as adults.
Frogs and toads can be difficult to see outside their breeding season. During the breeding season, males congregate at wetlands and call to attract breeding females. This is the only time of the year that you are likely to see some species. Because frogs vocalize very little outside of the breeding season, and because many species burrow below ground or sit quietly on vegetation, it is easy to underestimate how abundant frogs may be on any piece of land. Thus, it is also easy to underestimate the importance of frogs as predators, as well as food for other species.
Frogs are an important part of the diet of many animal species, including wading birds, the caracara, the red-shouldered hawk, snakes, and raccoons, just to name a few.
What determines the species you may find on your ranch?
First, different species have different geographic ranges. In other words, some species are specific to different areas of the state: Some species found in the Florida panhandle do not occur in south Florida.Assuming a species does occur in your area, there are many factors that influence its local distribution. Two factors have a large influence on species distribution and abundance: the habitat requirements of the adult and the habitat requirements for the tadpole. Both requirements must be met for a species to survive. It is partly because of their complex life cycle, with both aquatic and terrestrial phase, that management for frogs and toads requires consideration of both adult and larval habitat requirements.
Not all wetlands are the same: Permanent vs. temporary wetlands
Frogs have particular breeding association with certain types of wetlands. The hydrology of the aquatic site determines which species can successfully breed. Permanent aquatic sites such as lakes, deep ditches or retention ponds usually host large, predatory fish. These fish eat tadpoles; and so, many species cannot survive in the presence of predatory fish. However, tadpoles of some species can coexist with fish-either because fish dislike their taste, or because they have behaviors that decrease the chances of being eaten.In contrast, many species only breed in wetlands that undergo periodic dry-downs that eliminate their fish predators. Most frog and toad species in south Florida breed in this type of wetland.
The type of wetland that a species tends to breed in has a large influence on the way a tadpole develops, specifically how long it takes for a tadpole to develop into adult form. (For example, pig frogs usually breed in permanent water bodies and their tadpoles take more than 6 to 12 months to develop into adult life form.)
Squirrel treefrogs bred in very temporary wetlands and their tadpoles can develop in 3 to 4 weeks. In between these extremes, southern leopard frogs may breed in a wide range of wetlands, including permanent sites, and their tadpoles generally take 1.5 to 3 months to develop.
While predation makes permanent sites unsuitable breeding sites for many frog species, the breeding success of species using temporary wetlands depends on how long the wetland holds water. Because rainfall patterns are variable from year to year, the ability of a single wetland to provide suitable breeding habitat for different frog species can also differ. Sites with several wetlands that have differing filling and drying patterns provide good safeguards against breeding failure.
Ditching: a problem?
Altering the drainage pattern of a site through ditching will obviously result in a change in the amount of time a wetland holds water. Drainage can result in changing historically permanent sites to temporary sites, and decreasing the amount of time temporary sites hold water. Under extreme drainage conditions, former wetlands may functionally become uplands. Because most Florida frog and toad species do not require wetlands that hold water year-round, most drainage activities for cattle grazing are compatible with the breeding requirements of many frog and toad species.Managing the Landscape for Frogs and Toads
During 1992-1995, we conducted research on frog and toad populations at the MacArthur Agro-ecology Research Center (formerly known as Buck Island Ranch) near Lake Placid, Florida. Based on this research, we have identified some important aspects to consider for managing frog and toad populations on your property.The first consideration is wetland hydroperiod. Hydroperiod determines the suitability of a site for breeding. Many of the small wetlands that hold water for only a few weeks or months each year (and which may not hold any water at all in dry years) are the most valuable sites for many species. For example, species such as squirrel treefrogs, narrow-mouth toads (you may recognize this species' call-it sounds like a bleating sheep), chorus frogs and little grass frogs lay their eggs in such wetlands. These species cannot survive without these "ephemeral" wetlands.
Managing the landscape for enhanced grazing opportunities through wetland ditching is compatible with the breeding requirements of these species if small wetland sites remain interspersed throughout the landscape.
What about habitat requirements of adult frogs and toads?
Cattle ranchers can provide habitat for many species with little or no effort. Many species spend much of there adult lives either in or near the ground, and specific ground covers are not generally necessary. For some species, leaving clumps of cabbage palms interspersed throughout the landscape provides suitable habitat.Some species appear to require larger plots of land with tree structure. However, even in these cases the requirements may be compatible with the current land management practices employed by cattle ranching. At the MacArthur Agro-ecology Research Center pinewoods treefrogs-a species that requires upland-forested habitat as an adult-are found in upland hammock patches that are five to ten acres in size.
Setting priorities for wetland management on your ranch can go a long way toward protecting frogs and toads. Isolated, temporary wetlands should be given high priority for conservation. Ditches that connect these wetlands to larger ditches that contain predatory fish may decrease the usefulness of these wetlands for many species, particularly during wet years.
Further, because some species have specific upland requirements, isolated wetlands closest to hammock or other upland habitat may be the best management targets. Finally, where possible, maintaining some upland habitat adjacent to your wetlands will enhance the diversity of frog and toad species using your ranch.
It stands to reason that no one wetland type will provide appropriate breeding sites for all species in an area because the differing requirements of different frog and toad species. The varying developmental periods of species that breed in temporary sites means that a single temporary wetland also necessarily provide suitable breeding habitat for all species using temporary wetlands. Because wetlands that differ in size have different filling and drying patterns, cattle ranchers can easily gauge how valuable their land is to frogs and toads by recognizing the variety of wetlands that occur on their property.
Summary
Cattle ranches in south Florida can play an important role in conservation efforts for many frog and toad species. This role, particularly in a geographic region of such rapid growth in the human population,will become increasingly more valuable in the future. Because the land-use practices associated with cattle ranching are currently compatible with the conservation of many species, cattle ranchers can provide valuable habitat for frogs and toads with little or no extra effort. With the concern over world-wide declines in amphibian populations, as well as the important role frogs and toads have as a food source for so many other wildlife species, cattle ranches provide a good example of how conservation and agriculture can be compatible.See Table for types of breeding habitat for southern Florida frog and toad species.
Tables
Table 1.
Table. Breeding habitat associations for frogs and toads that may occur on ranch lands in southern Florida. Species
Permanent Water Bodies
Temporary Wetlands
Pig frog (Rana grylio) X O Southern leopard frog (Rana utricularia) O X Florida gopher frog(Rana capito)
X Squirrel treefrog(Hyla squirella)
X Green treefrog(Hyla cinerea)
O X Barking treefrog(Hyla gratiosa)
X Pinewoods treefrog(Hyla femoralis)
X Little grass frog(Pseudacris ocularis)
X Florida chorus frog(Pseudacris nigrita)
X Florida cricket frog(Acris gryllus)
O X Eastern narrowmouth toad (Gastrophryne carolinensis) X Oak toad (Bufo quercicus)
X Southern toad (Bufo terrestris)
O X X=primary or sole breeding habitatO=habitat used for breeding
Footnotes
1. This document is WEC16, one of a series of the Wildlife Ecology and Conservation Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date June, 1997. Reviewed September 1, 2002. Visit the EDIS Web Site at http://edis.ifas.ufl.edu. Please visit the FAIRS Website at http://hammock.ifas.ufl.edu.2. Kimberly J. Babbitt, former graduate assistant, and George W. Tanner, Ph.D., associate professor, Department of Wildlife Ecology and Conservation., Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
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