BACKGROUND

     Because of the public and scientific concern for the alarming trends in amphibian populations, the U.S. Geological Survey, Biological Resources Division has been asked to begin work assessing the status and trends of amphibians on lands managed by the Department of the Interior.  This national-level project has been named the Amphibian Research and Monitoring Initiative (ARMI). The Florida Integrated Science Center is leading the ARMI project in the southeastern United States (SEARMI). This poster describes the work being done by SEARMI in Everglades National Park, Big Cypress National Preserve, Biscayne National Park, Virgin Islands National Park, and Buck Island Reef National Monument,

INTRODUCTION

     Before a long-term monitoring project can be established to document the status and trends of amphibians in the greater Everglades and Virgin Islands parks, it is important that a thorough inventory be conducted. The primary goal of our study is to create an inventory of the amphibians in these parks. In addition to verifying the species list, we are examining the habitat associations and geographical distributions of the amphibians of the region. To accomplish this task, sites within each major habitat type are visited during each season so that habitat and seasonal effects can be examined. A secondary objective of this project is to develop new methods appropriate for sampling amphibians in these areas.  This will provide useful information to facilitate future long-term monitoring programs. In this poster we present the general survey methodologies of the project and discuss the preliminary results of the work in Everglades National Park.

METHODS

     We are using a variety of standard methods to sample amphibians.  Our primary sampling unit is 20m radius circular plot.  These are sampled at night with first a 10-minute vocalization survey and then a 30-minute visual encounter search by two observers.  Ancillary data including air and water temperature, relative humidity, cloud cover, and wind speed are also recorded.  In order to best describe the fauna of these geographically large parks, sites are scattered randomly throughout each park. These sites, termed "extensive surveys," will allow us to examine the geographical distribution of species within the region.  In addition, we sample a group of six "permanent sites" in each major habitat at each park every month.  These sites are used to look at the habitat associations of the species and to examine seasonal variation in habitat use and activity.

     Sampling is based on a "three-tiered approach" so that we can effectively sample on a region wide basis, but still gain an understanding of of local population dynamics.  To calculate species richness at the permanent sites, we are using the method of estimating species richness using mark-recapture models proposed by Nichols and Conroy (1996).  To estimate the proportion of the area occupied by each species in a habitat we are using mark-recapture models using observations of each species at a site sampled repeatedly. We are also estimating detection probabilities for some of the species which will allow us to better estimate the number of individuals in a population (Nichols et al. 2000).
 

Amphibian Inventory of the National Parks
of South Florida and the Virgin Islands

J. Hardin Waddle¹, Kenneth G. Rice²,
H. Franklin Percival³, Raymond R. Carthy³

2" PVC pipes are used to trap treefrogs in several different habitats of the Everglades.  The traps are hung on trees 2m from the ground and have end caps that allow some water to collect in the bottom. These traps have been especially effective at capturing Cuban treefrogs and green treefrogs.

¹U.S. Geological Survey
Big Cypress National Preserve
HCR61, Box 110, Ochopee, FL 34141

²U.S. Geological Survey
University of Florida Field Station
3205 College Ave, Ft. Lauderdale, FL 33314

³U.S. Geological Survey
Florida Cooperative Fish and Wildlife Research Unit
University of Florida
Building 810, Gainesville, FL 32611

The southern toad,
Bufo terrestris

The Florida leopard frog,
Rana sphenocephala

RESULTS

     To date, we have sampled 72 plots in Everglades National Park.  Field work in the other National Parks will begin later this month. We have made a total of 254 visits to these plots, and we have observed over 500 individual amphibians and reptiles. Our current counts of species richness in habitat strata range from 3 to 10 amphibian species (Table 1).

     We have captured three species in PVC treefrog traps so far.  Cuban treefrogs and green treefrogs are the most common species in the traps, but some squirrel treefrogs have also been captured (Table 2). No Cuban treefrogs have been captured in PVC traps, or observed during surveys at remote mangrove sites.  The populations of green treefrogs where Cuban tree frogs are present are very low, but the green treefrog population where Cuban treefrogs are absent is much larger.

CONCLUSION

     Our results are still preliminary because they do not yet encompass an entire wet season. This means that the behavioral changes of the amphibian species that occur as hydrological conditions change have not been documented.  Also, because of restricted access to remote slough sites because of low water levels, many areas of Everglades National Park remain unexamined.

     Preliminary results, however, indicate that species richness is probably greatest in forested habitats, perhaps because of increased habitat complexity or productivity (Duever et al. 1975). Cypress domes appear to be the most productive habitats, with the most individual amphibians.  They are nearly permanently inundated and probably serve as a refuge for many amphibian species during times of low water.

Results of our mark-recapture study on treefrogs suggest that the presence of Cuban treefrogs may significantly impact the native treefrogs in Everglades National Park. We are going to examine this problem in more detail in the coming year by following populations of native treefrogs in areas with and without the presence of Cuban treefrogs.
 

ACKNOWLEDGEMENTS

This project is funded by the National Park Service through grants to the U.S. Geological Survey, Biological Resources to conduct amphibian inventories in the Tropics Networks parks. Work was conducted through the University of Florida Cooperative Fish and Wildlife Research Unit (University of Florida, Florida Fish and Wildlife Conservation Commission, USGS, and Wildlife Management Institute cooperating).  The Restoration Ecology Branch of the USGS - Florida Integrated Science Center, and Everglades National Park have all provided equipment and support.

We would like to thank A. Finger, M. Caudill, A. Dove, and S. Howarter for hard work in the field.

LITERATURE CITED

Duever, M.J., J.E. Carlson, and L.A. Riopelle. 1975.  Ecosystem analyses at Corkscrew Swamp. Pp. 627-725 in H.T. Odum, K.C. Ewel, J.W. Ordway, and M.K. Johnston, eds. Cypress wetlands for water management, recycling, and conservation.  Center for Wetlands, University of Florida, Gainesville.

Nichols, J. D. and M. J. Conroy. 1996.  Estimation of species richness. Pp. 226-234 in Measuring and Monitoring Biodiversity: Standard Methods for Mammals. Wilson, D. E., F. R. Cole, J. D. Nichols, R. Rudran, and M. S. Foster (eds.) Smithsonian Institution Press, Washington D.C.

Nichols, J. D., J. E. Hines, J. R. Sauer, F. W. Fallon, J. E. Fallon, and P. J. Heglund. 2000.  A double-observer approach for estimating detection probability and abundance from point counts.  The Auk 117(2):393-408.

The locations surveyed to date.
This includes the permanent sites sampled monthly as well as the
extensive sites that have only been visited once or twice.

INTRODUCED AMPHIBIAN SPECIES

Cuban treefrogs appear to be more abundant near roads and buildings. Giant toads have only recently been discovered in Everglades National Park, but they will probably spread along roads and canals.  Greenhouse frogs are ubiquitous in the forested habitats of the parks.