Introduction 

 There are 18 species of amphibians native to southern 

Florida. Amphibians are found in virtually all habitats from pine 

forests to sawgrass marshes to mangrove estuaries, and they can 

become extremely abundant locally. Amphibians are predators 

on arthropods and some small vertebrates and are prey to many 

other animals. These trophic interactions and the high abundance of amphibians in southern Florida make them a vital part 

of the Everglades ecosystem. 

 Declines in amphibian populations have been documented 

by scientists worldwide from many regions and habitat types 

(Alford and Richards 1999). No single cause for declines has 

been demonstrated, but stressors such 

as acid precipitation, environmental contaminants, the introduction 

of exotic predators, disease agents, 

parasites, and the effects of ultraviolet 

radiation have all been suggested. 

Because of their susceptibility to 

these and other stressors, amphibians 

are important as indicators of ecosystem health (Welsh and Ollivier 1998). 

 Currently, hydrologic restoration in southern Florida is beginning 

under the Comprehensive Everglades 

Restoration Plan (CERP www.

evergladesplan.org), which includes 

more than 68 projects ranging from 

removing canals to creating alternative water-storage areas. The goals of 

the plan include increasing the spatial 

extent of natural areas, enhancing 

the quality of existing natural areas, 

and improving the abundance and 

diversity of native plants and animals. An important component 

of the plan is an adaptive assessment process that will be used 

to assess the performance of the plan and recommend changes 

as necessary. The community of amphibians in the Everglades 

was chosen as an important group for this assessment process 

because of the sensitivity of amphibians to changes in the environment. 

 Amphibians should be excellent indicators of the success 

of Everglades restoration, but a clear understanding of how 

amphibians will respond to changes in the environment is 

required. In a collaborative effort, the U.S. Geological Survey 

(USGS) and University of Florida are currently conducting a 

research program into the use of amphibians as ecosystem 

restoration indicator species. This program consists of coordi-

 U.S. Department of the Interior 

 U.S. Geological Survey 

 Fact Sheet 2004-3106 

 October 2004 

 Use of Amphibians as Indicators of 

Ecosystem Restoration Success 

Printed on recycled paper

nated research projects occurring across spatial and temporal 

scales throughout the Everglades ecosystem in Everglades 

National Park, Big Cypress National Preserve, and the Water 

Conservation Areas. The goal is to develop the tools needed to 

predict and monitor changes to amphibian communities due to 

restoration. 

 Local Scale, Single Species 

 As managers design and implement individual projects of 

CERP, impacts to indicator species over relatively small areas 

must be evaluated. Managers will require predictive tools and 

methods of monitoring that can 

detect change quickly and are 

applicable across the Everglades 

system. At this scale, the effects 

of restoration on population size, 

health, behavior, and reproduction of individual indicator species 

could be used to judge restoration 

success. Research at the local scale 

consists of perfecting methods to 

study and monitor amphibians in 

the field and using these methods to 

ask appropriate questions. 

 We have begun a radiotelemetry project on the greater siren 

(Siren lacertina) in Big Cypress 

National Preserve to determine how 

its movement patterns change as 

water levels rise and recede. This 

large fully aquatic salamander is 

locally abundant and is an important component of the ecosystem in 

terms of biomass and as prey to alligators and other predators, 

but its ecology is poorly understood due to its cryptic nature. 

This study is designed to measure response of this species to 

changes in water level particularly density, movement, survival, 

and habitat requirements. We are implanting digitally encoded 

transmitters into adult sirens and following their movements 

across several wet/dry cycles in the Everglades. The ultimate 

goal of this research is to provide monitoring protocols and 

predictive models of siren behavior and abundance in relation to 

changes in hydrology. These tools will provide managers with 

information concerning the effects of restoration projects over 

small areas and short time periods. 

An Okefenokee fishing spider (Dolomedes okefinokensis) 

digesting a green treefrog (Hyla cinerea) in a cypress dome 

in Big Cypress National Preserve. This is one of a few documented cases of arthropods as predators of frogs. 

Photograph by Brian Jeffery Photograph by Brian Jeffery
EXPLANATION

Squirrel Treefrog

Green Treefrog

Both Species

 Regional Scale, Multiple Species 

 The effects of restoration projects also can be measured on 

a regional (such as a habitat type or management unit) scale. 

In some instances, effects may be difficult to measure and may 

require the use of several similar species collectively to measure 

the success of restoration. 

 The green treefrog (Hyla cinerea) and squirrel treefrog (Hyla 

squirella) were the most commonly observed amphibian species 

during our recent inventories of Everglades National Park and 

Big Cypress National Preserve. These species were found in all 

habitats that we surveyed (fig. 1). While occurring together in 

many cases, the relative density of each species differs depending on local habitat conditions. The health and density of these 

species are indicators of both the health of lower trophic levels 

that they feed upon as well as their predators. We are using 

capture-mark-recapture techniques to examine movement and 

survival patterns of both species simultaneously in Big Cypress 

National Preserve. We are using multistate models to determine 

the probability that a treefrog will survive and move from one 

habitat to another at different water levels. These models take 

into account current and past water depths and temperature and 

allow us to calculate a probability of dispersal for each species 

under these conditions. Armed with this information, we are 

developing a predictive model of treefrog populations under 

different hydrologic scenarios. The objectives are to further 

develop our methods as a modeling and monitoring tool across 

all Everglades habitats. 

 Another major impact on amphibians in the Everglades may 

be the introduction of invasive species. We are using similar 

capture-mark-recapture methods to better determine the effect 

of the Cuban treefrog (Osteopilus septentrionalis) on native 

treefrog populations. Cuban treefrogs have been shown to 

be a predator of at least six species of native frogs and toads 

(Meshaka 2001) and at least one native snake (Maskell and 

others, 2003), and the Cuban treefrog has become established 

in natural areas within Everglades National Park. We monitored 

populations of both native and the introduced species using capture data from artificial refugia. After one year of monitoring, 

all Cuban treefrogs captured were removed from the area, and 

the recovery of native frogs was monitored. Results from this 

study indicated that Cuban treefrogs can cause severe reductions 

in native treefrog abundance and survival in areas where Cuban 

treefrog abundance is high. This estimation approach could also 

be applied to other stressors of amphibian populations, including alteration of the hydrologic cycle. 

 Landscape Scale, Communities 

 CERP managers will ultimately require knowledge concerning the success of restoration across the entire Everglades system. This will require not only methods that are applicable to all 

habitats and areas but to many species or communities as well. 

 Amphibians are present in all habitats and under all hydrologic regimes in the Everglades. The species present and 

occupancy rates—the proportion of an area, or habitat, occupied (PAO), by a particular species—differ greatly across those 

gradients. These differences are due to hydropattern, vegetation, 

and other environmental factors. The combination of species 

composition and proportion of each habitat occupied at a given 

time form unique communities defined by those environmental 

factors. Therefore, if these communities can be reliably defined 

and measured, Everglades restoration success can be evaluated, 

restoration targets can be established, and restoration alternatives can be compared. 

Aquatic funnel trap used to capture greater siren (Siren lacertina) in 

marshes and flooded prairies of southern Florida. The siren in the trap 

was transferred to the bucket to be measured, weighed, and permanently marked using a microchip transponder.

Figure 1. Location of green treefrogs (Hyla cinerea) and squirrel treefrogs (Hyla squirella) within Everglades National Park and Big Cypress 

National Preserve.

Photograph by Andy Mask Photograph by Andy Maskell
model to determine the suite of factors that best explains the 

distribution of the species. 

 In Everglades National Park and the adjacent Water Conservation Areas, we have begun a large scale study to determine 

the PAO by each amphibian species across habitats defined by 

hydropattern (the number of days of inundation each year). The PAO method estimates 

the abundance of sites at which each species 

occurs based on the capture results of several 

visits to each site (MacKenzie and others, 

2002). This method takes into account that 

some species are more difficult to detect, 

given that they are present, than others. This 

sampling is done along a hydrologic gradient 

from very long hydroperiod sloughs to the 

extremely short hydroperiod rocky glades of 

eastern Everglades National Park. The outcome of this research will be community profiles relating the PAO of several key amphibian species to the ecological community 

along this gradient. This information can then 

be used by managers to make predictions and 

monitor success of CERP (fig. 2). 

 Another way we are using this modeling 

approach is to determine the impact of offroad vehicle (ORV) use on amphibians in Big 

Cypress National Preserve. We first developed an index of ORV use using geographic 

information systems (GIS) (fig. 3). We 

then tested the PAO model using simulated 

selection techniques to determine if ORV 

use effected the distribution of amphibians 

within the Preserve. Results indicated that 

some species seem to be strongly negatively 

associated with ORV use, some seem to be 

strongly positively associated, and many do 

not seem to be affected by ORV use. This is 

one example of an application of this model 

to test if landscape scale processes affect the 

distribution of amphibian species in southern Florida. Other factors, such as habitat 

and hydroperiod, also can be included in the 

Polyvinyl chloride (PVC) pipes used as artificial refugia to capture 

treefrogs in a pine forest in Everglades National Park.

The southern leopard frog, Rana sphenocephala, a relatively large 

frog that frequents the shallow edges of grassy wetlands and flooded 

cypress forests in southern Florida. This is a species that will likely see 

a shift in the range during Everglades restoration.

Photograph by Hardin W Photograph by Hardin Waddle

Figure 2. Diagram showing how the proportion of an area occupied (PAO) by various 

amphibian species might differ in four habitat types. Arrows indicate direction of increasing hydroperiod from very few days in pineland habitat to almost permanent inundation in 

cypress habitat. The size of the circle around each amphibian species indicates the PAO for 

that species in that habitat. Little grass frogs (pink circle) are relatively abundant in pinelands, but decrease in terms of PAO in the wetter habitats. Greater sirens (red circle) are 

only found in wetter habitats, but reach their largest PAO in open marsh habitats.
OFF-ROAD VEHICLE (ORV) TRAIL

SAMPLING POINT—with 500 meter

sampling point buffer

0 0.5 1 KILOMETER

 Amphibians and Everglades Restoration 

 During Everglades restoration, managers will require predictions about how proposed changes might affect indicator species and 

monitoring data to ensure that success has occurred. Methods will be required from small spatial scales to landscapes and on single 

species to communities. By describing the current distribution and abundance of amphibians across the Everglades and better understanding the relationship between hydrology and amphibian populations, we will be able to make predictions about the effects of Everglades restoration. Monitoring of amphibians using the techniques we are developing will allow the testing of predictions and measurement of restoration success. Both the USGS Greater Everglades Priority Ecosystem Science (PES) Program and the U.S. National 

Park Service CESI program have supported this research. 

 For further information on USGS 

amphibian research in the Everglades, 

please contact 

 Ken Rice 

 U.S. Geological Survey 

 3205 College Ave 

 Davie, FL 33314 

 E-mail: ken_g_rice@usgs.gov 

 For further information on University 

of Florida amphibian research in the 

Everglades, please contact 

 Frank Mazzotti 

 University of Florida 

 3205 college Ave 

 Davie, FL 33314 

 E-mail: fjma@ufl.edu 

Trails left by off-road vehicles in the prairie habitat of Big Cypress 

National Preserve.

Photograph by Hardin W Photograph by Hardin Waddle

 References Cited 

 Alford, R.A., and Richards, S.J., 1999, Global amphibian declines: A problem in 

applied ecology: Annual Review of Ecology and Systematics, no. 30, p. 133-

165. 

 MacKenzie, D.I., Nichols, J.D., Lachman, G.B., and others, 2002, Estimating site 

occupancy rates when detection probabilities are less than one: Ecology, no. 83, 

p. 2248-2256. 

 Maskell, A J., Waddle, J.H., and Rice, K.G., 2003, Osteopilus septentrionalis: 

Diet: Herpetological Review, no. 34, p. 137. 

 Meshaka, W.E., 2001, The Cuban treefrog in Florida: Gainesville, University of 

Florida Press. 

 Welsh, H.H J., and Ollivier, L.M., 1998, Stream amphibians as indicators of 

ecosystem stress: A case study from California’s redwoods: Ecological Applications, no. 8, p. 1118-1132. 

Figure 3. Eight sampling points with a surrounding 500-meter buffer. 

The blue lines are off-road vehicle (ORV) trails, and the length of ORV 

trail segments within the green circles is the basis of the ORV index.