Amphibians

Robert Muxo (network biological technician) standing next to an automated recording device (ARD) used for frog monitoring in Big Cypress National Preserve.

NPS Photo/South Florida & Caribbean Network

Importance/Issues

Amphibians comprise a large amount of the resident vertebrate biomass and generally are a strong intermediate link in the food web. Amphibians have been used as a biological indicator for many environmental variables and are sensitive to changes in breeding habitat quality, invasive species, and contaminants. At Virgin Islands National Park (VIIS), the native frog species are strongly tied to water resources for reproduction. The white-lipped frog (Leptodactylus albilabris) has a tadpole stage and the other two species, Antillean frog (Eleutherodactylus antilliensis) and whistling frog (Eleutherodactylus cochranae), utilize moist vegetation for egg laying with direct development to the froglet stage. Additionally, these frogs typically exploit the numerous tank bromeliads for daytime refugia. There are a number of exotic species that may be out competing and preying upon native fauna such as the Cuban treefrog (Osteopilus septentrionalis). In Everglades National Park (EVER) and Big Cypress National Preserve (BICY), the pig frog, (Rana grylio), is a dominant anuran within the freshwater marsh lands and makes up a large amount of the vertebrate biomass. It is both a prey source and a major predator. The pig frog life cycle (eggs-tadpoles-adults) is strongly related to marsh hydrology. Shifts in pig frog population structure have been shown to be related to water management. Additionally, pig frogs bioaccumulate mercury and currently are being monitored by the Florida Fish and Wildlife Conservation Commission (FWRI) for mercury levels. Previous amphibian studies within these parks have documented exotic species immigration and shifts in population structures of native species due to exotic species. Community composition of the amphibian species community has been related to habitat type within these park units.

Monitoring Questions

• What are the status and trends in the distribution, abundance (or occupancy), and community composition of native and non-native amphibian species?
• What are the status and trends in pig frog demographic structure, especially in relation to water levels and Comprehensive Everglades Restoration Plan (CERP)/Modified Water Deliveries (MWD) Everglades restoration?
• What are the status and trends in mercury accumulation in pig frogs?

Approach

The South Florida/Caribbean Network plans to develop an “Amphibians” protocol to monitor amphibians at Big Cypress National Preserve, Everglades National Park, and Virgin Islands National Park. Biscyne National Park and Salt River Bay National Historical Park and Ecological Preserve are deferred. The protocol will build on the inventory work already completed. The primary parts of the protocol are to include:

1. Amphibians will be monitored in areas near roads and trails with Visual Encounter Surveys (VES), call surveys and tree pipes by developing a proportion of area occupied (PAO) methodology.
2. In Everglades National Park and Big Cypress National Preserve, the network will collect grab samples of pig frogs to determine size structure of populations, sex ratios, and juvenile to adult ratios. This sampling will build upon previously existing research.
3. The network will coordinate with the State of Florida mercury monitoring program. The network's goal is to include pig frogs from Everglades National Park and Big Cypress National Preserve in the state's regional assessments.