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Project Summary Sheet

U.S Geological Survey, South Florida Ecosystem Program: Place Based Studies

Project: Parameter Estimation and Population-Based Simulation Modeling of American Alligator Populations in Support of ATLSS



Principal Investigator: Kenneth G. Rice, USGS - Biological Resources Division, H. Franklin Percival, USGS - Florida Cooperative Fish and Wildlife Research Unit, Timothy S. Gross, USGS - Biological Resources Division, Jon C. Allen, University of Florida, Daniel H. Slone, University of Florida, Mark R. Palmer, University of Tennessee

Project Personnel: Donald L. DeAngelis, Phone: 305-284-1690, e-mail:

Other Supporting Organizations: USGS/BRD, NPS

Associated Projects: Component of the ATLSS Program

Overview & Status: The American alligator is not only a top consumer in south Florida, but also physically influences the system through construction and maintenance of alligator holes and trails (Mazzotti and Brandt 1994). The existence of this species is important to the faunal and floral character of the Everglades as it has evolved. Despite its prominence biologically and publicly in the system, many important questions about basic population parameters and strategies of alligators remain unanswered. In order to adequately understand alligator populations to model population growth, existing data must be assembled and new data collected for many parameters. A simulation model can then be constructed and validated both with existing data and through expert opinion. The ATLSS (Across Trophic Level System Simulation) project requires an alligator population model to simulate the south Florida ecosystem under varying management strategies. This project will provide estimation of population parameters and modeling frameworks for this simulation process. The estimation of population parameters will require all existing data on population size, alligator growth, nesting, egg viability rates, nest survival and flooding, mark-recapture of alligators, and any other collections to be assembled. Appropriate statistical estimation techniques (mark-recapture analysis, trend analysis, etc.) will be used to estimate or construct parameters and variances for inclusion into the simulation model.

Needs & Products: This study encompasses 2 of the critical projects for restoration of crocodilian populations determined by over 40 biologists, managers, and administrators. Alligators are a key indicator component and are used as ecological attributes and measures in the Everglades Ridge & Slough and Marl Prairie/Rocky Glades Conceptual Ecosystem Models. As an interim model and to provide guidance to currently ongoing restoration initiatives, an Alligator Reproductive Potential Index (API) was constructed to compare restoration alternatives for the Restudy and the Mod Waters project. This index uses hydrological, elevation, and habitat layers of the ATLSS model series to predict the reproductive potential of alligators across the south Florida landscape. Predictions of breeding potential, proportion of females nesting, habitat suitability, and flooding potential were used to construct the overall index. Very little data exist on present alligator population size in ENP. Since this population represents a substantial portion of the alligator's range in south Florida and data exist for estimation of many other parameters, it is essential that an accurate portrayal of the existing population be used in the simulation model. Night-light surveys conducted on representative habitats are used as an index to population size and size/age distributions. Alligators were captured and sacrificed from representative alligator populations in south Florida (ENP, WCA's II and III, Loxahatchee NWR, and Big Cypress National Preserve) to measure instantaneous growth rates, contaminant loads (mercury, organochlorines, etc.), hormonal concentrations, blood chemistry, and stomach contents. The initial framework for the alligator population model has been constructed.

Application to Everglades Restoration: This study develops an ATLSS American alligator production index and an ATLSS alligator population model for comparison of restoration alternatives.

Study Milestones





















Field Work






Data Analysis





Initial Reporting




Credibility Assurance





Results Published









Note: "x" indicates task completed, "o" indicates task planned, but not completed

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Last updated: 24 April, 2014 @ 12:00 PM (KP)