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Project Summary Sheet

U.S. Geological Survey, Greater Everglades Priority Ecosystems Science (GE PES) Initiative

Fiscal Year 2007 Project Summary Report

Project Title: Spatial and Age-Structured Population Model of the American Crocodile for Comparisons of CERP Restoration Alternatives
Project Start Date: 2007 Project End Date: Funding, 2008; Project, 2009
Web Sites:
Location (Subregions, Counties, Park or Refuge): Southern coast
Funding Source: USGS GE PES
Annual Costs: FY07
Principal Investigator(s): Daniel H. Slone, Kenneth G. Rice, Frank J. Mazzotti
Project Personnel: Timothy W. Green
Supporting Organizations: University of Florida

Associated / Linked Projects: GEPES study: American Alligator Ecology and Monitoring for CERP

Overview & Objective(s): Many important questions concerning the effects of Everglades restoration on crocodile remain unanswered such as the impacts of decompartmentalization and the effects of hydrology and salinity on population distribution and density. Also, we need to develop a population model for use in restoration alternative selection, performance measure development, and prediction. To adequately understand crocodile populations and model their population growth and distribution, existing data must be assembled and model parameters estimated. A simulation model can then be constructed and validated both with existing data and through expert opinion. A crocodile population model to simulate the south Florida ecosystem under varying management strategies is vital to evaluating and assessing restoration success under CERP.

The objectives of this project are to:

  1. Build an age and spatially structured crocodile population model suitable for comparison of CERP restoration alternatives.
  2. Couple the local age-structured models into a spatial dispersal model incorporating crocodile movement behavior.
  3. Use spatial parameter maps from the Florida Everglades as driving functions on the spatially structured model and to construct crocodile finite rate of increase maps under different management regimes.
  4. Validate model parameters and function through comparison of model results with field data.
  5. Perform sensitivity analysis on the model parameters, and release model concept and code for peer-review.

Status: The crocodile model will be based on the ATLSS Alligator Population Model, which has been completed and has undergone expert review, calibration, and some validation. A GS-9 Ecologist was hired late in FY-2007 to work on this task. He has begun training in Matlab programming, and is reviewing the alligator model. Meetings with crocodilian biologists are planned for the near future to outline changes that need to be made from the alligator model, and to begin parameterization of the crocodile model.

Recent & Planned Products:
In FY-2008, we plan to produce a working crocodile population model for testing and validation. Code for the model will be released for peer-review.

Specific Relevance to Information Needs Identified in DOI's Science Plan in Support of Ecosystem Restoration, Preservation, and Protection in South Florida (DOI's Everglades Science Plan): [See Plan on SOFIA's Web site:]:

The spatially explicit, stage-based model of American crocodile populations will address identified needs in the DOI science plan, including:

  • Florida Bay and Florida Keys Feasibility Study, Modeling of ecological responses to hydrologic change, emphasizing “information on the life history requirements of indicator species, including their responses to hydropattern change, will be needed to address anticipated changes in species populations. Indicator groups that should be represented in these evaluations include … federally listed species (American crocodiles).”
  • Landscape-Scale Science Needed to Support Multiple CERP Projects, Landscape-Scale Modeling, Spatially explicit demographic models, describing the approach desired for spatial models as “stage-structured models describe population dynamics as composed of a number of life stages, each stage having different size, physiology, and environmental requirements.”
    In addition to the DOI science plan needs, this study addresses needs identified in the Multi-species Recovery plan for south Florida, section H2.3: “Continue habitat and population modeling to determine operational schedules for structures associated with the Program to Modify Water Deliveries to Everglades NP, Canal 111, and the Central and Southern Florida Flood Control Project that provide optimal habitat for the American crocodile.”

Key Findings:

This is a new project and is still in the beginning phases. Expected findings include a better understanding of the role of salinity and hydroperiod on the population structure and distribution of crocodiles in south Florida, and the expected effect of CERP restoration alternatives on crocodiles.

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