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Computer Simulation Modeling of Intermediate Trophic Levels for Across Trophic Level Systems Simulations of the Everglade/Big Cypress Region

Project Proposal for 2001

Continuation Research Plan [Year 4 of 5 Years]

PROJECT TITLE: Computer Simulation Modeling of Intermediate Trophic Levels for Across Trophic Level Systems Simulations of the Everglade/Big Cypress Region

Investigator: Michael S. Gaines
Mail address:
University of Miami
Department of Biology
Coral Gables, Florida 33124


This project has had the goal of developing models for key components of the Everglades landscape as part of the overall Across Trophic Level System Simulation. There are four principal tasks within this project:

1. Develop models for two primary food bases; the functional group of small fishes, upon which many of the wading birds depend, and the main reptile and amphibian functional groups, which constitute much of the diet of the American alligator.

2. Develop models for the key wading bird species, particularly focusing on the effects of hydrology and fish availability on wading bird success.

3. Develop a validated model for the snail kite population of Florida. Make this available to relevant agencies working in central and southern Florida.

4. Develop a validated model for the population of American crocodiles, along with supporting empirical studies on hatchling crocodiles. Make this available to relevant agencies in working southern Florida.

The first two of these tasks has been completed. The focus of the continued work is the completion of the last two tasks, development of a snail kite model to use in assessment and both relevant field work and development of a crocodile model for use in assessement.

Snail kite modeling:

The snail kite is a raptor whose distribution in the United States is limited to the freshwater marshes of southern and central Florida, including the Everglades. The snail kite is listed as an endangered species in the United States. Although its numbers have appeared to increase in recent years, total population size is probably still below 2000. Because of its endangered status, the snail kite is among the species being given specific attention in the ongoing Everglades restoration project (Bennetts et al. 1994, Davis and Ogden 1994). A spatially-explicit model has been developed for the snail kite population of central and southern Florida. The model follows all of the snail kites in the population as individuals. This model is now being used to explore the dynamics of the snail kite population on the landscape. The model allows for the evaluation of the relation of spatial correlation of drought conditions and the response of the snail kite population, both in its spatial patterns and its survival. The model is being applied to both historical data on the spatial pattern of water levels throughout the snail kite's range as well as the pattern of water levels projected from models for changed water regulation conditions.

Crocodile modeling and empirical work:

The American crocodile individual-based model has been developed within the OSIRIS framework. The purpose of the model is to predict how the American crocodile population will respond to alterations in freshwater flow into the estuary habitat. In the working version of the model individuals grow, interact, breed and suffer mortality dependent upon a static hypothetical landscape, salinity, and interactions with other crocodiles. The most recent work has focused on creating a dynamic landscape dependent upon freshwater input. In support of this modeling effort, the American crocodile radio-tracking project seeks to test for salinity effects upon hatchlings; based on the literature it is expected that hatchlings would prefer freshwater and would lose weight in hypersaline habitats.


Snail kite modeling:

1. Version 1 of the snail kite model has been completed.

2. It has been used to evaluate the effects of the different Restudy and ModWater scenarios on the snail kite population. The AltD, AltD-13r, and AltD-13r4 scenarios out-performed all others.

3. Snail kite and fish landscape models used in Restudy assessments

4. Snail kite and fish landscape models used in ModWaters Project design.

Crocodile modeling and empirical work:

1. A preliminary model of the crocodile population in part of their habitat has been developed.

2. The empirical results to date are that hatchling crocodiles appear to increase in mass and behave normally both within the cooling canal system and in the surrounding freshwater habitats.

3. Radio-tracking work is being continued during the summer 2000 season to gain the needed replication to complete the proposed project.


There are two overriding objectives for work during FY2000.

1. Validate the snail kite model and get a working version into the hands of agencies concerned with the snail kite in Florida.

2. Complete development of the American crocodile individual-based model and make it available for use by agencies concerned with the American crocodile in Florida.

Achieving these major goals will involve require accomplishing several subsidiary goals.

Snail kite modeling:

1. Several assumptions have been built into the snail kite SEIB model in its current form. These include assumptions about the carrying capacity of the various wetland breeding sites. The assumptions must be improved. This will be done in part through a small workshop involving Wolf Mooij and two of the empirical scientists studying the snail kite, Dr. Rob Bennetts and Dr. Vicky Dreitz. Further testing against data on survival and movement patterns that are now coming available is needed. This will allow estimation of parameters for habitat selection by the snail kites.

2. The hydrology underlying the snail kite SEIB will be extended. Currently the hydrologic conditions of each of the 14 distinct wetlands in the model are represented by spatial avaerages. In the area covered by the South Florida Water Management Model, these averages will be replaced by hydrologic data at each 500 x 500 m spatial cell.

3. The detail of the snail kite model will be extended where data exist. This will include adding more realistic behavioral features to the individual snail kites and adding the effects of changes in apple snail availability.

Crocodile field studies and modeling:

1. Refinement of the dynamic hydroscape in the southern Everglades mangrove area, using data and salinity levels from the USGS Southern Inland Coastal (SICS) model.

2. Improvment in model parameterization, including fitting growth data to available models (von Bertalanffy, Gompertz, etc.) and acquisition of hatchling movement and survivorship data vis radio-tracking.

3. Addressing the central question of what the effects of altered hydrology are on the population of Florida crocodiles through a series of sensitivity analyses or 'experiments' with the model.

4. Continuation of radio-tracking of hatchling crocodiles to enhance the replication of these data.


Snail kite

One of the first choices made in the development of the model was the representation of the spatial structure of the range of the snail kite in central and southern Florida. The spatial structure of the model consists of several spatially disjunct habitat areas, which we will refer to as wetland habitat sites. Following Bennetts and Kitchens (1996) fourteen major wetlands in southern and central Florida were identified as suitable snail kite habitat: Everglades National Park, Big Cypress National Preserve, Water Conservation Areas 3A, 3B, 2A, 2B, and 1 (Loxahatchee National Wildlife Preserve), Loxahatchee Slough, Holey Land Wildlife Management Area, Lake Okeechobee, Upper Saint John's Marsh, Lake Kissimmee, Kissimmee Chain of Lakes, Lake Tohopekaliga and East Lake Tohopekaliga. A fifteenth habitat area was added to the model, representing the scattered pieces of peripheral habitat in the agricultural areas. This aggregate of peripheral habitat, while not suitable for nesting, can act as a refugium for the kites during a system-wide drought.

The hydrology of individual wetland habitat sites in particular years is critically important to whether that site can be used for nesting by snail kites. Apple snails die or estivate, becoming unavailable, when a site becomes dry. After a drydown a particular site may not be good habitat for a few years, until the apple snail population recovers. For purposes of modeling, the water levels in each wetland habitat site can be given by a historical record estimated from a single watergauge near the core habitat of the snail kites on the wetland site, or these water levels can be produced from hydrologic models applied to forecast future water levels under different water regulation conditions. Weekly water levels are entered in the model. Both in the simulations involving the historical record of water levels as well as for forecasts of water levels produced by hydrologic models, these levels are transformed into standardized levels by subtraction of the long term average and division by the long term standard deviation in historical water levels.

Each modeled kite goes through a fixed set of life stages. These life stages affect the probabilities with which the demographic processes of breeding, movement, and mortality occur. Each individual kite is simulated in the model on a weekly basis.

Crocodile field studies and modeling

The population of American crocodiles is being modeline using a spatially-explicit individual-based approach. Acquisition of the ESRI ArcView and Spatial Analyst has allowed the extraction of rastor grids at the 50m resolution that the crocodile IBM currently calls for from the estuary areas of S. Florida. The ability to convert available vector data (we are currently using U. Of Georgia data) to a rastor format allows us to import an initial estuary landscape into the Osiris based crocodile IBM and then run hypothetical water deliver scenarios which can alter the dominate vegetation types and salinity levels. Other work involves the model parameterization, which is currently focused on fitting growth data to available models (e.g. Von Bertalanffy, Gompertz, etc.) and acquisition of hatchling movement and survivorship data via radio-tracking. During the summer of 1999 we placed 11 radio-transmitters on hatchling (YOY) American crocodiles at the Florida Power and Light Company's. Turkey Point Power Plant (TP). Of these we successfully tracked 5 individuals for up to 82 days in both the hypersaline cooling canal system of TP and in surrounding freshwater or low saline habitats (the remaining 6 individuals were unsuccessfully tracked due to transmitter signal failure). The number of daily fixes beyond initial release ranged from 2 to 8. In addition 4 individuals were followed intensively for up to 36 hours. No transmitters were recovered and the fates of all 11 hatchlings that were radio-tagged is unknown. In addition 2 juvenile (approximately 1m total length) individuals have been radio-tagged and are currently being tracked.


Reports and Deliverables
Type of Product* No. of Copies: Due Date:
1. Brief letter report with the following: [1] date of receipt of executed contract (i.e., start date), [2] status of progress made towards providing data/metadata/model-source-code, [3] draft text with /graphics/slides for 2-pager Fact Sheet. Original +2+ electronic copy 60 days after award contract
2. 1st Trimeter Report - a brief report updating progress/problems to date and all data and metadata file, &/or model source code to date. Plus, final of 2-pager Fact Sheet. For ENDING projects, in addition to above, provide a plan for final report in a detailed outline format. Original +2 +electronic copy 120 days after award of contract
3. 2nd Trimester Report - with updated data/metadata file[s] &/or model source code. Plus, "Request for Continued Funding" for the next year funding. For ENDING projects, provide a DRAFT final report suitable for external review. Original +2 +electronic copy 240 days after award of contract
4. Annual or Final Report with all data to date with metadata file[s], fully documented model source code. For FINAL modeling projects, a fully executable, fully documented model source code is required. Original +2 +electronic copy 1 Year after award of contract
*Note: Manuscripts, peer reviewed publications, book chapters, graduate student thesis/dissertation, etc., are both acceptable and desirable as chapters or sections of annual/final reports. At least one 2-page fact sheet is required for each of these major types of publications.

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