A basic component of restoration planning in South Florida has been the development and use of computer simulation models for the major physical processes driving the system, notably models for freshwater hydrologic dynamics as it is affected by alternative human control systems and non-controlled inputs such as rainfall. The major objective of the ATLSS (Across Trophic Level System Simulation) Project has been to utilize the outputs of such physical systems models to drive a variety of models that attempt to compare and contrast the relative impacts of alternative hydrologic scenarios on the biotic components of South Florida. The biotic models are constructed at varying levels of spatial, temporal and organismal resolution, and have focused to date on intermediate and upper trophic level biotic components. The principal goal is to provide a rational, scientific basis for developing relative rankings of hydrologic scenarios as input to the planning process, and through this to aid development of appropriate monitoring and adaptive management schemes.

ATLSS is constructed as a multimodel, meaning that it includes a collection of linked models for various physical and biotic systems components. The component models utilize a variety of approaches and operate at different spatial and temporal resolutions, depending upon the level of detail appropriate for the organisms being addressed as well as limitations imposed by inadequate data to realistically model the system. The ATLSS models all are linked through a common framework which allows for the necessary interaction between spatially-explicit information on physical processes and the dynamics of organism response across the landscape. ATLSS models all include some mechanistic components, though some are considerably more detailed in the level of description of the organisms involved. ATLSS outputs all are interpreted in a relative assessment framework, in which an alternative is compared to a base scenario.

The ATLSS hierarchy starts with models which translate coarse resolution hydrologic information to a finer resolution appropriate for biotic components that operate at spatial extents much smaller than the 2-mile resolution of the main hydrologic model. The development of such a high resolution hydrology relies upon vegetation maps and the associated limitations on hydroperiod associated with these, to characterize a 28.5-meter resolution topography (pseudotopography) chosen to preserve the volumes of water derived from the 2-mile resolution hydrology model.

The ATLSS hierarchy next includes Spatially-Explicit Species Index (SESI) models which make use of the spatially-explicit, within-year dynamics of hydrology to compare the relative potential for breeding and/or foraging across the landscape. SESI models are viewed as approximations which are useful in coarse evaluations of scenarios and are an aid in interpreting the more detailed models. SESI models have been constructed and applied during the Central and Southern Florida Comprehensive Review Study (Restudy) to the Cape Sable Seaside Sparrow, The Snail Kite, Short- and Long-Legged Wading Birds, and White-tailed Deer, with an additional model for Alligators now near completion.

Considerably more detailed models have been developed for the distribution of functional groups of fish across the freshwater landscape. This model considers the size distribution of large and small fish as important to the basic food chain which supports wading birds. It has been applied to assess the spatial and temporal distribution of availability of fish prey for wading birds. Individual-based models, which track the behavior, growth and reproduction of individual organisms across the landscape, have been constructed for the Cape Sable Seaside Sparrow, the Snail Kite, The White-tailed Deer, the Florida Panther and various Wading Bird Species. The models include large mechanistic detail, and their outputs may be compared to the wide variety of organism distribution data available, including that from radio collared individuals. An advantage of these more detailed models is that they link each individual animal to specific environmental conditions on the landscape. These conditions (for example, water depth, food availability) can change dramatically through time and from one location to another, and determine when and where particular species will be able to survive and reproduce.

The ATLSS models are constructed in an object-oriented framework, in order to allow flexibility in modification and reuse of code. The models are written in C++, and much of the visualization utilizes the PV-Wave package. ATLSS models have been developed and tested in close collaboration with field scientists who have years of experience and data from working with the major animal species of South Florida.

The focus of ATLSS to date has been on the freshwater systems, with emphasis on the intermediate and upper trophic levels. The ATLSS structure was purposely formulated to provide for extension to estuarine and near-shore dynamic models once physical system models for these regions are completed. This would involve the construction of a variety of additional models for the biotic components. A further effort at lower trophic levels in the freshwater regions is needed to account for the impact of hydrologic plans on vegetation change and associated nutrient fluxes. Closely linked with these would be models for the effects of major disturbances to the system, including fire and hurricanes. Finally, ecotoxicological models coupled to transport models for toxicants such as mercury may be readily incorporated into the biotic components already constructed.

A significant part of the funding for this research was provided from the U.S. Department of the Interior South Florida Ecosystem Restoration Program "Critical Ecosystems Studies Initiative" (administered through the National Park Service) and from the U.S. Geological Survey, Florida Caribbean Science Center. Additional funding for the "Atlas Tropic Level System Simulation" was also provided by the U.S. Environmental Protection Agency and the U.S. Army Corps of Engineers.

REFERENCES

DeAngelis, D.L., Gross, L.J., Huston, M.A., Wolff, W.F., Fleming, D.M., Comiskey, E.J., Sylvester, S.M., 1998, Landscape modeling for Everglades Ecosystem Restoration: Ecosystems, v. 1, p. 64-75.

Gross, L.J., DeAngelis, D.L., and Huston, M.A., 1998, Approaches to large-scale ecosystem modeling across multiple trophic levels: Some early lessons from the South Florida ATLSS Experience, in Waide, J.B., and Gandy, L.M., editors, Proceedings of the Workshop on Aquatic Ecosystem Modeling and Assessment Techniques for Application within the U. S. Army Corps of Engineers: Miscellaneous Paper EL-98-1, Waterways Experiment Station, U.S. Army Corps of Engineers.

(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)

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