projects > across trophic level system simulation (atlss) - snail kite
Across Trophic Level System Simulation (ATLSS) - Snail Kite
The snail kite (Rostrhamus sociabilis) is an endangered raptor whose distribution in the United States is restricted to the South Florida Ecosystem, including watersheds of the Everglades, Lake Okeechobee, Kissimmee River, and Upper St. Johns River. Because snail kites feed almost exclusively on one species of aquatic snail (the apple snail, Pomacea paludosa), their survival depends directly on the hydrologic functioning of these watersheds. Each of these watersheds has experienced, and continues to experience, substantial degradation, resulting in the current planning for what probably will become the largest ecosystem restoration ever undertaken. Although other endangered species occur within the ecosystem, snail kites are probably the only species restricted to the watersheds within the South Florida Ecosystem and dependent on the entire network of wetlands within this ecosystem. Over half of the wetlands within central and southern Florida have been lost during the past century and those that remain have been highly fragmented and severely degraded (Weaver et al. 1994). This degradation has prompted planning for ambitious restoration efforts (e.g., the Central and South Florida Project Restudy, Kissimmee River Restoration, and the South Florida Ecosystem Restoration initiative). Because of the snail kite's restricted range and because their population is highly dependent on the success of restoration efforts, the snail kite is a key species to monitor throughout the restoration process.
The ATLSS Snail Kite Index (SKI) Model was developed as a crude indicator of potential habitat quality during the breeding season for snail kites in the Florida Everglades. All evidence suggests that the population dynamics for this species are influenced by environmental conditions occurring throughout its entire range in Florida. This model addresses only relative habitat quality within a limited area, ignoring larger spatial extent population dynamics that may have a much greater effect on this species than habitat quality in part of its range. Consequently, this model should not be interpreted to represent population dynamics or viability. The time scales at which evaluation of alternative scenarios are evaluated also are likely to be too short to encompass some long-term changes in habitat quality. Particularly, stabilized hydrologic regimes may result in a slow degradation of habitat that may be overlooked at the time scales evaluated with this model. In addition, very little verification of this model's performance has been performed and several of its parameter values are "best guess" approximations, for which data are either currently lacking or have not yet been fully analyzed. A spatially explicit full demographic model for snail kites based on available data is currently under development as part of the ATLSS project.
U.S. Department of the Interior, U.S. Geological Survey
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