White-tailed Deer Breeding Potential Index Basic Model Description Jane Comiskey and Louis Gross The Institute for Environmental Modeling University of Tennessee Knoxville, TN 37996-1610 (Copyright University of Tennessee -- 1997) Introduction: The white-tailed deer is the largest herbivore in the Everglades and a major prey source for the endangered Florida panther. Since the early 1960's, when intensive water management began, the greater Everglades and Big Cypress deer population has declined by almost 75%, from a high of 25-30,000 deer. Changing water management strategies for south Florida have impacted deer in several ways, affecting reproductive success and recruitment, movement and foraging, and forage production and availability (Fleming 1997). During wet years, extended periods of inundation with water depths over 2-ft. are common in the impounded marshes of the northern Everglades. During these high water events, deer move to elevated sites such as tree islands, where they often suffer deterioration of physical condition and increased susceptibility to parasites and disease as food stores became depleted. Does and fawns are particularly susceptible to the effects of prolonged high water. As part of the Central and Southern Florida Comprehensive Study Review (Restudy), the ecological impacts of a series of proposed alternative water management regimes will be evaluated. Each of these scenarios will affect potential breeding and foraging activity of deer across the landscape. The ATLSS White-tailed Deer Breeding Potential Index (BPI) uses knowledge of how hydrologic factors affect the production and availability of food resources and the availability of dry bedding sites during the breeding season to compute a BPI for deer. We express the effects of proposed scenarios as changes in the spatial pattern of breeding potential over the model area. Our sub-area reporting units are based on a combination of public area, drainage basin, and management unit subregion maps (see REPUNITS.PDF). Methods: SFWMM restoration scenario hydrology output is used to make spatially explicit estimates of surface area with water in the depth ranges which restrict and preclude deer movement and fawning success. The deer breeding cycle consists of mating, gestation, birth, lactation/nursing and fawn growth and maturation. Peak fawning occurs during the dry season (February -- March), when uninundated bedding sites are available. Fawns born in late winter to early spring will have grown enough to move about on the landscape when the wet seasons starts in May-June. The BPI focuses on the depth of ponded water which would serve as an impediment to fawning, movement and foraging during the breeding season. If the food supply is interrupted during this period, the health of mother and offspring may suffer, and fawns are less likely to be recruited into the herd. Elevated water levels can make beds uninhabitable, and high water can drown young fawns. For each landscape grid cell in the SFWMM model area, we compute a daily feedback term, the ratio of the current ponding depth to a threshold depth above which deer movement and foraging is precluded. These daily feedback terms are summed over the time period from January 1 to May 31. The Breeding Potential Index is computed as 1 - ((feedback sum)/(days in summing period)). This results in an index between 0 and 1, with 0 representing no breeding potential, and 1 representing maximum potential (no interference from ponded water). This index is further scaled by a measure of habitat quality, using a metric of hydroperiod for each cell during the previous year as an indication of forage productivity and availability. Deer densities have been reported to be highest in areas with moderate hydroperiods (Fleming 1997.) Overdrained marshes with annual hydroperiods of less than 2-3 months do not support quality forage production, especially for females with young. When the ATLSS high-resolution forage model has been calibrated, the BPI Model will use forage estimates simulated for each grid cell rather than hydroperiod metrics. The White-tailed Deer BPI model was initially run on SFWMM calibration/validation data for 1979-1995. Index values for subregions were compared to reported densities for deer in those years to determine optimal settings for water depth thresholds and habitat effects. A number of related indices and metrics, including yearly movement potential indices, are being computed to aid in scenario evaluation. Landscape grid cell index values will be represented pictorially as 3-panel difference maps, and spatial averages computed over landscape subregions will be reported in tabular form. The Deer BPI is a composite index of spatial and temporal patterns. Spatial patterns will be computed based on ATLSS High Resolution Hydrology (28.5 x 28.5 meter units). This resolution captures fine-scale spatial heterogeneity of the South Florida wetlands and permits model representation of the elevated tree island habitats that are critical for deer survival during extended periods of high water. References: Fleming, D.M., J. Schortemeyer, and J. Ault. 1997. Distribution, abundance and demography of white-tailed deer in the Everglades. Proceedings of the Florida Panther Conference, Ft. Myers Fla., November 1994, Dennis Jordan, ed., U.S. Fish and Wildlife Service, pp. 494-503. Loveless, C.M. 1959. The Everglades deer herd, life history and management. Tech. Bull. No. 6, Fla. Game and Fresh Water Fish Comm., Tallahassee, 104 pp. =============================================================== Output associated with the ATLSS White-tailed Deer Breeding Potential Index Model. In accordance with ATLSS file naming conventions, each file name will consist of the characters: UVXXYYZZ.EXT "U" or "_" => the Base, typically F for the F2050 base or E for the C1995 base "V" or "_" => the alternative scenario or base "XX" => "BD" for the ATLSS White-tailed Deer Breeding Conditions Index Model "YYZZ" => 4 character mnemonic, described below "." "EXT" = "PDF" or "TXT" or "DOC" => PDF, tabular text or documentation =============================================================== ATLSS White-tailed Deer Breeding Potential Index 1. Maps Map outputs used to characterize results of the White-tailed Deer Breeding Potential Index Model will consist of eight image files in PDF file format. Each map shows a "Set" of model results, comparing a Base case to a Scenario, following the conventions for ATLSS comparison of two model runs. Each map has three panels. The left panel displays index values for an alternative or base scenario; the right panel displays index values for a base scenario, typically the Future without Project Conditions Case. The middle panel displays the cell-by-cell difference between index values for the two compared scenarios (e.g., ALT-5 minus F2050). Grid cells in the left and right panels are color-coded to represent the (positive) values of the displayed index, which range between 0 and 1. Cell colors in the center panel represent either positive (shades of gold) or negative (shades of blue) differences between index values displayed in the left panel and those in the right panel. Color keys are provided at the bottom of each map. Each map depicts the model area at either a Fine (500-meter x 500-meter) or Coarse (2-mile) scale of resolution. For each of six selected years, images will provide a spatial display of index values for that year. In addition, an image file is provided for the mean of all simulated years. The selected years include years with high, low, and typical rainfall, and several additional years that serve to highlight differences between the compared scenarios. The mnemonic characters are composed according to the convention: "YY" = Last two digits of the year "ZZ" = CR - Coarse (2 mile) resolution, FR - Fine (500 meter) resolution Listing of ATLSS White-tailed Deer Breeding Potential Index map files: File Name Time Period ------------ -------------------------------------------- UVBD69ZZ.PDF A High Rainfall Year (1969) UVBD70ZZ.PDF Highlight Scenarios (1970) UVBD77ZZ.PDF A Typical Rainfall Year (1977) UVBD83ZZ.PDF Highlight Scenarios (1983) UVBD90ZZ.PDF A Low Rainfall Year (1990) UVBD95ZZ.PDF Highlight Scenarios (1995) UVBDMYZZ.PDF Mean of All Years (1965->1995) ======================================================== 2. Time Series None. 3. Histograms None. 4. Tables The tables associated with the ATLSS White-tailed Deer Breeding Potential Index Model will display the breeding indices by subregions and years. The tables will also be at either a 500 meter (FR = Fine Resolution) or 2 mile (CR = Coarse Resolution) scale as indicated by the file name. File Name Description ------------ ------------------------------------------------ U_BDBASE.TXT Breeding index listed by subregions and years for the indicated base scenario. _VBDALTN.TXT Breeding index listed by subregions and years for the indicated alternative scenario. UVBDDIFF.TXT The difference of the breeding indices listed by subregions and years between the alternative and base scenarios.