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)

        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).
        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
        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.
        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.

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