DRAFT: DO NOT CITE OR QUOTE

 

White-Tailed Deer

 

Breeding Potential Index (BPI)

 

 

Empirical basis and model assumptions:

 

The white-tailed deer are modeled, as they are an important prey species for the Florida panther.

 

Urban areas are not good for reproduction for white-tailed deer.

 

*         In the BPI spatial cells in urban areas are excluded (the index is set to zero).

 

The reproductive season is between January 1 and May 31. Ponded water can act as an impediment to fawning, movement and foraging during the breeding season. If the food supply is interrupted during this period, which can happen during high water, 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.

 

*         In the IBP a water depth of 55 cm is defined to be the depth above which movement and foraging are assumed to be absolutely precluded. Water of any depth during this season is assumed to restrict fawning and slow down movement, and so subtracts from the index. The degree to which water is an impediment is represented by calculating the ratio of (water-depth days)/(maximum possible water-depth days) during the reproductive season.

 

The hydroperiod during the year previous year is an indication of the quality and availability of forage prior to fawning. This will influence the health of the females and thus their likelihood to fawn. Too short a hydroperiod reduces the quality of the forage. Too long a hydroperiod reduces the availability of forage.

 

*         The BPI is weighted by a multiplicative factor that depends on hydroperiod. The values of this discounting factor for hydroperiods of 0, 1, 2, 3, 4,.. 12-month hydroperiods are {0.3, 0.4, 0.6, 0.9, 1.0, 1.0, 1.0, 0.9, 0.8, 0.6, 0.5, 0.4, 0.3}.

 

Selected 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.

 

 

 

Flow Chart for Construction of White-tailed Deer Breeding Potential Index

 

 

The flow chart shows the steps in computing an index value for a cell:

 

Variables of index computation (top box):

 

500-m cells that are in urban areas are excluded.

 

HIWATER - water level at which deer movement and foraging are absolutely precluded

HpDiscount[ ] - a function that discounts the value of a cell according to its hydroperiod the

previous year, which is an indication of foraging quality and availability.

 

 

Cycle through days of year to determine breeding conditions (middle):

 

For each spatial cell the model computes a daily term, the ratio of the current ponding depth to the (HIWATER x total days in the breeding season). When summed over the whole reproductive period, this sum then is the sum of ratios of (water-depth days in the reproductive season) to (maximum water-depth days in the reproductive season), or

 

I = S (WaterDepth(x,y)/HIWATER).

 

This sum of ratios over the days of the breeding season gives an indication of the difficulty of moving and fawning during the breeding period.

 

 

Calculation of total BPI (bottom):

 

The BPI for each cell, termed the IndexMap(x,y), is composed of two factors. The first factor measures the favorability of water conditions during the breeding season, and is computed as [1 - I(x,y)/MaxI], where MaxI is the maximum value that I(x,y) could obtain. 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 second factor, which is a measure of habitat quality, using the metric of hydroperiod (HpDiscount[ ]) for each cell during the previous year as an indication of forage productivity and availability.

 

 


For more information, see the original model description.

 


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