MODEL COMPONENTS

Nest Construction The mean water depth during the peak of the mating season from April 16 through May 15 is used as an indicator of the probability that mating and nest construction will occur in a given area. Two linear functions are applied to indicate the value of this model component such that the highest probability of nest construction occurs at a mean level of 1.3 feet. Mean water depth values higher or lower than this reduce the probability of nest construction.

Elevation of top of clutch: C = 0.889 + 0.663 * x3 Lowermost eggs in clutch: B = C - 0.169 (mean clutch cavity is 16.9 cm in height)

Nest Flooding The probability of a nest being flooded is calculated from a combination of the mean water level during nest construction and the maximum water level during egg incubation. Field observations indicate that the mean water level between June 15 and June 30 will determine the elevation at which a nest will be constructed. A linear function is applied to the difference between the maximum water level during the egg incubation period (July 1 through September 1) and the mean water level during nest construction to give the probability of nest flooding.

	Relative Habitat Quality Available evidence suggests that the type of vegetative cover and elevation within an area greatly influence the probability of nesting. This model uses a static ranking of the dominant vegetation type within a 500 meter spatial cell as a measure of habitat quality.
Habitat Preference Weights for Alligator BPI Model (dom: reweighted) [larger image]

Breeding Water levels encountered during the period ranging from May 16 of the current nesting year to April 15 of the previous year are used as an indicator of the probability of breeding occurrence in an area. The probability that nesting will occur correlates positively with the amount of time spent in flooded conditions during this period. This model component is defined to be the proportion of this period for which there was water depth greater than 0.5 feet.

Proportion of females nesting y1 = 1.5363 - 4.8782 * x1

The overall API is calculated as a weighted product of the described model components. This uses (1 - the probability of nest flooding) in the product and applies highest weight to the nest flooding component, a lower weight to the breeding and nesting components, and the lowest weight to habitat quality factor.

Next: Output

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