Half-weight Association Index

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Description

This function computes the Half-weight Association Index for examining the presence of dynamic interaction in wildlife telemetry studies. This implementation follows that outlined in the paper Atwood and Weeks (2003).

Usage

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HAI(traj1, traj2, OZ, tc = 0, dc = 50)

Arguments

traj1

an object of the class ltraj which contains the time-stamped movement fixes of the first object. Note this object must be a type II ltraj object. For more information on objects of this type see help(ltraj).

traj2

same as traj1.

OZ

spatial polygon associated with the home range (or some other form of) spatial overlap between traj1 and traj2. Required to be an object that coerces to class SpatialPolygons.

tc

time threshold for determining simultaneous fixes – see function: GetSimultaneous.

dc

distance tolerance limit (in appropriate units) for defining when two fixes are spatially together.

Details

This function can be used to test for the presence of dynamic interaction within the shared area (often termed the overlap zone) of the two animals home ranges. Specifically, HAI is calculated in identical fashion to that for Ca, but considers only those fixes in the shared area. Typically, the overlap zone (OZ) is easily obtained by taking the spatial intersection of two polygon home ranges.

Value

This function returns the numeric value of the HAI statistic. Values near 1 indicate attraction within the shared home range area, while values near 0 indicate avoidance within this shared area.

References

Atwood, T.C. and Weeks Jr., H.P. (2003) Spatial home-range overlap and temporal interaction in eastern coyotes: The influence of pair types and fragmentation. Canadian Journal of Zoology, 81: 1589-1597.

See Also

GetSimultaneous, Ca

Examples

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## Not run: 
data(deer)
deer37 <- deer[1]
deer38 <- deer[2]
library(adehabitatHR)
library(sp)
library(rgeos)
#use minimum convex polygon for demonstration...
hr37 <- mcp(SpatialPoints(ld(deer37)[,1:2]))
hr38 <- mcp(SpatialPoints(ld(deer38)[,1:2]))
OZ <- gIntersection(hr37,hr38)
#tc = 7.5 minutes, dc = 50 meters
HAI(deer37, deer38, OZ=OZ, tc=7.5*60, dc=50)

## End(Not run)