Half-weight Association Index
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).
HAI(traj1, traj2, OZ, tc = 0, dc = 50)
an object of the class
spatial polygon associated with the home range (or some other form of) spatial overlap between
time threshold for determining simultaneous fixes – see function:
distance tolerance limit (in appropriate units) for defining when two fixes are spatially together.
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.
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.
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.
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## Not run: data(deer) deer37 <- deer deer38 <- deer 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)
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