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
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.