Ca {wildlifeDI}

Coefficient of Association

Description

This function measures the dynamic interaction between two moving objects following the methods first described by Cole (1949), and more recently employed by Bauman (1998).

Usage

Ca(traj, traj2, tc = 0, dc = 0)

Arguments

traj

an object of the class move2 which contains the time-stamped movement fixes of at least two individuals. For more information on objects of this type see help(mt_as_move2).

traj2

(optional) same as traj, but for the second group of individuals. See checkTO

tc

temporal tolerance limit (in seconds) for defining when two fixes are simultaneous or together. Parameter passed to function GetSimultaneous.

dc

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

Details

This function can be used to calculate the Cole (1949) measure of dynamic interaction between two animals. Termed a coefficient of association, the Ca statistic tests the number of fixes the animals are observed together against the total number of fixes following:

Ca = \frac{2AB}{A+B}

where A (respectively B) is the number of times animal 1 (resp. 2) are observed, and AB is the number of times the two animals are observed together. Several works, including Bauman (1998) have suggested that Ca > 0.5 indicates affiliation or fidelity, while Ca < 0.5 indicates no association between the two animals. Note that this function calls GetSimultaneous to identify the temporal component of identifying when fixes together.

Value

This function returns a numeric result of the Ca statistic for each pair in the dataset.

References

Bauman, P.J. (1998) The Wind Cave National Park elk herd: home ranges, seasonal movements, and alternative control methods. M.S. Thesis. South Dakota State University, Brookings, South Dakota, USA.

Cole, L.C. (1949) The measurement of interspecific association. Ecology. 30, 411–424.

See Also

GetSimultaneous, Prox, HAI

Examples

data(deer)
#tc = 7.5 minutes, dc = 50 meters
Ca(deer, tc = 7.5*60, dc = 50)