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).
Ca(traj1, traj2, tc = 0, dc = 0)This function returns a numeric result of the Ca statistic.
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).
same as traj1.
temporal tolerance limit (in seconds) for defining when two fixes
are simultaneous or together. Parameter passed to function GetSimultaneous.
distance tolerance limit (in appropriate units) for defining when two fixes are spatially together.
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.
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.
GetSimultaneous, Prox, HAI
data(deer)
deer37 <- deer[1]
deer38 <- deer[2]
#tc = 7.5 minutes, dc = 50 meters
Ca(deer37, deer38, tc = 7.5*60, dc = 50)
Run the code above in your browser using DataLab