Ca | R Documentation |
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(traj, traj2, tc = 0, dc = 0)
traj |
an object of the class |
traj2 |
(optional) same as traj, but for the second group of individuals. See |
tc |
temporal tolerance limit (in seconds) for defining when two fixes
are simultaneous or together. Parameter passed to function |
dc |
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.
This function returns a numeric result of the Ca statistic for each pair in the dataset.
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)
#tc = 7.5 minutes, dc = 50 meters
Ca(deer, tc = 7.5*60, dc = 50)
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