Cs {wildlifeDI}

Coefficient of Sociality

Description

The function Cs computes the coefficient of sociality between two moving objects following the methods outlined by Kenward et al. (1993). It also uses a signed Wilcoxon-rank test to test for significance.

Usage

Cs(traj, traj2, tc = 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

time threshold for determining simultaneous fixes – see function: GetSimultaneous.

Details

This function can be used to calculate the Kenward et al. (1993) coefficient of sociality (Cs) between two animals. The Cs statistic tests the observed mean distance between simultaneous fixes against that expected by the overall distribution of distances between all fixes.

Cs=\frac{D_E-D_O}{D_O+D_E}

Where D_O is the mean observed distance between simultaneous fixes, and D_E is the mean expected distance between all fixes. Kenward et al. (1993) propose Cs as a useful metric for exploring attraction or avoidance behaviour. Values for Cs closer to 1 indicate attraction, while values for Cs closer to -1 indicate avoidance. Values of Cs near 0 indicate that the two animals' movements have no influence on one another.

Further, the difference between the observed and expected distances are compared using a paired signed-rank test (both one-sided tests, indicative of attraction or avoidance). See the function GetSimultaneous for details on how simultaneous fixes are determined from two trajectories.

Value

This function returns a list of objects representing the calculated values from the Cs statistic and associated p-values from the signed rank test.

• Do – The mean distance of simultaneous fixes.

• De – The mean expected distance, from all fixes.

• Cs – The coefficient of sociality, see Details.

• p.Attract – One sided p-value from signed rank test, testing for attraction.

• p.Avoid – One sided p-value from signed rank test, testing for avoidance.

References

Kenward, R.E., Marcstrom, V. and Karlbom, M. (1993) Post-nestling behaviour in goshawks, Accipiter gentilis: II. Sex differences in sociality and nest-switching. Animal Behaviour. 46, 371–378.

See Also

GetSimultaneous

Examples

data(deer)
#tc = 7.5 minutes
Cs(deer, tc = 7.5*60)