Benhamou's IAB Index

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Description

The function IAB computes the IAB index following the methods described in the paper by Benhamou et al. (2014). It facilitates global analysis, with the significance testing procedure described in the paper, but also a local level output, to explore the IAB statistic through time.

Usage

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IAB(traj1, traj2, tc = 0, dc = 50, local = FALSE)

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.

tc

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

dc

critical distance where the IAB function will show maximium slope – see Benhamou et al. (2014) for more advice on selecting this parameter.

local

logical value indicating whether a dataframe (local = TRUE) containing the IAB index for each simultaneous fix should be returned, or (if local = FALSE - the default) the global index along with associated p-value.

Details

The function IAB can be used to test for direct interaction in wildlife telemetry data and affords a novel significance testing procedure that takes into account the serially correlated structure of telemetry data. Specifically, it computes an index analogous to the Bhattacharyya coefficient between the potential influence domains of two animals. Like the other indices, IAB is dependent on the selection of an appropriate value for dc (which is termed Delta in the article). The dc parameter here is not a threshold distance, but rather the distance at which the function shows maximum slope (see Benhamou et al. 2014).

The significance testing procuedure uses a wrapped shifting method in order to maintain the serially correlated structure of the data. At each shift, a sample value of IAB (termed MAB) is computed in order to generate a distribution of values to test against (for more information see Benhamou et al. 2014).

Value

If local=FALSE (the default) IAB returns the numeric value of the IAB index and the associated p-value. If local=TRUE IAB returns a dataframe (containing the date/times of all simultaneous fixes, along with the distance between fixes at each time, and the IAB index value for each simultaneous fix.

References

Benhamou, S., Valeix, M., Chamaille-Jammes, S., Macdonald, D., Loveridge, A.J. (2014) Movement-based analysis of interactions in African lions. Animal Behaviour, 90: 171-180.

See Also

GetSimultaneous, DI, Prox

Examples

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data(deer)
deer37 <- deer[1]
deer38 <- deer[2]
#tc = 7.5 minutes, dc = 50 meters
IAB(deer37, deer38, tc=7.5*60, dc=50)
df <- IAB(deer37, deer38, tc=7.5*60, dc=50, local=TRUE)