IAB {wildlifeDI} | R Documentation |
Benhamou's IAB Index
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
IAB(traj, traj2, tc = 0, dc = 0, local = FALSE, rand = 99)
Arguments
traj |
an object of the class |
traj2 |
(optional) same as traj, but for the second group of individuals. See |
tc |
time threshold for determining simultaneous fixes – see function: |
dc |
critical distance where the IAB function will show maximum slope – see Benhamou et al. (2014) for more advice on selecting this parameter. |
local |
logical value indicating whether a dataframe ( |
rand |
number of permutations to use in the local permutation test. |
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 procedure 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). Here a local version of this statistical testing procedure is implemented by taking rand
samples of the (n^2 - n
permutations of unpaired fixes. The p-values are computed following Benhamou et al. (2014), z-scores are calculated based on the mean and standard deviation of this hypothetical distribution.
Value
If local=FALSE
(the default) IAB returns a dataframe with the values of the IAB index and the associated p-values for one-sided tests for attraction or avoidance. If local=TRUE
IAB returns a dataframe (containing the date/times of all simultaneous fixes (NOTE: times are associated with traj1), along with the distance between fixes at each time , and the IAB index value for each simultaneous fix. A localized p-value (.pa signifies the test for attraction and pb the test for avoidance) and z-score is computed based on rand
permutations of the fixes. The row.name columns can be used to match the simultaneous fixes to the original trajectory.
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
data(deer)
#tc = 7.5 minutes, dc = 50 meters
IAB(deer, tc=7.5*60, dc=50)
df <- IAB(deer, tc=7.5*60, dc=50, local=TRUE)