move (version 3.2.2)

corridor: Corridor behavior identification

Description

This function identifies movement track segments whose attributes suggest corridor use behavior

Usage

# S4 method for .MoveTrackSingle
corridor(x,speedProp=.75, circProp=.25, plot=FALSE, ...)
  # S4 method for .MoveTrackStack
corridor(x,speedProp=.75, circProp=.25, plot=FALSE, ...)

Arguments

x

a move, moveStack or moveBurst object.

speedProp

numeric between 0 and 1, defines the proportion of speeds which are high enough to be a valid corridor point (default value selects speeds that are greater than 75 % of all speeds).

circProp

numeric between 0 and 1, defines the proportion of the circular variances that is low enough to be a valid corridor point. Low values of the circular variance indicate that the segments are (near) parallel (default value selects variances that are lower than 25 % of all variances).

plot

logical, if TRUE the track is plotted together with dots that indicate corridor points when a move object is provided (color scale indicates how many corridor points are near by, few: blue, many: pink).

...

cex argument can be set specifying the size of the points when plot=TRUE. Optional.

Value

The function returns a moveBurst object or a list of moveBurst objects (if a MoveStack is supplied). The MoveBurst date.frame stores the following information: - segment midpoint - speed - azimuth - pseudo-azimuth - circular variance The object is bursted by the factor that indicates whether the segment belongs to a corridor segment or not, and is specified in the "burstId" slot.

Details

The corridor function uses the attributes of a movement step (segment) to identify movement steps that exhibit corridor use behavior. For each segment, the speed and the azimuth are calculated and assigned to the segment midpoint. A circular buffer is created around the midpoint of each segment whose radius is equal to half the segment length. The segment azimuth (180 >= azimuth > -180) is converted into a new unit, the 'pseudo-azimuth' (0 <= 360), removing the directional information. Subsequent, the circular variance of the pseudo-azimuths of all segment midpoints that fall within the circular buffer is calculated. Low values of the circular variance indicate that the segments are (near) parallel. Next, it is determined whether a segment's speed is higher than speedProp (by default the upper 25% speeds) and its circular variance is lower than circProp (by default the lower 25% of all variances). Segment midpoints that meet both of these requirements are considered as a 'corridor' point, all others are considered 'non-corridor' points. Finally, a corridor point is determined to be within a true corridor if within its circular buffer there are more 'corridor' points than 'non-corridor' points.

References

LaPoint, S., Gallery, P., Wikelski, M. and Kays, R. (2013), Animal Behavior, Cost-based Corridor Models, and Real Corridors. Landscape Ecology. doi:10.1007/s10980-013-9910-0.

Examples

# NOT RUN {
## with a move object 
  data(leroy)  
  tmp <- corridor(leroy, plot=TRUE)
  plot(tmp, type="l", col=c("red","black")[c(tmp@burstId,NA)])
  
## with a moveStack object   
  data(fishers)
  stacktmp <- corridor(fishers[c(1:400,sum(n.locs(fishers))-(400:1)),])
  plot(stacktmp[[2]], col=c("red","black")[stacktmp[[2]]@burstId])
  lines(stacktmp[[2]], col=c("red","black")[c(stacktmp[[2]]@burstId,NA)])
# }