wildlifeDI (version 0.5.1)

Prox: Proximity Index

Description

The function Prox simply computes the proportion of (simultaneous) fixes that are proximal, based on some spatial threshold -- dc (Bertrand et al. 1996). It also facilitates local-level proximity analysis

Usage

Prox(traj1, traj2, tc = 0, dc = 50, local = FALSE, GetSimultaneous = TRUE)

Value

If local=FALSE (the default) Prox returns the numeric value of the Prox index. If local=TRUE Prox returns a dataframe containing the date/times of all simultaneous fixes from traj1, and in the case of GetSimultaneous = FALSE the time of the fixes that were deemed simultaneous in traj2. If GetSimultaneous = TRUE (the default) the Prox considers only the simultaneous fixes, as defined in GetSimultaneous. If FALSE Prox considers all the fixes in traj1 relative to traj2. The latter functionality is useful when the time between fixes for one trajectory (traj1) is much shorter than the second trajectory.

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

distance tolerance limit (in appropriate units) for defining when two fixes are spatially together.

local

logical value indicating whether or not a dataframe, containing the distance between each simultaneous fix, should be returned.

GetSimultaneous

logical value indicating whether proximity analysis is based on simultaneous fixes (if TRUE the default) -- see function GetSimultaneous or (if FALSE) a one-way mapping from traj1 to traj2 is used.

Details

The function Prox can be used to test for the presence of attraction (via proximity) in wildlife telemetry data. Prox is simply the proportion of simultaneous fixes within the threshold distance -- dc. The local output (dataframe) can be useful for examining variation in proximity through time.

References

Bertrand, M.R., DeNicola, A.J., Beissinger, S.R, Swihart, R.K. (1996) Effects of parturition on home ranges and social affiliations of female white-tailed deer. Journal of Wildlife Management, 60: 899-909.

See Also

GetSimultaneous, contacts

Examples

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