Description -
This package contains functions and associated routines to analyze line transect data, and functionality for point count data is forthcoming. A large suite of classical, parametric detection functions are included (see F.dfunc.estim), and the package can also accommodate user-defined detection functions (see package vignettes).
Background -
Line transect surveys are conducted by traversing randomly
placed transects in a study area with the objective of estimating
density or abundance of a particular organism. Data collected during line
transect surveys consists of sighting records for targets, usually either individuals or
groups of some species. Among the collected data,
off-transect distances are recorded or computed from other information such as sighting distance and angle (see perp.dists). Off-transect distances are
the perpendicular distances from the transect to the location of the initial
sighting cue. The physical locations of sighted targets are often recorded or computed. When groups are the target, the number of individuals in the group is recorded.
A fundamental characteristic of distance sampling analyses is that sightability (probability of detection) of targets is assumed to decline as off-transect distances increase. Targets far from the transect are assumed to be harder to detect than targets close to the transect. In most classical line transect studies, targets on the transect (off-transect distance = 0) are assume to be sighted with 100% probability. This assumption allows estimation of the proportion of targets missed during the survey, and thus adjust the actual number of sighted targets by this proportion. Some studies utilize two observers searching the same areas to estimate the proportion of indivivduals missed and thereby eliminating the assumption that all individuals on the line have been observed.
Relationship to other software -
A detailed comparison of Rdistance to other options for distance sampling analysis
(e.g., Program DISTANCE, R package Distance, and R package unmarked) is forthcoming. Our intent is for Rdistance to provide rigorous and flexible analysis of distance-sampling data. We understand that beginning users often need software that is both easy to use and easy to understand, and that advanced users often require greater flexibility and customization. Our aim is to meet the demands of both user groups. Rdistance is under active development, so please contact us with issues, feature requests, etc. through the package's GitHub website (https://github.com/tmcd82070/Rdistance).
The best place to start learning the routines of Rdistance is the Rdistance Tutorial for Beginners vignette avialable through the package's GitHub website (https://github.com/tmcd82070/Rdistance) or CRAN. Additionally, the examples in the help files for F.dfunc.estim, F.abund.estim, and F.automated.CDA highlight the package's primary functionality.
| Package: | Rdistance |
| Type: | Package |
| License: | GNU General Public License |
A list of routines can be obtained by loading Rdistance and
issuing ls(pos="package:Rdistance").