A practical look at the variable area transect.
The variable area transect (VAT) is a plotless density estimator that has received little attention in the ecological literature despite having potentially robust estimation properties. VAT allows for density estimations without the lengthy search times associated with other plotless density estimators. In spite of this, little has been written about the effect of varying transect widths on its density estimation properties or on the practical implementation of the VAT in field settings. An artificial population sampler was used to examine the effect of transect width on density estimates obtained using the VAT. Three transect widths were chosen corresponding to the mean object size, the largest object size, and twice the size of the largest object. Transect width had a marked effect on the quality of the density estimation, with the largest transect width resulting in significant negative biases in estimation. For the narrowest width, most estimates were within 10% of the true value for a nonrandomly distributed population. The practical considerations of choosing a VAT transect width are enumerated.
Dobrowski
Solomon Z
SZ
University of California, Davis, Tahoe Environmental Research Center, One Shields Avenue, Davis, California 95616, USA. szdobrowski@ucdavis.edu
Murphy
Shannon K
SK
D003198:Computer Simulation; D017753:Ecosystem; D008954:Models, Biological; D011156:Population Density