This function uses the output of 'getivz' (and, optionally, similar output from the bootstrap procedure) to sum z scores across taxa associated with each indicator direction (- or +) at each level of the environmental gradient.
ivzsums(allivz)ivzsums.f(allivz, sppmax)
The output matrix from the function 'getivz' that contains four submatrices, the first two of which include indicator direction and z scores.
A completed summary output table for all taxa, used to ascertain which taxa should be filtered and which retained.
A matrix of two (z- and z+) parallel vectors with length (nrow) equal to the number of candidate partitions of an environmental gradient.
The function selects taxa identified as either increasing or decreasing at each level of the environmental gradient and combines their IndVal z scores to generate an assemblage-wide sum. The sum(z) scores are interpreted as the magnitude of community change at each level of the environmental gradient.
The alias 'ivzsums.f' uses the output of 'getivz' to sum z scores across taxa filtered by purity and reliability associated with each indicator direction (- or +) at each level of the environmental gradient. Filters are provided by the final column ("filter") in the 'sppmax' table that is part of each TITAN object and an argument for 'ivzsums.f'. All taxa with a value of either 1 or 2 are pure and reliable decreasers or increasers, respectively, and are selected for summation. Filtered sums are used by the 'plot.sumz' function to create estimates of robust community change more precise than the original unfiltered sum(z) in TITAN v1.0.
Baker, ME and RS King. 2010. A new method for detecting and interpreting biodiversity and ecological community thresholds. Methods in Ecology and Evolution 1(1): 25:37.