search for: pielou

...ons *This index scans the columns of the presence-absence matrix and keeps track of the number of unique species combinations that are represented in different sites. For an assemblage of n species, there are 2n possible species combinations, including the combination of no species being present (Pielou and Pielou 1968). In most real matrices, the number of sites (= columns) is usually substantially less than 2n, which places an upper bound on the number of species combinations that can be found in both the observed and the simulated matrices. Presence-absence Data (Each row represents different...

Dear Friends, Using package Vegan, I need to calculate Shannons Diversity index and Pielou's Evenness for a set of 20 study areas. Each area is represented by a matrix of 25 sample plots x tree species. The code is as following, where data stands for the data matrix of any of the 20 areas: S <- specnumber(data) H <- diversity(data) J <- H/log(S) I indexed the 20 areas...

Hi! My question(s) in the end might be silly but I am no expert on this, so here it goes: Noy-Meir (1973), Pielou (1984) and a few others have pointed to non-centered PCA being in some cases useful. They clearly explain that "it is the case" when multi-dimensional data display distinct clusters (which have zero, or near-zero, projections in some subset of the axes) and the task is (exactly) to se...