Ecological community statistics using the PAST statistical software

In this post I want to run you guys through a series of screencasts describing how to perform ecological community statistical analysis using the PAST statistical software.

PAST is a statistical software developed by Oyvind Hammer from the Norwegian natural history museum. Initially it was designed to perform paleontological statistics, but has become an  extremely useful and easy to learn statistical software. The fact that PAST is distributed free of charge makes it an alternative to other programs, in my case I use it as an alternative to PRIMER-E when performing benthic statistics. In the PAST website you can also find a very lightweight easy to understand user guide.

In most cases you will perform the sampling on field and organize the data using Microsoft excel  where columns represents the taxa and rows represent each sample the values in the cells are a measure of taxa aboundance in each sample. the first two screencast describes how to organize your ecological data and upload it to PAST.

The procedures the help you get a "feeling" of your data includes non metric multi-dimensional scaling (Kenkel and Laszlo, 1986) and cluster analysis, the analysis results help you see if there are trends in your data, to better see the internal organization of the data you can use a "grouping" variable to add color to you results. this is all described in the following two screencasts.

After distinct sample groups were identified in your data you will want to determine if they are significantly different from one another. This can be performed using ANOSIM (analysis of similarity, Anderson, 2001).

The last step in the screencast series is understanding which species control the community change, this can be performed using a statistical test called SIMPER (similarity percentage, Clarke1993) as displayed in the last screencast.

Anderson, M. J. 2001. A new method for non-parametric multivariate analysis of variance. Austral Ecology 26: 32-46.
Clarke, K.R. 1993. Non-parametric multivariate analyses of changes in community structure. Australian Journal of Ecology, 18, 117143.
Kenkel, Norm C., and Laszlo Orlóci. "Applying metric and nonmetric multidimensional scaling to ecological studies: some new results." Ecology(1986): 919-928.