How does Biomapper work?

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This page describe step by step how to conduct a complete analysis, beginning with environmental data and ending with a validated Habitat Suitability map.

A. Preliminaries

You begin by converting the data you have collected (field sampling, official databases, etc.) into Idrisi-formatted maps. These operations can be done with Idrisi or Biomapper, or any other tool you want (I frequently use Corel Draw, MapInfo, ASCII editors as well as home made programs).

When you have got maps that are usable by Biomapper and Idrisi, you can work with them. There are two kind of operations you will want to do:

  1. Deriving the available maps into biologically more meaningful maps (by reference to the focal species)
  2. Transforming the maps in order to make them suitable for the ENFA.

B. Preparing the maps

Now that your ecogeographical maps are at hand, you must prepare them for the ENFA. Basically, it means to make them overlayable and, as far as possible, normally distributed. You will also verify that there are no discrepancies between them. You shall create a project that will be used for all the subsequent operations.
Rock frequency Elevation Distance to towns

C. Analyses

You are now ready to perform the Ecological Niche Factor Analysis. This will give you many output (scores matrix, etc.) that you should examine attentively in order to verify them and to get ecological understanding about the focal species. Now, you have got your Habitat Suitability model.

D. Map production

Finally, you can use this HS model to compute a HS map. This map should then be validated with independent data (prepared during the step B).

Habitat Suitabilit map of Capra ibex in Switzerland

Ecological Niche Factor Analysis (ENFA)
This analysis is the central part of Biomapper. It is designed to compute the factors (like the Principal Components Analysis) that explain the major part of the ecological distribution of the species. Like in the PCA, the extracted factors are totally (by construction) uncorrelated but in this case they have biological signification: the first factor is the marginality factor, which describes how far the species optimum is from the mean habitat in the study area. The specialisation factors are sorted by decreasing amount of explained variance; they describe how specialised the species is by reference to the available range of habitat in the study area. Therefore, only a few of the first factors explain the major part of the whole information.

  [More details on ENFA]

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Updated 05.11.2001