Summarize diversity indicators per area

On the DistDiv calculate form, note the option Create diversity sum table. If selected, a second summary table is created, this summarizing the diversity indicators per area. This table can be opened using DistSum > Summarize DSTdiversity indicators per area.

An example result showing the calculated diversity indicators, here for 1/10th degree squares. For each gridcell area, you have fields

FATOTAL (total number of families)

GETOTAL (total number of genera)

SPECIES (total number of species - grouping infra taxa)

TAXA (total number of all taxa - counts infra taxa separately)

CHAO2 (see below)

CHAO2R (see below)

RWD (see below)

GHI (see below)

VOUCHERS (count of vouchers)

SEEDTOTAL (count of seed records)

OBSTOTAL (count of observations)

SAMPTOTAL (count of sample plot records)

... together with a range of lat/long and cell related details.

The map grid bounding coordinates of each cell are provided enabling BRAHMS to draw polygons on Google Earth or in Arcview.

CHAO2R (see below)

RWD (see below)

Taxtotalx is the total number of taxa (families, genera, species, infra as calculated) and s1x and s2x are the number of taxa with 1 vouchers and 2 vouchers per geo-area (gridcell, country, etc. as calculated) respectively.

CHAO2 calculation

IF s2x = 0

CHAO2 = 0

ENDIF

IF s2x = 0 AND s1x = 0

CHAO2 = taxtotalx

ENDIF

IF s2x <> 0

CHAO2 = taxtotalx + s1x*s1x /(2*s2x)

ENDIF

CHAO2R calculation

CHAO2R = taxtotalx +(vouchertotx-1)/vouchertotx * s1x*(s1x-1)/(2*(S2x+1))

For more information on Chao2 and especially Chao2r, please refer to the website of EstimateS.

RWD calculation (Rarity Weighted Diversity)

The RWD calc (available with gridcell calculation mode only) first calculates the number of grid cells a taxon occurs in and stores these result in fields in the family, genus, species files called GRIDCELLS and CELLMODE, the latter indicating the cell size. It then lists all taxa in a cell and uses:

rwdx = rwdx + 1/gridcellsx

to total the RWD for each cell, storing the result in the diversity totals table.

The basic idea behind the RWD calculation is that all species have an equal weight (1) that is spread over the total area that species occurs in. So a species occuring in a single gridcell ‘donates’ its weight to that one cell, while a species that occurs in 100 gridcells only adds 0.01 to all of them. This measure has meaning for conservation issues: it is a measure how many species an area is ‘responsible’ for, where 1 may mean 100% responsible for 1 species, or 10% each for 10 species.

Note that results from the DST and DSTsummary tables can be plotted to maps and, if using Google Earth, you can use the cell boundaries to plot polygons to represent cell areas. Use map styles to shade cells relative to taxa counts or diversity indexes.

The cell boundary fields can also be used in Arcview. The easiest way to create gridcell-polygons using the boundary fields is to use a special script that is incorporated in an Arcview project that can be downloaded (together with a help file) from Wageningen (link to script to be added).

Genetic Heat Index (GHI) calculation

For GHI details, refer to e.g. page 26 in Forest Protection in Ghana WD Hawthorne and M. Abu-Juam) and for a more general background to biodiversity and bioquality, see e.g. Forests, Biodiversity and Livelihoods: Linking Policy and Practice in Living off Biodiversity.

GHI values are based on a weighted species scoring system devised by William Hawthorne.

These are 'bioquality' scores that can be applied to samples of species at any scale, and show the degree of localness or edemicity of the species in the sample. 'Each species is assigned a star value (black, gold, green, blue, etc.), each representing global distribution, refined by local factors such as local distribution and taxonomic relatedness. A separate BRAHMS table lists stars and their adjustable numeric weights, which are determined by mean global range on a degree square resolution of the species of each Star. The GHI field in the diversity table sums speciesÏstar-weight value per selected area, divided by number of species. Areas with large number of species may therefore have a lower GHI than areas with a small number of high scoring species. Hotspots can be detected at any scale.