Guild table: relative abundance

Science, Research & Data
1

Hello everyone,
my question is about the relative abundance in the guild table: should all rows sum up to one? is it meant in regard to the individuals or the species?
Thank you,
Sabine

2

Welcome to the forum @Sabine!
The relative abundance values are relative to the sum of all values in the column, for example, in the sample guild table from the user’s guide:

SPECIES  ...  relative_abundance
Apis              0.75
Bombus            1
Apis2             0.75
Bombus2           1

The sum of relative abundance values is 3.5. 0.75/3.5 = 0.214 and 1/3.5 = 0.286, thus, you could equivalently write the table so it sums to one like this:

SPECIES  ...  relative_abundance
Apis              0.214
Bombus            0.286
Apis2             0.214
Bombus2           0.286

It is kind of confusing. If you have data on the actual abundance of each pollinator, you could use that directly, for example:

SPECIES  ...  relative_abundance
Apis              55 (bees per hectare)
Bombus            70 (bees per hectare)

If you don’t have this data, but just an estimate, like “there are twice as many Bombus as Apis”, you could write that as

SPECIES  ...  relative_abundance
Apis              1
Bombus            2

If you have no data at all, you could weight them equally:

SPECIES  ...  relative_abundance
Apis              1
Bombus            1
2 Likes
3

Dear @esoth

Thanks a lot for the comprehensive answer.

In my case I use the parameters from nested species distribution values. Relative values representing habitat suitability index (each species 0-1) for the bee species. So similar to the sample guild table (values don’t sum to one). SDM are at larger scale including environmental (bioclimataic and land-use) variables, so I intend to use the second InVEST step with the local habitat filters.

My additional question
The three different possibilities to prepare an input table, do they have an effect on the output and interpretation of the pollinator supply index and pollinator abundance index (PS and PA)? I think not, because all the pixel values are related to the total (100% = 1 or >1…).
As far as I can see PS and PA also do not sum up to 1 (over all pixels and also not over all species at a pixel). So what is 100% in PS and PA, all pixels together that also not need to sum up to 1? I am still looking for the exact wording of PS and PA in the context of the input guild table. Someting like this so that non-experts and non-modelleres can understand: For species 1, pixel 1 with (PA =0.1) has 10% of all species 1 from the total country and pixel 2 with (PA=0.2) has 20% of all species 1 from the total country.

Kind regards
Sibylle