Maxent 2.3 Bias File
Dani Villero
I am PhD student working on the modelling of amphians distribution in
relation to climate change.
We developing now our models using Maxent. Since we have a strong bias
in our data set, but are working with a large number of species we are
very interested in using the sampling bias file option in Maxent.
However we are encountering some problems in using it. We want to
apply the information gathered from the input species file (species,
coordx, coordy) with 9 different species as sampling bias (we
understand that more information on overall species presence is likely
to be related to biases in record collection). But when we run Maxent
we obtain an error: "suffix not recognised". We are using as bias file
the same ".csv" file we are using as input file.
We do not understand the error. Could it be that bias file has a
different structure than the input file? In this case this is a change
with respect to older version of Maxent, isn't it?
Well, sorry for all this load of questions but we are very interested
in taking into account sampling bias in our analyses!!
Thanks in advance for all your help and kindness.
Dani Villero
Steven Phillips
If you have a set of samples that you think is representative of
sampling bias, such as presence data for a group of species that are
all detected using the same methods or by the same researchers, then
you can use them in Maxent by providing them as background data. You
need to have those samples in SWD format, with the environmental data
given for each point. You then use that file instead of the
environmental layer grids; you can project the resulting model onto
your original layers to get a prediction for the whole study area.
(We have a paper in preparation that discusses how this can counteract
sampling bias.)
If you instead use a "sampling bias" file, it needs to be a grid,
typically in .asc format. A bias file describes the relative sampling
intensity across the whole study area.
-- Steven