[R-sig-eco] Error in Maxent maps

[Bede-Fazekas Ákos]

Dear Irene,

Since your background points are not real occurrences (so you do not 
know the prevalence of the species), and MaxEnt is a presence-only 
method, the predicted value can not directly treated as probability of 
occurrence. Also you should never compare the raw predicted values 
between species (or between different models), even if you use 
presence-absence data/method. 0.005 for Species1 is not better/worse 
than 0.95 for Species2. So I would say that the predicted values are OK.
If you really want to compare predictions between species, I recommend 
you to rescale the raw values to a 5-level ordinal scale using specific 
thresholds that account for observed presences. Please refer to Somodi 
et al. (2017): 
https://www.researchgate.net/publication/318561746_Implementation_and_application_of_multiple_potential_natural_vegetation_models_-_a_case_study_of_Hungary

Have a nice week,
Ákos Bede-Fazekas
Hungarian Academy of Sciences

2021.01.12. 13:47 keltezéssel, Irene Rojo írta:
> Dear all,
>
> My name is Irene and I am performing Maxent SDM in R with the dismo
> package.
>
> I am working with several species, performing one analysis for each
> species, and all are working fine, i.e. the models have sense, except two
> of them. For those species, I can run Maxent models and I get a very high
> value of AUC (0.99) but the resulting maps show values between 0 and 0.005,
> when for the rest of the species they are between 0 and (almost) 1. So maps
> have no sense. The predictor variables are the same, and those two species
> are not the ones with the lowest number of occurrences (this is the first
> reason I thought that could be affecting the results).
>
> I know it is not easy to know what is going on, but I am doing exactly the
> same with all species. If anyone can guess the error or know which part of
> the analysis is more sensitive so I can check it again I would be very
> grateful.
>
> Thanks a lot in advance,
>
> Irene
>
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>
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