How to include absence data in MAXENT?

[AL]

Hy there:

I'm running a model on MAXENT, in a specific case that I have presence
and absence data. Does anyone can help me, explaining me how to
include this kind of data, or recomend me some readings?

Thanks in advance

[Alberto Jiménez]

Hi Al,

If you have true absence data, and you are interested in modelling realized distribution, why don´t you use a discrimination technique (GLMs, GAMs, NNET...) instead of a presence-only method?
Bests

Alberto

Alberto Jiménez Valverde
Dpto. Biodiversidad y Biología Evolutiva
Museo Nacional de Ciencias Naturales
C/José Gutiérrez Abascal 2
28006 Madrid, Spain
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[Ângela Lomba]

Hi...thanks for your answer...

My dataset includes true presences and absences, but the target specie
is an endemic Daffodil, with a low number os total records (16
presences and 16 absences) recorded in a 1km grid, within a 200 km2
area (drainage basin). The main problem ie related with the dataset,
and when I performed a GLM, I didn't obtain a good fit.

Despite this fact, I read that MAXENT allows the inclusion of true
absence data...and I'm study this option...

Still, I'll try to explore other alternatives...

Cheers

[Paco Rodríguez]

Hi Angela,

 

Probably you should include those recorded absences as background points. Have a look at the help file for directions on how to do it

 

Good luck

 

Paco

 

**********************************

Francisco Rodriguez Sanchez

Dept. Biologia Vegetal y Ecologia

Universidad de Sevilla

Apdo. 1095, E-41080 Sevilla, SPAIN

Phone: +34 954557056

Email: frodr...@us.es

 

2007/11/23, Ângela Lomba <angel...@gmail.com>:

[Ângela Lomba]

Hi again, and thanks for you kind answer...I was reading again Help
file, but still didn't find the procedure to include the absence
points recorded in field.

I'm not ready ro give up yet:)
Any suggestion is welcome...

Cheers

[Jesús Muñoz]

You have to sample in a GIS the environmental variables using a grid
that includes both presence and absence points (or make two samples and
mix them in a text editor or Excel, depending on the outfile format...
there are very many ways).

In Maxent, the "species.csv" (or whatever the name) with the
environmental information of the presence points would go to "samples"
box, and the "absences.csv" file with the environmental information of
the absence points, to the "Environmental layers" box.

Hope this helps,
Jesus

*******************************************************************
Jesús Muñoz e-mail: jmu...@rjb.csic.es
Real Jardín Botánico (CSIC)
Plaza de Murillo 2 tlf. +34 91 420 3017
E-28014 Madrid fax. +34 91 420 0157
ESPAÑA (Spain)

http://www.rjb.csic.es/fichapersonal.php?id_investigador=76

http://kraken.unex.es/kraken/ KRAKEN research group
(environmental modelling, data processing & analysis)
http://www.synthesys.info/index.htm (SYNTHESYS: EU funds short
visits to our institution)
*******************************************************************

Ângela Lomba escribió:

[Lutra]

Non Parametric Multiplicative Regression is great for estimating
probability from presence/absence data. Hyperniche is a useful piece
of software for running NPMR. http://oregonstate.edu/~mccuneb/NPMR.htm

[Ângela Lomba]

Hi;

 

Thank you all for the suggestions to my research project:) and I'm sorry didn't write sooner but I was in ECEM07 Conference in Italy.

I'll keep in touch

 

Cheers