I have a presence dataset that is composed of satellite tracking data, in-person observations, and verified citizen-science sightings.
The presence points span across the entire Caribbean, but are generally restricted to areas close to the shore, leaving big gaps between clusters of sightings.
Because of this, using a simple random selection of pseudoabsences within the whole study area results in many pseudo absences being located in areas vastly different from the presence points, hence affecting the evaluation of the importance of environmental variables and the perceived accuracy of the models.
I am looking to restrict the area in which pseudo-absences can be selected to be in a circle around presence points, but I can't figure out the best way to determine the radius of these circles.
Thanks in advance for any help!
Our bear article (Italy) and one of our elephant papers (Tanzania) contain a method to establish such radius that may apply to your case as well. Hope it helps.
There are many different strategies to select pseudo-absences (you can find many reviews on this topic). In my opinion, instead of arbitrary selecting a buffer area (or radius of circles), I would suggest to randomly select pseudo-absences from your study area (but if you have precise estimation of species movement ability, then you can use this radius). That being said, I strongly suggest to choose a proper extent of study area.
Hein Van Gils thank you for the help!
Could you possibly share a pdf version of the papers? I can't access them online...
Francesco Garzon - Is your study species closely associated with the littoral zone (inshore fishes)? Beaches (turtles)? Offshore / nearshore transitions (some sharks)? Or shoreline associated terrestrial species?
Not knowing what you are studying, makes it a little hard to suggest solutions. Assuming you are discussing a marine species, and you mention that most occurrences for telemetry data are near the shore, you could simply buffer a terrestrial layer a reasonable distance that encompasses most of your presence points.
If you are studying a terrestrial species, I would likely keep all land areas, unless you know for sure that your species never / rarely occurs greater than X metres from the high tide line.
Ian
- Badges
- Science topic