background bias file in MaxEnt weighted to species density

[Mohamed Sallam]

Dear all, 

I'm working on distribution niche modeling of some mosquito species.Some of these mosquito species have limited flight range, so I created buffer zones around the sampling points and weighted these buffer zones to the collected mosquito density. I used ArcGIS to create the buffer zones and converted it to ASCII to be used as background file. The background ascii file has densities ranges from 0-300 within the extent of my study area.

I understand that MaxEnt depends on presence records only and the background file should represent the pseudo-negative records. However, I noticed that the generated risk maps from MaxEnt using density weighted Background ascii file is totally different than when I use pseudo-absence background file. 

Is that mean that MaxEnt distinguish between different mosquito densities in the background?

Any thoughts why this happen?

Thanks 

Mohamed