[R-sig-Geo] Density of population

[alice schaffhauser]

Hi everybody,
I have a data base (baseat_part.txt) on a plant species with records attached to the centers of grid cells.
Because I don't have softwares as arcgis, I'd like to learn spatial analyses with R.
I have wgs84 coordinates and 3 status for the species population (casual=50 plants; unknown=500; established=1500).I just tried to see data with a simple plot (scriptat_part.R) but I must represent the density of population. I found kde2d but I don't know if kernel suits and what it means. 
The grid resolution can vary (not in this partial base but in others; '1' means 3km and '2' means 6 km so I must assign them to the first ones).
I just heard about krigeage and nearest neighbors but I don't know how to use them to calculate the number of plants by grid cell.
The objective is to have 'net cbf' format because I will transfer the distribution map to emission map (with estimated quantities of pollen production).
Thanks a lot for your help.
Alice
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Alice SCHAFFHAUSER 
Post-doctoral fellow 
ATOPICA project
Plant and fire ecology (FIRE PARADOX) 
Paleoecology of peatlands and pedogeomorphology 
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aliceschaffhauser at yahoo.fr 
alice.schaffhauser at lsce.ipsl.fr 
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Work address:  
LSCE-CEA Orme des Merisiers,  
91191 Gif-sur-Yvette cedex 
France 
Tel : 33 (0)1 69 08 77 23 
Fax : 33 (0)1 69 08 77 16
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