I beg all of you your excuses, because the stupid question. I am exploring niche conservatism in five species of Ericaceae. I created two backgrounds sets in order to explore niche similarity (using R package ecospat). In the first set, backgrounds were defined by the predicted (thresholded) distribution of each species, while in the second set backgrounds were defined through minimum convex polygons 50 Km radius from each occurence point. The fact is that I've got similar similarity (p) values using both backgrounds, except for two species (C and D in the following table), for which I got higher similarity values when using the smaller background (values in bold) and smaller values when using the widest background (values in italics below the values in bold).
Can anybody be so kind as explain in an idiot-proof style what is going on here? Your answer(s) will be very appreciated,