Complex sentence: In New Guinea, they are likely to have evolved for some time in the absence of microbats, which has resulted in some smaller megabats of the genus "Nyctimene" becoming (partly) insectivorous to fill the vacant microbat ecological niche.
Split into simpler sentences: In New Guinea, they are likely to have evolved for some time in the absence of microbats. This has resulted in some smaller megabats of the genus "Nyctimene" becoming (partly) insectivorous to fill the vacant microbat ecological niche.