Fig. 4.

Eye parameter of the investigated species. The eye parameter P _eye (rad.µm) was calculated from the ommatidia number and mean facet diameter. It represents a measure for facet size in relation to its diffraction limit. A value of 0.3 is the minimum at which the ommatidium operates above its diffraction limit (assuming λ = 550 nm; Land 1997). Higher values indicate facet diameters that are larger than necessary to avoid diffraction artifacts and hint at a morphological adaptation to increase light sensitivity in very small bees