 The OFD is also known as the species-range size distribution in literature.A typical form of OFD is a bimodal distribution, indicating the species in a community is either rare or common, known as Raunkiaer's law of distribution of frequencies.That is, with each species assigned to one of five 20%-wide occupancy classes, Raunkiaer's law predicts bimodal distributions within homogenous plant formations with modes in the first (0-20%) and last (81-100%) classes.