Species coexistence by wide constant size spacing

We consider the distribution of fruit pigeons of the genera Ptilinopus and Ducula on the island of New Guinea. Of the 21 species, between six and eight coexist inside humid lowland forests. We conducted or analyzed 31 surveys at 16 different sites, resurveying some sites in different years. The species coexisting at any single site in a single year are a highly nonrandom selection of the species to which that site is geographically accessible. Their sizes are both much more widely spread and more uniformly spaced than in random sets of species drawn from the locally available species pool. We also present a detailed case study of a highly mobile species that has been recorded on every ornithologically explored island in the West Papuan island group west of New Guinea. That species’ rareness on just three well-surveyed islands within the group cannot be due to an inability to reach them. Instead, its local status decreases from abundant resident to rare vagrant in parallel with increasing weight proximity of the other resident species.