title: Ecological correlates and conservation implications of overestimating species geographic ranges.
abstract: Species range maps based on extents of occurrence (EOO maps) have become the basis for many analyses in broad-scale ecology and conservation. Nevertheless, EOO maps are usually highly interpolated and overestimate small-scale occurrence, which may bias research outcomes. We evaluated geographical range overestimation and its potential ecological causes for 1158 bird species by quantifying EOO map occurrence across 4040 well-studied survey locations in Australia, North America, and southern Africa at the scale of 80-742 km2. Most species occurred in only 40-70% of the range indicated by their EOO maps. The observed proportional range overestimation affected the range-size frequency distribution, indicating that species are more range-restricted than suggested by EOO maps. The EOO maps most strongly overestimated the distribution of narrow-ranging species and ecological specialists with narrow diet and habitat breadth. These relationships support basic ecological predictions about the relationship between niche breadth and the fine-scale occurrence of species. Consequently, at-risk species were subject to particularly high proportional range overestimation, on average 62% compared with 37% of nonthreatened species. These trends affect broad-scale ecological analyses and species conservation assessments, which will benefit from a careful consideration of potential biases introduced by range overestimation.
authors.affiliation: Division of Biological Sciences, University of California San Diego, 9500 Gilman Drive MC 0116, La Jolla, CA 92093-0116, USA. wjetz@ucsd.edu
authors.forename: Walter
authors.initials: W
authors.lastname: Jetz
authors.forename: Cagan H
authors.initials: CH
authors.lastname: Sekercioglu
authors.forename: James E M
authors.initials: JE
authors.lastname: Watson
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D003247:Conservation of Natural Resources / Q000379:methods*; D003710:Demography; D017753:Ecosystem