Patterns of disjunction in western hemisphere birds, amphibians, crocodilians, and mammals

ABSTRACT To assess the patterns and severity of disjunction at multiple taxonomic levels for birds, amphibians, crocodilians, and mammals in the western hemisphere, we compiled over 10,100 species ranges and analyzed each range using ERSI ArcMap (10.8.1). After identifying species ranges that were disjunct by 500 km or more, we calculated the mean distance between the disjunct range polygon and primary polygon (d) and relative disjunct area (A) and analyzed disjunction by geographic area and latitude. Birds are the most commonly disjunct taxa (19.3%), followed by mammals (6.4%) and amphibians (2.8%). According to distance and relative area, birds are more severely disjunct than amphibians and mammals. Geographically, South America is home to the largest number of disjunctions across all taxa and latitudinal trends show that disjunction varies by latitude and, coincident with species richness, peaks in the southern tropics. Similarities in disjunction patterns, particularly between mammals and amphibians, suggest that geographic factors, along with dispersal ability, play a key role in creating disjunct distributions.