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.

KEYWORDS:

• Disjunction
• species distributions
• species ranges
• biogeography
• macroecology

Acknowledgments

We are grateful to BirdLife International for Bird Distribution data, the ICUN Red List for amphibian and reptile data, and to NatureServe in collaboration with Bruce Patterson, Wes Sechrest, Marcelo Tognelli, Gerardo Ceballos, The Nature Conservancy—Migratory Bird Program, Conservation International—CABS, World Wildlife Fund—U.S., and Environment Canada—WILDSPACE for the mammal data. We are also grateful to James Russell for assistance with preliminary analysis of mammal data and to Berry College for providing financial support to M. Owen during this project. We thank two anonymous reviewers for helpful comments that greatly improved this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

Information for species identified as disjunct is available in the supplementary material (Appendix S1). Data for mammal disjunctions are available in Taylor (2017). The GIS data that made our analysis possible are available from BirdLife International (birds), the ICUN Red List (amphibians and crocodilians), and NatureServe (mammals).http://datazone.birdlife.org/species/requestdis ICUN Red List https://www.iucnredlist.org/resources/spatial-data-download Mammals https://www.natureserve.org/products/digital-distribution-maps-mammals-western-hemisphere