A comparison of hull methods for estimating species ranges and richness maps

Abstract

Background: The combined analysis of species ranges allows the detection of overall species richness patterns. As such, the reliability of richness maps is directly related to the accuracy of individual range estimates.

Aims: We compared how species ranges and richness patterns are influenced according to the use of different methods (convex hull and alpha hull) and evaluated if differences in range estimates are related to the Wallacean shortfall.

Methods: We used occurrence records of 386 species from the tribe Bignonieae (Bignoniaceae) to build richness maps by stacking species ranges, using the convex hull and alpha hull methods. We evaluated the behaviour of the richness estimates in relation to other variables (i.e., other richness measures, environmental and spatial variables). We correlated the differences in range estimates to proxies of Wallacean shortfall (i.e., species description date and variation of pseudo-ranges generated by jack-knife).

Results: Convex hull estimated larger ranges than alpha hull. The Wallacean shortfall affected range estimates equally regardless of the hull method used. Both hull methods generated similar richness maps. Richness estimates showed similar correlation patterns in relation to other variables regardless of the hull method used.

Conclusions: Despite the slight differences in range estimates, both hull methods can be used in equivalence to map species richness.

Keywords:

• alpha hull
• Bignonieae
• convex hull
• species richness patterns
• Wallacean shortfall

Acknowledgements

We thank the curators from various herbaria, especially G, K, MO, NY, P, US, RB, SP and SPF, for allowing us to examine their collections. We also thank Juan Pablo Narváez and Luiz Henrique Fonseca for assistance with geo-referencing and data-cleaning.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was partly supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) through a Ph.D. fellowship to the first author; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) through Grants [301799/2016-4 and 307781/2013-5]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for a collaborative FAPESP-Biota/NSF-Dimensions of Biodiversity Grant [2012/50260]. This work is developed in the context of National Institutes for Science and Technology (INCT) in Ecology, Evolution and Biodiversity Conservation, supported by CNPq [465610/2014-5] and Fundação de Amparo à Pesquisa do Estado de Goiás (FAPEG).

Notes on contributors

Leila Meyer

Leila Meyer is a Ph.D. student in ecology and evolution; her research interests focus on macroecology, biogeography and community ecology.

José A. F. Diniz-Filho

José A. F. Diniz-Filho is a Professor; he conducts research in ecology and evolutionary biology, with an emphasis on macroecology, geographical ecology, phylogenetic comparative methods and genetics.

Lúcia G. Lohmann

Lúcia G. Lohmann is a Professor; her primary research interest is to understand patterns of plant diversification and biogeography in the tropics. For that, she combines studies in classic taxonomy, phylogeny, ecology, evolutionary biology and conservation. Most of her research uses the plant family Bignoniaceae as a model.