Corresponding author: Jorge Soberón ( jsoberon@ku.edu ) Academic editor: Linton Winder
© 2018 Jorge Soberón, A. Townsend Peterson, Luis OsorioOlvera.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Soberón J, Peterson TA, OsorioOlvera L (2018) A comment on “Species are not most abundant in the centre of their geographic range or climatic niche”. Rethinking Ecology 3: 1318. https://doi.org/10.3897/rethinkingecology.3.24827

A study published recently argued against a relationship between population density and position in geographic and environmental spaces. We found a number of methodological problems underlying the analysis. We discuss the main issues and conclude that these problems hinder a robust conclusion about the original question.
population density, niche centrality, niche distances
The question of whether population density is related to position in geographic (
1) The largest dataset analyzed by
2)
Geographic and environmental spaces for Dipodomysmerriami. Top: extent of occurrence polygon for the distribution of D.merriami in the United States (gold, centroid shown by black and white circle), representing the range area analyzed by
A similar problem exists in environmental space. We downloaded the 2dimensional principal components (PC) used by
3)
GBIF points for Dipodomysmerriami in environmental space, showing differences between methods for delimiting niches and calculating nichecentroid distances. The black circle is the centroid of the convex hull (grayshaded polygon), showing the strong effect of one outlier point. The white circle is the centroid of a 95% minimum volume ellipsoid that is able to ignore the outlier. Circles are Euclidean distances of radii 1 and 2, for the convex hull centroid; the dashed ellipsoids are the equivalent distances (Mahalanobis distances) taking into account the covariance shown by the points in gold (see text). Note the striking differences between the two methodologies in both shape of the niche estimated and the distances that result. In particular, note that the centroid estimated via convex hulls falls at the periphery of the cloud of points for the species’ occurrence.
4) The data provided in the Supplementary Materials of
In this communication, we identify a series of methodological problems underlying the results of
JS and TP discussed and conceived the paper. JS wrote the first version and TP rewrote the second version. LO reviewed the code in
Authors  Contribution  ACI 

JS  0.4  1.333 
TP  0.3  0.857 
LO  0.3  0.857 