Abstract
Aim Museum and herbarium specimen records are frequently used to assess species’ conservation status and responses to climate change. Typically, occurrences with imprecise geolocality information are discarded because they cannot be matched confidently to environmental conditions, and are thus expected to increase uncertainty in downstream analyses. However, using only precisely georeferenced records risks undersampling of species’ environmental and geographic distributions. We present two related methods to allow the use of imprecisely georeferenced occurrences in biogeographic analysis.
Innovation Our two procedures assign imprecise records to the 1) locations or 2) climates that are closest to the geographic or environmental centroid of the precise records of a species. For virtual species, including imprecise records alongside precise records improved the accuracy of ecological niche models projected to the present and the future, especially for species with ~20 or fewer precise occurrences. Using only precise records underestimates loss in suitable habitat and overestimates the amount of suitable habitat in both the present and future. Including imprecise records also improves estimates of niche breadth and extent of occurrence. An analysis of 44 species of North American Asclepias (Apocynaceae) yielded similar results.
Main conclusions Existing studies examining the effects of spatial imprecision compare outcomes based on precise records to the same records with spatial error added to them. However, in real-world cases, analysts possess a mix of precise and imprecise records and must decide whether to retain or discard the latter. Discarding imprecise records can undersample species’ geographic and environmental distributions and lead to mis-estimation of responses to past and future climate change. Our method, for which we provide a software implementation in the enmSdmX package for R, is simple to employ and can help leverage the large number of specimen records that are typically deemed “unusable” because of spatial imprecision in their geolocation.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
adam.smith{at}mobot.org, stephenjosephmurphy{at}gmail.com, hdavid{at}wustl.edu, kerickson{at}mobot.org
Major changes include: We have rewritten the entirety of the Methods section. Specifically, we rewrote the description of our procedures for using imprecise records and reworked Figure 2 to illustrate how the procedures are applied. We have also moved the detailed description of methods describing the virtual species analysis entirety out of an appendix and put it into the main text. Please note that Figure 3 also provides a graphical summary of these procedures. We have paid particular attention to details that were overlooked or missing in the original text (e.g., spatial resolution, MaxEnt tuning parameters, use of PCA, etc.). We have added a section in the Discussion about the applicability of our methods to other contexts (LL 336-361). We think this new section makes the manuscript even stronger because it helps readers consider how the proposed method would work in their particular situations. Given this, the methods are fairly universal and should be able to be implemented reliably in nearly every situation. Geometrically, the methods nearly always yield the most conservative estimates of niche breadth and geographic extent of a species, regardless of the size of the area of likely collection of "imprecise" records (i.e., countries, provinces, atlas cells, etc.). So we do not contemplate difficulties in applying the method elsewhere. In the few cases we do, we highlight them (LL 349-361).
