Distribution, habitat associations, and conservation status updates for the pilose crayfish Pacifastacus gambelii and Snake River pilose crayfish Pacifastacus connectens of the western United States
- Published
- Accepted
- Subject Areas
- Ecology, Freshwater Biology
- Keywords
- ecological niche model, Faxonius virilis, signal crayfish, boosted regression trees, virile crayfish, species distribution modeling, invasive species, exotic species, Pacifastacus leniusculus
- Copyright
- © 2018 Egly et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2018. Distribution, habitat associations, and conservation status updates for the pilose crayfish Pacifastacus gambelii and Snake River pilose crayfish Pacifastacus connectens of the western United States. PeerJ Preprints 6:e27001v1 https://doi.org/10.7287/peerj.preprints.27001v1
Abstract
Our study evaluates the distribution, habitat associations, and current conservation status of the pilose crayfishes Pacifastacus connectens and Pacifastacus gambelii, two little-studied and data-deficient species endemic to the western United States. We first developed a species distribution model (SDM) for the pilose crayfishes based on their historical occurrence records using boosted regression trees and freshwater GIS data layers. We then sampled 163 sites in the summers of 2016 and 2017 within the distribution of these crayfishes, including 50 where these species were observed historically. We next compared our field results to modeled predictions of suitable habitat from the SDM. Our SDM predicted 73 sites (45%) we sampled as suitable for the pilose crayfishes, with a moderate AUC value of 0.824. The pilose crayfishes were generally predicted to occur in larger streams and rivers with less extreme upstream temperature and precipitation seasonality. We found the pilose crayfishes at only 20 (12%) of the 163 total sites we sampled, 14 (20%) of the 73 sites predicted as suitable for them by our SDM, and 12 (24%) of 50 historical sites that we sampled. We found the invasive virile crayfish Faxonius virilis at 22 sites total and 12 (24%) historical sites for the pilose crayfishes, and the “native invader” signal crayfish Pacifastacus leniusculus at 29 sites total and 6 (12%) historical locations. We subsequently used a single classification tree to identify factors associated with our high rate of false positives for contemporary pilose crayfish distributions relative to our SDM. This classification tree identified the presence of invasive crayfishes, impairment of the benthic community, and sampling method as some of the factors differentiating false positives relative to true positives for the pilose crayfishes. Our study identified the historical distribution and habitat associations for P. connectens and P. gambelii using an SDM and contrasted this prediction to results of contemporary field sampling. We found that the pilose crayfishes have seemingly experienced substantial range declines, attributable to apparent displacement by invasive crayfishes and impairment or change to stream communities and habitat. We recommend increased conservation and management attention to P. connectens and P. gambelii in response to these findings.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Other species distribution models
Suitable crayfish habitat in the western United States predicted for combinations of background points (50, 300, and 1000) and pilose crayfish occurrence records (P. connectens individually, P. gambelii individually, and both pilose crayfish species combined). These predictions were developed from boosted regression tree models using historical crayfish occurrence records and the EarthEnv habitat layers (Domisch et al., 2015). Our chosen model for main text analyses (1000 background points, both pilose crayfish species combined) is outlined in bold.
Historical occurrences table
Table of historical Pacifastacus connectens and Pacifastacus gambelii occurrence records (N=63) from various sources. Site number corresponds to our sampling sites in APPENDIX G; those without site numbers were not sampled. Year collected is given when known. Additional information regarding source is given in footnotes.
Classification histograms
Histograms showing number of true positives, true negatives, false positives, and false negatives for models with varying number of background points included (50, 300, and 1000) and pilose crayfish species included (Pacifastacus connectens, Pacifastacus gambelii, and pilose crayfish species combined). We chose to combine the individual models for P. connectens and P. gambelii here to simplify or standardize comparison to the single model of both pilose crayfishes together; if either individual P. connectens or P. gambelii predicted a location as suitable for one crayfish we accepted it as suitable for either, with absences locations where neither model predicted habitat as suitable for these crayfishes.
Sampling method histograms
Frequency (number of sites) of crayfish catch-per-unit efforts (CPUE) for both timed searching and baited trapping across crayfish species sampled in this study.
Field sampling results table
Table of field sampling results in the western U.S. in the summers of 2016 and 2017, in order of date sampled. We provide latitudes and longitudes in North American Datum 1983 (NAD 83), whether the site was sampled using baited trapping or timed search, whether the site was lentic or lotic, crayfish species detected, and whether the site had a historical species record. Crayfish species detected include Pacifastacus connectens (N=10), Pacifastacus gambelii (N=10), Faxonius virilis (N=22), and Pacifastacus leniusculus (N=29).