title: Detecting the influence of rare stressors on rare species in Yosemite National Park using a novel stratified permutation test.
abstract: Statistical models often use observational data to predict phenomena; however, interpreting model terms to understand their influence can be problematic. This issue poses a challenge in species conservation where setting priorities requires estimating influences of potential stressors using observational data. We present a novel approach for inferring influence of a rare stressor on a rare species by blending predictive models with nonparametric permutation tests. We illustrate the approach with two case studies involving rare amphibians in Yosemite National Park, USA. The endangered frog, Rana sierrae, is known to be negatively impacted by non-native fish, while the threatened toad, Anaxyrus canorus, is potentially affected by packstock. Both stressors and amphibians are rare, occurring in ~10% of potential habitat patches. We first predict amphibian occupancy with a statistical model that includes all predictors but the stressor to stratify potential habitat by predicted suitability. A stratified permutation test then evaluates the association between stressor and amphibian, all else equal. Our approach confirms the known negative relationship between fish and R. sierrae, but finds no evidence of a negative relationship between current packstock use and A. canorus breeding. Our statistical approach has potential broad application for deriving understanding (not just prediction) from observational data.
authors.affiliation: United States Geological Survey, Yosemite Field Station, 40298 Junction Drive, Suite A, Oakhurst, California 93644, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Matchett
authors.affiliation: University of California, Berkeley, Department of Statistics, Berkeley, California 94720-3860, USA.
authors.forename: Philip B
authors.initials: PB
authors.lastname: Stark
authors.affiliation: United States Forest Service, Sierra National Forest, 1600 Tollhouse Road, Clovis, California 93611, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Ostoja
authors.affiliation: University of California, Sierra Nevada Aquatic Research Laboratory, 1016 Mount Morrison Road, Mammoth Lakes, California 93546, USA.
authors.forename: Roland A
authors.initials: RA
authors.lastname: Knapp
authors.affiliation: National Park Service, PO Box 9, Denali National Park 99755, USA.
authors.forename: Heather C
authors.initials: HC
authors.lastname: McKenny
authors.affiliation: United States Geological Survey, Yosemite Field Station, 40298 Junction Drive, Suite A, Oakhurst, California 93644, USA.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Brooks
authors.affiliation: RMIT University, School of Mathematical and Geospatial Sciences, GPO Box 2476, Melbourne, VIC 3000, Australia.
authors.forename: William T
authors.initials: WT
authors.lastname: Langford
authors.affiliation: Microsoft Research, Computational Science Laboratory, 21 Station Road, Cambridge, UK CB1 2FB.
authors.forename: Lucas N
authors.initials: LN
authors.lastname: Joppa
authors.affiliation: Vibrant Data, Inc., 943 Clay St, San Francisco, California, 94108, USA.
authors.forename: Eric L
authors.initials: EL
authors.lastname: Berlow
mesh_terms: D000818:Animals; D044822:Biodiversity; D002140:California; D017753:Ecosystem; D005843:Geography; D000068316:Parks, Recreational