Spatial patterns of reproduction suggest marginal habitat limits continued range expansion of black bears at a forest-desert ecotone

Sean M. Sultaire, Robert A. Montgomery, Patrick J. Jackson, Joshua J. Millspaugh

Research output: Contribution to journalArticlepeer-review


Investigating spatial patterns of animal occupancy and reproduction in peripheral populations can provide insight into factors that form species range boundaries. Following historical extirpation, American black bears (Ursus americanus) recolonized the western Great Basin in Nevada from the Sierra Nevada during the late 1900s. This range expansion, however, has not continued further into the Great Basin despite the presence of additional habitat. We aimed to quantify whether reduced reproduction toward the range edge contributes to this range boundary. We analyzed black bear detections from 100 camera traps deployed across black bear distribution in western Nevada using a multistate occupancy model that quantified the probability of occupancy and reproduction (i.e., female bears with cubs occupancy) in relation to changes in habitat type and habitat amount toward the range boundary. We detected a strong effect of habitat amount and habitat type on the probability of black bear occupancy and reproduction. At similar levels of landscape-scale habitat amount (e.g., 50%), estimated probability of occupancy for adult bears in piñon-juniper woodlands near the range boundary was 0.39, compared to ~1.0 in Sierra Nevada mixed-conifer forest (i.e., core habitat). Furthermore, estimated probability of cub occupancy, conditional on adult bear occupancy, in landscapes with 50% habitat was 0.32 in Great Basin piñon-juniper woodlands, compared to 0.92 in Sierra Nevada mixed-conifer forest. Black bear range in the western Great Basin conforms to the center–periphery hypothesis, with piñon-juniper woodland at the range edge supporting ecologically marginal habitat for the species compared to habitat in the Sierra Nevada. Further geographic expansion of black bears in the Great Basin may be limited by lower occupancy of reproducing females in piñon-juniper woodland. Center–periphery range dynamics may be common in large carnivore species, as their dispersal ability allows them to colonize low-quality habitat near range edges.

Original languageEnglish
Article numbere10658
Pages (from-to)e10658
JournalEcology and Evolution
Issue number11
StatePublished - Nov 2023


This publication was supported by the Nevada Department of Wildlife and the United States Fish and Wildlife Service with Wildlife Restoration funds and is solely the responsibility of the authors and does not necessarily represent the official views of the Nevada Department of Wildlife or the United States Fish and Wildlife Service. We thank the Nevada Department of Wildlife and the $3 Predator Fee Program for funding this research. We also thank field technicians W. Ortiz, D. Heit, J. Eaton, S. Miller, L. Margadant, N. Everett, and C. Blommel for their work maintaining the camera‐trap grid over the 3 years of this study and classifying camera‐trap photos.

FundersFunder number
Nevada Department of Wildlife


    • Great Basin
    • Ursus americanus
    • black bear reproduction
    • center–periphery hypothesis
    • multistate occupancy model
    • piñon-juniper woodland
    • range boundary


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