Influences on Recruitment of Northern Mountain Caribou (Rangifer tarandus caribou)

  • Author / Creator
    Gonet, Jared MG
  • Northern mountain caribou (NMC) (Rangifer tarandus caribou) face a unique combination of demographic influences among woodland caribou in Canada. To build knowledge of how NMC may respond to these influences, the potential effects of road and fire disturbance, climate (pacific decadal oscillation (PDO)), and harvest of moose (Alces alces), wolf (Canis lupus), black bear (Ursus americanus), grizzly bear (Ursus arctos), and adult NMC on calf recruitment in thirteen NMC populations in the Yukon Territory were explored. Seasonal range maps (annual, winter, and summer) for each population were created using elevational distributions of NMC locations from radio-collared individuals. Elevational use varied by season and population, with some overlap between seasons. Seasonal disturbance values were then assigned for each population. Sensitivity to buffers on roads were tested (0m, 500m, 1000m, 1500m, 2000m, 3000m, 4000m) using boosted regression trees (BRTs). No distinction was found in reduction of model deviance among buffers, therefor 0m and 500m buffer ranges were used for further analysis. The highest road disturbance was found in the Carcross population, with 5.4% of its annual range affected by roads within a 500m buffer. The highest combined disturbance was recorded for the Tatchun population, with 43% of its annual range affected by non-overlapping roads and fire.
    Boosted regression trees were further used to parse variables of interest for inclusion in linear mixed models (LMMs). Natural disturbance on annual ranges, road disturbance on summer ranges, average yearly PDO, and moose, grizzly bear and caribou harvest density were all influential variables affecting annual caribou recruitment. Top LMMs did not include an effect of road and fire disturbance on recruitment, but did show moderate positive relationships
    of both average PDO and moose harvest with recruitment, with no effects from other harvest variables. Higher average PDO values correspond to milder winters and earlier springs, which could lead to higher overwinter calf survival and improved body condition of parturient females, more robust calves, and greater ease in spacing away from predators. Rates of moose harvest were also positively associated with disturbance levels (road access), thus effects on caribou recruitment may be confounded. The ability to address effects of anthropogenic disturbance was severely constrained by the lack of comprehensive mapping of related features throughout the study area. This is a critical need for further investigation of relationships. This study highlights the importance of considering interactive effects between species, and between climate and caribou, when managing NMC populations, and the opportunity for pro-active management of Yukon NMC ranges to avoid potential declines due to human disturbance, as documented for woodland caribou elsewhere.

  • Subjects / Keywords
  • Graduation date
    Spring 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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