Can occupancy-abundance models be used to monitor wolf abundance?

PLoS One. 2014 Jul 23;9(7):e102982. doi: 10.1371/journal.pone.0102982. eCollection 2014.

Abstract

Estimating the abundance of wild carnivores is of foremost importance for conservation and management. However, given their elusive habits, direct observations of these animals are difficult to obtain, so abundance is more commonly estimated from sign surveys or radio-marked individuals. These methods can be costly and difficult, particularly in large areas with heavy forest cover. As an alternative, recent research has suggested that wolf abundance can be estimated from occupancy-abundance curves derived from "virtual" surveys of simulated wolf track networks. Although potentially more cost-effective, the utility of this approach hinges on its robustness to violations of its assumptions. We assessed the sensitivity of the occupancy-abundance approach to four assumptions: variation in wolf movement rates, changes in pack cohesion, presence of lone wolves, and size of survey units. Our simulations showed that occupancy rates and wolf pack abundances were biased high if track surveys were conducted when wolves made long compared to short movements, wolf packs were moving as multiple hunting units as opposed to a cohesive pack, and lone wolves were moving throughout the surveyed landscape. We also found that larger survey units (400 and 576 km2) were more robust to changes in these factors than smaller survey units (36 and 144 km2). However, occupancy rates derived from large survey units rapidly reached an asymptote at 100% occupancy, suggesting that these large units are inappropriate for areas with moderate to high wolf densities (>15 wolves/1,000 km2). Virtually-derived occupancy-abundance relationships can be a useful method for monitoring wolves and other elusive wildlife if applied within certain constraints, in particular biological knowledge of the surveyed species needs to be incorporated into the design of the occupancy surveys. Further, we suggest that the applicability of this method could be extended by directly incorporating some of its assumptions into the modelling framework.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alberta
  • Animals
  • Conservation of Natural Resources
  • Ecosystem*
  • Models, Theoretical*
  • Population Dynamics
  • Wolves*

Grants and funding

Funding was provided by the Alberta Caribou Committee, Alberta Conservation Association, Alberta Cooperative Conservation Research Unit, Alberta Pacific Forest Industries, Alberta Sport, Recreation, Parks and Wildlife Foundation, Alberta Sustainable Resource Development, Canadian Association of Petroleum Producers, Canadian Circumpolar Inst., Conoco Phillips, Forest Resource Improvement Association of Alberta, NSERC Integrated Landscape Management Chair, Petroleum Technology Alliance Canada, and the Univ. of Alberta. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.