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Diffusion modeling reveals effects of multiple release sites and human activity on a recolonizing apex predator

Authors
  • Eisaguirre, Joseph M.1, 2
  • Williams, Perry J.1
  • Lu, Xinyi3
  • Kissling, Michelle L.2, 4
  • Beatty, William S.2, 5
  • Esslinger, George G.6
  • Womble, Jamie N.7, 8
  • Hooten, Mevin B.3, 9
  • 1 University of Nevada Reno, Reno, NV, USA , Reno (United States)
  • 2 United States Fish & Wildlife Service, Marine Mammals Management, Anchorage, AK, USA , Anchorage (United States)
  • 3 Colorado State University, Fort Collins, CO, USA , Fort Collins (United States)
  • 4 University of Montana, Missoula, MT, USA , Missoula (United States)
  • 5 Present address: U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, WI, USA , La Crosse (United States)
  • 6 U.S. Geological Survey, Alaska Science Center, Anchorage, AK, USA , Anchorage (United States)
  • 7 Southeast Alaska Inventory and Monitoring Network, National Park Service, Juneau, AK, USA , Juneau (United States)
  • 8 Glacier Bay Field Station, National Park Service, Juneau, AK, USA , Juneau (United States)
  • 9 Colorado Cooperative Fish and Wildlife Research Unit, U.S. Geological Survey, Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO, USA , Fort Collins (United States)
Type
Published Article
Journal
Movement Ecology
Publisher
BioMed Central
Publication Date
Jun 30, 2021
Volume
9
Issue
1
Identifiers
DOI: 10.1186/s40462-021-00270-w
Source
Springer Nature
Keywords
Disciplines
  • Research
License
Green

Abstract

BackgroundReintroducing predators is a promising conservation tool to help remedy human-caused ecosystem changes. However, the growth and spread of a reintroduced population is a spatiotemporal process that is driven by a suite of factors, such as habitat change, human activity, and prey availability. Sea otters (Enhydra lutris) are apex predators of nearshore marine ecosystems that had declined nearly to extinction across much of their range by the early 20th century. In Southeast Alaska, which is comprised of a diverse matrix of nearshore habitat and managed areas, reintroduction of 413 individuals in the late 1960s initiated the growth and spread of a population that now exceeds 25,000.MethodsPeriodic aerial surveys in the region provide a time series of spatially-explicit data to investigate factors influencing this successful and ongoing recovery. We integrated an ecological diffusion model that accounted for spatially-variable motility and density-dependent population growth, as well as multiple population epicenters, into a Bayesian hierarchical framework to help understand the factors influencing the success of this recovery.ResultsOur results indicated that sea otters exhibited higher residence time as well as greater equilibrium abundance in Glacier Bay, a protected area, and in areas where there is limited or no commercial fishing. Asymptotic spread rates suggested sea otters colonized Southeast Alaska at rates of 1–8 km/yr with lower rates occurring in areas correlated with higher residence time, which primarily included areas near shore and closed to commercial fishing. Further, we found that the intrinsic growth rate of sea otters may be higher than previous estimates suggested.ConclusionsThis study shows how predator recolonization can occur from multiple population epicenters. Additionally, our results suggest spatial heterogeneity in the physical environment as well as human activity and management can influence recolonization processes, both in terms of movement (or motility) and density dependence.

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