Invasive Species

Invasive Species

Invasive species are one of the leading causes of species extinction globally.  The barred owl, a species native to eastern North America, expanded its range owing to climate and land use change in the Great Plains. They have become established and achieved high densities in many western forests, and now threaten spotted owls with extinction and potentially threaten many other native species. Our group works closely with wildlife management agencies to understand the effects of invasive barred owls on native species and ecosystems, and to assess management options. 


Modeling Barred Owl Dispersal

Genomics Approach:

Successful invasions occur in a series of stages where initial arrival is followed by establishment, spread, and ultimately saturation. Populations at the leading edge of the invasion may not exhibit intrinsic population growth due to small population size driven by processes such as limited mate options at low densities. Therefore, invasion front populations can act as a sink population that is supported by the dispersal of individuals from already established, high-density, populations. We are characterizing the dispersal dynamics and range expansion of Barred Owls into the Sierra Nevada region of California using genetic kinship methods. We combine whole genome sequencing with reduced representation sequencing (ddRAD) to obtain thousands of single nucleotide polymorphisms to build wild pedigrees and determine close kinship dyads within the Sierra Nevada and between the Sierra Nevada and already established population in Coastal and Northern California.

Satellite-tag Approach:

To better understand the invasion process, our research group satellite-tagged juvenile barred owls in coastal California. Tagged owls dispersed soon after fledgling and often traveled long distances (up to several hundred km) before establishing breeding territories. Importantly, larger unforested landscapes acted as strong filters and even barriers to dispersal suggesting that some areas are naturally protected from the spread of barred owls.

Figure: In the top landscape-scale resource selection function logistic regression model, relative probability of use by juvenile Barred Owls increased with (A) proportion forest and (B) proportion shrub/scrub, and decreased with (C) proportion grassland, (D) proportion burned area 2011–2020, and (E) elevation. Average values of non-focal covariates were used in plotting marginal effects. Lighter polygons show 95% confidence intervals. (Watson et al. 2023a)

Barred Owl Management

Our work demonstrates conclusively that early management intervention can effectively curb barred owl numbers and lead to rapid recolonization of territories by spotted owls. While barred owl management is challenging for a variety of reasons, preventing the extinction of spotted owls is feasible.

Figure: Acoustic detections of barred owls and barred owl × spotted owl hybrids in 2018 and 2020 (a) in the northern Sierra Nevada and southern Cascade Mountains, California. (b) Estimates of barred owl site occupancy for the pre-removal season (April to August, 2018) and post-removal season (April to August, 2020). (c) Site colonization and extinction estimates between the primary sampling periods (from 2018 to 2020), with all estimates derived from passive acoustic monitoring. The 85% confidence intervals are symbolized by the vertical bars in both (b) and (c). (Hofstadter et al. 2022)

The Invasion Pathway of Barred Owls into the Pacific Northwest

Expansion of invasive species into novel ranges poses a combination of ecological and evolutionary forces on invasive populations which impacts genetic diversity and can influence genetic drift. Using whole genome sequencing in combination with reduced representation sequencing (ddRAD) we are unravelling the ecological and evolutionary history of Barred Owls to investigate patterns of genetic diversity and signatures of selection throughout their native and non-native range, as well as identify population of origin for individuals at the leading edge of the invasion. The extensive non-invasive sampling for this project involves important collaborations with rehab facilities and wild-life sanctuaries throughout the Barred Owls native range and emphasizes the important role these places play in the conservation of species.

Relevant Publications

Hofstadter*, D. F., N.F. Kryshak*, C.M. Wood*, B.P. Dotters, K.N. Roberts, K.G. Kelly*, J.J. Keane, S.C. Sawyer, P.A. Shaklee, H.A. Kramer*, R.J. Gutiérrez*, and M.Z. Peery (2022). Arresting the spread of invasive species in continental systemsFrontiers in Ecology and the Environment doi: 10.1002/fee.2458

Watson*, W.A., D.F. Hofstadter*, G.M. Jones*, H.A. Kramer*, N.F. Kryshak*, C.J. Zulla*, S.A. Whitmore*, V. O’Rourke, J.J. Keane, R.J. Gutiérrez*, and M.Z. Peery (2023). Characterizing juvenile dispersal dynamics of invasive Barred Owls: Implications of managementOrnithological Applications duad061.

Watson*, W.A., C.M. Wood*, K.G. Kelly*, D.F. Hofstadter*, N.F. Kryshak*, C.J. Zulla*, S.A. Whitmore*, V. O’Rourke, J.J. Keane, R.J. Gutiérrez*, and M.Z. Peery (2023). Passive acoustic monitoring indicates Barred Owls are established in northern coastal California and management intervention is warrantedOrnithological Applications, 125(3).

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