Movement models and simulation reveal highway impacts and mitigation opportunities for a metapopulation-distributed species

Abstract

Context When human-made barriers impact wildlife by limiting habitat connectivity, simulation can reveal movements lost to fragmentation, strategies to restore corridor function, and potential benefits of corridor restoration. Objectives Guided by previous genetic research, we examined desert bighorn sheep movement near two highways that restrict gene flow and modelled their movement and habitat selection behavior. The ultimate goal was to simulate movement without highway barriers as a means to site crossing structures that mitigate fragmentation and to reveal their benefits for habitat reachability. Methods We fit integrated step selection functions (iSSFs) to GPS data from 9 bighorn populations near highways in California. After comparing iSSF simulations to validation data, we simulated 8200 bighorn-years of movement—200 year-long tracks each for 41 individuals—on a landscape with and without highways. We derived utilization distributions (UD) from simulations to identify probable high-use locations along the highways, compare these locations to previously predicted genetic corridors and roadkill events, and estimate changes in habitat reachability and elevation without these barriers. Results Simulation UDs correlated well with observed bighorn movements. Barrier-free simulations indicated preferred corridors across highway-blocked valleys, often at the same locations predicted by landscape genetics models (4 of 6 genetic-based corridors matched simulation-based corridors), and where bighorn roadkill events occurred (3 of 3 roadkill events occurred at simulation-predicted corridors). Relative to barrier-present simulations, barrier removal increased accessible habitat for 8 of 9 populations, with increases ranging from 7 to 138% per population. Barrier-free conditions allowed movement to higher elevations in two populations. Conclusion Animal movement simulation can effectively assess fragmentation impacts and reveal mitigation options when other data sources are scarce. Our simulations confirm previously predicted corridors, provide detailed locations for targeted mitigation, and suggest certain corridors pose greater habitat-related benefits.

Predicting fine-scale distributions and emergent spatiotemporal patterns from temporally dynamic step selection simulations

“…Other applications include running near-term trajectories that assess the likelihood of an area being used by an animal in the future, which may be useful to assess colonisation and invasion potential of introduced species (Lustig et al, 2017; Lustig et al, 2019; Patterson et al, 2024), or to plan upcoming management when the locations of animals are currently known. Trajectories from SSFs have already seen useful application for connectivity, and there is potential to identify movement corridors and understand metapopulation dynamics in fragmented environments (Hooker et al, 2021; Whittington et al, 2022; Aiello et al, 2023; Hofmann et al, 2023; Sells et al, 2023), particularly when combined with additional data such as genetics to assess historic connectivity (Lowe & Allendorf, 2010; Dussex et al, 2015).…”

“…Recently, SSFs have been gaining popularity for generating predictions, both for estimating utilisation distributions (UDs) of an individual (or set of individuals) in a given area (Signer et al, 2017; Potts, Börger, et al, 2022; Signer et al, 2023) and for predicting conservation-relevant measures such as connectivity and movement corridors (Osipova et al, 2019; Hooker et al, 2021; Whittington et al, 2022; Aiello et al, 2023; Hofmann et al, 2023; Sells et al, 2023). Using the estimated parameters of an SSF, several approaches have been developed to generate predictions, which include analytic and simulation-based approaches (Barnett & Moorcroft, 2008; Avgar et al, 2016; Signer et al, 2017; Potts & Schlägel, 2020; Potts, Börger, et al, 2022; Potts, Giunta, & Lewis, 2022).…”

“…There have been a number of recent studies generating stochastic trajectories for assessing conservation-relevant measures such as connectivity (Osipova et al, 2019; Hooker et al, 2021; Whittington et al, 2022; Aiello et al, 2023; Hofmann et al, 2023; Sells et al, 2023), although these simulations have not considered continuous temporal dynamics on both the movement and external selection processes. To contribute towards this emerging approach, we incorporate continuous temporal dynamics into the movement, external selection and memory processes of SSFs, for the specific goal of generating trajectories.…”

Simulating animal space use from fitted integrated Step‐Selection Functions (iSSF)

“…Simulations from iSSFs have been used to investigate emergent patterns of space use from fitted iSSFs (Potts & Schlägel, 2020; Signer et al., 2017), to model connectivity between different animal populations or habitat patches (Aiello et al., 2023; Hofmann et al., 2023; Whittington et al., 2022), and to evaluate and validate fitted models (Fieberg et al., 2023; Potts et al., 2022; Sells et al., 2023). Although analytical approximations of various estimation targets exist for some situations (Potts & Börger, 2023; Potts & Schlägel, 2020), simulations are more intuitive, flexible, and applicable to a wider range of problems.…”

“…Although analytical approximations of various estimation targets exist for some situations (Potts & Börger, 2023; Potts & Schlägel, 2020), simulations are more intuitive, flexible, and applicable to a wider range of problems. Despite the already widespread use and interest in simulations in movement ecology (Aiello et al., 2023; Whittington et al., 2022; Zurell et al., 2010), a general simulation routine is missing from available software, requiring analysts to write custom code. We address this gap by providing a user‐friendly tool that can be used to address the various use cases described above.…”