Abstract: Understanding the temporal dynamics shaping environmental response is key to clarifying a species' conservation status. Habitat suitability modeling (HSM) is an established approach to studying these issues; however, technical complexities often limit its application beyond the academic community. To improve our understanding of the environmental factors affecting the range, population health, and overall ecology of Cassin's Sparrow (Peucaea cassinii), we combined data from NASA's Modern-Era Reanalysis for Research and Applications, Version 2 (MERRA-2) with field observations spanning the past 40 years to perform an exploratory, longitudinal analysis of the species' evolving environmental niche. MERRA-2 combines past observations with numerical models to generate a consistent time series of hundreds of physical drivers of the Earth's observed climate as it has evolved over the past half century. Our primary goal was to examine historical patterns of change in habitat suitability for Cassin's Sparrow and the environmental drivers influencing those changes. In doing so, we also addressed some of the technology challenges that have impeded this type of work. This has resulted in the MMX Toolkit, a prototype workflow and semi-automated technology suite that greatly simplifies our approach and can potentially broaden its cross-sector application to a wide range of species conservation efforts.
We obtained Cassin's Sparrow occurrence records for the years spanning 1980-2019 from the Global Biodiversity Information Facility (GBIF). We employed time-specific HSM in our analysis, aligning MERRA-2 predictors with observations within five-year intervals across the 40-year period of the study. We used NASA's MERRA/Max system to do automatic variable screening within each of the temporally-aligned, five-year intervals (https://doi.org/10.1371/journal.pone.0257502). With these inputs, we used MaxEnt to construct HSM time series. Theil-Sen trend analysis was performed on both the HSM time series and the most contributory environmental variables across the series. We also computed species-specific biotic velocity maps and variable-specific climate velocity maps. The resulting data products provide a novel perspective on potential refugia for Cassin's Sparrow, reveal patterns of habitat suitability change that help explain uncertainties surrounding the species' conservation status, and provide insights into the low-level environmental factors that may be driving distributional changes in the species. The MMX Toolkit's collection of R, bash, and Python scripts automated much of the work, making an otherwise difficult study possible. Positive responses from federal and state conservation agencies and private sector collaborators suggest that the MMX Toolkit could facilitate the transfer of this particular aspect of ecological science to a wider community.
