Tracking spatial regimes as an early warning for a species of conservation concern.

In this era of global environmental change and rapid regime shifts, managing for core areas that species require to survive and persist is a grand challenge for conservation. Because wildlife monitoring data are often limited or local in scale, the emerging ability to map and track spatial regimes (i.e., the spatial manifestation of state transitions) using advances in geospatial vegetation data has the potential to provide earlier warnings of habitat loss because many species of conservation concern strongly avoid spatial regime boundaries. Using 23 years of Greater Prairie-Chicken (Tympanuchus cupido; GPC) lek location data in a remnant grassland ecosystem, we demonstrate how mapping changes in the boundaries between grassland and woodland spatial regimes provides a spatially-explicit early warning signal for habitat loss for an iconic and vulnerable grassland-obligate known to be highly sensitive to woody encroachment. We tested whether a newly proposed metric for the quantification of spatial regimes captured well-known responses of GPC to woody expansion into grasslands. Resource selection functions showed that the grass:woody spatial regime boundary strength explained 80% of relative lek occurrence probability, and GPC strongly avoided grass:woody spatial regime boundaries at broad scales. Both findings are consistent with well-known expectations derived from GPC ecology. These results provide strong evidence for vegetation-derived delineations of spatial regimes to serve as generalized signals of early warning for state transitions that have major consequences to biodiversity conservation. Mapping spatial regime boundaries over time provided interpretable early warnings of habitat loss: woody plant regimes displaced grassland regimes starting from the edges of the study area and constricting inward. The relative probability of lek occurrence constricted correspondingly in space. Similarly, the temporal trajectory of spatial regime boundary strength increased over time, moving closer to the observed limit of GPC lek site usage relative to grass:woody boundary strength. These novel spatial metrics allow managers to rapidly screen for early warnings of spatial regime shifts and adapt management practices to defend and grow habitat cores at broad scales.