Change in habitat over time for the rare, endemic Pediocactus paradinei

Abstract

Conservation management is critical to species with limited distributions, narrow habitat preferences, and slow growth rates. Pediocactus paradinei is one of many rare endemic cacti on the Colorado Plateau, southwestern US. While its basic habitat requirements are relatively well understood, less is known about how ongoing ecological changes, including those affecting the habitat of its likely pollinators, may influence its persistence. In 2022, we assessed current and historical plant and pollinator habitat conditions across the species' range by resampling ecological monitoring sites originally surveyed in 2005, as well as other sites. Our analyses focused on site characteristics relevant to the regional pollinator community, including ground cover composition, woody litter, and co‐flowering plant richness. Over the 17‐year period, there were significant declines in plant richness, particularly among forbs with flowering periods overlapping phenologically with P. paradinei, alongside shifts in ground cover that may affect native bees. To consider how habitat availability may change in the future, we developed weighted ensemble species distribution models, which identified isothermality, precipitation seasonality, and mean temperature of the coldest quarter as the strongest factors limiting the cactus's distribution. Projections across multiple climate scenarios suggest contraction and shift in climatically suitable habitat by mid‐century. If these changes manifest, it will be necessary for conservation management to incorporate pollinator habitat quality across the broader ecoregion. Our findings highlight the importance of incorporating both abiotic factors and biotic interactions into recovery planning for rare plants.