Linking a cougar decline, trophic cascade, and regeneration in Zion

This study compared a canyon in Zion National Park, where heavy human visitation had driven cougars away, with a less-visited canyon where cougars remained. Where cougars were scarce, mule deer were far more abundant, browsing suppressed young cottonwoods, and streambanks eroded with reduced plant cover, while the cougar-occupied canyon retained tree regeneration, stable banks, and greater abundance of wildflowers, amphibians, butterflies, and lizards. The authors argued that the loss of a top predator triggered a trophic cascade that degraded the riparian ecosystem through unchecked deer browsing. The work became an influential example of how big cats can shape whole ecosystems and how their removal reverberates down to plants, rivers, and biodiversity. It strengthened the case that predators like cougars perform keystone ecological functions worth conserving.