The strength of top-down forces in terrestrial food webs is highly debated as there are few examples illustrating the role of largemammalian carnivores in structuring biotic and abiotic systems. Based on the results of this studywe hypothesize that an increase in human visitation within Zion Canyon of Zion National Park ultimately resulted in a catastrophic regime shift through pathways involving trophic cascades and abiotic environmental changes. Increases in human visitors in Zion Canyon apparently reduced cougar (Puma concolor) densities, which subsequently led to higher mule deer (Odocoileus hemionus) densities, higher browsing intensities and reduced recruitment of riparian cottonwood trees (Populus fremontii), increased bank [...]
