The Consequences of Trophic Downgrading, and the Promise of Trophic Upgrading

<jats:title>Abstract</jats:title> <jats:p>The widespread decline of apex carnivore species has had profound consequences for ecosystems worldwide. ‘Trophic downgrading’, defined as the loss of the top consumers in a food web, can change the abundance and behaviour of other species like prey and meso-predators. Carnivore loss can therefore disrupt trophic cascades and set off chain reactions that alter fundamental ecological processes or drive ecosystems into alternative states. However, the prevalence and strength of these downstream effects of trophic downgrading varies widely across ecological contexts, and the ability of carnivore reintroduction to restore ecosystems remains the subject of debate. Here, we review the pathways through which carnivore loss can reshape biotic, abiotic, and socioecological processes, drawing on classic case studies of trophic downgrading. We discuss the ecological contexts in which such effects are most salient. Finally, we explore the potential of carnivore recovery to ‘upgrade’ ecosystems and reverse the effects of trophic downgrading. Given ongoing threats to many carnivore species and significant investment in carnivore restoration efforts, it is critical to understand the top-down ecological effects of these iconic animals and elucidate the context-dependent consequences of their removal and reintroduction.</jats:p>