Learning from the past to restore trophic complexity with carnivorous mammals in the Anthropocene

The structure of the world’s mammal communities had remained remarkably consistent for millions of years before modern humans (Homo sapiens) encountered them. However, following their global dispersal during the Late Pleistocene (~130,000 − 11,700 years ago), humans began modifying the structure of mammal communities by driving global and local extinctions. Human-induced extinctions were biased towards the largest mammals, which reduced ecosystem trophic complexity by removing top-down interactions that influence ecological dynamics. By acknowledging these past impacts, conservationists now recognise the potential benefits to reversing them through restoring species that are missing from ecosystems. In this thesis, I investigated the extent of modification to terrestrial carnivorous mammal communities as well as the existing opportunities to restore trophic complexity through (i) recolonisations, (ii) reintroductions, and (iii) former introductions. I show that defaunation disproportionately affected once widespread and diverse large-bodied hypercarnivorous mammals, with those remaining being smaller-bodied and less carnivorous. Yet, if extant hypercarnivores recolonised their past geographic ranges, I found that structural modifications to hypercarnivore assemblages could largely be reversed across Africa, much of Eurasia and, to an extent, North America. As a complement to recolonisations, I show that geographically widespread opportunities for evidence-based reintroductions exist, but future research of species interactions should prioritise unstudied environmental contexts Page | v to increase opportunities further. Finally, for mainland Australia, the continent most affected by past human-induced extinctions, I found that formerly introduced carnivorous mammals could act as counter-currents to past defaunation, particularly in contexts without the widespread persecution of an apex predator. Overall, the findings in this thesis reveal diverse opportunities to restore ecosystem trophic complexity with carnivorous mammals across the world to reverse past, and ongoing, human impacts in the Anthropocene.