Why Bringing Back Apex Predators Is Harder Than Scientists Expected

We found that apex predator recovery programs around the world face significant challenges beyond the well-documented ecological hurdles. A new theoretical framework developed by conservation biologists reveals why full recovery of viable apex predator populations is currently the exception rather than the rule.

We wanted to understand what factors encourage versus impede progress in apex predator recovery. They examined existing research on recovery efforts across ecosystems, from gray wolves in Yellowstone to harbor seals in the Northeast Pacific to cheetahs in Tanzania, analyzing both successes and failures to identify patterns.

Our analysis of existing literature revealed that many apex predator recovery efforts have not yet met their potential or have encountered unanticipated problems along the way. Existing research shows sobering statistics: a review of 198 reintroduction studies found that herbivore reintroductions exhibited 29% higher success compared to carnivore reintroductions. Higher-trophic level species consistently exhibited the slowest recovery rates. There are cases where a focal predator recovered successfully in one location - like sea otters in central California - but not in another, such as sea otters in western Alaska.

What the framework reveals are three underappreciated factors that complicate predator recoveries beyond the well-known problems of slow life histories and continued exploitation. First, identifying the suite of trophic interactions that will influence recovery can be extremely difficult. Second, the timing of recovery efforts in dynamic ecosystems determines the relative density of apex predators and other predators, which affects competitive outcomes. Third, successful programs require adaptive sequences of management strategies.

Our research matters because it challenges the simple assumption that removing threats will automatically lead to predator recovery. The widespread occurrence of unsuccessful or stalled recovery efforts suggests a need for a more nuanced understanding of ecosystem context and historical contingency. The findings emphasize the importance of a social-ecological perspective in facilitating long-lasting predator restoration while avoiding unintended consequences. Recovery pathways are not necessarily identical to pathways of decline due to hysteresis effects.

Many questions remain for future research. Scientists still don't fully understand how to predict which trophic interactions will be most important for any given recovery effort. The role of timing in community assembly needs much more research, and better tools are needed for designing adaptive management sequences. The complexity revealed suggests that successful apex predator recovery will require embracing uncertainty rather than trying to eliminate it.

Citation

Stier, Adrian C.; Samhouri, Jameal F.; Novak, Mark; Marshall, Kristin N.; Ward, Eric J.; Holt, Robert D.; Levin, Phillip S. (2016). Ecosystem context and historical contingency in apex predator recoveries. Science Advances.

Read the full paper

This paper is Open Access.