Reciprocity in restoration ecology: When might large carnivore reintroduction restore ecosystems?

Abstract

Carnivore reintroduction is often expected to revert community and ecosystem properties to their natural states via risk effects and the direct killing of prey. Because large carnivore extirpation and reintroduction are usually believed to have symmetric and offsetting effects, fulfilling this "assumption of reciprocity" is crucial to realizing the potential of large carnivores to passively restore community structure and ecosystem function. We were unable to find any study in which the assumption of reciprocity was rigorously tested in predator-prey systems featuring large carnivores, their ungulate prey, and primary producers through a comprehensive literature search. We therefore used studies involving (1) the reintroduction of any native apex predator (including but not limited to large mammalian carnivores); and (2) the removal of any introduced apex predator (also including but not limited to large mammalian carnivores) to examine the assumption of reciprocity. Reintroduction of native apex predators did not affect any of four trophic groups (mesopredator, omnivore, herbivore, primary producer) in a positive or negative way, but removal of introduced apex predators consistently increased the abundance and biomass of mesopredators. Further, outcomes of apex predator reintroduction and removal were variable across systems, regardless of system complexity (ranging from single predator-single prey to multiple predator-multiple prey systems). We suggest that the assumption of reciprocity-in which predator extirpation and reintroduction are believed to have consistent, counterbalancing effects-is unsupported by current evidence, and perhaps unrealistic. We discuss potential directions for research that might illuminate when and why the assumption of reciprocity would be valid.

Temporal partitioning of activity: rising and falling top‐predator abundance triggers community‐wide shifts in diel activity

“…This study demonstrates that rising or falling abundance of a top predator can have far-reaching effects on the behaviour of other carnivore and prey species. While there is much evidence of the cascading effects that often follow toppredator removal, there is less evidence about the reversal of effects following predator recovery (Alston et al 2019). Our study provides valuable evidence that top predator recoveries can reinstate anti-predator behaviours in other species (Berger et al 2001, Estes et al 2011, Cunningham et al 2019b).…”

“…While there is much evidence of the cascading effects that often follow toppredator removal, there is less evidence about the reversal of effects following predator recovery (Alston et al 2019). While there is much evidence of the cascading effects that often follow toppredator removal, there is less evidence about the reversal of effects following predator recovery (Alston et al 2019).…”

An applied ecology of fear framework: linking theory to conservation practice

“…Although fear‐mediated effects of predation are often much more difficult to quantify than numerical effects, they may play an important role in shaping prey habitat use and prey demography, which are relevant to the conservation of prey populations (Creel et al ., 2007). Reintroduction or removal of predators, for instance (Alston et al ., 2019), will reshape risk cues and can change patterns of risk perception and prey behavior (Berger, 2007a; Dellinger et al ., 2018). For example, removal of coyotes ( Canis latrans ) in central Georgia, USA, led to changes in the foraging behavior of white‐tailed deer ( Odocoileus virginianus ), an important game species (Gulsby et al ., 2018).…”

Reintroducing extirpated herbivores could partially reverse the late Quaternary decline of large and grazing species

“…Our method also assumes that extirpations and reintroductions have ‘symmetric counterbalancing effects’ (Alston et al, 2019), the so‐called assumption of reciprocity. Case studies show that reintroducing herbivores can restore ecological processes, in certain cases.…”

“…However, reciprocity effects are poorly studied. Evidence suggests they are variable, likely because ecosystems have changed since the time species disappeared (Alston et al, 2019): novel species may have appeared, habitats may have changed and past predators may now be absent. As such, it remains to be seen how widely the results of the examples above can be extrapolated.…”