Translocate predators for ecosystem restoration
Overall effectiveness category Likely to be beneficial
Number of studies: 2
Background information and definitions
In areas where predators have historically been made locally extinct or populations severely reduced, often due to hunting, they may be translocated from other areas and released in an attempt to restore the ecosystem. Predators may help to reduce medium to large herbivore populations for example, and thus allow some recovery of the habitat and other species groups.
Supporting evidence from individual studies
A before-and-after study in 1986–2004 in a grassland and forest reserve in Wyoming, USA (White & Garrott 2005) found that after the translocation of wolves Canis lupus to the reserve, adult elk Cervus canadensis numbers and elk calf:cow ratios approximately halved. Results were not subjected to statistical analysis. Nine years after wolves were translocated, there were fewer adult elk (8,335) and a lower calf:cow ratio (12 calves/100 female elk) than the average before wolf translocation (adult elk: 16,664; 25 calves/100 female elk). A similar number of elk that had migrated out of the park were killed by hunters before (1,148 elk/year) and after (1,297 elk/year) wolves were translocated. Wolves were translocated into Yellowstone National Park in 1995. Between 1996 and 2004 wolf numbers increased from 21 to 106. Elk adults and calves were counted from aeroplanes annually during December–January 1986–2004. No counts were conducted during the winters of 1996 and 1997.Study and other actions tested
A before-and-after study in 1990–2010 of riparian and adjacent upland habitat in a national park in Wyoming, USA (Ripple & Beschta 2012) found that following reintroduction of wolves Canis lupus, populations of beavers Castor canadensis and bison Bison bison increased. There were more beaver colonies in a monitored area 13 years after wolf reintroduction began (12 colonies) than at the start of reintroduction (one colony). Average summer bison counts were higher in the decade after wolf reintroduction began (1,385 bison) than in the preceding decade (708 bison). Following the start of reintroduction in 1995–1996, wolf numbers in the study area increased to 98 in 2003, followed by a decline and substantial fluctuations. Their establishment was associated with a fall in elk Cervus canadensis numbers from >15,000 in the early 1990s to approximately 6,100 in 2010. Elk browsing on woody vegetation reduced, increasing resources available to beaver and bison. Beaver and bison numbers were derived from annual surveys.Study and other actions tested