Ecosystem-level effects of keystone species reintroduction: a literature review

The keystone species concept was introduced in 1969 in reference to top-down regulation of communities by predators, but has expanded to include myriad species at different trophic levels. Keystone species play disproportionately large, important roles in their ecosystems, but human-wildlife conflicts often drive population declines. Population declines have resulted in the necessity of keystone species reintroduction; however, studies of such reintroductions are rare. We conducted a literature review and found only 30 peer-reviewed journal articles that assessed reintroduced populations of keystone species, and only 11 of these assessed ecosystem-level effects following reintroduction. Nine of 11 publications assessing ecosystem-level effects found evidence of resumption of keystone roles; however, these publications focus on a narrow range of species. We highlight the deficit of peer-reviewed literature on keystone species reintroductions, and draw attention to the need for assessment of ecosystem-level effects so that the presence, extent, and rate of ecosystem restoration driven by keystone species can be better understood.