The Role of Endangered Species Reintroduction in Ecosystem Restoration: Tortoise–Cactus Interactions on Espan ˜ ola Island, Gala ´ pagos James P. Gibbs, 1,2 Cruz Marquez, 3 and Eleanor J. Sterling 4 Abstract We evaluated the role that endangered species reintro- duction efforts can play in the larger context of ecosys- tem restoration. To do so, we examined interactions between endangered giant tortoises (Geochelone nigra hoodensis), currently being reintroduced to Isla Espan ˜ o- la, Gala ´pagos, and an arboreal cactus (Opuntia mega- sperma var. megasperma), which is itself endangered and a keystone resource for many animals on the island. We collected information on spatial patterns of occurrence of cacti, tortoises, and woody vegetation and compared recruitment of juvenile cacti in areas occupied versus unoccupied by tortoises. Reintroduced tortoises ap- peared to suppress cactus recruitment near the few re- maining adult cacti at the study site, but facilitate it at longer distances, with tortoise–cactus interactions medi- ated by the presence of woody vegetation, which likely alters tortoise movements and thereby patterns of cactus seed dispersal. The net effect of tortoises on cacti ap- peared to be positive insofar as tortoise presence was associated with greater recruitment of juveniles into cac- tus populations. Our study provides support for reintro- ducing endangered reptiles and other animals to aid ecosystem restoration in areas where they might once have played an important role in grazing upon and dis- persing plants. Key words: cactus, endangered species, Gala ´ pagos Islands, Geochelone, Opuntia, reintroduction, restoration ecology, tortoise. Introduction Species reintroduction typically involves establishment from translocated stock of a new population of a threat- ened or endangered species after harmful conditions in the original habitat have been corrected. Reintroduction is a key component of integrated strategies for recovery of many endangered species (Griffith et al. 1989; Dodd & Siegel 1991; Falk & Olwell 1992). In general, reintroduc- tion studies focus on the autecology of the species being reintroduced, particularly when they are endangered spe- cies (see Sarrazin & Barbault 1996). However, endan- gered species reintroduction can also reinstate key ecological processes, particularly where important mutual- isms have been disrupted (Bond 1994). One recent exam- ple involves wolves in Yellowstone National Park in the western United States, where the reintroduced animals have altered herbivore feeding patterns and thereby changed patterns of woody plant regeneration and avian diversity over large areas (Ripple & Beschta 2004). Simi- larly, a reintroduced population of European beavers in France rejuvenated riparian forests and helped stabilize riverbanks (Fustec et al. 2001). Unfortunately, a lack of comparable assessments for other endangered taxa and other regions hinders our understanding of whether endan- gered species reintroduction efforts can play a significant role in the larger context of ecosystem restoration or whether their primary purpose is recovery of lost amenity value associated with species extinction (e.g., Langford et al. 2001). Similarly, little information is available regarding the time it takes for systems to adapt to the reintroduc- tions, although evidence from wolf reintroductions in North America point to rapid (within one generation) develop- ment of predator–prey relationships (Berger et al. 2001). We conducted a preliminary assessment of the ecologi- cal consequences of a species reintroduction program on Espan ˜ ola Island in the Gala ´ pagos Archipelago—the site of one of the most successful and ambitious yet least her- alded species reintroduction efforts. Our focus was giant tortoises (Geochelone nigra hoodensis), which once num- bered perhaps 3,000 on the island, but by 1965, had been reduced to just 14 individuals primarily by hunters from sealing, whaling, and pirate ships (Pritchard 1996). As an emergency conservation measure in the mid-1960s, re- maining tortoises were transferred to the Breeding Center of the Charles Darwin Research Station and Gala ´ pagos National Park on Isla Santa Cruz. During the 1970s, about 3,000 goats were eliminated from Espan ˜ ola as the result of an intense campaign by guards of the Gala ´ pagos National 1 State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210, U.S.A. 2 Address correspondence to J. P. Gibbs, email jpgibbs@esf.edu 3 Charles Darwin Research Station, Puerto Ayora, Santa Cruz, Gala ´ pagos Islands, Ecuador 4 Center for Biodiversity and Conservation, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, U.S.A. Ó 2007 Society for Ecological Restoration International doi: 10.1111/j.1526-100X.2007.00265.x 88 Restoration Ecology Vol. 16, No. 1, pp. 88–93 MARCH 2008