title: Equivalency of Galápagos giant tortoises used as ecological replacement species to restore ecosystem functions.
abstract: Loss of key plant-animal interactions (e.g., disturbance, seed dispersal, and herbivory) due to extinctions of large herbivores has diminished ecosystem functioning nearly worldwide. Mitigating for the ecological consequences of large herbivore losses through the use of ecological replacements to fill extinct species' niches and thereby replicate missing ecological functions has been proposed. It is unknown how different morphologically and ecologically a replacement can be from the extinct species and still provide similar functions. We studied niche equivalency between 2 phenotypes of Galápagos giant tortoises (domed and saddlebacked) that were translocated to Pinta Island in the Galápagos Archipelago as ecological replacements for the extinct saddlebacked giant tortoise (Chelonoidis abingdonii). Thirty-nine adult, nonreproductive tortoises were introduced to Pinta Island in May 2010, and we observed tortoise resource use in relation to phenotype during the first year following release. Domed tortoises settled in higher, moister elevations than saddlebacked tortoises, which favored lower elevation arid zones. The areas where the tortoises settled are consistent with the ecological conditions each phenotype occupies in its native range. Saddlebacked tortoises selected areas with high densities of the arboreal prickly pear cactus (Opuntia galapageia) and mostly foraged on the cactus, which likely relied on the extinct saddlebacked Pinta tortoise for seed dispersal. In contrast, domed tortoises did not select areas with cactus and therefore would not provide the same seed-dispersal functions for the cactus as the introduced or the original, now extinct, saddlebacked tortoises. Interchangeability of extant megaherbivores as replacements for extinct forms therefore should be scrutinized given the lack of equivalency we observed in closely related forms of giant tortoises. Our results also demonstrate the value of trial introductions of sterilized individuals to test niche equivalency among candidate analog species.
authors.affiliation: State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210, USA. eahunter@uga.edu
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Hunter
authors.forename: James P
authors.initials: JP
authors.lastname: Gibbs
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Cayot
authors.forename: Washington
authors.initials: W
authors.lastname: Tapia
mesh_terms: D063147:Animal Distribution / Q000502:physiology; D000818:Animals; D003247:Conservation of Natural Resources / Q000379:methods*; D017753:Ecosystem; D004484:Ecuador; D060434:Herbivory / Q000502:physiology*; D019370:Observation; D012044:Regression Analysis; D013045:Species Specificity; D014426:Turtles / Q000502:physiology*
keywords: Chelonoidis spp; ecological replacement species; ecosystem restoration; equivalencia de nicho; especies de reemplazo ecológico; niche equivalency; restauración de ecosistemas; saddlebacked giant tortoise; tortuga de las Galápagos