Colonization record of the Galápagos' vertebrate clades: Biogeographical issues plus a conservation insight

Abstract

Our focus is the colonization history of the Galápagos' vertebrate clades: 11 land-bound groups (eight reptiles, three rodents) and 13 taxa of flyers and swimmers (ten winged birds, two pinnipeds, one penguin). Using 'colonization intervals' and 'colonization profiles', it is clear that the two sets of taxa assembled very differently. The former includes older clades with between one, and potentially eight, predating the emergence of the oldest island (4 Mya). For the origin of some lineages, now-sunken landmasses associated with the Galápagos mantle-plume hotspot must have been involved, but for others it could reflect taxonomic uncertainties. In contrast, the taxa of flyers and swimmers are markedly younger, indicating either higher rates of colonization and extirpation for these sorts of animal, or continued genetic influx from mainland populations, or some combination of both factors. Concerning the first, possible drivers are the environmental stressors associated with the El Niño–La Niña climate system; the recent clades may be vulnerable to extreme events within the oscillation sequence, perhaps on ≥104-year timescales. Therefore, loose temporal thresholds might exist for the archipelago's vertebrate groups beyond which selection fortifies them from the most challenging of seasonal states. Moreover, in a world of climate uncertainty, the findings appear relevant to conservation initiatives suggesting a focusing on the younger elements within the Galápagos' biota.