May 27 2015

12:00 LSB 2320

Ben Wilder
Department of Botany and Plant Sciences, University of California, Riverside

Historical Biogeography of the Midriff Islands, Gulf of California, Mexico Historical Biogeography of the Midriff Islands of the Gulf of California, Mexico


While the processes that led to the formation of modern plant communities are often cryptic, biogeographic patterns of extant species can provide clues to their origin. The Midriff Islands, an archipelago in the Gulf of California at the center of the Sonoran Desert, provide an opportunity to investigate the origins of the desert. This presentation will address three case studies at three different time scales to better understand the factors responsible for modern biodiversity. I will revisit the theory of island biogeography and incorporate the long history of humans on the Midriff Islands to determine factors controlling plant species richness. Secondly, I will address the unique history of bighorn sheep \(Ovis canadensis\) on Isla Tiburn to explore Holocene extinctions. In 1975, bighorn sheep were introduced as a novel element to Isla Tiburn as a conservation measure. However, fossil dung found on Isla Tiburn support that bighorn sheep went locally extinct on the island sometime in the last \~1500 years prior to their unintentional rewilding. This discovery questions the definition of a non-native species and extends an ecological and conservation baseline. The effects of Pleistocene glacial periods can be seen in disjunct long-lived plant taxa on Isla Tiburn, which suggest climate and vegetation change on the Midriff Islands at the last glacial maximum. A phylogeographic study of the desert edge species Canotia holacantha \(Celastraceae\) tests whether Canotia on Isla Tiburn is a Pleistocene relict or a recent dispersal event. Results support long isolation and divergence of Canotia on Tiburn and raise interesting questions about the expansion of arid adpated taxa from glacial refugia in Sonora or Chihuahua. Collectively, this research helps illuminate the history of the desert and establishes baselines to support management decisions of the worlds best-preserved archipelago.











































































































































































































































































































































































































































































































































































































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