Floristic diversity and dynamics of Isla Rasa, Gulf of California – A globally important seabird island

Abstract


 Isla Rasa, a small (0.68 km2) but globally important seabird island in the Gulf of California, has a flora of only 14 vascular plant species found in three vegetation zones. Significant physical alteration of the island’s surface and the introduction of non-native rodents, eradicated in 1995, add restoration ecology to the remarkable biology of the island. Over a century of botanical collections and observations record a consistently depauperate flora, best understood in the context of extreme aridity, isolation, and elevated levels of nitrogen and phosphorus from bird guano. The shaping factor of guano on the dearth of floristic diversity illustrates close connection between marine and terrestrial ecosystems in the Gulf of California. El Niño events that trigger collapses in marine productivity and crashes in seabird reproduction bring above-average winter rainfall pulses and rapid plant growth. Two new island records are reported (Rhizophora mangle and Viscainoa geniculata ). Matched photographs show significant increase in the cholla cactus (Cylindropuntia fulgida ) since 1971. Baseline knowledge of sea bird breeding ecology and the flora of the island position Isla Rasa as a preeminent locality to study and monitor the ecological dynamics of a desert island in the context of restoration ecology and global environmental change.