Aaron Collins

An analysis of modern pollen representation and climatic conditions on the Galápagos Islands

In the first modern pollen trapping study conducted in the Galápagos Islands, 58 clusters of pollen traps were established on four islands: Genovesa, Rocas Bainbridge, Santa Cruz, and San Cristobal. HOBO data loggers collected temperature, humidity, and dew point every 30 min for 1 year at eight locations. The trapping locations were selected to provide a wide diversity of Galápagos habitat types and to support active or future analyses from bog and lake core records recovered from the islands. Pollen influx to the traps was generally low (<100 grains/cm 2 per yr), but broad habitat types were clearly identifiable based on the pollen collected. More precise identification of trapping sites and vegetation zones within the islands were identified using ordinations of the pollen and climate data. Long-distance dispersal from the mainland and neighboring islands were found to be significant elements of pollen records, particularly those where local pollen production was low (<150 grains/cm 2 per yr). Over-representation and under-representation of ecological dominants was documented, as was the significant representation of invasive exotic species in some settings. Temperature and relative humidity data were used to reconstruct the presence of ground-level cloud (garúa). Garúa caused substantial cooling, beyond what would be expected from adiabatic lapse rate, in the highlands. The cloud formation associated with garúa caused low-elevation temperatures to be cooler than maximum sea-surface temperatures. The data emphasize the importance of garúa to the endemic flora of the islands and their long-term conservation.

Microrefugia and species persistence in the Galápagos highlands: a 26,000-year paleoecological perspective

The Galápagos Islands are known to have experienced significant drought during the Quaternary. The loss of mesophytic upland habitats has been suggested to underlie the relatively lower endemism of upland compared with lowland plant assemblages. A fossil pollen record spanning the last 26,000 years from an upland bog on Santa Cruz Island, revealed the persistent presence of highland pollen and spore types during the last glacial maximum and a millennial-scale series of droughts in the mid Holocene. The absence of lowland taxa and presence of mesic taxa led to the conclusion that the highland flora of the Galápagos persisted during both these periods. The resiliency of the highland flora of the Galápagos to long-term drought contradicts an earlier hypothesis that an extinction of highland taxa occurred during the last glacial maximum and that rapid Holocene speciation created the modern plant assemblage within the last 10,000 years. Based on the palynological data, we suggest that, even during the height of glacial and Holocene droughts, cool sea-surface temperatures and strong trade-wind activity would have promoted persistent ground level cloudiness that provided the necessary moisture inputs to maintain microrefugia for mesophytic plants. Although moist conditions were maintained, the lack of precipitation caused the loss of open water habitat during such events, and accounts for the known extinctions of species such as Azolla sp., and Elatine sp., while other moisture dependent taxa, i.e., Cyathea weatherbyana, persisted.

Tropical Pacific climate variability over the last 6000 years as recorded in Bainbridge Crater Lake, Galápagos

National Science Foundation (NSF) RAPID, Program [AGS-1256970, AGS-1561121]; NOAA Climate Program Office; University of Arizona Department of Geosciences; Philanthropic Education Organization; National Science Foundation (NSF) P2C2, Program [AGS-1256970, AGS-1561121]; National Science Foundation (NSF) Geospace Sciences Paleoclimate Program [AGS-1256970, AGS-1561121]