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Ecology

Studies of Human Influences on the Ecosystems — Work in collaboration with the University of Colorado and the Australian National University has documented that the extinction of most large mammals and birds in Australia took place within a few thousand years after the arrival of humans to this continent. The extinction was tied to widespread ecosystem changes at the base of the food chain roughly 45-50 thousand years ago (Pleistocene), which could have been altered by increased fire regimes practiced by Aboriginal people. These conclusions have been confirmed in three animal species, the extant emu (both modern and fossil samples), the extinct flightless bird, Genyornis, and the southern hairy-nosed wombat (both modern and fossil samples) each with fossil records extending from recent to 120,000 years ago. As part of this work, we have conducted a continental-scale monitoring of the stable isotope ecology of plants adapted to fire and drought.

Biocomplexity of Mangrove Ecosystems — Our work on mangrove ecosystems has determined how these important plants survive in high stress environments. Mangrove species in the tropics and subtropics worldwide protect the coastlines and people from violent hurricanes, coastline erosion, and the effects of tsunamis. Increasingly, mangrove forests are being cleared for tourism or aquaculture in third world countries and have been inundated with the wastes from population centers. Our work has focused on how mangrove trees deal with nutrient stress, increases in salinity, and changes in sea level. We have also determined the importance of mangrove ecosystems to the food webs of important fish species living in the nearby oceanic environments. For the past 5 years, we have used what we know about stable isotope ecology in modern mangroves to interpret the paleoclimate record during the Holocene period so as to determine the paleoccology as sea level rose in the tropics over the past 8,000+ years.

Stable Isotope Ecology of Animals — Birds that undergo yearly migration from northern geographical regions to the tropics each winter are increasingly threatened by loss of habitat, environmental degradation, and changes in recent climate. We are conducting two major studies with scientists from the Smithsonian Institution and other univerisites to track the migration patterns:

  1. Juvenile and adult black-throated blue warblers, collected from Georgia to the top of their range in Canada, are being analyzed for C, N, H, and O isotopes in their feathers to determine whether juveniles return to the exact area of their of birthplace after their first long distance migration.
  2. The Great Gray Owl, one of the world’s largest owls, makes periodic winter invasions into regions well south of its core breeding range in the northern boreal forests of North America and Eurasia.

However, little is known about the underlying causes of irruptive movements, the geographic origin of the immigrants, or the fate of individual owls. The most spectacular such invasion in the past 150 years occurred during the winter of 2004-2005 in Minnesota, where 5200+ owls were observed or banded. We are using stable isotopes in feather, liver and muscle tissue to track their origins, diets, and level of potential starvation. The resulting data will provide much needed data for modeling local and regional population dynamics of GGO as well as critical information for conservation programs.

Postdoctoral researcher Seth Newsome (Ph.D., UC Santa Cruz) is involved in multiple studies on marine mammals, including sea otters, killer whales, dolphins, and seals, from the Pacific and as far south as Argentina. A recent visitor to the Laboratory from Argentina worked with Seth on the trophic structures of dolphins and porpoises from the Southern Ocean. Very little is known about these species that inhabit cold waters surrounding Antartica, however, with stable isotope technology, within a couple of weeks we now know which species are dependent on coastal ecosystems and which depend on open ocean food webs for survival.

For Stable Isotopes studies, we have the following equipment:

Infrared CO2 laser fluorination system for analysis of oxygen isotopes in silicate, phosphate and oxide whole mineral grains
Finnigan MAT 252 mass spectrometer for C, H, N, and O isotopes
Ultraviolet excimer laser fluorination system for in situ analysis of 16O/17O/18O in silicate, phosphate and oxide minerals
Finnigan Delta + XL mass spectrometer with an elemental analyzer for analysis of C, N and S at the natural abundance level, a gas chromatographic combustion interface for compound specific analysis of organic molecules for C, H and N (new model to be delivered in 2008), and a high temperature pyrolysis unit for analysis of O and D/H in inorganic and organic materials
UV laser plus CO2 laser system for laser fluorination of sulfide minerals for δ33S, δ34S, and δ36S
Finnigan MAT 253 isotope-ratio mass spectrometer for measuring the four isotopes of S