Presentation on theme: "Andes to Amazonia: What we think we know and what we don’t. Mark Bush Florida Institute of Technology & Miles Silman Wake Forest University."— Presentation transcript:
Andes to Amazonia: What we think we know and what we don’t. Mark Bush Florida Institute of Technology & Miles Silman Wake Forest University
Some of the big questions before us: To what extent can Andean records inform us about Amazonia? How much climatic variation was there within ice age Amazonia? How robust are the data for a 5 o C cooling in the terrestrial Neotropics? How dry was Amazonia during the last ice-age?
Refugia Raised on modern biogeographic data but no reliable paeleocological data. Most recent manifestation is untestable as it has no time or habitat constraints (Haffer and Prance Amazoniana 2002). Brown (1991)
Dry Forest Arcs Modern biogeographic data used to suggest the presence of a past habitat bridge of dry forests. Assumed to be ice-age But there is no basis for this assumption. Nor a real difference from modern required to allow movement of species. Pennington et al. ( J. Biogeogr. 2000)
Different ideas about Arcs Pennington et al. (J. Biogeogr. 2000) Wüster et al. (Molec. Ecol. 2005)
GISP Titicaca pollen concentration D-O cycles in Titicaca
Lake level and insolation Lake Titicaca and the Salar de Uyuni, Bolivia, respond to DJF insolation. Lake level at Titicaca varies synchronously with Pata for the last 70,000 years. 20 40 K yr BP Baker et al. (Science 2001)
Lake level fluctuation in Amazonia Lakes Pata and Verde show continuous forest cover through last two glacial periods. Periods of low lake level correlate with periods of high K + concentrations in sediment in Pata. Low lake level due to reduced precipitation.
Lake level and orbital forcing Peak low-lake level corresponds to 11 K BP and 33 K BP with 22 K BP wet (matches Titicaca). Aligns to orbital rhythm of variation in insolation. Continuous forest cover suggests decrease in precipitation in the wet season rather than dry season. Bush et al. (J. Paleolimn. 2002)
Linking Amazon and Andean forests –Single system –Space and Time Fully vouchered 1 ha plots lowlands to treeline (17 to date) Series of lakes along transects Peru and Bolivia Andes Biodiversity Consortium
L L L L L L LL L L L L L L L L L L L L L L L L L L L Modern Ecology: 77 ha (Peru) -17 Montane, 60 Lowlandw 3 tropicos database Paleoecology: 24 Lakes
Representation of pollen taxa Continuous wet forest taxa for 50,000 yrs Gradual change in community composition Bush et al. (Science 2004)
Consuelo Ordination Two basic states (1)30 kyr (2)11 kyr Evidence of cycles
DCA Axis 1 vs. Time Two major forest types Periodic changes –ENSO, drought cycles, D-O events Gradual ~8-10 ky transition Non-equilibrium?
~1200m 0.0055 °C m -1 ~6.6 °C cooler Elevation for taxa found 21,000 years ago (500 cm pollen assemblage) Q: What does time course look like? If taxa were found co-occurring today, most likely elevation would be 2400m
What is cooling? All these sites provide evidence of a 5-7 o C cooling at the LGM 13 o C 8oC8oC Plants probably respond to minimum temperatures, and absolute modern minima are very different across the basin. Were absolute minima in the north reduced while monthly minima were reduced in the south?
Extract sub- region for training and recognition One way forward: Improving pollen recognition Using SEM and vector- based computer modeling we aim to improve identification of key taxa to species or species group. More precise taxonomy = more precise bioclimatic envelope modeling
What we think we know: Strong decline in species diversity with elevation. Species migrate individualistically in response to climate change. Strong cooling signature in all Pleistocene records with some species’ ranges typically moving 1000 m -1500 m downslope. Lowland taxa are adapted to Pleistocene cooling. Amazonian paleoclimates were temporally and spatially heterogeneous. Refugia and savanna corridors are not grounded in reality.
What we don’t know: Do we have to reconcile the terrestrial record with the marine record? Difference in temperature could be absolute minima (NH) or mean temperature (SH)? To what extent forest structure changed. Fine-resolution climate change from the lowlands. The full impact of Holocene human activities.
The Coring Gang Andrea Gomez Alex Correa Dunia Urrego Jen Hanselman Dr. Will Gosling