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What were the ecological effects of the Pleistocene megafaunal extinctions?

While the causes of the extinctions of mammoths and other Pleistocene “megaherbivores” have been extensively studied, we know little about the ecological effects of that extinction and the role megaherbivpres played in ice-age ecosystems. At the end of the last ice age, plant communities in the Great Lakes region were unlike any found on landscapes today, even though the individual components (like spruce or ash trees) would have been recognizable to modern ecologists. We are researching how such novel ecosystems arose, particularly in response to climate change and the loss of large herbivores.

People involved with this project include Jacquelyn Gill and Jack Williams

1) Paleoecological reconstructions using fossil pollen, charcoal, and the dung fungus Sporormiella

Goal: Reconstruct the spatiotemporal patterns of the late-glacial no-analog communities and megafaunal collapse

We are generating several new high-resolution lake sediment records from classic no-analog sites, with updated chronologies and multi-proxy analyses. These records include reconstructions of past fire regimes from sediment charcoal analysis, generated by Williams Lab undergraduate Grace Schellinger. Spores from the dung fungus Sporormiella preserved in lake sediments are used as a proxy for megaherbivore population collapse, allowing us to test the response of vegetation change to the loss of herbivores. Vegetation dissimilarity from present is calculated by comparing fossil pollen assemblages to the North American Modern Pollen Database, using a squared-chord distance metric.

Our results suggest that the extinction of the Pleistocene megafauna may have resulted in the herbivory release of palatable hardwoods, as well as enhanced fire regimes due to a build-up of landscape fuel loads (Fig. 1) (Gill et al. 2009). This work is part of a broader, NSF-funded project investigating causes and spatiotemporal patterns of the late-glacial no-analog communities in eastern North America, in collaboration with Steve Jackson at the University of Wyoming.

BenchmarkSites

Figure 1. Appleman Lake, IN Summary pollen diagram from Appleman Lake, IN. The decline in Sporormiella was immediately followed by 1) an increase in minimum vegetation dissimilarity from present, due to the coexistence of temperate deciduous (particularly Fraxinus and Ostrya) and boreal taxa (Picea, Abies), and 2) an increase in fire activity. Samples with SCD scores >0.3 are “no-analog.” From Gill et al. 2009.

2) Modern process study of the Sporormiella proxy at Konza Prairie LTER

Goal: Assess whether the dung fungus Sporormiella is a qualitative, presence-absence indicator of megaherbivores, or whether it can be used to infer local changes in megafaunal biomass.

Given the novelty of the Sporormiella proxy (Fig. 2), it is crucial that we understand more about its production, dispersal, taphonomy, and megafaunal associations. To address this, we are conducting a modern process study at Konza Prairie Biological Research Station, in collaboration with Kendra McLauchlan at Kansas State University. Our project makes use of Konza’s free-roaming bison herd, which are kept in a large enclosure, to better understand the relationship between spores and local megaherbivore biomass.

gdmFigure 2. A Sporormiella spore cell from Silver Lake, OH (17.5 ka BP). Spores have distinct sigmoid slits and distinct cell walls, and are typically found broken into individual cells (or, “subspores”) in the fossil record.

PUBLICATIONS

Gill, J. L., Williams, J. W., Jackson, S. T., Lininger, K., and Robinson, G. S. (2009). Pleistocene megafaunal collapse preceded novel plant communities and enhanced fire regimes. Science 326: 1100-1103.

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