Paleontologists can't always get what they want, to paraphrase the Rolling Stones, but sometimes they can get what they need, according to a study that will appear in the May issue of the American Naturalist.
The fossil record captures both the broad sweep of evolutionary changes in life on earth as well as ecological responses to shorter-term local and regional environmental shifts. And yet the amount of variability seen among successive fossil assemblages tends to be low compared to that ecologists see over shorter time periods. This suggests that communities are extremely resilient or resistant to change over decades to centuries.
In the American Naturalist article, University of Chicago paleontologists Adam Tomaovch and Susan Kidwell used data on living and fossil communities to explore where the low variability in fossil assemblages comes from. Does it come from the natural "time averaging" of skeletal remains that occurs during postmortem accumulation, or from biological processes actively maintaining a particular community composition?
Processes in the latter category include strong species preferences for particular niches that may enable them to avoid extinction owing to high growth rates at small population sizes, or the buffering of population growth during unfavorable times.
On most seafloors, lake bottoms and land surfaces, however, sediment accumulates quite slowly compared to the rates at which local animal populations generate skeletal remains. Multiple generations of skeletal remains may therefore become mixed within a single fossil assemblage. "Samples from a series of such time-averaged fossil assemblages are thus very different from the snapshots that come from repeatedly sampling a living community," said Tomaovch, a postdoctoral scientist in Geophysical Sciences at UChicago.
Simulating the effects of time-averaging on living communities from a Texas lagoon and an east African la
|Contact: Steve Koppes|
University of Chicago