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Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)

Paper No. 17
Presentation Time: 1:30 PM-5:35 PM

ASSESSING LIFE SPAN BIAS ON RELATIVE SPECIES ABUNDANCE IN COASTAL MARINE FOSSIL ASSEMBLAGES


EDIE, Stewart M., Geological Sciences, University of North Carolina, Chapel Hill, NC 27599, DIETL, Gregory P., Paleontological Research Institution, 1259 Trumansburg Road, Ithaca, NY 14850-1398 and KELLEY, Patricia H., Department of Geography and Geology, University of North Carolina Wilmington, 601 South College Road, Wilmington, NC 28403-5944, sedie@email.unc.edu

Paleontologists must analyze species relative abundance by processing a time-averaged sample of usually unknown duration. A time-averaged death assemblage may be composed of multiple generations of a short-lived species relative to a longer-lived species. The abundance of a specimen with a one-year life span is expected to be ten fold that of a specimen with a ten-year life span assuming similar fertility and fecundity between those specimens (Vermeij and Herbert, 2004). We evaluated the prediction that a death assemblage is subject to an abundance bias using the short-lived bivalve, Chione elevata, and the longer-lived bivalve, Mercenaria mercenaria. The high turnover rate in Chione is predicted to distort its “real” relative abundance compared to Mercenaria.

Sixteen bulk samples of ~2 liters were collected from a tidal flat near Masonboro Inlet, NC on June 12, 2008 and again on June 22, 2009. The June 2008 death assemblage has a total of 573 Chione and 280 Mercenaria for an average dead-dead ratio of 2.1:1 Chione to Mercenaria per bulk sample. The June 2009 death assemblage (829 Chione and 315 Mercenaria) yields an average dead-dead ratio of 2.7:1 Chione to Mercenaria per bulk sample. The average live-live ratio of each collection was calculated from bulk samples containing at least one individual of both species. The live assemblage from June 2008 (28 Chione and 25 Mercenaria) yields an average live-live ratio of 1.6:1 Chione to Mercenaria per bulk sample. The June 2009 live assemblage (19 Chione and 22 Mercenaria) yields an average live-live ratio of 1.6:1 Chione to Mercenaria per bulk sample. A collection on October 17, 2009 (14 Chione and 13 Mercenaria) yields an average live-live ratio of 1.2:1 Chione to Mercenaria per bulk sample. Preliminary results show that Chione is approximately twice as abundant in the death assemblage as it is in the live assemblage.

Work currently underway will attempt to correct for this overabundance of Chione in the death assemblage by normalizing the number of individuals per species in the death assemblage to one generation.

Session No. 80--Booth# 52

Paleontology II, Mesozoic and Cenozoic (Posters)
Tuesday, 16 March 2010: 1:30 PM-5:35 PM
International ABCDF (Sheraton Baltimore City Center)
Geological Society of America Abstracts with Programs. Vol. 42, No. 1, p.188
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