Assessing life span bias on relative species abundance in coastal marine fossil assemblages (2010)
Undergraduate: Stewart Edie
Faculty Advisor: Donna Surge
Department: Geology
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 in June 2008 and again in June 2009. Samples have been collected every three months since June 2009. The average dead:dead ratio recorded from the death assemblage is 2.6 Chione to 1 Mercenaria. The average live:live ratio recorded from the live assemblage is 1.4 Chione to 1 Mercenaria. 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.