(Appendix) Bathyal benthic foraminifera in ODP Hole 166-1006A sediments

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The percent carrying capacity Kp is the equilibrium population in percentage terms of a species that an area can support while adequately meeting the needs of every individual. It is readily determined from a time series of percentage abundances for a species, in which pit is the percentage abundance of the ith species at time t. The percentage point change in abundance of a species Dpi between two samples is given by Dpi = pit + 1 − pit, where pit + 1 is the percentage abundance at a subsequent time t + 1. The rate of population change in percentage points for each percent at a given time or point t, here termed rt, is given by rt = Dpi/pit. Linear regression of rt against pit gives rt = rm–s · pit, in which the constant rm is the rate of increase in rt where pit approaches zero, and the negative slope s represents the combined strength of intraspecific, interspecific and abiotic interactions for the species investigated. Setting rt = 0, so that pit = Kp and rm–s · Kp = 0, gives Kp = rm/s. The Upper Quaternary of ODP 1006A contains two subsections with rich bathyal benthic foraminiferal assemblages separated by samples yielding few specimens. Values of rm, s and Kp were calculated for five species (Globocassidulina subglobosa, Planulina ariminensis, Cibicidoides pachyderma, Cassidulina laevigata, Uvigerina laevis) within these subsections and 95% confidence intervals were computed for rm and s. The rate of change of the percentage abundance for each percent rt, as indicated by the slope s, differs between species (P. ariminensis and C. pachyderma vs. C. laevigata) and can also vary within a single species over time (G. subglobosa). Likewise, values of rm differ between species (P. ariminensis vs. C. pachyderma) and can also change within a single species over time (G. subglobosa). Points of change from one value of Kp to another in a stratigraphic section mark regime shifts and have potential for ecostratigraphic correlation. Within the Upper Quaternary of ODP Hole 1006A they apparently reflect an increase in the organic matter flux in the uppermost part of the section. The method described here can be applied to any species in any taxon for which percentage data are available. For those in the hydrocarbon industry it should prove especially useful for detailed studies of intervals of economic interest.

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