Abstract:
The percent carrying capacity K (sub p) 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 p (sub it) is the percentage abundance of the ith species at time t. The percentage point change in abundance of a species Delta p (sub i) between two samples is given by Delta p (sub i) =p (sub it+1) -p (sub it) , where p (sub it+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 r (sub t) , is given by r (sub t) =Delta p (sub i) /p (sub it) . Linear regression of r (sub t) against p (sub it) gives r (sub t) =r (sub m) -s.p (sub it) , in which the constant r (sub m) is the rate of increase in r (sub t) where p (sub it) approaches zero, and the negative slope s represents the combined strength of intraspecific, interspecific and abiotic interactions for the species investigated. Setting r (sub t) =0, so that p (sub it) =K (sub p) and r (sub m) -s.K (sub p) =0, gives K (sub p) =r (sub m) /s. The Upper Quaternary of ODP 1006A contains two subsections with rich bathyal benthic foraminiferal assemblages separated by samples yielding few specimens. Values of r (sub m) , s and K (sub p) 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 r (sub m) and s. The rate of change of the percentage abundance for each percent r (sub t) , 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 r (sub m) 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 K (sub p) 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. Abstract Copyright (2012) Elsevier, B.V.