Document: DEB-3-39-14

Density dependence in per-capita rates of population growth.

OVERATH, R.D.* ¹, N.L.FOWLER ¹ and C.M.PEASE ²

University of Texas, Austin, TX 78712, U.S.A ¹
Vermont Law School, S. Royalton, VT U.S.A. ²

Abstract:
Intra-specific density dependence in natural plant populations can be tested by manipulating density and measuring effects on demographic parameters such as survival rate. What are the relationships between such results and effective population regulation? To answer this question, we calculated rates of per-capita population growth () in a population whose demographic parameters have been shown to respond to density manipulations. Size-based population projection matrices were calculated for each of 24 plots (4 treatments by 6 replicate plots each). Three measures of per-capita 'population' growth were calculated for each plot in each of three annual intervals: the principal eigenvalue (LAMBDA_potential), the observed rate of 'population' growth (_observed), and a predicted rate of 'population' growth based upon the previous years' demographic parameters and size structure (_predicted). Negative density dependence was sporadic, as it was in the underlying demographic parameters. However, negative density dependence was more apparent in the values of LAMBDA than it was in the underlying demographic parameters, especially if the measure of density was total number of tillers (an estimate of conspecific biomass) not total number of conspecific individuals in the plot. Another common method of detecting density dependence is analyzing temporal sequences of population sizes. This was done with the six control plots using data from 14 sequential annual intervals. Three of the six plots had evidence of negative density dependence in these sequences.

Keywords: density dependence, population growth rate, population projection matrix

This abstract is being presented at: 10:30 AM in session:
PLANT DEMOGRAPHY