COMPARATIVE DEMOGRAPHY AND POPULATION-DYNAMICS OF 2 COEXISTING COPEPODS IN A VENEZUELAN FLOODPLAIN LAKE

I used an inverse matrix projection model to estimate vital rates (gro wth, survival, and reproduction) for two coexisting copepod species in a Venezuelan floodplain lake as a first step in identifying the ultim ate environmental factors that determine distribution and abundance of a species. Zooplankton were sampled four times a week from June throu gh December 1984, and the resulting abundance data were used together with the estimation technique to extract time series of vital rates ov er a 6-month period. There were marked temporal differences in populat ion maxima of each species. Abundance of Diaptomus negrensis fluctuate d with changes in recruitment and mortality of stages NV, NVI, CIII, a nd CIV. Peak abundance of D. negrensis coincided with a peak in the ab undance of the invertebrate predator Chaoborus sp. In contrast, popula tion size of Oithona amazonica was unrelated to recruitment but direct ly related to survival of the youngest copepodite stages, which was po or until October when abundance of Chaoborus declined. These demograph ic analyses target the stages most susceptible to environmental (selec tion) pressures, providing a basis for understanding the evolution of life-history strategies, and suggest the hypothesis (as yet untested) that prolonged coexistence is facilitated between species whose abunda nce is determined by different demographic (and thus environmental) fa ctors.