Ref ID : 6627
Andrea Pasteris, Giuliano Bonomi, and Carla Bonacina; Age, stage and size structure as population state variables for Tubifex tubifex (Oligochaeta, Tubificidae). Hydrobiologia 334:125-132, 1996
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Age based demography is not applicable to tubificid worms, because of the lack of any reliable method for assessing the age of individuals. 'Stage', namely the degree of reproductive development, and/or size could be used instead of age, if that knowledge improved prediction of an individual's fate and fecundity. We measured, under laboratory conditions, the influence of age, size, and maturation stage on the fate and fecundity of individuals, by means of a modification of the standard cohort experiment. As expected all of the three state variables significantly affect the fecundity, though the residual variance is considerable. As a first step in the evaluation of the effectiveness of a size and/or stage based demography for tubificids, the results are used to establish a size-stage structure matrix population model. The asymptotic behaviour of the model is studied and a basic sensitivity analysis is performed, to evaluate the effects of the observed variability of the matrix elements, on the eventual finite growth rate.