Population ecology of a colonizing species: The pelagic tunicate Thalia democratica

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Abstract
The salp Thalia democratica has one of the highest rates of population increase of any multicellular animal. Age distribution and survivorship were calculated for a natural population at sea, using serial size distributions and known age-length relationship. Methods were developed to estimate infinitesimal rate of population increase r, even though the birth-rate was highly periodic and the sampling period did not cover a full cycle of birth-rate. Values of r between 0.47 and 0.91 per day, indicate that this population was increasing by between 1.6 times and 2.5 times per day. Comparison of the salp with other organisms shows that its rate of population increase is close to the rates of increase of the algae and other micro-organisms on which it feeds. Examination of the factors contributing to high rate of increase in the salp, emphasize the ecological characteristics required in a colonizing species.