Comparative Demography of Forest Floor Collembola Populations

Populations of two Collembola species, occurring in a coniferous forest in the Netherlands, were studied by quantitative analysis of bi-weekly changes in the frequency distribution of body lengths over one and a half year. The data revealed a succession of two generations per year for both species; each generation was analysed separately, by applying an improved version of a model presented previously. The jack-knife procedure was used to estimate confidence limits for demographic parameters. By temperature-dependent time-scale transformation the moulting frequencies of both species were adjusted to a constant value pertaining to 15?C. All demographic analysis used physiological time. Juvenile survivorship was estimated as 0.7% to 6.9% and was highest in the spring generations. The autumn generations showed persistent body growth and delayed reproduction. The main difference between the species concerned higher fertility and higher mortality (thus higher population turnover) in the species Orchesella cincta, compared with Tomocerus minor; this difference was interpreted in the light of the physiological and behavioural ecology of the species. The crucial point seems to be a more superficial and active way of life of 0. cincta, which on the one hand increases its risk of being preyed upon, but on the other hand allows a more effective reproduction. Life history patterns in Collembola seem to follow a trend similar to that in earthworms.