ECOLOGICAL TIME VERSUS STANDARD CLOCK TIME - THE ASYMMETRY OF PHENOLOGIES AND THE LIFE-HISTORY STRATEGIES OF SOME SOIL ARTHROPODS FROM MEDITERRANEAN ECOSYSTEMS

A model is formulated aiming to describe census data for populations changing non-symmetrically with time. The model is based on the concept of ecological time. conceived as an environmental gradient. A method of changing time scales, by using a periodic equation relating ecological to standard clock time unit, is presented. The model has been applied to simulate phenological curves of population abundance for oribatid mites and Collembola from a Mediterranean ecosystem. The concept of ''phase difference continuum'' is introduced and the life history strategies of oribatids and Collembola are discussed. Asymmetries as well as synchronizations in population development, annual periodicity and inter-annual stability, are common features for almost all populations studied, summer drought being the adverse period for the majority of them. Precocity, iteroparity and high rate of juvenile development into successive stages during the favourable period, hold for all phenological patterns. Adults' demographic parameters and the animals' ability for altering their physiological status are the characteristics discriminating between various strategies. Most Collembola display left-skewed phenology, while most oribatids display a right-skewed one.