Life Table Data and Population Dynamics of the Rotifer Brachionus calyciflorus Pallas as Influenced by Periodically Oscillating Temperature

Abstract

The life table data and the population dynamics of Brachionus calyciflorus are influenced by a number of abiotic and biotic factors (Halbach, 1969a, b, 1970, 1972). Under constant environmental conditions in a limited system (constant volume and constant daily dose of food) rotifers have very characteristic population dynamics as demonstrated schematically in Fig. 1. After a phase of exponential growth, oscillations are observed around an average density, which is determined by food quantity. The curve is characterized by three parameters: the intrinsic rate of natural increase r, the carrying capacity K and the duration of one period λ, which is the reciprocal of the frequency. The oscillations are caused by the time lag between food uptake and the resulting production of offspring. The lag leads to primary overshoot and subsequent oscillations. Amplitudes and frequencies of these population curves are drastically affected by temperature (Fig. 2): the fluctuations are more pronounced at high than at low temperatures. The carrying capacity decreases with increasing temperature, whereas the intrinsic rate of increase as well as the frequency of oscillations grow with increasing temperature (Table 1). These differences in the population dynamics are mainly due to changes in the duration of life and in fertility (Fig. 3): both life expectancy and immaturation time are reduced at increased temperatures. Fertility increases with increasing temperature, but the duration of the fertile phase becomes shorter.