title: [Influence of temperature on the population dynamics of the rotifer Brachionus calyciflorus pallas].
abstract: Experiments were designed to test the influence of temperature on the life table data of the rotifer Brachionus calyciflorus Pallas. It is examined how well the observed modifications agree with theoretical models, and how they influence the temporal changes of population densities in limited and unlimited laboratory populations. On the basis of the experimental results, the population dynamics of planktonic rotifers in several natural habitats were analysed and interpreted. Laboratory Studies at 15, 20, and 25° C. 1. In individual cultures, the duration of all developmental stages (eggs, juvenils, adults) decreased with increasing temperature (Table 1, Fig. 1). On the other hand, the rate of reproduction was positively correlated with temperature. As a result of this twofold influence of temperature, the mean number of offspring per female shows an optimum at 20° C. 2. Unlimited populations which grew exponentially were characterised by a stable age distribution. Within the temperature range under study, the intrinsic rate of natural increase of unlimited populations rose with increasing temperature. 3. In populations limited by food supply, the mean population densities as well as the type and the intensity of oscillations was determined (Table 4, Figs. 2-5). Egg ratios and proportions of immature animals were also determined. Highest mean population densities occured at low temperatures, highest maximum densities at high temperatures. The latter fact is the result of stronger oscillations at higher temperatures: at 15° C oscillations were damped, at 20° C permanent or just increasing (no extinction within 60 days), at 25° C clearly increasing (extinction within 30 days). Amplitude and frequence of the oscillations were positively correlated with temperature. 4. The optima for the population growth and abundance were apparently not at the same temperature (Table 4). 5. The mictic rate, measured as the proportion of sexual females in the population, was relatively small; in limited populations it was larger than in unlimited populations. Temperature had a positive influence at high population densities. Test of Population Models. 1. Using life table data of individuals, theoretical predictions about the growth rate and the age structure of populations during exponential growth have been made by several authors. It is shown that at all temperatures the predictive power of the well known demographic model of Lotka is about as good as that of a recent model by Edmondson (Table 2). It is suggested that both models give adequate causal descriptions of exponential growth inspite of their manifold and different simplifications. As a consequence it is concluded that the observed influences of temperature on exponential growth are the result of direct influences of temperature on the life table data. 2. When mean population densities were estimated by theoretical calculations of energy balance, a rather good agreement with the empirical data was found. 3. Determination of the animal's food efficiencies on the basis of the observed production of biomass suggest that the coefficient of efficiency is significantly larger at 15° C (37%) than at 20 and 25° C (27 and 28%, resp.). 4. According to Cook and to Ricker, the mean generation length T permits predictions about type and frequency of the oscillations. When T was calculated from the life table data, the predictions about the oscillations were in fairly good agreement with the results on limited populations. The meaning of the parameter T in species with overlapping generations is discussed. Field Observations. During 1967 measurements of temperature and population densities of Brachionus calyciflorus were carried out in 15 artificial basins (0.3-50 m3) and 7 ponds (Figs. 6-8). An analysis of these data gave the following results: 1. During sudden population explosions, the growth rates were, on the average, positively correlated with environmental temperature. The agreement with laboratory data is quite good (Fig. 9). It is concluded, that temperature co-determines this aspect of population dynamics in the field. 2. The largest maxima of population densities were found at 20-28° C. With about 105individuals/liter they are in the same order of magnitude as the corresponding data of laboratory populations. Average population densities seem to be independent of temperature within the range of 12-28° C; outside this range they appear to decrease (Fig. 10). Average densities in the field were clearly lower (10-102individuals/liter) than long-term means of population densities in experimental populations (about 104-105individuals/liter). 3. Fluctuations were stronger at high than at low temperatures. The degree of temperature dependence is about the same in the laboratory and in the field. However, at all temperatures the absolute values were greater in the field than in laboratory populations of the same temperature (Fig. 11). Modifying influences of biotic factors (phytoplankton, competitors, predators) are discussed.
authors.affiliation: Zoologisches Institut der Universität München, München, Deutschland.
authors.forename: Udo
authors.initials: U
authors.lastname: Halbach