Einflu� der Temperatur auf die Populationsdynamik des planktischen R�dertieres 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 th...

The effect of temperature on life history parameters and cost of reproduction in the rotiferBrachionus calyciflorus

“…Typically, there is a strong positive relationship between the R o and the total number of offspring produced; however, here we notice a consistent weakening of this relationship as we approach lower temperatures. This can be explained by a flattening of the fecundity curve with a decrease of temperature, as observed in our study as well as that of others (Halbach 1970;Snell and King 1977;Xi et al 2005).…”

“…Therefore, much like the work of Snell and King (1977) on the carnivorous rotifer A. brightwelli, our study was designed to explore a number of life history parameters in relation to the cost of reproduction in the rotifer Brachionus calyciflorus at different temperatures. In addition to similar temperaturebased longevity studies using B. calyciflorus in which limited numbers of life history parameters were examined (Halbach 1970;Xi et al 2005), the detailed analysis of interrelationships between the longevity and fecundity described here could provide impetus to future studies that might explore the molecular mechanisms underlying such relationships.…”

The dynamics of food chains under climate change and nutrient enrichment

“…There are, however, cases where warming destabilizes population dynamics. Warming increased population oscillations of the rotifer Brachionus calyciflorus [36] and also induced the development of defensive spines [37]. Inducible defences thus might attenuate not only the detrimental effects of enrichment [33,35] but also the effects of temperature we found.…”

Disrupted seasonal clockwork in the population dynamics of a freshwater copepod by climate warming

“…These studies demonstrate that increasing temperature within the tolerance range of a species accelerates both growth and developmental rates of individual organisms given sufficient resources. Changes in these vital parameters caused by elevated temperature ultimately affect population dynamics (McCauley and Murdoch 1987) and have the potential to generate a shift from stable to more fluctuating dynamics (Halbach 1970;Beisner et al 1997). Larger-amplitude cycles further increase the likelihood of extinction because of stochastic processes, as the population trajectory approaches zero density more closely and more often (Murdoch and McCauley 1985).…”