PREDATOR PREY SERIES
They ran several trials and produced time series representing a total of about 2000 measurement days. The researchers observed the two populations over a period of approximately one year, which corresponded to more than 50 oscillations and about 300 generations of rotifers. As in other predator-prey relationships, a constant cycle was established: algae numbers fluctuated over a period of 6.7 days, as did rotifer numbers but with a time lag of about 40 hours. In the experiments, which were carried out at the University of Potsdam, the rotifers were the predators and the green algae the prey. This system allowed the researchers to define continuous external conditions, for example a constant amount of nutrients for the algae. To clarify this question, Blasius and his colleagues from the University of Potsdam and McGill University in Canada brought together Brachionus calyciflorus, a planktonic rotifer species that occurs in fresh water, and unicellular green algae in experimental containers. This led to the assumption that in real life, predator-prey cycles do not last on their own over extended periods of time, but are driven by an external factor, for example seasonal fluctuations in the food supply. In previous experiments, however, one of the two species died out after a few oscillations or the oscillations gradually disappeared. But the question of how long these cyclical fluctuations last in real-life communities had not been clarified: in field conditions, such oscillations frequently extend over a period of several years, so biologists have mainly relied on experiments with short-lived species. To predict such oscillations, scientists use simple mathematical models according to which populations of predator and prey species can theoretically coexist indefinitely. This in turn leads to a rapid increase in the prey population and a new cycle begins. Soon afterwards, predator numbers likewise decrease due to starvation. Predator-prey cycles are based on a feeding relationship between two species: if the prey species rapidly multiplies, soon afterwards the number of predators increases - until the predators eventually eat so many prey that the prey population goes down again. "Our experiments confirm the theoretical concept of self-generated predator-prey cycles," says lead author Blasius, who heads the Mathematical Modelling group at the University of Oldenburg's Institute for Chemistry and Biology of the Marine Environment (ICBM). In an article published in the current issue of the scientific journal Nature, the researchers report that although there were brief periods when the regular oscillations in the two populations were interrupted by random swings, they always returned to their normal rhythm on their own. Bernd Blasius from the University of Oldenburg, Germany, observed these oscillations in rotifer and unicellular algae populations across 50 cycles - a record period of time for this kind of study. In a long-term experiment, an international team of researchers led by Prof. Predator-prey cycles are among the fundamental phenomena of ecological systems: the population sizes of predators and their prey, for instance foxes and hares, are frequently subject to regular oscillations. view moreĬredit: Guntram Weithoff/ University of Potsdam The research also sheds light on how such cycles can persist.
Bernd Blasius from the University of Oldenburg, Germany, observed these oscillations across 50 cycles - a record period of time for this kind of study. In a long-term experiment with the planktonic freshwater rotifer Brachionus calyciflorus and unicellular algal populations, an international team of researchers led by Prof. Image: Predator-prey cycles are among the fundamental phenomena of ecological systems.
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