Although the article does not explain precisely why the weakest of three species in a cyclical hierarchy, it is an interesting read nevertheless. It compares the process to the rock, paper, scissors game where each species has at least one advantage over the other.
LMU researchers have now simulated the progression of a cyclic competition of three species. It means that each participant is superior to one other species, but will be beaten by a third interaction partner. “In this kind of cyclical concurrence, the weakest species proves the winner almost without exception,” reports Professor Erwin Frey, who headed the study. “The two stronger species, on the other hand, die out, as experiments with bacteria have already shown. Our results are not only a big surprise, they are important to our understanding of evolution of ecosystems and the development of new strategies for the protection of species.”
“Such cyclical interaction is also familiarly termed “rock-paper-scissors” interaction. This is where the rock blunts the scissors, which cut the paper, which in turn wraps around the rock. Together, these non-hierarchical relationships form a cyclical motion. “The game can help describe the diversity of species,” explains Frey. “The background is a branch of mathematics called game theory, and in this case evolutionary game theory. It helps analyze systems that involve multiple actors whose interactions are similar to those in parlor games.”
“This “law of the weakest” even held true when the difference between the competing species was slight. “This result was just as unexpected for us,” reports Frey. “But it shows once more that chance plays a big part in the dynamics of an ecosystem. Incidentally, in experiments that were conducted a couple of years ago on bacterial colonies, in order to study cyclical competition, there was one clear result: The weakest of the three species emerged victorious from the competition.