Evolution saves animals from “kill the winner” catastrophes

Computer simulations find evidence that a combination of competition, predation and evolution should push ecosystems to biodiversity in any part of the universe.

Environmentalists have long been pondering how different species of plankton competing for the same resources in marine ecosystems may experience such diversity.

At a meeting of the American community of naturalists in 1960, the famous British ecologist J. Evelyn Hutchinson described the " plankton paradox ." If we consider a flask of sea water, it will be filled with various representatives of plankton competing for the same vital elements and nutrients. At the same time, natural selection asserts that, over time, one ecological niche should take one form - this concept is known as the principle of competitive exclusion . What is true for plankton is true for many protozoa, plants, birds, fish, and other organisms. How can ecosystems have so many competing species in stable coexistence?

Since then, environmentalists have been thinking about this annoying paradox, but usually calm down, putting forward the “ kill the winner ” (KTW) hypothesis as a solution. It is based on the predator-prey relationship existing in the ecosystem that arises between certain species. When one species begins to squeeze out competitors, the growth of its population allows flourishing and predators eating it. Predators ultimately reduce the number of victims (hence the "kill the winner"). The combination of competition and predation allows several populations of warring species to coexist in equilibrium. The UE hypothesis has become a convenient explanation for biodiversity for many ecologists.


Nigel Goldenfeld and Chi Sue from the NASA Institute of Astrobiology and Universal Biology and the Gorky Institute of Biological Genomics. Karla Wose

When Nigel Goldenfeld, director of the NASA Institute of Astrobiology and Universal Biology, and Chi Sue, a graduate student in his laboratory at the Institute of Biological Genomics. Karl Wöse, began to study in more detail the UP-hypothesis in 2015, they were not going to refute it. They studied exactly which properties of life and ecosystems can be found everywhere in space. Biodiversity seemed like a good candidate for such a property. “If you look at the various isolated Earth’s ecosystems, you can find biodiversity everywhere,” said Sue. They wondered what could create and maintain this biodiversity, and whether similar factors would work on other planets.

But they found the unrealistic calculations that were commonly used in models to confirm the UE hypothesis. “They describe populations as if there are no separate individuals. It’s as if we were describing a liquid, disregarding atoms, ”Goldenfeld explained in the letter. Since these models allowed populations to recover even after the number of individuals fell to a few percent, they underestimated the likelihood of extinction. Goldenfeld and Sue called this problem the absence of “stochastic noise”, since the calculations do not reflect the mathematically random sequence disturbances imposed by the restriction of the real world.

Sue and Goldenfeld decided to re-do the models, giving them realism. “We did not expect the UE hypothesis to stop working,” said Sue. “We just wanted to see if something changes when you add noise.”

The results they described recently in the journal Physical Review Letters were disastrous. The numbers on biodiversity and coexistence of species did not just fall - they disappeared. "Essentially, all species are extinct," said Sue. In the repeated tests, the fluctuating populations of the victims constantly fell to zero, and then the predators died out due to lack of food. Sometimes the system degraded to a single pair of species, prey and predators, which existed for quite a long time, but these options were not always stable. There was no rich type of diversification inherent to nature.

But Sue and Goldenfeld took another step, incorporating something unaccounted for by previous simulations: evolution. They allowed victims to improve their ability to escape from predators, and predators to become better at catching prey.

As a result, the arms race unfolded, when the rising possibilities of preys and predators evolved in parallel, and that changed everything. This competition added species diversity to the system, and UE effects prevented the victory of one of the species. Biodiversity has flourished.

Sue and Goldenfeld see evidence of the dynamics of co-evolution in nature in genomics. "If you study the bacterium and find parts of the genome that are developing more quickly, then it turns out that these areas are associated with resistance to viruses," said Sue. As their UE-model of joint evolution indicates, the effect of natural selection in the field of resistance to viruses enhances another motivation — for example, it is better to compete with other bacteria.

But still this is not fully convincing evidence, and the researchers plan to carefully study the generalizability of their findings. They want to see what happens if the predators are less picky about the victims. Another topic to think about, says Goldenfeld, is that besides killing bacteria and other cells, viruses sometimes carry genes between them. This dual role - “predator and taxi driver for genes,” he said, could have serious consequences for the evolution and stability of ecosystems.

It is also unclear whether the UE model of co-evolution is applicable equally to all types of life. “In principle, the interaction of predators and preys is not limited to microorganisms. It goes everywhere, even hares and foxes, ”said Sue. But she also noted that their model suggests that evolutionary changes (mutations) and environmental changes (birth and death of organisms) occur on the same time scale and with approximately equal frequency. "For species such as hares and foxes, this is not true, but it is often found in microorganisms."

According to Jed Furman, a professor of biological sciences at the University of Southern California, modeling usually turns out to be a useful approach, but needs to be treated with caution. "Some assumptions and aspects are directly applicable to complex natural systems, and some are not." Because even microbial communities apply different strategies for survival, he said, “models may be applicable to some parts of the community more than others.”

But if the model demonstrates broad applicability, then, according to Goldenfeld, “it will show that there are very general approaches to obtaining diverse populations in an ecosystem, and that monocultures are the exception rather than the rule”. It can be expected that the evolution of life, even on other planets and moons, will lead to a variety of complex ecosystems. He said that one of the future directions of his laboratory’s work would be to study the “emergence of social metabolism” from various organisms, each of which processes materials in a general environment in its own way.


Saturn’s sixth largest satellite, Enceladus, is considered one of the most promising places in the solar system where extraterrestrial life could have developed. Streams of water make their way through cracks in its icy surface, indicating the presence of a vast ocean of water beneath the ice.

This idea can be useful for exploring the cosmos when we send probes in search of life in the oceans under the ice covering the surface of the moon of Jupiter, Europe, and the moon of Saturn, Enceladus. If there is life there, they will have to see the biochemical signs of whole ecosystems, rather than individual organisms.

According to Kevin Peter Hand, deputy project manager at NASA's Jet Propulsion Laboratory, tools being developed for probes traveling to Mars, Europe, Enceladus, and other potential shelters for life are already looking for signs related to ecosystems. He said that the proposed concept of a probe for Europe, on which he is working, is specifically designed to “take at least nine different, complementary measurements that do not respond to individual species”, for example, the complexity and chirality of organic compounds and the presence in the samples of structures resembling cellular.

But if astrobiologists cope with the question of the fundamental existence of extraterrestrial life and can begin to study how much the dynamics of alien ecosystems resemble the earth's, then knowledge of the solution of the plankton paradox can play a decisive role.