Researchers from WUR (and colleagues from elsewhere) demonstrate this in a study in PNAS. According to Egbert van Nes, Marten Scheffer (Aquatic Ecology) and co-authors, rarity is a ‘sticky condition’. That is, a rare species does not simply escape its situation.
It is the same in nature as elsewhere: everything is unevenly distributed. There are many specimens of some species and very few of many species. To start with, the researchers mapped out how few species account for half of the biomass for numerous organisms. That turns out to be only a few percent of all species.
Hyperdominant
‘This not only applies to the trees in the Amazon,’ says Scheffer, ‘but also to the bacteria in our intestines, the mushrooms in the forest, the birds, the plankton and so on. A few species are hyperdominant, the rest are rare.’ But why is that? Are the dominant species superior? No, that is not necessary, say Scheffer and his team. A simple mathematical model shows that rarity and dominance are inevitable, even if all species are equally competitive.
It is not necessarily the ‘most adapted’ species that occupies a vacant spot
Marten Scheffer, professor of Aquatic Ecology and Water Quality Management
Coincidence plays a major role in this. According to the model, today’s dominant species may be an ‘accidental elite’. That dominance can also disappear again, if circumstances force it to do so. “It is not necessarily the ‘most adapted’ species that occupies a vacant spot,” says Scheffer, “but an accidental species within the group of species that perform the same function in the ecosystem.”
According to Scheffer, there is also evidence for the latter. ‘For organisms that we can follow for hundreds of generations, such as bacteria and plankton, you see this change of dominance happen every now and then. This evidence is lacking for other organisms due to a lack of data from long-term time series.’
According to the researchers, this change of penny also shows the importance of rare species. They form the reserve bank, in case the need arises and a replacement has to enter the field to take over the function of a dominant species. ‘So they are not superfluous, all those rare species,’ says Scheffer. ‘Rare species ensure stability in the functioning of the community.’
Lotka-Volterra
According to Scheffer, the great thing is that this results from perhaps the best-known and most accepted model in biology, the Lotka-Volterra equation. All you need to add is a pinch of serendipity, which affects different species differently. No one had noticed that in the past century since that comparison was drawn up.’
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2024-01-19 08:38:13
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