(ORDO NEWS) — One of the global environmental problems is the reduction of plant biodiversity, that is, the species richness of ecosystems. A new study has shown that it is determined not by the extinction of individual species, but by the spread of invasive (that is, alien) plants outside their natural ranges.
The Anthropocene is a vanishingly short period of human dominance on Earth, by geological standards, which is accompanied by a sharp decrease in species diversity and a change in the ranges of various organisms.
They lead to the homogenization of plant communities, that is, the gradual erasure of differences between them. As a result, neighboring or even distant ecosystems differ less and less from each other in terms of species composition.
Its authors are an international group of researchers led by Barnabas Daru from Texas A&M University (USA). Scientists used a massive dataset of the distribution of more than 200,000 plant species and confirmed a widespread decline in biodiversity.
Biologists note that land biomes (the so-called set of similar ecosystems occupying large territories) have already undergone strong homogenization, and biological invasions should be considered its main reason.
If some species – be it plants, animals or other organisms – fell outside their natural range, then they are called alien or adventitious. If they were also able to naturalize in a new territory and turned out to be a threat to the stability of local ecosystems, then such species are considered invasive.
Massive plant invasions began in the 16th century, after the voyage of Columbus and the beginning of regular communication between the Old and New Worlds. This is natural, because trade and economic activity were accompanied by the active spread of species (including agricultural crops) far beyond their natural ranges.
The authors of the new study decided to test the so-called naturalization hypothesis of Darwin, which the great biologist expressed back in 1859. It is curious that in recent years many articles have been devoted to it.
According to this hypothesis, alien organisms are more successfully integrated into new communities if they have few related species in them. However, new results refute Darwin’s assumption: the relationship of species does not affect the success of the invasion.
It follows from the calculations that plant invasions have a much greater effect on local plant communities than the extinction of individual species: they affected 4.9% and 0.5% of the 200 thousand species considered, respectively. At the same time, both scientists and journalists traditionally pay more attention to extinctions.
Invasive species can start an invasion from any territory, but Asia and North America turned out to be their main “hotbeds”. Meanwhile, Australia and Oceania, as well as Europe, are the suppliers of a few invasive plants representing systematic groups that are uncharacteristic of new habitats.
It also follows from the article that North America (especially California and Florida), Central America, the Amazon, the Himalayas and adjacent territories, Southeast Asia, as well as the southwestern part of the Australian continent, were most affected by the decline in biodiversity.
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