The city of Manila holds the human world record for the most densely
populated space and now an international team of ecologists are seeking
the natural equivalent, the most species rich area on earth. The team’s
findings, published in the Journal
of Vegetation Science, reveal the record is contested between
South America’s tropical rainforests and Central European meadows.
“The coexistence of large numbers of species in one space and the
questions it raises have long fascinated ecologists,” said Professor
Bastow Wilson, from the University of Otago, New Zealand. “For example
it’s a core ecological principle that two species occupying the same
niche cannot co-exist long-term, so how can 942 plant species co-exist
in one hectare of tropical rainforest?”
While tropical rainforests of South America and Central Africa are often
believed to be the most species rich areas on Earth, Professor Wilson’s
team sought to establish if this is true, especially if smaller spatial
scales are analysed.
"We surveyed the global literature to find records of plant species
richness at scales from 1 mm² up to 1 hectare. Above 50 m², all the
maximum values were from tropical rainforests in Costa Rica, Columbia or
Ecuador,” said Wilson. “However, looking at smaller scales we have found
that long-grazed or mown grasslands are the most species rich places on
Earth.”
These very rich grasslands were found in the eastern half of Europe,
from the German border through to Romania, although two examples were
also found in Argentina. Most were over limestone, and two were from
wooded meadow, a landscape once common over northern Europe but now very
rare.
Using these data the team asked if there is a theoretical maximum for
the number of species which can co-exist in one area. They extrapolated
the relationship up to 1 hectare, predicting the number of plant species
over the whole earth.
“Any scientific hypothesis should be tested in a new situation, and the
strongest test is extrapolation, even if school teachers warn their
pupils not to do it,” concluded Wilson. “This left us with a predicted
number of 219,204 species, remarkably close to the latest estimate of
the world’s vascular flora at 275,000 species.”
