Revealed a universal pattern of species abundance

2023-09-04 17:19:58

The Sri Lankan hanging parrot (Loriculus beryllinus) lives only in Sri Lanka. It is a very rare species worldwide, which means that there are few individuals. -COREY CALLAGHAN

MADRID, 4 Sep. (EUROPA PRESS) –

More than 100 years of observations in nature have revealed a universal pattern of species abundance: most are rare but not very rare, and only a few species are very common.

These so-called global species abundance distributions have been fully revealed for some well-monitored species groups, such as birds. However, for other groups of species, such as insects, the veil remains partially raised.

These are the findings of an international team of researchers led by the German Center for Integrative Biodiversity Research (iDiv), Martin Luther University Halle-Wittenberg (MLU) and the University of Florida (UF), published in the journal Nature. Ecology and Evolution. The study demonstrates the importance of monitoring biodiversity to detect the abundance of species on planet Earth and understand how they change.

“Who can explain why one species is widely distributed and very numerous, and why another allied species is limited in distribution and rare?” This question was asked by Charles Darwin in his groundbreaking book “On the Origin of Species,” published over 150 years ago. A related challenge has been understanding how many species are common (numerous) and how many are rare, the so-called global species abundance distribution (gSAD).

Two main models of gSAD have been proposed in the last century: RA Fisher, a statistician and biologist, proposed that most species are very rare and that the number of species decreases for more common species (so-called log series model) . On the other hand, FW Preston, an engineer and ecologist, argued that only a few species are actually very rare and that most species have some intermediate level of commonality (the so-called log-normal model). However, until now and despite decades of research, scientists did not know which model describes the true gSAD of the planet.

Solving this problem requires large amounts of data. The study authors used data from the Global Biodiversity Information Facility (GBIF) and downloaded data representing more than 1 billion observations of species in the wild from 1900 to 2019.

“The GBIF database is an incredible resource for all types of biodiversity-related research, particularly as it brings together data collected from professional and citizen scientists around the world,” he says. it’s a statement first author, Dr. Corey Callaghan. He started the study while working at iDiv and MLU and now works at UF.

Callaghan and his fellow researchers divided the downloaded data into 39 species groups, for example, birds, insects or mammals. For each, they compiled the respective global species abundance distribution (gSAD).

The researchers detected a potentially universal pattern, which emerges once the abundance distribution of species is fully revealed: most species are rare but not very rare, and only a few species are very common, as predicted in the log-normal model. However, the researchers also found that the veil has been fully lifted for only a few groups of species, such as cycads and birds. For all other species groups, the data is still insufficient.

“If you don’t have enough data, it seems that most species are very rare,” says lead author Professor Henrique Pereira, head of the iDiv and MLU research group.

“But as you add more and more observations, the picture changes. You start to see that there are, in fact, more rare species than very rare species. You can see this change for cycads and birds by comparing observations of species since 1900. When less data was available, with the more comprehensive species observations we have today, it’s fascinating: we can clearly see the phenomenon of revealing the full distribution of species abundance, as predicted by Preston decades ago, but only now being demonstrated on a planetary scale.”

“Although we’ve been recording observations for decades, we’ve only lifted the veil for a few groups of species,” Callaghan says. “We still have a long way to go, but for me GBIF and data exchange They truly represent the future of biodiversity research and monitoring.”

The findings of the new study allow scientists to assess the extent to which gSADs have been revealed for different groups of species. This allows answering another long-standing research question: How many species are there? This study finds that while for some groups such as birds almost all species have been identified, this is not the case for other taxa such as insects and cephalopods.

The researchers believe their findings may help answer Darwin’s question as to why some species are rare and others common. The universal pattern they found may point to general ecological or evolutionary mechanisms that govern how common and rare a species is.