How many species exist on Earth right now?

The question is simple enough, but answering it, unfortunately, is virtually impossible. We don’t even have an exact estimate of how many plant and animal species currently exist, and when it comes to an estimate of Earth’s microbial diversity, scientists are pretty sure they’re not even in the ballpark.

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A team of researchers from the University of Chicago has now developed a model that estimates the number of undiscovered species living in a region based on the past rates of discovery and description of the species now known from that region. The model, described in a study published in the latest edition of the Proceedings of the National Academy of Sciences, is based on an extensive database of 5,744 marine bivalve species.

After poring over more than 62,000 records of where marine bivalve species are found, the researchers were able to establish patterns that they used to estimate their number living in 18 different geographic regions.

“This is the first time anyone has been able to predict in a robust, quantitative way the number of species that live in a specific region, and then rank those regions,” study co-author David Jablonski, a professor of geophysical sciences at the University of Chicago, said in a statement. “There's a huge range of biological questions where it helps to have a strong picture of where the most biodiverse places are, and how they compare to the less biodiverse places. We wanted to put some numbers on how reliable the differences among regions are.”

Bivalves are a class of mollusks (clams, oysters, mussels and scallops) that are characterized by the presence of a two-part hinged shell. The bodies of these animals are compressed and enclosed within the shells.

Using their database, the researchers created a model that suggested that for the foreseeable future, most of the newly-described species of bivalves would probably come from coastlines in the Indo-West Pacific region, which is already rich in bivalve diversity.

“Global distribution of bivalves, as well as extensive data on the living species, was critical. Bivalves have a long history of taxonomic study, which allowed us to demonstrate that the model’s predictions are accurate through the many different eras of species discovery,” study lead author Stewart Edie said in the statement. “We have a high level of confidence in the model and will continue to develop it so we can help to fill in gaps in our knowledge of biodiversity.”

Although this particular study focused on the global distribution of bivalve species, the researchers believe their model can be applied to any species.

“Nearly all groups, from palm trees to tortoises, have a documented record of where and when their species were discovered,” Edie said. “We can run those numbers through the model and predict how their biodiversity status will change, or not, with ongoing discoveries.”