Anyone who studied biology, watched documentaries about nature or, in that regard, simply enjoyed the time spent outside, is probably amazed by the diversity of plant and animal life on our planet.
To date, about 1.5 million species have been formally described in scientific literature, and most are insects. Proportionally, bacteria making less than 1 percent of all species described.
Scientists generally agree that there are many more species than we have described but can not agree on what the numbers are about. Some studies have estimated that they have two million or less, while others mention numbers up to 12 million (one recent study suggested that the Earth could be home to a trillion species).
In a new paper published in The Journal of Biology scientists from the University of Arizona estimated that about 2 billion living species reside on Earth, a thousand times more than today's number of species described.
To reach this estimate, scientists have benefited from the fact that most estimates are consistent with the number of insects, about 6.8 million. They also included new estimates of boundaries between species detected by DNA sequencing, and found that six times more insects could be found, bringing the total to 40 million insects.
They then reviewed all groups of insect-related organisms, such as parasites and symbiotes. They found that each type of insect is likely to host a unique type of nests, obliques, monocular mushrooms Microsporidia or unicellular organisms Apicomplex protist (a cause of malaria in humans).
Most important, scientists have estimated that each insect species is likely to host at least 10 bacterial species that are not found elsewhere. Based on these estimates, they concluded that there are about two billion animal species on Earth.
The authors also suggest that the chart of taxa that contains the most species, or "Pita Life" (Pie of Life ) is quite different from traditional estimates. Rather than being dominated by insects, as they traditionally show, their estimates suggest that bacteria (70 to 90 percent of all species) dominate "pit" and insects (and other animals) take up much smaller part.