photo credit: Via Tsuji, “DODO (Raphus cucullatus)”
Life on earth is remarkably diverse. Globally, it is estimated that there are 8.7 million species living on our planet, excluding bacteria. Unfortunately, human activities are wiping out many species and it’s been known for some time that we are increasing the rate of species extinction. But just how dire is the situation? According to a new study, it’s 10 times worse than scientists previously thought with current extinction rates 1,000 times higher than natural background rates. The work has been published in Conservation Biology.
In order to determine how humanity is affecting the rate of species loss, we must first establish a background, or pre-human, extinction rate. It’s relatively straightforward to calculate recent rates of species extinction even though there is some uncertainty given there is a chance that a species is still alive despite not having been observed for a period of time. However, establishing background levels for comparison is a little trickier.
Previous estimates that relied on fossil data came up with a ballpark figure of 1 extinction per million species per year. While fossil data provides us with direct estimates of extinction rates, it is largely limited to hard-bodied organisms. Furthermore, it can sometimes be difficult to identify a fossil’s species, meaning they can only be assigned to a specific genus. However, the fossil record has been useful in demonstrating clearly that biodiversity has slowly increased over time.
In order to produce a more reliable estimate of the pre-human extinction rate, researchers based at Brown and Duke Universities went one step further than the fossil record and carried out phylogenetic analyses of numerous plant and animal species. Phylogenetics involves examining evolutionary relationships by comparing DNA sequences of different organisms.
After estimating average extinction estimates, the researchers also estimated the rates of speciation, or the formation of new species. This allowed the researchers to estimate rates of species diversification, which is the difference between speciation and extinction rates.
The researchers couldn’t find any evidence for recent or pre-human declines in diversity. In fact, the total number of species on Earth has either been steady or slightly increasing. This implies that average diversification rates are similar to or higher than average extinction rates.
Based on their results, the team concluded that the average pre-human extinction rate was0.1 extinction per million species per year. The current extinction rate is approximately 100 extinctions per million species per year, or 1,000 times higher than natural background rates. They also predict that future rates may be as much as 10,000 times higher.
“This reinforces the urgency to conserve what is left and try to reduce our impacts. It was very, very different before humans entered the scene,” lead author Jurriaan de Vos said in a news-release.
It is generally agreed that human activities, such as the destruction of habitats in order to accommodate our ever growing population, are largely responsible for this increase in species extinction rate. However, it’s also evident that conservation projects have been effective for some species. We need to continue with these efforts if we want to stand a chance in preventing this current crisis from worsening.