Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and decline
Gerardo Ceballos, Paul R. Ehrlich, and Rodolfo Dirzo
Data: The scientists used a large data set of vertebrate populations (27,600 species and a more detailed data set of 177 mammal species from 1900 to 2015) to examine how the ranges of vertebrate animals have become smaller due to growing populations of humans that are pushing the animals out of their natural habitat. A lot of animals that are not considered endangered have experienced a huge decline in their numbers, indicating that animals all over the world are being IUCN Red List of Threatened Species. This data was was superimposed in a 22,000 grid of 10,000 km3 quadrats covering continental lands. A species was considered decreasing if their ranges (where that species lives) shrunk over time, or if there was a reduction in the number of species. This approach was also applied to 177 species of land mammals to see how their populations have changed through time.
Results: The scientists found that even in populations of animals that are not considered threatened, the rate of population loss is extremely high. In this study, 32% of the known vertebrate species are decreasing, meaning they have shrunk in population size and the ranges, or land in which they live. In the more detailed data set of 177 mammals, all of them have lost 30% or more of their ranges, and more than 40% of the mammal species have experienced severe population declines.
Why is this study important? This study uses a large data set of vertebrates to examine patterns of species through time to specifically assess how humans are impacting the ranges and populations of the animals. The current decline of species on Earth isn’t happening slowly; instead, it is happening at an accelerated rate. This study highlights the idea that Earth and all its creatures may be in the Sixth Mass Extinction, and remediation efforts are necessary and need to be enacted now in order to save animal populations.
The Big Picture: Humans are fundamentally changing the Earth and the animals that live on it. Through habitat destruction and expansion of housing and urban areas, to name just a few causes, we are taking habitats away from animals. Combined with climate change, the Earth’s animals are experiencing a biodiversity decline.
Citation: Ceballos, G., Ehrlich, P. R., and Dirzo, R., 2017. Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines. PNAS. DOI: 10.1073/pnas.1704949114