Earth has experienced five mass extinctions in the past and scientists now believe that the planet is experiencing a sixth mass extinction, this one primarily attributed to human activity. The last time that the Earth experienced such high rates of biodiversity loss in a relatively short time period was at the end of the Cretaceous period, 65 million years ago, when most dinosaurs went extinct (Wake and Vredenburg 2008). Biodiversity loss, in turn, compromises ecosystem functioning, resilience, and stability, which negatively impacts the ecosystem services that human communities depend on (Cleland 2012).
There are estimated to be anywhere from 6 to 15 million species on Earth, excluding microbes, of which about 1.5 million have been identified. New species continue to be discovered every year all over the world; for example, more than 350 new species, including many new insects, were found in the remote rainforests of Borneo from 1999 to 2004 (Pimm et al. 2008). Often, these new discoveries are of species that are endemic to a specific geographic area, meaning that they are found nowhere else (Swenson et al. 2012).
Of the 1.5 million species that have been identified, the International Union for the Conservation of Nature (IUCN) assessed more than 63,000 for vulnerability and risk of extinction for its 2012 Red List of Threatened Species. Among those assessed, the IUCN has classified species into eight different categories: data deficient, least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild, and extinct. A species is recognized as threatened with extinction if it falls into the vulnerable, endangered, or critically endangered categories. Among all the species that were assessed, IUCN estimates that:
• Almost one third are at risk of extinction
• One in four of the world’s mammal species is vulnerable, endangered, or critically endangered
• More than one third of amphibian species are threatened with extinction
• One in three coral species is at risk of extinction
• One in eight bird species is threatened with extinction (IUCN 2012a)
Terrestrial ecosystems, including forests, savannas, and grasslands, support 80% of identified species. It is estimated that about half of the planet’s land surface has already been altered through human activity, with profound impacts on biodiversity (Chivian and Bernstein 2008, Grosberg et al. 2012).Read more
Marine ecosystems are still relatively unexplored compared with terrestrial systems; along with freshwater systems, they are estimated to support about 20% of all known species. About half of the global population lives within 60 km of a coastal area, making these areas some of the most degraded of all marine ecosystems (Chivian and Bernstein 2008, Grosberg et al. 2012).Read more
Freshwater ecosystems cover less than 1% of the planet’s total surface area but are relatively rich in biodiversity, with high rates of endemism. These ecosystems are currently the most threatened globally, with biodiversity loss among freshwater species occurring faster than among terrestrial and marine species (Chivian and Bernstein 2008, Strayer and Dudgeon 2010).Read more