A new assessment conducted by 174 scientists from around the world underscores a growing concern about the health of the world's biodiversity, quantifying the rate of decline among vertebrate species on a global scale for the first time. The team's results support the idea that our planet is currently experiencing its sixth mass extinction—nearly one fifth of all known vertebrate species are currently classified as Threatened on the International Union for the Conservation of Nature (IUCN) Red List, and an average of 52 species of mammals, birds, and amphibians move one category closer to extinction each year. The team, which includes California Academy of Sciences mammalogist Dr. Galen Rathbun, notes that over the past four decades, species extinction rates have exceeded normal background rates by two to three orders of magnitude. However, the team reports that species losses and declines would have been 20% worse in the absence of conservation efforts to protect threatened species. Thus, while current conservation efforts remain insufficient to offset the main drivers of biodiversity loss—including habitat loss, over-exploitation, and invasive alien species—targeted conservation efforts have had a measurable positive impact on the planet's vertebrate species. The research is reported in the October 26 issue of Science Express, the website for the journal Science (publication in the print version of Science will follow at a later date).
The study used data for 25,000 species from The IUCN Red List of Threatened Species™ to investigate the status of the world's vertebrates (mammals, birds, amphibians, reptiles and fishes) and how this status has changed over time. Their results indicate that approximately 20% of the worlds vertebrates are currently classified as Threatened (assigned the IUCN Red List status of Critically Endangered, Endangered, or Vulnerable), including 25% of all mammals, 13% of birds, 22% of reptiles, 41% of amphibians, 33% of cartilaginous fishes, and 15% of bony fishes. While vertebrates comprise just 3% of the known species on Earth, they play vital roles in their ecosystems and have great cultural and economic significance for humans. The new report demonstrates that these species continue to decline at an alarming rate, particularly in tropical areas. Global patterns of rising extinction risk are most marked in Southeast Asia, where agricultural expansion, logging, and hunting are the primary forces behind accelerating extinction rates.
California Academy of Sciences mammalogist Dr. Galen Rathbun contributed data to the report on the status of the members of the Afrotheria supercohort, an ancient group of African mammals that includes elephants, sea cows, hyraxes, sengis (also known as elephant-shrews), tenrecs, golden moles and aardvarks. Of the 83 species currently recognized in this supercohort, 30 are considered Threatened, and an additional eight species are considered data deficient—these species are quite possibly threatened, but scientists don't know enough about their distribution to be able to assign them a status. Therefore, somewhere between 36% and 46% of the world's Afrotheria species are currently threatened with extinction.
The Afrotheria supercohort represents one of the world's major mammalian evolutionary radiations. By one count, the seven groups that make up the Afrotheria represent nearly a third of all the living orders of mammals. However, the number of species within this supercohort is relatively low, totaling only about 1.5% of the world's mammals. This means that with relatively few species extinctions, entire groups of afrotherian mammals would cease to exist, thus terminating over 100 million years of evolution in Africa and drastically reducing that region's biodiversity.
"Almost any loss within the Afrotheria supercohort would be profound in terms of its evolutionary significance, because the members of this group carry such unique genes," says Rathbun. "Like many other groups, the afrotherian mammals are threatened predominantly by habitat loss and habitat degradation. For instance, all four of the forest-dwelling sengis are threatened with extinction, because the forests in Africa are rapidly disappearing."
The gray-faced sengi (Rhynchocyon udzungwensis) is known to exist in only two populations that cover about 300 square kilometers (115 square miles) of forest in Tanzania, in the Udzungwa Mountains. It was described in 2008 by California Academy of Sciences mammalogists Dr. Galen Rathbun. This charismatic mammal is just one of many species in need of protection in the Udzungwa Mountains, which serve as an important dry-season refuge for many animals from adjacent areas. A recent survey suggests that the few remaining wildlife corridors linking the mountains to surrounding protected areas are critically threatened, and will be lost imminently without intervention.
(Photo Credit: California Academy of Sciences)
While habitat loss and degradation are the primary drivers of rising extinction rates around the world, they are not the only culprits. The study authors noted several new threats that have emerged in recent years, including the use of a veterinary drug called diclofenac, an anti-inflammatory drug similar to ibuprofen that was introduced to the veterinary market on the Indian subcontinent in the early 1990s. While cattle can tolerate high doses of the drug, it soon became apparent that Asian vultures cannot—shortly after feeding on dead livestock treated with diclofenac, the birds die from renal failure. Since 1992, the population of Oriental White-backed Vultures has declined by more than 99%.
Based on the current trends, scientists estimate that the Oriental White-backed Vulture will be extinct in the wild in less than a decade. The only hope for the bird's survival is to establish an aggressive captive breeding program, which would enable scientists to reintroduce vultures to the wild once diclofenac is no longer in use. California Academy of Sciences ornithologist Dr. David Mindell has been studying genetic diversity in current and historical Oriental White-backed Vulture populations to help guide these captive breeding efforts and assess species status of the bird's closest relatives. His research has provided a clear course of action for ensuring that this species survives with a healthy, diverse gene pool.
Captive breeding programs are just one of the conservation strategies that are helping to mitigate species extinctions. The study authors also found evidence of notable conservation successes through legislation to limit hunting, establishment of new protected areas, and efforts to remove invasive alien species.
"The stark reality of accelerating species losses can lead to a feeling of hopelessness," says Mindell, Dean of Science at the California Academy of Sciences. "However, the IUCN data analyzed in this assessment show that concerted efforts by biologists and conservationists can make a positive difference in slowing rates of endangerment. Hopefully, these findings will bolster existing efforts at conservation—and spawn new initiatives as well."
Source: California Academy of Sciences