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Extinction of species

The loss of all individuals belonging to a single species is an irreversible process called extinction. Once the last member of a given species dies, it disappears forever from the face of the earth.

Over time, there have been species that have become extinct, as there have been species that appeared through evolution and the processes associated with natural selection. Life on Earth originated about 3,500 million years ago. It is estimated that since then, 99% of the species that have emerged have become extinct naturally.

The best known case of extinction is that of the dinosaurs. About 65 million years ago, towards the end of the Cretaceous period, a large meteorite struck the Earth north of the Yucatan Peninsula in Mexico, creating a crater of an extraordinary size. Scientists have developed the hypothesis that this impact was the main factor leading to the Cretaceous-Tertiary mass extinction event, which resulted in the end of the dinosaur era and the loss of about 75% of all existing species at that time. Throughout the history of the Earth, there have been a total of five mass extinctions, during which a very large number of species disappeared, the Cretaceous-Tertiary being the latest among them.

In more recent times, during the Pleistocene glaciations (the so-called ice ages), many species also became extinct, including the mammoth, the giant Irish deer, the woolly rhinoceros, and the cave bear. These species disappeared when they were no longer able to survive against other competitors (including humans who became devoted to intensive hunting), or changing environmental conditions caused by variations in climate, among other things. It is estimated that, on average, a species disappears after some 10 million years, although there are species that reach a hundred million years. At the same time, it is estimated that approximately 99.9% of all species that ever existed are now extinct.

The Holocene Mass Extinction

We are currently experiencing a new period of extinction, called the Holocene extinction. This time, the process of extinction is caused entirely by humans. Furthermore, experts believe that the current extinction is a phenomenon worse than what had previously been anticipated. In fact, we are witnessing a dramatic drop in the number of animal and plant species. Some experts estimate that this modern extinction will result in the loss of half of the species by the end of 2100.

The modern extinction, the sixth mass extinction, started to accelerate when European explorers began to sail the seas in the late Middle Ages, at the start of the Renaissance era. The best known example is the dodo, a bird in the family of pigeons, the size of a turkey, which inhabited the island of St. Mauritius in the Indian Ocean. European navigators eradicated the species in less than 100 years after the arrival of Portuguese sailors in 1598. Many dodos were caught to feed the hungry crews while the rest were killed by feral cats and other introduced species. In the late seventeenth century, the last specimen disappeared forever.

According to recent assessments by specialists, during the last decades, the number of species whose survival is threatened has increased significantly. Some of the factors causing this rapid extinction include habitat loss and degradation, commercial exploitation (such as plant collection, hunting, and commercialization of animal parts), environmental pollution, climate changes and the introduction of exotic species. Of all these causes, the direct destruction of habitat is the one that is threatening the largest number of species.

The Red List of Threatened Species

The World Conservation Union (IUCN) based in Geneva, Switzerland, regularly publishes its "Red List of Threatened Species," many of which are in danger of becoming extinct. Prepared by the IUCN Species Survival Commission, it is the most widely recognized worldwide inventory on the status of threatened species. According to the IUCN Red List (2009) there are more than forty-seven thousand species in the List, of which 17,291 are considered threatened with extinction, compared with 16,306 in the year 2007.

The results indicate that 21% of all known mammals, 30% of known amphibians, 12% of birds, 28% of reptiles, 37% of freshwater fish, 70% of plants and 35% of the invertebrates tested so far are threatened. Of the world's 5,490 mammals, 79 have been classified as extinct or extinct in the wild. In addition, a total of 469 reptiles are endangered and 22 are already in the category of extinct or extinct in the wild. As for amphibians, the IUCN Red List shows that of the planet's 6,285 amphibian species, 1,895 are threatened with extinction, which makes them the most threatened group of species known to date. A total of 39 species are already listed in the category of extinct or extinct in the wild. Finally, of the 12,151 listed plants, 8,500 are endangered and 114 are already listed in the category of extinct or extinct in the wild.

The list reports that the total number of extinct species has reached 875, while the other 66 species are only found in captivity or crops (extinct in the wild). There are species that disappear even before they are discovered. These data indicate that globally, one in four mammals, one in eight birds, one third of all amphibians and 70% of the plants that have been assessed by the IUCN are at risk. Fortunately, the list is increasingly being used as a reference by politicians and scientists around the world for decision making in the field of the environment.

Worldwide, the largest and best known endangered animals are the Sumatran tiger, the panda, the koala, the gorilla, the Java rhinoceros, the lynx, the condor, and the vaquita (the world's smallest cetacean at risk, with fewer than 600 individuals located in the Gulf of California, Mexico).

In Latin America and the Caribbean, there are at least 29 species declared extinct by the IUCN, including the Caribbean monk seal (Monachus tropicalis), Darwin's Galapagos Mouse and the Indefatigable Galapagos Mouse (Nesoryzomys darwini and Nesoryzomys indefessus, respectively.) The hawksbill sea turtle (Eretmochelys imbricata) that inhabits the Caribbean Sea waters has been classified in the Red List as a critically endangered species.

The Caribbean Martin (Progne dominicensis) is a species of swallow that has been classified by the IUCN in the Least Concern category. It lives mainly in the Caribbean in the Hispaniola Island (Haiti and the Dominican Republic) and in Jamaica, and to the east and south in the Lesser Antilles, Tobago and Curacao. It is common in the Bahamas, Cayman Islands and Cozumel. It is expected that the population of this species can recover its size as there are now more individuals in the region than there were a few years ago.

Endangered species of the Dominican Republic

According to the latest IUCN estimates (2010), the country has a total of 126 threatened taxonomic species, 30 plant and 96 animal species.

The most threatened amphibians are the more than 25 frog species of the Eleutherodactylus genus. For example, the Eleutherodactylus nortoni species, which lives in the Sierra de Bahoruco, is critically endangered, as a population reduction of over 80% is expected during the next 10 years, according to a prediction of severe degradation of its habitat in the Hispaniola. Another critically endangered amphibian is the Peltophryne fluviatica toad, whose distribution is very restricted as it is found in only two locations, in the northwest of the Dominican Republic, at an elevation of between 150 and 200 meters.

Some of the reptiles listed by the IUCN as suffering some degree of threat are the American crocodile (Crocodylus acutus) and iguanas of the Cyclura genus. Among the endangered sea turtles are the loggerheads (Caretta caretta), the green turtles (Chelonia mydas), the leatherbacks (Dermochelys coriacea) and the aforementioned hawksbill turtles (Eretmochelys imbricata).

Endangered birds on the Red List include the Hispaniola's Ridgway Hawk (Buteo ridgwayi), a bird of prey, seen as critically endangered as it has a highly fragmented population that continues to decline. In 2006, there were a total of 80 to 120 pairs of these birds in the country. An estimated 5 to 10% of pairs disappear annually in Los Limones, within the Haitises National Park, and it is believed that only the effective protection of this area as a whole, together with captivity breeding programs, can save this falcon from extinction.

The threatened mammal species in the Hispaniola include whales, dolphins, seals, bats, and a variety of rodents, the solenodonte, and the manatee. Eight of the species listed by the IUCN for the Dominican Republic are considered extinct: the aforementioned Caribbean monk seal (Monachus tropicalis), which has not been seen since 1952; four Capromyidae species (a rodent family) which are locally known as hutias or zagoutis: Hexolobodon phenax, Isolobodon montanus, and Isolobodon portoricensis and the Plagiodontia ipnaeum (the latter known through fossils found recently on the island); the Hispaniolan spiny edible rat (Brotomys voratus), which was described by Gonzalo Fernandez de Oviedo y Valdez, who lived on the island from 1536 to 1546, during which time it was called Mohuy; the Nesophontes hypomicrus species ,the Atalaye nesofontes, a non-flying mammal known through skulls and skeletons recently found on the island and which apparently became extinct with the arrival of rats (Rattus spp.) aboard Spanish ships in the early sixteenth century; and finally the Solenodon marcanoi, an insectivorous species that also became extinct when the first Europeans arrived on the island.

Nowadays, a surviving relative of this last species, the Hispaniolan solenodon (Solenodon paradoxus), is endemic to the island and is considered a living fossil, as it evolved some 60 million years ago. This solenodon, together with the only hutia currently living on the island (Plagiodontia aedium), are the last survivors, or rather living fossils, of a diverse fauna of terrestrial mammals that once existed in the Dominican Republic and Haiti.

With regard to endangered plants, the Red List highlights a total of 30 species for the Dominican Republic. The Sideroxylon rubiginosum tree is the one most at risk because it is considered critically endangered. This Sapotaceae species is found only on a hill near Santo Domingo, where it was picked early last century. Other threatened plants include the Cóbana Polisandro (Stahli monosperma), a very rare leguminous plant; the Ekmanianthe longiflora, a bignoniaceae found in Cuba and in the Sierra de Barahona in the Hispaniola; the Guayacan Real (Guaiacum sanctum) and the Roughbark Lignum-vitae (Guaiacum officinale), also known as Palo de Vida or Palo Santo, two extremely rare species of timber trees, of great economic interest, and which have historically been extensively felled in many parts of the island.

It is expected that, by creating and consolidating protected areas in the Dominican Republic, the last populations of all these endangered species can be preserved, thus preventing their disappearance. Intensive reforestation programs are also required to connect the remaining forest fragments, so that the existing sub-populations can exchange genetic material, which is essential to avoiding the mating of close relatives within individual subpopulations (in-breeding). Additionally, the creation of banks containing genetic material (seed banks, for example) and breeding in captivity are strategies that may help reduce the levels of threat. We hope that the actions taken in this direction will contribute to the withdrawal from the Red List of the many species currently threatened in the island nation.