664 Loss of Biodiversity, Overview invading animals, these can spread epidemically and can destroy the native populations It is thought, for example, that the almost complete destruction of the Hawaiian avifauna – since 1850, 85% of the endemic species have become extinct or have been reduced to very small populations – is due to the spread of variola and bird malaria, introduced together with the mosquito Culex quinquefasciatus in 1826 Extinctions caused by human activities in insular communities are much more frequent than generally recognized Thus, the rate of extinction on the order of 1% given earlier is a gross underestimate of the true value Current estimates indicate that 25% of endemic bird species have disappeared from islands as a result of human activities There are, for example, only three species of winged rails today, while thousands have existed during the past 2000 years We are justifiably worried by the current wave of mass extinctions threatening the tropical forests, but should also recognize that the oceanic islands have already undergone such mass extinctions scenarios (1.8–2.0 1C, which looks very optimistic!) for 2050, that 15–37% of species in their sample of regions (Europe, Mexico, South Africa, and Queensland) and taxa (terrestrial vertebrates, butterflies and some other invertebrates, and plants) will be committed to extinction The results of this kind of scenario depend on various hypotheses, such as the different levels of dispersal abilities of the species (Thomas et al., 2004) In the case of marine species, the impact of climate change is not limited to the effects of warming: there is also a direct effect of the increase of CO2 in the atmosphere through ocean acidification It appears as a pervasive stressor that could affect marine organisms and cause profound ecological shifts that may facilitate species extinction (Krocker et al., 2010) Calcifying organisms such as crustaceans or corals are particularly sensitive to such acidification (see Box 5) Climate Change All organisms modify their environment, and humans are no exception Thus, in a strategic document, jointly published by the World Resources Institute (WRI), the World Conservation Union (IUCN), and the United Nations Environmental Programme (UNEP), six fundamental causes for the impoverishment of biodiversity are recognized: Climate change over the past decades has produced shifts in the distributions and abundances of many species (Lovejoy and Hannah, 2005; Moăller et al., 2004) In some cases, it has been implicated in species extinctions (Box 4) Thus, using projections of species distributions for various climate scenarios, extinction risks for sample regions covering 20% of the Earth’s terrestrial surface have been estimated by an international team led by Thomas et al (2004) Exploring various approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, they predict, on the basis of midrange climate-warming Ecological Reflection on the Primary Causes of the Current Crisis of Extinction The rapid and unsustainable growth of human populations and the consumption of natural resources The continued reduction of the range of products in agriculture, forestry, and fishing The economic and political systems that not take into account the environment and its resources Box A mass extinction associated with pathogen outbreaks tied to global warming As the Earth is becoming warmer, many species are likely to disappear, often because of changing disease dynamics (Pounds et al., 2006) For instance, it appears that a recent mass extinction in amphibians is associated with pathogen outbreaks tied to global warming During the 1990s, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) disappeared along with the golden toad (Bufo periglenes) An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid waterborne fungus, Batrachochytrium dendrobatidis is implicated Chytriomycosis is an infectious disease that affects amphibians worldwide It is capable of causing sporadic deaths in some species and 100% mortality in others For instance, mass die-offs in populations of the midwife toad Alytes obstetricans at high altitude in the western Pyrenees in both France and Spain were observed as early as 2002 and are spreading (http://www.bd-maps.eu; http://www.sosanfibios.org) Box Marine species face an elevated risk of extinction from global changes Marine ecosystems are centrally important to the ecology of the planet: covering 71% of the Earth’s surface, the ocean nurtured life on our planet and continues to play a dominant role in regulating the climate Recent studies indicate that rapidly increasing greenhouse gas concentrations are causing a decrease in ocean productivity, altered food web dynamics, shifting species distributions, and elevated risk of extinction in many species (Hoegh-Guldberg and Bruno, 2010) Let us focus here on the case of coral species Coral reefs harbor the highest concentration of marine biodiversity and are facing increasing threats at local and global scales In particular, rapid buildup of carbon dioxide in the atmosphere is leading to both rising sea surface temperatures and water acidification The conservation status of 704 reef-building coral species was assessed using Red List criteria and measures of population reduction over time One-third of these are in categories with an elevated risk of extinction Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with the risk of extinction further exacerbated by local-scale anthropogenic disturbances A recent investigation of 328 colonies of massive Porites corals from 69 reefs of the Great Barrier Reef in Australia shows that calcification has declined by 14.2% since 1990 The data suggest that such a severe and sudden decline in calcification is unprecedented in at least the past 400 years It could be a response to the declining pH of the upper seawater layers due to the absorption of increasing atmospheric CO2 (De’Ath et al., 2009)