190 Endangered Mammals the fossil record, and this rate will very likely increase in the near future The status of 5488 species of mammals was reviewed in the 2010 IUCN Red List of Threatened Animals Of those reviewed, approximately 25% were considered at risk of extinction This percentage is undoubtedly an under-estimate, as the status of many mammal species is still unknown Causes and Threats Many of the dangers that threaten other taxa also threaten mammals These dangers include habitat loss, exploitation, disease, and exotic introductions, but there are some differences in the manner and level of these threats for mammals as compared to other taxa For example, human persecution and harvesting pressure is probably greater for mammals than for most other taxa, with the probable exception of fish True mammalian specialists are rare compared to taxa such as insects, where many species are entirely dependent on only one species of plant and thus are extremely vulnerable to habitat changes that alter community structure However, many mammals are relatively large, and their habitat needs in terms of area are greater than for most other taxa, putting them at high risk of habitat loss and fragmentation A number of historical mammalian extinctions have occurred due to human exploitation or introductions rather than habitat loss Of 18 mammal species that have become extinct since 1600 and whose cause of extinction is known, eight became extinct due to direct human persecution, eight became extinct as the result of introduced predators and competitors, and only two became extinct because of habitat destruction At present, many mammalian species are now under a growing threat from habitat changes in addition to direct human persecution According to the Third edition of the Global Biodiversity Outlook (2010), mammals have suffered the steepest increase in risk of extinction in South and South-East Asia due to the combined impact of hunting and loss of habitat Mammalian Physiology and Its Relationship to Threats Mammals constitute a class of organisms that span an enormous size range of approximately eight orders of magnitude, from g in some bats and shrews to 190,000 kg in the blue whale However, the majority of mammals tend toward large sizes compared to other taxa, and they tend to have a correspondingly long maturation and slow reproductive rate This puts them at risk from exploitation and other threats, as breeding rates may not be able to keep up with losses in a population An extreme example is the blue whale (Balaenoptera musculus), whose population has been depleted by at least 70%, and possibly as much as 90%, in less than a century Despite a halt in whaling that targeted this species in 1966 (identified as the key driver of the decline of the species), the blue whale remains endangered It has been proposed that its subspecies, the Antarctic blue whale (B m intermedia), be separately listed as Critically Endangered given the population decline over the same period of more than 97% Large body size often means large habitat needs, which also puts mammals at risk Estimates for self-sustaining populations of carnivores such as brown bears (Ursus arctos) and African wild dogs (Lycaon pictus) range from 1000 to more than 10,000 km2 of suitable habitat, which means that many protected areas are too small to sustain long-term populations of these species However, for some species it is not simply a question of large habitat For tigers (Panthera tigris) the actual available prey density is a key determinant of tiger numbers – areas such as India that contain high densities of deer, boar, and other prey have tiger densities roughly 10 times that of the Russian Far East, where prey densities are similarly lower (Miquelle et al., 2010; Karanth et al., 2004) Habitat Loss, Degradation, and Encroachment Habitat loss and fragmentation is the single greatest threat to biodiversity worldwide, and this certainly holds true for mammals today Conversion of habitats by humans into other land uses can fragment and separate mammal populations and increase the likelihood of local population extinctions and eventual species extinction Rapid deforestation of tropical areas is a growing threat to a number of mammalian species, including many large, wide-ranging, or specialist species of primates, cats, and forest ungulates, as well as numerous small species with restricted ranges such as rodents, insectivores, and marsupials Most of these species cannot adapt to a highly fragmented or altered landscape, and the few that adapt may come into conflict with humans by feeding on crops or livestock The example of the giant panda (Ailuropoda melanoleuca) shows some of the complexities related to fragmentation and habitat loss Pandas feed primarily on bamboo that may live for decades but then tends to flower, seed, and die en masse within certain areas When this happens pandas must switch to other bamboo species, often having to move to new locations to find these alternative food sources According to studies following the latest major bamboo die-off in the early 1980s, pandas were still able to survive by finding patches that had not flowered, moving to new locations or switching to other less-favored species of bamboo The increase in human population within the panda’s range in China has now limited most populations of pandas to very small islands of habitat Widely separated and very small populations of pandas may not be viable over the long term, even without the problems faced from the fluctuations in their food source Because mammals are often relatively poor dispersers, the creation of corridors linking habitats has been suggested as a way to help some species, especially large or wide-ranging (including nomadic or migratory) ones But for many mammals the necessary size and structure of corridors is unknown, and few management plans have yet to put this idea into practice Genetic Loss It is generally assumed that a population’s long-term survival is at least partly dependent on sufficient genetic variation for individual fitness and population adaptability Loss of genetic diversity and reduced fitness from inbreeding depression and the chance fixation of detrimental alleles has been presumed to reduce adaptive potential and increase the probability of