The decline of wild mammal populations globally has been an occurrence spanning over the past 50,000 years, at the same time as the populations of humans and livestock have increased. Nowadays, the total biomass of wild mammals on land is believed to be seven times lower than its prehistoric values, while the biomass of marine mammals had declined fivefold. At the same time, the biomass of humans is "an order of magnitude higher than that of all wild mammals", and the biomass of livestock mammals like pigs and cattle is even larger than that. Even as wild mammals had declined, the growth in the numbers of humans and livestock had increased total mammal biomass fourfold. Only 4% of that increased number are wild mammals, while livestock and humans amount to 60% and 36%. Alongside the simultaneous halving of plant biomass, these striking declines are considered part of the prehistoric phase of the Holocene extinction. [2] [1]
Since the second half of the 20th century, a range of protected areas and other wildlife conservation efforts (such as the Repopulation of wolves in Midwestern United States) have been implemented. These have had some impact on preserving wild mammal numbers. [3] There is still some debate over the total extent of recent declines in wild mammals and other vertebrate species. [4] [5] In any case, many species are now in a worse state than decades ago. [6] Hundreds of species are critically endangered. [7] [8] Climate change also has negative impacts on land mammal populations. [3]
Historically, the Quaternary extinction event was the most dramatic episode of wild mammal decline, as it saw the disappearance of appromixately half of all terrestrial mammal species with a body mass greater than 40 kg. [2] Statistically, this meant a 14% reduction in the average body size of wildlife over the past 125,000 years. [9] [10] [11] While some researchers attribute that eradication of all non-African megafauna to prehistoric climate change, [12] [13] [14] most now believe it was wholly or predominantly driven by human activity. [15] [16] [17] [18] [19] [20] Many wild mammal species continued to decline at a slower rate afterwards. Prominent examples on land include the collapse of historic American bison herds on the Great Plains, [21] or the extinction of a wide range of small marsupials in Australia. [22] On sea, whaling drove similarly severe declines in the numbers of marine mammals. [23] The total numbers of wild mammals are unlikely to recover to anywhere near their prehistoric peaks, as the historic replacement of forests and wetlands with cropland and pasture means that the Earth's carrying capacity for wild terrestrial species will remain lowered unless it is reversed. [24]
As the human population grew and colonization pushed deeper around the globe, and as the environmental footprint of the average human has grown, so has the pressure on ecosystems, and their inhabitants, including wild mammals. [25] [8] [6] [26] Over the past several centuries, wild mammal extinctions tended to be concentrated among the small island species, whose endemic populations are constrained in size and range by their limited habitat, [27] and in Australia, where similar dynamics have played out. Since the European settlement 10% of Australia's 273 terrestrial mammals went extinct, (a loss of one to two species per decade). Currently, 21% of Australia's mammals are threatened, and unlike in most other continents, the main cause is predation by feral species, such as cats. [28]
In general, habitat degradation, through activities such as deforestation for land development, is currently the main anthropogenic cause of species extinctions. The main cause of habitat degradation worldwide is agriculture, with urban sprawl, logging, mining and some fishing practices close behind. [29] Disease can also be a factor: white nose syndrome in bats, for example, is causing a substantial decline in their populations and may even lead to the extinction of a species. [30] Another example is the Devil facial tumour disease, which has devastated populations of Tasmanian devils. [31] [32] For wild mammals, overhunting can have a proportionally greater impact than on the other wild animals. Terrestrial mammals, such as the tiger and deer, are mainly hunted for their pelts and in some cases meat, and marine mammals can be hunted for their oil and leather. Specific targeting of one species can resonate through the wider ecosystem due to coextinction processes, especially if the targeted species is a keystone species. Sea otters, for example, were hunted in the maritime fur trade, and their drop in population led to the rise in sea urchins—their main food source—which decreased the population of kelp—the sea urchin's and Steller's sea cow's main food source—leading to the extinction of the Steller's sea cow. [33] The hunting of an already limited species can easily lead to its extinction, as with the bluebuck whose range was confined to 1,700 square miles (4,400 km2) and which was hunted into extinction soon after discovery by European settlers. [34]
Such pressures on wild species can be alleviated through wildlife conservation efforts, such as the establishment of protected areas. From 1996 to 2008, conservation efforts in 109 countries reduced the extinction risk of their wild mammals and birds by 29%, while conservation action throughout 2010s lowered the average extinction risk of birds, mammals and amphibians by at least 20%. [3] Some mammal-specific successes include the conservation of ungulates, 6% of which would have likely been extinct or extinct in the wild without them. Another example is the rebound of wolf populations across much of Europe and North America, including through measures such as Repopulation of wolves in Midwestern United States. [35] [36] On sea, the decline of whaling had seen rebounds of a range of species, such as blue whales and humpback whales. [37] [38] However, about a third of marine mammals are still considered to be at risk of extinction. [3]
There is some debate over the severity of declining trends in the global mammal and the broader vertebrate population: while the Living Planet Report of the World Wide Fund for Nature reported a 68% decline in the aggregate wild vertebrate populations since 1970, [39] [40] [4] a scientific reanalysis of its data in Nature found that 98.6% of vertebrate populations show no global trend over that period, with vertebrate declines disproportionately driven by 1% of the species, mostly clustered in the Indo-Pacific region and among several reptile and amphibian groups. Even so, that "extremely declining" cluster also includes many "larger animals", which are often mammals. [5] A separate analysis of 177 mammal species with the most-detailed data found that all of them have lost over 30% of their geographic range, and over 40% retain less than a fifth of their past range, which is impossible without a severe decline in population. Examples of notable mammals with declining populations include pangolins, cheetahs (around 7,000 individuals) and Sumatran and Borneo orangutans (no more than 5,000 combined), or even the 43% drop for the African lion population since 1993 due to declines in West Africa. [6] Globally, 27% of mammal species are threatened with extinction, while 233 species are critically endangered. [7] 74 mammal species are believed to be "on the brink", meaning that they retain fewer than 1000 members, with many of those possessing fewer than 250 members. [8]
Current climate change influences species survival in a given area. Some of the first studies of the influence of climatic variables on wild mammals took place in the United States in 1960s. They analysed the impacts of severe winter weather events on the survival and reproduction of species such as Missouri cottontails and northern Montana Pronghorns., [42] [43] sometimes using radio transmitters. [44] As the warming progressed, such severe winter weather decreased, [45] and instead, warming of previously very cold places, such as the High Arctic can wreak havoc with the ecosystems. For instance, warming-driven increase in precipitation causes warm rain to fall onto the permafrost, which becomes unstable and can collapse from the mountainsides in avalanches. On multiple instances, this has blocked the winter food supply of reindeer populations, and led to their mass starvation in places like the Svalbard of Norway and the Yamal Peninsula of Russia: in the latter area, 61,000 reindeer died over the 2013–2014 winter as the result. [41] [46]
In 2019, historical records from the past 300 years were used to quantify both anthropogenic and climate stressors and their role in te local extinction of 11 medium- and large-sized animals in China. [47] Both climate warming and cooling can cause range shifts and local extinction of animals, but quantitative evidence is rare due to the lack of long-term spatial-temporal data. In [47] Extreme temperature change was negatively associated with increased local extinction of mammals such as the gibbon, macaque, tiger, and water deer. Researchers concluded that while premodern cooling trend may have contributed to extinctions of tiger subspecies in the west and north of China, the recent global warming might contribute to the complete extinction of tigers in southern China. [47]
In all, climate change is already believed to have had negative impacts on 47% of flightless land mammals. [3] While "flightless" excludes bats, there's also substantial evidence of them being negatively affected. For instance, Brazilian free-tailed bats are forced to emerge to feed earlier in the evening as their region becomes drier, even if it exposes them to more predators or competitor insectivores. [48] In other places, bats have been exposed to increased mortality due to heat stress. In Australia, flying foxes live comfortably below 42 °C (108 °F), but climate change caused a heatwave in 2014, which led to thousands of flying fox deaths. Mass mortality was highly visible, to the point fire trucks were deployed to spray the bats in an attempt to cool them down. A third of the entire species is believed to have been lost in that event. [49] [50] 2019–2020 Australia bushfire season had killed over 1 billion animals and displaced around 2 billion more, including large numbers of threatened or endangered mammal species such as koalas. [51] And in the wake of 2019 Amazon rainforest wildfires, the World Wildlife Fund concluded that the jaguar is already "near threatened" and the loss of food supplies and habitat due to the fires make the situation more critical. [52] The fires affect water chemistry (such as decreasing the amount of dissolved oxygen in the water), temperature, and erosion rates, which in turn affects fish and mammals that depend on fish, such as the giant otter (Pteronura brasiliensis). [52]
Relative to the rate of climate change, evolutionary change is usually considered to be too slow to allow for genetic adaptation among species. However, microevolution is a genetic adaptation that deals with heritable shifts in allele frequencies in a population and is not characterized by the slow process of speciation, or the formation of a new distinct species. [53] However, larger terrestrial animals (including many mammals) usually cannot adapt with microevolution, as the rate of climate change is still too fast for this evolutionary process. Some, like the kangaroo, can still benefit from a very broad climatic tolerance. [54] Others would have to rely on phenotypic plasticity. [55] A plastic response to climate change includes expressing a different phenotype that may lead to differing morphology, phenology, or rate of activity . [56] Unlike genetic adaptation, phenotypic plasticity allows the animal itself to respond to climate change without a change in its genetic makeup. This mechanism that allows this process involves changes in DNA packaging in the nucleus that alters the chance of a particular gene being expressed. [57] Phenological changes are observed and taken as evidence that species are adjusting to environmental changes.
Although species may adapt to changing climates, either through genetic or phenotypic adaptation, all species have limits to their capacity for adaptive response to changing temperatures. [58] However, only around 4% of all mammals that are deemed climate sensitive by the IUC have been studied in regards to linking their demographic composition (i.e. survival, development, and reproduction) to climate change. [59] There is a large discrepancy between the locations of demographic studies and the species that are currently assessed as most vulnerable to climate change. [59] It is also incredibly difficult for studies to focus specifically and determine a straightforward relationship between limited tolerance to high temperatures and local extinction, as a diverse set of factors, such as food abundance, human activity, and mismatched timing, can all play a role in a species’ local or mass extinction. [60] To assess population viability under climate change, more coordinated actions need to be prioritized and taken to collect data on how different species’ demographic rates can persist and respond to climate change. [59]
A 2023 paper concluded that under the high-warming SSP5–8.5 scenario, 50.29% of mammals would lose at least some habitat by 2100 as the conditions become more arid. Out of those, 9.50% would lose over half of their habitat due to an increase in dryness alone, while 3.21% could be expected to lose their entire habitat ad the result. These figures go down to 38.27%, 4.96% and 2.22% under the "intermediate" SSP2-4.5 scenario, and to 22.65%, 2.03% and 1.15% under the high-mitigation SSP1-2.6. [62]
In 2020, a study in Nature Climate Change estimated the effects of Arctic sea ice decline on polar bear populations (which rely on the sea ice to hunt seals) under two climate change scenarios. Under high greenhouse gas emissions, at most a few high-Arctic populations will remain by 2100: under more moderate scenario, the species will survive this century, but several major subpopulations will still be wiped out. [63] [64]
In 2019, it was estimated that the current great ape range in Africa will decline massively under both the severe RCP8.5 scenario and the more moderate RCP4.5. The apes could potentially disperse to new habitats, but those would lie almost completely outside of their current protected areas, meaning that conservation planning needs to be "urgently" updated to account for this. [65]
A 2017 analysis found that the mountain goat populations of coastal Alaska would go extinct sometime between 2015 and 2085 in half of the considered scenarios of climate change. [66] Another analysis found that the Miombo Woodlands of South Africa are predicted to lose about 80% of their mammal species if the warming reached 4.5 °C (8.1 °F). [67]
In 2008, the white lemuroid possum was reported to be the first known mammal species to be driven extinct by climate change. However, these reports were based on a misunderstanding. One population of these possums in the mountain forests of North Queensland is severely threatened by climate change as the animals cannot survive extended temperatures over 30 °C (86 °F). However, another population 100 kilometres south remains in good health. [68] On the other hand, the Bramble Cay melomys, which lived on a Great Barrier Reef island, was reported as the first mammal to go extinct due to human-induced sea level rise, [61] with the Australian government officially confirming its extinction in 2019. Another Australian species, the greater stick-nest rat (Leporillus conditor) may be next. Similarly, the 2019–20 Australian bushfire season caused a near-complete extirpation of Kangaroo Island dunnarts, as only one individual may have survived out of the population of 500. [69] Those bushfires have also caused the loss of 8,000 koalas in New South Wales alone, further endangering the species. [70] [71]The Cenozoic is Earth's current geological era, representing the last 66 million years of Earth's history. It is characterized by the dominance of mammals, birds, conifers, and angiosperms. It is the latest of three geological eras, preceded by the Mesozoic and Paleozoic. The Cenozoic started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian dinosaurs, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor.
The Holocene extinction, or Anthropocene extinction, is the ongoing extinction event caused by humans during the Holocene epoch. These extinctions span numerous families of plants and animals, including mammals, birds, reptiles, amphibians, fish, and invertebrates, and affecting not just terrestrial species but also large sectors of marine life. With widespread degradation of biodiversity hotspots, such as coral reefs and rainforests, as well as other areas, the vast majority of these extinctions are thought to be undocumented, as the species are undiscovered at the time of their extinction, which goes unrecorded. The current rate of extinction of species is estimated at 100 to 1,000 times higher than natural background extinction rates and is increasing. During the past 100–200 years, biodiversity loss and species extinction have accelerated, to the point that most conservation biologists now believe that human activity has either produced a period of mass extinction, or is on the cusp of doing so. As such, after the "Big Five" mass extinctions, the Holocene extinction event has also been referred to as the sixth mass extinction or sixth extinction; given the recent recognition of the Capitanian mass extinction, the term seventh mass extinction has also been proposed for the Holocene extinction event.
A mammal is a vertebrate animal of the class Mammalia. Mammals are characterized by the presence of milk-producing mammary glands for feeding their young, a neocortex region of the brain, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 29 orders.
Biodiversity is the variety and variability of life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Earth. It is greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. Tropical forest ecosystems cover less than one-fifth of Earth's terrestrial area and contain about 50% of the world's species. There are latitudinal gradients in species diversity for both marine and terrestrial taxa.
Extinction is the termination of a taxon by the death of its last member. A taxon may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" after a period of apparent absence.
Wildlife refers to undomesticated animal species, but has come to include all organisms that grow or live wild in an area without being introduced by humans. Wildlife was also synonymous to game: those birds and mammals that were hunted for sport. Wildlife can be found in all ecosystems. Deserts, plains, grasslands, woodlands, forests, and other areas including the most developed urban areas, all have distinct forms of wildlife. While the term in popular culture usually refers to animals that are untouched by human factors, most scientists agree that much wildlife is affected by human activities. Some wildlife threaten human safety, health, property and quality of life. However, many wild animals, even the dangerous ones, have value to human beings. This value might be economic, educational, or emotional in nature.
In zoology, megafauna are large animals. The precise definition of the term varies widely, though a common threshold is approximately 45 kilograms (99 lb), with other thresholds as low as 10 kilograms (22 lb) or as high as 1,000 kilograms (2,200 lb). Large body size is generally associated with other traits, such as having a slow rate of reproduction, and in large herbivores, reduced or negligible adult mortality from being killed by predators.
Conservation biology is the study of the conservation of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an interdisciplinary subject drawing on natural and social sciences, and the practice of natural resource management.
Habitat conservation is a management practice that seeks to conserve, protect and restore habitats and prevent species extinction, fragmentation or reduction in range. It is a priority of many groups that cannot be easily characterized in terms of any one ideology.
Wildlife conservation refers to the practice of protecting wild species and their habitats in order to maintain healthy wildlife species or populations and to restore, protect or enhance natural ecosystems. Major threats to wildlife include habitat destruction, degradation, fragmentation, overexploitation, poaching, pollution, climate change, and the illegal wildlife trade. The IUCN estimates that 42,100 species of the ones assessed are at risk for extinction. Expanding to all existing species, a 2019 UN report on biodiversity put this estimate even higher at a million species. It is also being acknowledged that an increasing number of ecosystems on Earth containing endangered species are disappearing. To address these issues, there have been both national and international governmental efforts to preserve Earth's wildlife. Prominent conservation agreements include the 1973 Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the 1992 Convention on Biological Diversity (CBD). There are also numerous nongovernmental organizations (NGO's) dedicated to conservation such as the Nature Conservancy, World Wildlife Fund, and Conservation International.
The Late Pleistocene is an unofficial age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a stratigraphic perspective. It is intended to be the fourth division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently defined as the time between c. 129,000 and c. 11,700 years ago. The late Pleistocene equates to the proposed Tarantian Age of the geologic time scale, preceded by the officially ratified Chibanian. The beginning of the Late Pleistocene is the transition between the end of the Penultimate Glacial Period and the beginning of the Last Interglacial around 130,000 years ago. The Late Pleistocene ends with the termination of the Younger Dryas, some 11,700 years ago when the Holocene Epoch began.
Environmental vegetarianism is the practice of vegetarianism that is motivated by the desire to create a sustainable diet, which avoids the negative environmental impact of meat production. Livestock as a whole is estimated to be responsible for around 15% of global greenhouse gas emissions. As a result, significant reduction in meat consumption has been advocated by, among others, the Intergovernmental Panel on Climate Change in their 2019 special report and as part of the 2017 World Scientists' Warning to Humanity.
There are several plausible pathways that could lead to an increased extinction risk from climate change. Every plant and animal species has evolved to exist within a certain ecological niche. But climate change leads to changes of temperature and average weather patterns. These changes can push climatic conditions outside of the species' niche, and ultimately render it extinct. Normally, species faced with changing conditions can either adapt in place through microevolution or move to another habitat with suitable conditions. However, the speed of recent climate change is very fast. Due to this rapid change, for example cold-blooded animals may struggle to find a suitable habitat within 50 km of their current location at the end of this century.
The Late Pleistocene to the beginning of the Holocene saw the extinction of the majority of the world's megafauna, which resulted in a collapse in faunal density and diversity across the globe. The extinctions during the Late Pleistocene are differentiated from previous extinctions by its extreme size bias towards large animals, and widespread absence of ecological succession to replace these extinct megafaunal species, and the regime shift of previously established faunal relationships and habitats as a consequence. The timing and severity of the extinctions varied by region and are thought to have been driven by varying combinations of human and climatic factors. Human impact on megafauna populations is thought to have been driven by hunting ("overkill"), as well as possibly environmental alteration. The relative importance of human vs climatic factors in the extinctions has been the subject of long-running controversy.
Defaunation is the global, local, or functional extinction of animal populations or species from ecological communities. The growth of the human population, combined with advances in harvesting technologies, has led to more intense and efficient exploitation of the environment. This has resulted in the depletion of large vertebrates from ecological communities, creating what has been termed "empty forest". Defaunation differs from extinction; it includes both the disappearance of species and declines in abundance. Defaunation effects were first implied at the Symposium of Plant-Animal Interactions at the University of Campinas, Brazil in 1988 in the context of Neotropical forests. Since then, the term has gained broader usage in conservation biology as a global phenomenon.
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term applies to natural resources such as water aquifers, grazing pastures and forests, wild medicinal plants, fish stocks and other wildlife.
Biodiversity loss happens when plant or animal species disappear completely from Earth (extinction) or when there is a decrease or disappearance of species in a specific area. Biodiversity loss means that there is a reduction in biological diversity in a given area. The decrease can be temporary or permanent. It is temporary if the damage that led to the loss is reversible in time, for example through ecological restoration. If this is not possible, then the decrease is permanent. The cause of most of the biodiversity loss is, generally speaking, human activities that push the planetary boundaries too far. These activities include habitat destruction and land use intensification. Further problem areas are air and water pollution, over-exploitation, invasive species and climate change.
Insects are the most numerous and widespread class in the animal kingdom, accounting for up to 90% of all animal species. In the 2010s, reports emerged about the widespread decline in insect populations across multiple insect orders. The reported severity shocked many observers, even though there had been earlier findings of pollinator decline. There has also been anecdotal reports of greater insect abundance earlier in the 20th century. Many car drivers know this anecdotal evidence through the windscreen phenomenon, for example. Causes for the decline in insect population are similar to those driving other biodiversity loss. They include habitat destruction, such as intensive agriculture, the use of pesticides, introduced species, and – to a lesser degree and only for some regions – the effects of climate change. An additional cause that may be specific to insects is light pollution.
The Global Assessment Report on Biodiversity and Ecosystem Services is a report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, on the global state of biodiversity. A summary for policymakers was released on 6 May 2019. The report states that, due to human impact on the environment in the past half-century, the Earth's biodiversity has suffered a catastrophic decline unprecedented in human history, as an estimated 82 percent of wild mammal biomass has been lost. The report estimates that there are 8 million animal and plant species on Earth, with the majority represented by insects. Out of those 8 million species, 1 million are threatened with extinction, including 40 percent of amphibians, almost a third of reef-building corals, more than a third of marine mammals, and 10 percent of all insects.
Much less frequently mentioned are, however, the ultimate drivers of those immediate causes of biotic destruction, namely, human overpopulation and continued population growth, and overconsumption, especially by the rich. These drivers, all of which trace to the fiction that perpetual growth can occur on a finite planet, are themselves increasing rapidly
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: CS1 maint: multiple names: authors list (link)The overarching driver of species extinction is human population growth and increasing per capita consumption.