Biodiversity loss

Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, depending on whether the environmental degradation that leads to the loss is reversible through ecological restoration/ecological resilience or effectively permanent (e.g. through land loss). The current global extinction (frequently called the sixth mass extinction or Anthropocene extinction), has resulted in a biodiversity crisis being driven by human activities which push beyond the planetary boundaries and so far has proven irreversible.

Even though permanent global species loss is a more dramatic and tragic phenomenon than regional changes in species composition, even minor changes from a healthy stable state can have dramatic influence on the food web and the food chain insofar as reductions in only one species can adversely affect the entire chain ( coextinction), leading to an overall reduction in biodiversity, possible alternative stable states of an ecosystem notwithstanding. Ecological effects of biodiversity are usually counteracted by its loss. Reduced biodiversity in particular leads to reduced ecosystem services and eventually poses an immediate danger for food security, but also can have more lasting public health consequences for humans.

International environmental organizations have been campaigning to prevent biodiversity loss for decades, public health officials have integrated it into the One Health approach to public health practice, and increasingly preservation of biodiversity is part of international policy. For example, the UN Convention on Biological Diversity is focused on preventing biodiversity loss and proactive conservation of wild areas. The international commitment and goals for this work is currently embodied by Sustainable Development Goal 15 "Life on Land" and Sustainable Development Goal 14 "Life Below Water". However, the United Nations Environment Programme report on "Making Peace with Nature" released in 2020 found that most of these efforts had failed to meet their international goals.

Loss rate

The current rate of ''global'' diversity loss is estimated to be 100 to 1000 times higher than the (naturally occurring) background extinction rate, faster than at any other time in human history, and expected to still grow in the upcoming years. These rapidly rising extinction trends impacting numerous animal groups including mammals, birds, reptiles, amphibians and ray-finned fishes have prompted scientists to declare a contemporary biodiversity crisis, in both terrestrial and marine ecosystems.

Locally bounded loss rates can be measured using species richness and its variation over time. Raw counts may not be as ecologically relevant as relative or absolute abundances. Taking into account the relative frequencies, many biodiversity indexes have been developed. Besides richness, evenness and heterogeneity are considered to be the main dimensions along which diversity can be measured.

As with all diversity measures, it is essential to accurately classify the spatial and temporal scope of the observation. "Definitions tend to become less precise as the complexity of the subject increases and the associated spatial and temporal scales widen." Biodiversity itself is not a single concept but can be split up into various scales (e.g. ecosystem diversity vs. habitat diversity or even biodiversity vs. habitat diversity) or different subcategories (e.g. phylogenetic diversity, species diversity, genetic diversity, nucleotide diversity). The question of net loss in confined regions is often a matter of debate but longer observation times are generally thought to be beneficial to loss estimates.

To compare rates between different geographic regions, latitudinal gradients in species diversity should also be considered.

In 2006, many more species were formally classified as rare or endangered or threatened; moreover, scientists have estimated that millions more species are at risk which have not been formally recognized.

In 2021, about 28 percent of the 134,400 species assessed using the IUCN Red List criteria are now listed as threatened with extinction—a total of 37,400 species compared to 16,119 threatened species in 2006.

A 2022 study published in '' Frontiers in Ecology and the Environment'', which surveyed more than 3,000 experts, states that "global biodiversity loss and its impacts may be greater than previously thought," and estimates that roughly 30% of species "have been globally threatened or driven extinct since the year 1500."

Causes

Biodiversity is commonly defined as the variety of life on Earth in all its forms, including the diversity of species, their genetic variations, and the interaction of these lifeforms. However, since the late 20th century loss of biodiversity caused by human behavior has caused more severe and longer-lasting impacts.Biodiversity loss
(Encyc. Brit.) Top scientists and the landmark IPBES ''Global Assessment Report on Biodiversity and Ecosystem Services'' assert that human population growth and overconsumption are the primary factors in this decline. Human drivers of biodiversity loss include habitat alteration, pollution, and overexploitation of resources.

Change in land use

Examples of changes in land use include deforestation, intensive monoculture, and urbanization.

The 2019 IPBES ''Global Assessment Report on Biodiversity and Ecosystem Services'' asserts that industrial agriculture is the primary driver collapsing biodiversity. The UN's Global Biodiversity Outlook 2014 estimates that 70 percent of the projected loss of terrestrial biodiversity are caused by agriculture use. Moreover, more than 1/3 of the planet's land surface is utilised for crops and grazing of livestock. Agriculture destroys biodiversity by converting natural habitats to intensely managed systems and by releasing pollutants, including greenhouse gases. Food value chains further amplify impacts including through energy use, transport and waste. According to a 2020 study published in '' Nature Sustainability'', more than 17,000 species are at risk of losing habitat by 2050 as agriculture continues to expand to meet future food needs. The researchers suggest that greater agricultural efficiency in the developing world and large scale transitions to healthier, Plant-based diets could help reduce habitat loss. Similarly, a Chatham House report also posited that a global shift towards largely plant-based diets would free up land to allow for the restoration of ecosystems and biodiversity, because in the 2010s over 80% of all global farmland was used to rear animals. A 2022 report published in ''Science'' concluded that at least 64 million square kilometers (24.7 square miles)—44% of terrestrial area—require conservation attention (ranging from protected areas to land-use policies) in order to secure important biodiversity areas, ecologically intact areas, and optimal locations for representation of species ranges and ecoregions.

The direct effects of urban growth on habitat loss are well understood: building construction often results in habitat destruction and fragmentation. The rise of urbanization greatly reduced biodiversity when large areas of natural habitat are fragmented, leading to selection for species that are adapted to urban environments. Small habitat patches are unable to support the same level of genetic or taxonomic diversity as they formerly could while some of the more sensitive species may become locally extinct. Species abundance populations are reduced due to the reduced fragmented area of habitat, this causes an increase of species isolation and forces species towards edge habitats and adapt to foraging elsewhere. Human caused habitat fragmentation tends to create barriers to dispersal which prevent species from moving with its ideal environment as its shifted by climate change. While the negative effects of fragmentation tend to be well known, the risk of fragmentation tends to have smaller effects on biodiversity, and can even change and strengthen certain inter-species relationships.

Pollution

Air pollution

Four greenhouse gases that are commonly studied and monitored are water vapor, carbon dioxide, methane, and nitrous oxide. In the past 250 years, concentrations of carbon dioxide and methane have increased, along with the introduction of purely anthropogenic emissions such as hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride into the atmosphere. These pollutants are emitted into the atmosphere by the burning of fossil fuels and biomass, deforestation, and agricultural practices which amplify the effects of climate change. As larger concentrations of greenhouse gases are released into the atmosphere, this causes the Earth's surface temperature to increase. This is because greenhouse gases are capable of absorbing, emitting, and trapping heat from the Sun and into the Earth's atmosphere. With the increase in temperature expected from increasing greenhouse gases, there will be higher levels of air pollution, greater variability in weather patterns, intensification of climate change effects, and changes in the distribution of vegetation in the landscape.

Other pollutants that are released from industrial and agricultural activity are sulfur dioxide and nitrogen oxides. Once sulfur dioxide and nitrogen oxide are introduced into the atmosphere, they can react with cloud droplets (cloud condensation nuclei), raindrops, or snowflakes, forming sulfuric acid and nitric acid. With the interaction between water droplets and sulfuric and nitric acids, wet deposition occurs and creates acid rain. As a result, these acids would be displaced into various environments and vegetation during precipitation, having significant aerial distance (hundreds of kilometres) from the emission source. Sulfur dioxide and nitrogen oxide can also be displaced onto vegetations through dry deposition.

Sulfur dioxide and nitrous oxide concentration has many implication on aquatic ecosystems, including acidity change, increased nitrogen and aluminum content, and altering biogeochemical processes. Typically, sulfur dioxide and nitrous oxide do not have direct physiological effects upon exposure; most effects are developed by accumulation and prolonged exposure of these gases in the environment, modifying soil and water chemistry. Consequently, sulfur largely contributes to lake and ocean acidification, and nitrogen initiates eutrophication of inland and coastal water bodies that lack nitrogen. Both of these phenomena alter the native aquatic biota composition and influence the original food web with higher acidity level, minimizing aquatic and marine biodiversity.

Nitrogen deposition has also affected terrestrial ecosystems, including forests, grasslands, alpine regions, and bogs. The influx of nitrogen has altered the natural biogeochemical cycle and promoted soil acidification. As a result, it is likely that plant and animal species composition and ecosystem functionality will decline with increased soil sensitivity; contribute to slower forest growth, tree damage at higher elevations, and replacement of native biota with nitrogen-loving species. Additionally, sulfate and nitrate can be leached from the soil, removing essential nutrients such as calcium and magnesium, and be deposited into freshwater, coastal, and oceanic environments, promoting eutrophication.

Noise pollution

Noise generated by traffic, ships, vehicles, and aircraft can affect the survivability of wildlife species and can reach undisturbed habitats. Although sounds are commonly present in the environment, anthropogenic noises are distinguishable due to differences in frequency and amplitude. Many animals use sounds to communicate with others of their species, whether that is for reproduction purposes, navigation, or to notify others of prey or predators. However, anthropogenic noises inhibit species from detecting these sounds, affecting overall communication within the population. Species such as birds, amphibians, reptiles, fishes, mammals, and invertebrates are examples of biological groups that are impacted by noise pollution. If animals cannot communicate with one another, this would result in reproduction to decline (not able to find mates), and higher mortality (lack of communication for predator detection).

Noise pollution is common in marine ecosystems, affecting at least 55 marine species. For many marine populations, sound is their primary sense used for their survival; able to detect sound hundreds to thousands kilometers away from a source, while vision is limited to tens of meters underwater. As anthropogenic noises continue to increase, doubling every decade, this compromises the survivability of marine species. One study discovered that as seismic noises and naval sonar increases in marine ecosystems, cetacean, such as whales and dolphins, diversity decreases. Noise pollution has also impaired fish hearing, killed and isolated whale populations, intensified stress response in marine species, and changed species' physiology. Because marine species are sensitive to noise, most marine wildlife are located in undisturbed habitats or areas not exposed to significant anthropogenic noise, limiting suitable habitats to forage and mate. Whales have changed their migration route to avoid anthropogenic noise, as well as altering their calls. Noise pollution also impacts human livelihood. Multiple studies have noticed that fewer fishes, such as cod, haddock, rockfish, herring, sand seal, and blue whiting, have been spotted in areas with seismic noises, with catch rates declining by 40–80%.

Noise pollution has also altered avian communities and diversity. Anthropogenic noises have a similar effect on bird population as seen in marine ecosystems, where noises reduce reproductive success; cannot detect predators due to interferences of anthropogenic noises, minimize nesting areas, increase stress response, and species abundances and richness declining. Certain avian species are more sensitive to noises compared to others, resulting in highly-sensitive birds migrating to less disturbed habitats. There has also been evidence of indirect positive effects of anthropogenic noises on avian populations. In a study conducted by Francis and his colleagues, nesting bird predators, such as the western scrub-jay ('' Aphelocoma californica''), were uncommon in noisy environments (western scrub-jay are sensitive to noise). Therefore, reproductive success for nesting prey communities was higher due to the lack of predators.

Invasive species

Invasive species have major implications on biodiversity loss and have degraded various ecosystems worldwide. Invasive species are migrant species that have outcompeted and displaced native species, altered species richness and food webs, and changed ecosystems' functions and services. According to the Millennium Ecosystem Assessment, invasive species are considered one of the top five factors which result in biodiversity loss. In the past half century, biological invasions have increased immensely worldwide due to economic globalization, resulting in biodiversity loss. Ecosystems that are vulnerable to biological invasions include coastal areas, freshwater ecosystems, islands, and places with a Mediterranean climate. One study conducted a meta-analysis on the impacts of invasive species on Mediterranean-type ecosystems, and observed a significant loss in native species richness. Invasive species are introduced to new habitat, either intentionally or unintentionally, by human activities. The most common methods for the introduction of aquatic invasive species are by ballast water, on the hulls of ships, and attached to equipment such as fishing nets.

Global warming has changed typical conditions in various environments, allowing greater migration and distribution of species dependent on warm climate. This phenomenon could either result in greater biodiversity (new species being introduced to new environments), or reduce biodiversity (promotion of invasive species). A biological invasion is deemed successful if the invasive species can adapt and survive in the new environment, reproduce, disperse, and compete with native communities. Some invasive species are known to have high dispersal rates and have major implications on a regional scale. For example, in 2010, muskrat, raccoon dog, thrips, and Chinese mitten crab were identified to have affected 20 to 50 regions in Europe.

Invasive species can become financial burdens for many countries. Due to ecological degradation caused by invasive species, this can alter the functionality and reduce the services that ecosystems provide. Additional costs are also expected to control the spread of biological invasion, to mitigate further impacts, and to restore ecosystems. For example, the cost of damage caused by 79 invasive species between 1906 and 1991 in the United States has been estimated at US$120 billion. In China, invasive species have reduced the country's gross domestic product (GDP) by 1.36% per year. Management of biological invasion can also be costly. In Australia, the expense to monitor, control, manage, and research invasive weed species was approximately AU$116.4 million per year, with costs only directed to central and local government. In some situations, invasive species may have benefits, such as economic returns. For instance, invasive trees can be logged for commercial forestry. However, in most cases, the economic returns are far less than the cost caused by biological invasion.

Not only have invasive species caused ecological damage and economical losses, but they can also affect human health. With the alteration in ecosystem functionality (due to homogenization of biota communities), invasive species have resulted in negative effects on human well-being, which includes reduced resource availability, unrestrained spread of human diseases, recreational and educational activities, and tourism. With regard to human health, alien species have resulted in allergies and skin damage to arise. Other similar diseases that invasive species have caused include human immunodeficiency virus (HIV), monkey pox, and severe acute respiratory syndrome (SARS).

Overexploitation

Fossil fuel

Due to human dependency and demands, fossil fuel remains the dominant energy source globally; in the United States and other countries, approximately 78% of energy production derive from fossil fuels. Extraction, processing, and burning of fossil fuels indirectly impacts biodiversity loss by contributing to climate change, while directly causing habitat destruction and pollution. At fossil fuel extraction sites, land conversion, habitat loss and degradation, contamination, and pollution impacts biodiversity beyond terrestrial ecosystems; it impacts freshwater, coastal, and marine environments. Once fossil fuels have been extracted, they are transported, processed, and refined, which also impacts biodiversity as infrastructure development requires removal of habitats, and further pollution is emitted into the environment. For example, the construction of roads, well pads, pipelines, reserve pits, evaporation ponds, and power lines leads to habitat fragmentation and noise pollution.

Fossil fuel exploitation tends to occur in areas with high species richness and abundances, usually located in coastal and terrestrial environments. In one study, Harfoot and his colleagues identified 181 possible "high-risk" areas for fossil fuel exploitation, which were areas that also supported high levels of biodiversity. Out of the 181 identified locations, 156 of these high-risk fields were not protected areas, indicating that further biodiversity could be lost with fossil fuel exploitation. It is predicted that future exploration for fossil fuel will occur in areas with low species richness and rarity, such as the oceans and in the Arctic. However, this prediction does not apply to Western Asia, Asia-Pacific, Africa, South America, and the Caribbean, where fossil fuel and coal exploitation is expected to occur in areas with high species richness. For example, the Western Amazon (located in Brazil) is known to have high biodiversity. However, this region is also threatened by exploitation due to the large quantity of oil and natural gas reservoirs. Typically, areas with large fossil fuel reservoirs have a greater likelihood of being extracted (based on the country's priorities). This is of concern as tropical environments contain high levels of biodiversity, which will indirectly result in greater deforestation for agricultural purposes and financial gains (e.g., exporting timber).

Overfishing

Human demands and consumption have resulted in overfishing, which leads to a loss in biodiversity with reduction of fish species richness and of population abundances, and to depletion of large predatory fishes at the top of marine food webs.

Reduction in global fish populations were first noticed during the 1990s. Currently, many commercial fishes have been overharvested: a 2020 report by FAO classified as overfished 34 percent of the fish stocks of the world’s marine fisheries. By the same period, global fish populations were reduced by 38% compared to 1970. Regional examples abound: in the United States approximately 27% of exploited fish stocks are considered overfished. In Tasmania, over 50% of major fisheries species, such as the eastern gemfish, the southern rock lobster, southern bulkefin tuna, jack mackerel, or trumpeter, have declined over the past 75 years due to overfishing.

Fishery methods, such as bottom trawling and longline fishing

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