Biodiversity loss includes the extinction of species worldwide, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity

Biodiversity loss includes the extinction of species worldwide, 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.

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,6 and expected to still grow in the upcoming years.789 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.

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 absoluteclarification needed 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."11 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 diversity11) 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.

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.15 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.
In 2017, various publications described the dramatic reduction in absolute insect biomass and number of species in Germany and North America over a period of 27 years.8586 As possible reasons for the decline, the authors highlight neonicotinoids and other agrochemicals. Writing in the journal PLOS One, Hallman et al. (2017) conclude that "the widespread insect biomass decline is alarming."87

For example, the critical decline of earthworms (over 80% on average) has been recorded under non-ecological agricultural practices.88 Earthworms play an important role in ecosystem function.88 For example, they help with biological processing in soil, water, and even green house gas balancing.89 The decline of earthworm populations are said to be due to five reasons; soil degradation and destruction of habitat, climate change, biological invasion of nonnative species, poor soil management, and pollutant loading.90 Factors like tillage practices and intensive land use decimate the soil and plant roots that earthworms use to create their biomass, causing carbon and nitrogen cycles to be impacted negatively. Knowledge of earthworm species diversity is quite limited as not even 50% of them have been described. More studies upon earthworms and how they provide their ecosystem services must be done to gain a better understanding of going about preserving their diversity.90 With earthworm populations dwindling, this has caused for the Secretariat of the Convention on Biological Diversity to take action and promote the restoration and maintenance of the many diverse species of earthworms.90

Birds loss
Certain types of pesticide, neonicotinoids, probably contribute to the decline of certain bird species.91 A study funded by BirdLife International confirms that 51 species of birds are critically endangered and 8 could be classified as extinct or in danger of extinction. Nearly 30% of extinction is due to hunting and trapping for the exotic pet trade. Deforestation, caused by unsustainable logging and agriculture, could be the next extinction driver, because birds lose their habitat and their food. The biologist Luisa Arnedo said: "as soon as the habitat is gone, they're gone too".92

Within the Amazon rainforest there is an area called Bele´m and it is an area of endemism. In Bele´m 76% of the land has already been stripped of its natural resources, including the trees of the forest.93 Within the area bird species are strongly affected by the deforestation, due to being put in that situation 56% of the birds are now in danger of going into extinction. With the climate changing as well as their habitat, the population of the birds will continue to decline. Even with protected areas of land, the efficiency in which birds are conserved are low.93

Freshwater species loss
Freshwater ecosystems ranging from swamps, deltas, to rivers make up to 1% of earths surface. Although making up such little proportion of the earth, freshwater ecosystems are important because these kind of habitats are home to approximately one third of vertebrate species.94 Freshwater species are beginning to decline at twice the rate of other species such as those located on land or within the ocean, this rapid loss has already placed 27% of 29,500 species dependent on freshwater upon the IUCN Red List.94 With freshwater species declining so quickly, it is due to the poor systems in place that don't provide any protection to their biodiversity.

A study by 16 global conservation organizations found that the biodiversity crisis is most acute in freshwater ecosystems, with a rate of decline double that of oceans and forests. Global populations of freshwater fish are collapsing from anthropogenic impacts such as pollution and overfishing. Migratory fish populations have declined by 76% since 1970, and large "megafish" populations have fallen by 94% with 16 species declared extinct in 2020.95

Native species richness loss
Humans have altered plant richness in regional landscapes worldwide, transforming more than 75% of the terrestrial biomes to "anthropogenic biomes." This is seen through loss of native species being replaced and out competed by agriculture. Models indicate that about half of the biosphere has seen a "substantial net anthropogenic change" in species richness.96

Marine species richness loss

Marine biodiversity encompasses any living organism which resides in the ocean, and describes various complex relationships within marine ecosystems.58 On a local and regional scale, marine communities are better understood compared to marine ecosystems on a global scale. In 2018, it was estimated that approximately 240,000 marine species have been documented.57 Based on this prediction, the discovery of total marine species ranges between 11% to 78% due to uncertainties regarding global marine biodiversity.57 However, the number of described marine species remains low compared to terrestrial species due to various factors, which includes the assignment of different names for the same species, and insufficient taxa classification.58 It is likely that many undocumented species has already disappeared. Because not all marine species have been described, it is difficult to provide an accurate estimate of global extinction in marine ecosystems. As a result, abundances of marine species remain uncertain, with estimates ranging between 178,000 and 10 million oceanic species.58

With anthropogenic pressure, this results in human activities having the strongest influences on marine biodiversity, with main drivers of global extinction being habitat loss, pollution, invasive species, and overexploitation.9798 Greater pressure is placed on marine ecosystems with human settlements near coastal areas.99 Other indirect factors that have resulted in marine species to decline include climate change and change to oceanic biochemistry.97

Overexploitation has resulted in the extinction of over 20 described marine species, which includes seabirds, marine mammals, algae, and fishes.58 Examples of extinct marine species include the Steller's sea cow (Hydrodamalis gigas) and the Caribbean monk seal (Monachus tropicalis). However, not all extinctions are because of humans. For example, in 1930, the eelgrass limpet (Lottia alveus) became extinct once the Zostera marina seagrass population declined upon exposure to a disease. The Lottia alveus were greatly impacted as the Zostera marina were their sole habitats.58

Impacts
Ecological effects of biodiversity loss

Biodiversity loss also threatens the structure and proper functioning of the ecosystem. Although all ecosystems are able to adapt to the stresses associated with reductions in biodiversity to some degree, biodiversity loss reduces an ecosystem's complexity, as roles once played by multiple interacting species or multiple interacting individuals are played by fewer or none.32 The effects of species loss or changes in composition, and the mechanisms by which the effects manifest themselves, can differ among ecosystem properties, ecosystem types, and pathways of potential community change. At higher levels of extinction (40 to 60 percent of species), the effects of species loss ranked with those of many other major drivers of environmental change, such as ozone pollution, acid deposition on forests and
An October 2020 analysis by Swiss Re found that one-fifth of all countries are at risk of ecosystem collapse as the result of anthropogenic habitat destruction and increased wildlife loss.
In 2019, the UN's Food and Agriculture Organization produced its first report on The State of the World's Biodiversity for Food and Agriculture, which warned that "Many key components of biodiversity for food and agriculture at genetic, species and ecosystem levels are in decline."103104 The report states that this is being caused by "a variety of drivers operating at a range of levels" and more specifically that "major global trends such as changes in climate, international markets and demography give rise to more immediate drivers such as land-use change, pollution and overuse of external inputs, overharvesting and the proliferation of invasive species. Interactions between drivers often exacerbate their effects on biodiversity for food and agriculture (BFA). Demographic changes, urbanization, markets, trade and consumer preferences are reported by the countries that provided inputs to the report to have a strong influence on food systems, frequently with negative consequences for BFA and the ecosystem services it provides. However, such drivers are also reported to open opportunities to make food systems more sustainable, for example through the development of markets for biodiversity-friendly products."105 It further states that "the driver mentioned by the highest number of countries as having negative effects on regulating and supporting ecosystem services in food and agricultural production systems is changes in land and water use and management" and that "loss and degradation of forest and aquatic ecosystems and, in many production systems, transition to intensive production of a reduced number of species, breeds and varieties, remain major drivers of loss of BFA and ecosystem services."

The health of humans is largely dependent on the product of an ecosystem. With biodiversity loss, a huge impact on human health comes as well. Biodiversity makes it possible for humans to have a sustainable level of soils and the means to have the genetic factors to have food.106

Many activists and scholars have suggested that there is a connection between plant patent protection and the loss of crop biodiversity,107 although such claims are contested.
There are so many conservation challenges when dealing with biodiversity loss that a joint effort needs to be made through public policies, economic solutions, monitoring and education by governments, NGOs, conservationists etc.113 Incentives are required to protect species and conserve their natural habitat and disincentivize habitat loss and degradation (e.g. implementing sustainable development including targets of SDG 15). Other ways to achieve this goal are enforcing laws that prevent poaching wildlife, protect species from overhunting and overfishing and keep the ecosystems they rely on intact and secure from species invasions and land use conversion.114 Furthermore, conservation based models like the Global Safety Net are continuously being developed to consider the ecological connections that need to be addressed to effectively mitigate biodiversity loss.115 According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) action to protect biodiversity is very cost effective because it reduces the risk of pandemics due to pathogens from wildlife.116

Conservationists and sustainable research scientists around the world have also developed systems-based approaches to help mitigate biodiversity loss. This methodology allows scientists to create contextual frameworks that consider the many nuances and linkages of environmental conservation like ecological footprints, planetary boundaries, ecological economics, etc.117 Considering all the many ways in which the natural and human world intersect can help researchers understand the intricacies that lead to biodiversity loss and find patterns that can be applied to similar situations. One example of these type of frameworks is the triple bottom line, which has been adopted by many businesses and organizations to evaluate their impact and progress towards the marriage of social, environmental, and economic

There are many organizations devoted to the cause of prioritizing conservation efforts such as the Red List of Threatened Species from the International Union for Conservation of Nature and Natural Resources (IUCN) and the United States Endangered Species Act. British environmental scientist Norman Myers and his colleagues have identified 25 terrestrial biodiversity hotspots that could serve as priorities for habitat protection.118

Many governments in the world have conserved portions of their territories under the Convention on Biological Diversity (CBD), a multilateral treaty signed in 1992–3. The 20 Aichi Biodiversity Targets, part of the CBD's Strategic Plan 2011–2020, were published in 2010.119 Since 2010, approximately 164 countries have developed plans to reach their conservation targets, including the protection of 17 percent of terrestrial and inland waters and 10 percent of coastal and marine areas.

In 2019 the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), an international organization formed to serve a similar role to the Intergovernmental Panel on Climate Change (IPCC),120 published the Global Assessment Report on Biodiversity and Ecosystem Services which said that up to a million plant and animal species are facing extinction because of human activities.11416 An October 2020 report by IPBES stated that the same human activities which are the underlying drivers of climate change and biodiversity loss, such as the destruction of wildlife and wild habitats, are also the same drivers of pandemics, including the COVID-19 pandemic.

According to the 2020 United Nations' Global Biodiversity Outlook report, of the 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only 6 were "partially achieved" by the deadline of 2020.122 The report highlighted that if the status quo is not changed, biodiversity will continue to decline due to "currently unsustainable patterns of production and consumption, population growth and technological developments".123 The report also singled out Australia, Brazil and Cameroon and the Galapagos Islands (Ecuador) for having had one of its animals lost to extinction in the past 10 years.124 Following this, the leaders of 64 nations and the European Union pledged to halt environmental degradation and restore the natural world. Leaders from some of the world's biggest polluters, namely China, India, Russia, Brazil and the United States, were not among them.125 Some experts contend that the refusal of the United States to ratify the Convention on Biological Diversity is harming global efforts to halt the extinction crisis.126 Top scientists say that even if the 2010 targets had been met, it likely would not have resulted in any substantive reductions of current extinction rates.181 Others have raised concerns that the Convention on Biological Diversity does not go far enough, and argue the goal should be zero extinctions by 2050, along with cutting the impact of unsustainable food production on nature by half. That the targets are not legally binding has also been subject to criticism.