لخّصلي

The weight of biodiversity loss is most pronounced on species whose populations are decreasing.That is, it ceases to be what it was (e.g., a tropical forest, a temperate swamp, an Arctic meadow, etc.) and undergoes a rapid restructuring, becoming something else (e.g., cropland, a residential subdivision or other urban ecosystem, barren wasteland, etc.).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.Declining biodiversity lowers an ecosystem's productivity (the amount of food energy that is converted into the biomass) and lowers the quality of the ecosystem's services (which often include maintaining the soil, purifying water that runs through it, and supplying food and shade, etc.).The loss of genes and individuals threatens the long-term survival of a species, as mates become scarce and risks from inbreeding rise when closely related survivors mate.Beyond a critical point of species removal or diminishment, the ecosystem can become destabilized and collapse.The wholesale loss of populations also increases the risk that a particular species will become extinct.Biodiversity loss also threatens the structure and proper functioning of the ecosystem.As parts are lost, the ecosystem loses its ability to recover from a disturbance (see ecological resilience).Biodiversity is critical for maintaining ecosystem health.

The weight of biodiversity loss is most pronounced on species whose populations are decreasing. The loss of genes and individuals threatens the long-term survival of a species, as mates become scarce and risks from inbreeding rise when closely related survivors mate. The wholesale loss of populations also increases the risk that a particular species will become extinct.

Biodiversity is critical for maintaining ecosystem health. Declining biodiversity lowers an ecosystem’s productivity (the amount of food energy that is converted into the biomass) and lowers the quality of the ecosystem’s services (which often include maintaining the soil, purifying water that runs through it, and supplying food and shade, etc.).

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. As parts are lost, the ecosystem loses its ability to recover from a disturbance (see ecological resilience). Beyond a critical point of species removal or diminishment, the ecosystem can become destabilized and collapse. That is, it ceases to be what it was (e.g., a tropical forest, a temperate swamp, an Arctic meadow, etc.) and undergoes a rapid restructuring, becoming something else (e.g., cropland, a residential subdivision or other urban ecosystem, barren wasteland, etc.).

Reduced biodiversity also creates a kind of “ecosystem homogenization” across regions as well as throughout the biosphere. Specialist species (i.e., those adapted to narrow habitats, limited food resources, or other specific environmental conditions) are often the most vulnerable to dramatic population declines and extinction when conditions change. On the other hand, generalist species (those adapted to a wide variety of habitats, food resources, and environmental conditions) and species favoured by human beings (i.e., livestock, pets, crops, and ornamental plants) become the major players in ecosystems vacated by specialist species. As specialist species and unique species (as well as their interactions with other species) are lost across a broad area, each of the ecosystems in the area loses some amount of complexity and distinctiveness, as the structure of their food chains and nutrient-cycling processes become increasingly similar.

Economic and societal effects
Biodiversity loss affects economic systems and human society. Humans rely on various plants, animals, and other organisms for food, building materials, and medicines, and their availability as commodities is important to many cultures. The loss of biodiversity among these critical natural resources threatens global food security and the development of new pharmaceuticals to deal with future diseases. Simplified, homogenized ecosystems can also represent an aesthetic loss.

Economic scarcities among common food crops may be more noticeable than biodiversity losses of ecosystems and landscapes far from global markets. For example, Cavendish bananas are the most common variety imported to nontropical countries, but scientists note that the variety’s lack of genetic diversity makes it vulnerable to Tropical Race (TR) 4, a fusarium wilt fungus which blocks the flow of water and nutrients and kills the banana plant. Experts fear that TR4 may drive the Cavendish banana to extinction during future disease outbreaks. Some 75 percent of food crops have become extinct since 1900, largely because of an overreliance on a handful of high-producing crop varieties. This lack of biodiversity among crops threatens food security, because varieties may be vulnerable to disease and pests, invasive species, and climate change. Similar trends occur in livestock production, where high-producing breeds of cattle and poultry are favoured over lower-producing, wilder breeds.

Mainstream and traditional medicines can be derived from the chemicals in rare plants and animals, and thus lost species represent lost opportunities to treat and cure. For example, several species of fungi found on the hairs of three-toed sloths (Bradypus variegatus) produce medicines effective against the parasites that cause malaria (Plasmodium falciparum) and Chagas disease (Trypanosoma cruzi) as well as against human breast cancer.