https://www.earthday.org/2018/05/18/populations-of-living-things-across-all-species-are-declining-and-this-is-very-worrisome/

What You Need to Know About Declining Species

What is happening to our species and their habitat?

There is no doubt that a vast number of animals and plants have gone extinct in recent centuries due to human activity, especially since the industrial revolution. [1] The number of individuals across species of plants and animals[2] has declined as well – in many cases severely – affecting genetic variation, biodiversity, among other issues.

All around the world, areas where humans exploit natural resources or undergo encroaching development all have the same outcome: a deteriorating natural environment. As a result of human action, ecosystems face threats such as unhealthy production and consumption; in today’s interconnected world, it doesn’t take much to see these unsustainable forces to take hold. [3]

This is a trend that cannot continue. If ecosystems are too severely depleted, their ability to remain replenish, sustain our species, and meet human needs is drastically threatened.

Many of us have seen images depicting open prairies covered by massive herds of bison that no longer exist, enormous flocks of birds congregated in marshes and lagoons that have seen their numbers reduced dramatically, or beautiful and impressive animals such as elephants, giraffes, and whales, which — in many cases — are in danger of becoming extinct.

Other people have cherished memories of less imposing animals that nonetheless bring deeply felt emotions, such as the sound of thousands of frogs croaking in the middle of the night, birds visiting a backyard feeder year after year, or millions of bats flying to their resting place at dusk. Others might remember that when traveling by car through the countryside, their car’s windshield ended up covered with hundreds of dead insects, which sadly was a signal of abundance that now hardly ever happens.

If you lived close to the ocean or spent much time there, you have probably heard that fish stocks have declined dramatically or read stories about whales, dolphins, and other marine mammals washing up dead on beaches, [4] occasionally in large numbers.

In the last decades, we have learned countless stories of new species of plants or animals being discovered in tropical forests across the globe, giving us a sense of wonder and possibility. At the same time, millions of acres of natural forests are being destroyed every year.

Let’s check some numbers: [5]

• The number of animals living on the land has fallen by 40% since 1970.[6]
• Marine animal populations have also fallen by 40% overall.[7]
• Overall, 40 percent of the world’s 11,000 bird species are in decline.[8]
• Animal populations in freshwater ecosystems have plummeted by 75% since 1970.[9]
• Insect populations have declined by 75% in some places of the world.[10]
• About a quarter of the world’s coral reefs have already been damaged beyond repair, and 75 percent of the world’s coral reefs are at risk from local and global stresses.[11]
• It is estimated that humans have impacted 83% of Earth’s land surface, which has affected many ecosystems as well as the range in which specific species of wildlife used to exist. [12]

Developed nations have seen benefits in economic growth not only from the exploitation of their ecosystems and species, but from the exploitation of the ecosystems and species of undeveloped nations as well. [13] Currently, the biggest declines in animal numbers are happening in low-income, developing nations, mirroring declines in wildlife that occurred in wealthier nations long before. The last wolf in the UK was killed in 1680. [14] For instance, between 1990 and 2008, around a third of products that cause deforestation – timber, beef, and soya – were imported to the EU.[15]

Academics and others debate if we are already facing a new process of mass extinction, such as the ones the world has experienced over the millennia. But even if that is not the case, we know that thousands of species are endangered, and most land and sea flora and fauna have seen their numbers severely reduced, with few exceptions.

Many species have disappeared already and many more are following the same path. As reported by The World Conservation Union (IUCN), there have been 849 species that have disappeared in the wild since 1500 A.D.; most strikingly, this number greatly underestimates the thousands of species that disappeared before scientists were able to identify them. [16]Most troublingly, around 33% and 20% of amphibians and mammals are in danger of becoming extinct in the coming decades. [17]

We also know that some people have argued that species have disappeared before and how the current decline is just part of a natural process. But this conclusion is way off base. All other processes of global mass extinction in the history of the planet happened because of a catastrophic natural event. They were not the result of human intervention, as is the case for the current mass extinction. According to Peter Ward from the University of Washington, what we are experiencing today is strikingly similar to the dinosaur-killing event of 60 million years ago, when a planet already stressed by sudden changes in its climate was knocked into mass extinction by the impact of asteroids. [18] This mass extinction we are going through has been unfolding because of the intervention of a single species, us. Humans are having an outsized negative impact on all other species. Human activity has caused a dramatic reduction in the total number of species and the population sizes of specific species; thousand have already disappeared, and many more are threatened with extinction.

The marine extinction crisis is not as widely grasped as the crises in tropical forests and other terrestrial biomes. [19] We do not know how many species are in the ocean as the bulk of marine species are undiscovered. Therefore, we do not know how many have disappeared or how many are in danger of disappearing. Furthermore, we are also losing species or unique types within a species (for example a type of salmon), before we even know of them.

We know that overfishing is a major global concern. Current assessments cover only 20% of the world’s fish stocks, so the true state of most of the world’s fish populations is not clear. Although, recent findings suggest that those unstudied stocks are declining, [20] and nearly three-quarters of the world’s commercially fished stocks are overharvested and at risk.

Along with species extinction, the devastation of genetically unique populations and the loss of their genetic variation[21] leads to an irreversible biodiversity loss. The evidence all points to the unfolding of a global tragedy with permeant consequences.[22]

What is driving this process of extinction?

• Overexploitation of species either for human consumption, use, elaboration of byproducts, or for sport. [23]
• Habitat Loss: [24]
  • Habitat destruction: A bulldozer pushing down trees is the iconic image of habitat destruction. Other ways people directly destroy habitat include filling in wetlands, dredging rivers, mowing fields, and cutting down trees.
  • Habitat fragmentation: Much of the remaining terrestrial wildlife habitat has been cut up into fragments by roads and development. Aquatic species’ habitats have been fragmented by dams and water diversions. These fragments of habitat may not be large or connected enough to support species that need a large territory where they can find mates and food. Also, the loss and fragmentation of habitats makes it difficult for migratory species to find places to rest and feed along their migration routes.
  • Habitat degradation: Pollution, invasive species, and disruption of ecosystem processes (such as changing the intensity of fires in an ecosystem) are some of the ways habitats can become so degraded they can no longer support native wildlife.
• Climate Change:
  • As climate change alters temperature and weather patterns, it also impacts plant and animal life. Scientists expect that the number and range of species, which define biodiversity, will decline greatly as temperatures continue to rise.[25]
  • The burning of fossil fuels for energy and animal agriculture are two of the biggest contributors to global warming, along with deforestation. Livestock accounts for between 14.5 percent and 18 percent of human-induced greenhouse gas emissions.[26] Those emissions come from cattle belches, intestinal gasses, and waste; the fertilizer production for feed crops; general farm associated emissions; and the process of growing feed crops. [27] According to research conducted by the Worldwatch Institute’s Nourishing the Planet project, animal waste releases methane and nitrous oxide, greenhouse gases that are much more potent than carbon dioxide. As people increase their level of income, they consume more meat and dairy products. The populations of industrial countries consume twice as much meat as those in developing countries.[28] Worldwide meat production has tripled over the last four decades and increased 20 percent in just the last ten years. This information suggests that we should cut back on our consumption of meat and dairy. “The privilege we have over these animals, it would appear, now comes at a hefty price [to the planet].”[29]

• The spread of non-native species around the world; a single species (us) taking over a significant percentage of the world’s physical space and production; and, human actions increasingly directing evolution.[30]
  • The first factor is also known as the global homogenization of flora and fauna. Biotic homogenization[31] is an emerging, yet pervasive, threat in the ongoing biodiversity crisis. Originally, ecologists defined biotic homogenization as the replacement of native species by exotics or introduced species, but this phenomenon is now more broadly recognized as the process by which ecosystems lose their biological uniqueness and uniformity grows.[32] As global transportation becomes faster and more frequent, it is inevitable that species intermixing will increase. When unique local flora or fauna become extinct, they are often replaced by already widespread flora or fauna that is more adapted to tolerate human activities. This process is affecting all aspects of our natural world. For example, we grow the same crops anywhere in the world at the expense of the local varieties that in many cases disappear; introduce animals into places where they did not exist, and often do not have natural enemies, becoming a plague, such as rats introduced to the Galapagos Islands; or destroy other species that cannot defend themselves from the new predator, such as in Guam where over the years ten of Guam’s twelve original forest bird species have been lost due to the introduction of the brown tree snake.[33] Biological homogenization qualifies as a global environmental catastrophe. The Earth has never witnessed such a broad and complete reorganization of species distribution, in which animals and plants (and other organisms for that matter) have been translocated on a global scale around the planet.
  • Over the last few centuries, humans have essentially become the top predator not only on land, but also across the sea. In doing so, humanity has begun using 25-40% of the planet’s net primary production for its own. [34] As we keep expanding our use of land and resources, the capacity of species to survive is constantly reduced.
  • Humanity has become a massive force in directing evolution. This is most apparent, in the domestication of animals and the cultivation of crops over thousands of years. But humans are directing evolution in numerous other ways as well, manipulating genomes by artificial selection and molecular techniques, and indirectly by managing ecosystems and populations to conserve them, said co-author Erle Ellis, an expert on the Anthropocene with the University of Maryland. He added that even conservation is impacting evolution.[35]
• Other: In countries around the world, policies have been enacted that have led to extinction or near extinction of specific species, such large predators in the US and Europe. Also, chemical products associated with agriculture or other productive processes have affected many species such as honeybees and other pollinators.