Why do animals disappear?
7.8 billion humans and our domesticated animals (pets and livestock) make up 96% of all mammals alive on Earth. The other 4% of mammals are the remaining wildlife populations, and unfortunately, due to man-made (anthropogenic) pressures, their numbers are decreasing rapidly.
1. Habitat loss: destruction, degradation & fragmentation
Human activities exert pressure on over 90% of the world’s land. Undamaged natural habitats account for just 28% of the land on Earth and are under continual threat. Habitats and populations of wild animals
become fragmented and divided as industries and cities expand.
Rivers are polluted and fragmented by dams and reservoirs, and over a third of the world’s wetlands have disappeared since 1970. Human interactions with the ocean are so varied and profound that there is a gap in our understanding: The magnitude of our footprint or the speed at which our cumulative impacts change the ocean is largely unknown. We know that 59% of the ocean is experiencing increasing anthropogenic pressure, with coral reefs, seagrasses, and mangroves most at risk.
Habitat loss means that particular habitat is so degraded or destroyed that it can no longer support its indigenous wildlife. The animals that once lived there die or become displaced. Cheetah habitats used to span from Africa to the Middle East and central India. Today, a single population of 12 Asiatic cheetahs in central Iran is all that is left of the Asiatic subspecies. In Africa, cheetah habitats are so fragmented that only 20 – 30 isolated populations are left in the wild. They are often killed due to human-wildlife conflict, which increases with human encroachment on habitats. Habitat loss poses the greatest threat to 85% of threatened and endangered species.
2. Climate change
Our global greenhouse gas emissions continue to increase as the human population grows. In May 2021, atmospheric carbon dioxide levels peaked at 419 ppm – the highest since accurate measurements began in 1959. Climate change affects the global environment, causing extreme shifts in weather patterns with increasing frequency and severity of droughts, flooding, forest fires, and natural disasters. It has also resulted in increased temperatures globally.
Due to their polar locations, the Arctic and Antarctic regions are warming at the double the rate of the rest of the planet. Ice-dependent species such as penguins, polar bears, walruses, and narwhals are losing their
habitats due to the shrinking sea ice. Since the 1970s, there has been a 50% reduction in sea ice cover due to global warming.
Coral reefs support 25% of marine life and experience stress if water temperatures increase (or decrease) as little as 1℃. Rising temperatures and ocean acidification cause coral bleaching. Coral bleaching describes how stressed corals expel the algae that provide them with bright colors and food. The corals turn white and starve to death. Their decay often leads to the collapse of the reef’s ecosystem. From 2014 to 2017, 70% of the world’s coral reefs were damaged due to climate change. Invasive alien species are shown to cope with rapid environmental changes, while endangered and endemic species often cannot adapt, placing their dwindling populations under further strain.
3. Freshwater pollution
Rivers, lakes and wetlands become polluted when harmful substances enter from:
- Domestic sewage
- Agricultural runoff and waste
- Wastewater, chemicals, and heat from power generation, mining and heavy industries
This deadly pollution cocktail has severe impacts on aquatic wildlife. Human and livestock pathogens spill over into wildlife populations causing disease outbreaks. Algae use the extra nutrients available for uncontrolled growth and cover the water’s surface with algal blooms. Sunlight can’t penetrate through the layer of algae so aquatic plants below the surface die. As the water’s oxygen levels are depleted, fish and other life forms die due to respiratory failure, and the ecosystem collapses.
4. Marine pollution
Nitrogen-rich nutrients enter oceans from polluted rivers, which again causes excessive algae and phytoplankton growth in the form of poisonous algal tides. Our oceans are also threatened by plastic waste and the commercial shipping industry. Oil and contaminant spills have toxicological impacts on the entire affected area. If we do not reduce plastic waste disposed of in the sea, there will be more plastic than fish by 2050.
Plastic takes hundreds of years to degrade and has accumulated in large floating garbage patches across the ocean. There is an estimated 200 million tons of plastic in the world’s seas, with an average of 8-14 million tons being dumped into the oceans every year. Marine animals mistake plastic for food and eat it.
This can cause intestinal blockages, poisoning, or the bellies of marine animals being so full of plastic that they cannot eat and starve. Ingested plastic accumulates in food chains, with the top predators most affected (biomagnification). Dugongs, seals, dolphins, sharks, turtles, and marine birds are just some animals that become entangled in abandoned plastic fishing nets and inevitably die through suffocation, starvation, or laceration.
Deforestation is permanently removing large areas of trees and/ or forests. On average, 2,400 trees are cut down each minute for wood and to create land for urban or commercial use. Deforestation is the the leading cause of habitat destruction and the second leading cause of climate change.
While forests cover just 30% of global land, they are home to more than 80% of the world’s animal and plant species. Forests aren’t just made up of trees; rather, they are complex ecosystems where plants, fungi, and animal life interact in interdependent networks. Rainforests are biodiversity hotspots with multitudes of endemic species (species that exist only in their particular forest). Most of the world’s rainforest biomes are concentrated in The Amazon of South America, The Congo Basin of West Africa, the lush tropical forests of Malaysia, and the Indonesian islands of Sumatra and Borneo.
The Orangutans of Indonesia are the most endangered of the Great Apes, with all three orangutan species experiencing sharp population declines in recent times. The Tapanuli Orangutan is the rarest species, found only in the forests of South Sumatra. This species has a population of fewer than 800 individuals.
Only 7 viable populations of Sumatran Orangutans are left, and Bornean Orangutan populations have halved in the past 60 years. This is due to the mass clearing and burning of more than 55% of their tropical rainforest habitat over the past 20 years. Unfortunately, the most extreme and concentrated deforestation occurs in the largest tropical rainforests. In 2020, the world lost 12.2 million hectares of tropical forest, with the most significant primary forest loss occurring in the Amazon, the Congo Basin, and Indonesia.
Primary rainforest loss in the Congo Basin has accelerated since 2002. In 2019 alone, 5900 square km have been lost. By the end of 2020, deforestation levels in the Brazilian Amazon had soared to 27% (the highest in 15 years). At the current rate of deforestation, 27% of the Amazon rainforest will be completely devoid of indigenous forests and wildlife by 2030, and the tropical rainforests of Indonesia will vanish altogether.
6. Land loss and demand
Land degradation accelerated during the 20th and 21st centuries. Every year, an estimated 12 million hectares of agricultural land is lost due to degradation and abandonment. Land degradation is often a side effect of intensive farming practices (e.g., overgrazing, overutilization, irrigation) and extreme weather events such as drought. When the soil becomes too arid, nutrients leached and erode, farmers abandon it and require more areas where rich life-supporting soil still exists.
- Globally, commercial agriculture accounted for 40% of tropical deforestation between 2000 and 2010, and local subsistence agriculture for another 33%.
- 91% of cleared land in the Amazon is used to raise cattle and grow animal feed such as soya beans.
- In Indonesia and Malaysia, cleared forests create land for palm oil plantations where 90% of the world’s palm oil is produced.
- Similarly, both cocoa and oil palm plantations have replaced vast areas of the Congo forest in West Africa.
7. Unsustainable Fishing practices
Overfishing refers to catching more fish than can be naturally reproduced by the remaining population.
Over 30% of the world’s fisheries have been overfished, and the demand for specific types of fish like tuna is changing marine communities. Overfishing affects the targeted fish populations and the related species of marine animals within the same ecosystem.
Because of commercial fishing, the Atlantic Bluefin tuna populations have declined to the point where their survival as a species is threatened. Bluefin tuna are predators in their ecosystems and a food source for sharks, marine mammals, large fish, and seabirds. Juvenile Bluefins eat fish, squid, and crustaceans, and adults feed mainly on ‘baitfish’ such as herring, bluefish, and mackerel. Oceanic ray and shark populations have been reduced by 71% since 1970, largely due to the overfishing of their prey species, and over 75% of species in this group are threatened with extinction.
Bycatch refers to the non-targeted species that are killed in fishing nets. Up to 40% of the global marine catch is bycatch. Every year an estimated 650 000 dolphins, whales, and seals are killed in fishing nets. The other victims of bycatch include turtles, marine birds, and juvenile fish(which are crucial in maintaining fish populations).
8. Hunting, poaching & wildlife trafficking
Hunting is the seeking, pursuing, capturing, and killing of wild animals. The controversial practices of hunting and killing marine mammals(whales and dolphins), both recreationally and commercially, are fraught with ethical and legal issues. People often hunt wild animals to harvest animal products (meat, skin, organs) as a source of food or income. The added pressure from international wildlife trafficking drives the decline and extinction of wildlife populations globally.
The growing list of victims includes thousands of orangutans, Javan tigers, leopards, elephants, and rhinos. The bodies of these animals are bought, sold, and reduced to symbols of wealth and power or ingredients in traditional medicines. Three species of Rhino are critically endangered of extinction due to poaching for rhino horn and habitat loss:
- Only 60 Javan Rhinos in a single National Park in Java, Indonesia.
- Only 80 Sumatran rhinos are left in Indonesia.
- The species’ mainland counterpart was declared extinct in Vietnam in 2011.
9. Invasive alien species
Alien species are those plants and animals that have been introduced to an environment where they are generally not found. Invasive aliens thrive and rapidly multiply, wreaking havoc on the native wildlife of the area by spreading a disease or outcompeting native species for food or space. A classic example is that of the domestic cat. Multiple studies have shown that cats kill billions of birds and wild mammals annually, in the USA. In Australia, feral and domestic cats are responsible for 66% of native mammal extinctions.
Unfortunately, pet cats were just the beginning…
The multibillion-dollar global pet trade of exotic animals has resulted in many of these ‘pets’ being accidentally or intentionally released into natural spaces. Florida has experienced an explosive invasion of alien reptiles, amphibians, and fish, including the Nile monitor (lizard), Asian carp (fish), cane toads, red-eared slider (turtle), and the infamous Burmese python. The Burmese python is native to South East Asia. In Florida, these alien pythons outcompete threatened species of local snakes and prey on endangered native species such as the Key Largo woodrat.
10. Parasites & diseases
Anthropogenic pressures increase the stress placed on wild animals’ immune systems, invariably increasing their susceptibility to infectious diseases and parasites. In addition, populations with fewer individuals have decreased genetic diversity and in turn, decreased immune resilience.
While we commonly think of wildlife as a source of the disease that infects humans and domestic animals(COVID-19 “bat virus”), in reality, it works both ways. Some parasites and biological infections that use humans and domesticated animals as hosts are transmitted to wild animal populations. Wild populations that are in closer contact with people are more at risk. Since those wildlife populations have never encountered the parasite or virus, they have no preexisting resistance to it and become sick.
- In the USA, outbreaks of toxoplasmosis in sea otters are thought to be due to terrestrial water run-off contaminated with domestic cat feces.
- In Australia, sarcoptic mange or scabies has spread from people and dogs to wombats, with small isolated populations being most at risk of severe illness and death.
- In East Africa, gorillas have contracted scabies from people during habituated ecotourism experiences. Human respiratory diseases such as pneumonia and tuberculosis have also accounted for the deaths of habituated gorillas and chimpanzees.
11. Noise pollution
Noise pollution is regular exposure to an environmental sound that negatively impacts wildlife. The sources of these sounds vary from commercial air travel and shipping to industrial machinery. Anthropogenic noise is a global pollutant that places stress on a range of wildlife, including insects, birds, bats, fish, and marine
Noise pollution causes hearing impairment and interferes with animal communication, reproduction, navigation, and echolocation. It upsets the delicate balance in prey-predator interactions and increases the
risk of death. Noise pollution can also synergize with other disturbances, such as light pollution.
12. Light pollution
While city lights can be seen from space, and their impacts are visible on Earth. Artificial lights are fatally attractive to moths and affect insect movement, foraging, reproduction, and predation. Nocturnal animals
find artificial light at night disturbing, and even cloudy skies are much brighter than they were 200 years ago. Birds that migrate or hunt at night can become disorientated by artificial light, resulting in more
collisions and higher bird mortality.
Nesting sea turtles are discouraged from nesting on beaches because of artificial light. Sea turtle hatchlings are guided to the ocean by the moonlit horizon. Artificial light is disorientating and leads hatchlings inland
away from the sea. Millions of hatchlings die under vehicles’ tires or through dehydration and predation every year.