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MAN VS. WILD: Biodiversity at Riskbackground reading | biodiversity unit

Studies For Our Global Future

Long before Homo sapiens walked the Earth, the planet belonged to an enormous array of mammals, reptiles, insects, fish, birds and plants. From the tiniest organism, these species evolved over hundreds of millions of years into a rich collection of flora and fauna. We call this richness and variety of life biodiversity. Scientists have named just a fraction of species – about 2 million out of an estimated 8-9 million.

Over the course of Earth’s history, species have come and gone – sometimes dying off gradually, sometimes catastrophically, as with the dinosaurs 65 million years ago. Scientists have recorded five past mass extinction events and believe that we are in the midst of a sixth mass extinction. The first five events pre-dated humans. The sixth and current event is being caused by humans. Our growing numbers, resource consumption and land conversion have made us the dominant species on the planet, much to the peril of fellow animals and plants.

Extinction and endangerment occur for a variety of reasons. Some species are lost through natural occurrences. The natural or background extinction rate is believed to be from one to three species a year. Biologists estimate that current extinction rates are 1,000 times higher than natural background rates of extinction, and that future rates are likely to be 10,000 times higher.1 That’s because of the delicate web of interdependent species in an ecosystem. The removal of one species can accelerate the extinction of other species, eventually leading to a collapse of an ecosystem. The biggest threats to biodiversity can be remembered by using the mnemonic H.I.P.P.O (Habit Loss, Invasive Species, Pollution, Human Population and Overharvesting).

The IUCN Red List of Threatened Species is the world’s most comprehensive inventory of the global conservation status of plant and animal species. Currently, there are more than 79,800 species on the IUCN Red List, and more than 23,000 are threatened with extinction, including 41 percent of amphibians, 34 percent of conifers, 33 percent of reef-building corals, 25 percent of mammals and 13 percent of birds.2

Losing their homes

Habitat loss is the largest driver of biodiversity loss worldwide. As human numbers have grown 7-fold in the past 200 years, we have converted more and more wilderness for agriculture and human settlements. Most ecologists agree that reducing the size of a species’ natural habitat increases its risk of extinction. Timber clearcutting, mining, farming and urbanization have squeezed many of our native plants and animals into smaller and more fragmented areas. Over half of the planet’s land has been completely converted for human uses, with 4.5 million km2 (an area more than half the size of the lower 48 U.S. states) converted in the past 20 years alone.3

Source: IUCN Red List of Threatened Species

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Two biomes in particular, tropical rainforests and wetlands, have been especially impacted by habitat destruction. More than half of the world’s plants and animals live in tropical rainforests. Each day, some 125 square miles is destroyed. In terms of biodiversity, this translates to a loss of approximately 135 plant and animal species each day.4 That’s because so many of the species who call rainforests home live in microhabitats, existing in very specialized areas of the forest, making them more vulnerable to extinction. Primates are a case in point. Over half of the world’s primates are threatened by extinction, especially those that live in areas of tropical rainforest that are rapidly being cleared, such as orangutans in Indonesia, lemurs in Madagascar and gorillas in central Africa.

Wetlands are among the most productive ecosystems in the world and are home to an immense variety of species of microbes, plants, insects, amphibians, reptiles, birds, fish and mammals. They are found on every continent except Antarctica and range from mangroves in the tropics to sugar maple swamps around the Great Lakes. In the United States, more than one-third of threatened and endangered species live only in wetlands and nearly half use wetlands at some point in their lives. Wetlands also provide protection from floods, filter water and store carbon instead of releasing it into the atmosphere. Since 1780, the continental U.S. has lost half of its wetlands to land conversion.5

The clash between humans and wildlife is evident in other parts of the United States as well. Consider Florida, where the population has doubled since 1980, crowding out such native species as the West Indian manatee and the Florida panther. The dwindling manatee population falls victim to power boat propellers while grazing on sea beds. The nearly extinct panther has lost its home to subdivisions, citrus groves and other development. According to the U.S. Fish and Wildlife Service, there are now fewer than 100 panthers left in the wild.6

In addition to direct habitat destruction from expansion of agriculture and development, population pressures also contribute to habitat loss through climate change. Most climatologists concur that fossil fuel combustion is the main driver of climate change. The evidence is mounting on the effects of climate change on a variety of habitats. Coral reefs are dying off at accelerating rates from warmer temperatures and the ocean is acidifying from greenhouse gases. The polar bear population is expected to decline by 30 percent by 2050 due to melting ice in their Arctic habitat.7 Many species can only exist in a specific climate and lack the ability to move or adapt.

Human technology, too, has altered habitat in ways that threaten wildlife. River dams disrupt spawning patterns of salmon that live in the ocean and lay their eggs upriver in fresh-water streams. In order to help young salmon downstream, some biologists have resorted to removing the fish from rivers, transporting them around the dams, and then returning them to the water. In Florida, hatching sea turtles are fatally lured away from the ocean when they mistake the reflected city lights for the starlit sky over the water.

Coral reef in the tropics.

Photo Credit: vlad61/iStockphoto.com

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Polluting habitats

Even when habitats are left intact, wildlife populations can be affected by the pollutants that find their way into our air, land and waterways. Birds, mammals, fish, shellfish and their food sources are all vulnerable to human-generated toxins.

Consider the Chesapeake Bay, the nation’s largest estuary. Steady population growth in the Chesapeake Bay watershed has turned the bay into a catch basin that collects pollutants from factories, farms and sewage treatment plants. Runoff from lawns, roads, parking lots and farmland carries pesticides, oil and other toxins into the bay. According to the Chesapeake Bay Foundation, roughly 300 million pounds of polluting nitrogen enter the bay, mostly from agricultural runoff.8 This pollution has reduced the bay’s seafood catch to a shadow of its 19th century levels. Catches of crabs, oysters and fish decline, while algae bloom counts increase, due to excess nitrogen

and phosphorus. When the algae die, they decompose and consume oxygen. This causes some channels to become so low in oxygen that the water is uninhabitable to fish and other marine life. Such areas are referred to as dead zones.

The Chesapeake Bay is just one of many waterways in the United States (and the world) suffering the destructive effects of this oxygen depleting process known as eutrophication. As the Mississippi River empties into the Gulf of Mexico, it carries with it agricultural and industrial pollution. During certain times of the year, this creates a dead zone in the gulf as large as the state of New Jersey. The problem has been intensifying over the past 50 years. In 1960, there were only 10 documented cases of dead zones around the world; by 2007 there were 169.9 Most of these dead zones are located along the eastern coasts of the United States, the coasts around Europe’s Baltic States, Japan and the Korean peninsula.

Many agricultural and industrial chemicals are persistent organic pollutants (POPs) that are found in highest levels in larger species due to bioaccumulation. This is the process of chemicals becoming increasingly concentrated in animal tissues as they move up the food chain. So, if POPs contaminate phytoplankton at the bottom of the food chain and then are ingested by larger fish, the concentration of the POPs in the larger fish increases. Anything that eats high on the food chain (including people) is at risk of the impacts from bioaccumulation of toxins. For example, pregnant women are routinely cautioned from eating larger fish, which are more likely to contain higher concentrations of mercury – a pollutant that can cause developmental problems in children.

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Killing for profit

In addition to habit destruction and pollution, over-exploitation of wildlife poses a significant threat to many species. Over-exploitation occurs when a plant or animal is killed or removed from the environment faster than it can replace its numbers.

Many of the world’s most beloved mammals, such as tigers, gorillas, rhinoceros and elephants, are victims of illegal over-exploitation commonly known as poaching. Hunters often kill these animals in order to bring sought-after products to the black market, such as ivory, furs, trophies and medicinal preparations. For instance, the bones and teeth of tigers are highly valued as ingredients in traditional Asian medicines. While the tiger is also threatened by habitat destruction, poaching has accelerated so much in recent years that it is now considered the leading threat to tigers’ survival, according to the World Wildlife Fund.10 The worldwide tiger population has dwindled from around 100,000 in 1900 to fewer than 4,000 today. The West African Black Rhinoceros was hunted to extinction by 2011, all for its prized horn.

According to a report by the Royal Society Open Science, more than a quarter of the 1,169 mammals listed as “threatened,” face extinction from hunting. The species at greatest risk include more than 60 percent of large land mammals (weighing over 1,000 kg), such as rhinos and hippos.11 Removing these large carnivores from their ecosystem, in turn, affects other plants and animals on which they feed. Without predators, plant-eating antelopes overconsume the savannas’ grasses.

Not all over-exploitation happens illegally. Many species have been overhunted or overfished because of inadequate regulation. In the oceans, populations of top predators, a key indicator of ecosystem health, are disappearing at an alarming rate. Ninety percent of the large fish we eat – tuna, swordfish, marlin, cod, halibut and flounder – have been fished out since large-scale industrial fishing began in the 1950s.12 Populations of sharks, rays and skates are also severely threatened due to overfishing. The depletion of these top predator species endanger the structure and functioning of marine ecosystems.

Unwelcome neighbors

Ecosystems evolve over many years to be a complex systems of plants and animals that depend on each other for survival. When invasive species, wildlife that is not native to the area, arrives in a new location it can have detrimental and unintended consequences. Sometimes these new neighbors prey on native species or crowd them out entirely. Either way, native species suffer, giving way to a whole host of problems.

A black rhino mother and her young offspring.

Photo Credit: Christophe Cerisier/iStockphoto.com

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The brown tree snake is just one example. Introduced by humans to the Pacific island of Guam after World War II from New Guinea or the Solomon Islands, the brown tree snake had no natural predators on its new island home and plenty of prey, in the form of native birds and small mammals. As a result, the snake population skyrocketed (up to 13,000 snakes per square mile) and every species of songbird on the island was wiped out.

Up until a century ago, the American chestnut was once a dominant tree of North America. Growing to nearly 100 feet, the wood was valuable for timber, and the trees produced abundant nuts that were important sources of food for people and wildlife. In 1904, scientists discovered a fungus growing on chestnuts in New York City. The fungus, which is fatal to American chestnuts, had been brought by humans to America, probably from Asia. It spread rapidly, 20 to 50 miles each year, killing virtually every tree it encountered. By 1950, the trees were essentially gone from U.S. forests.

Myriad other exotic pests exist, from Zebra mussels in the Great Lakes to Mediterranean fruit flies in California. As our population increases and economies expand, more and more commerce and travel happens between different ecosystems. We are continually increasing the chance that a person will, purposefully or accidentally, release the next unwelcome neighbor. The predatory lionfish that have been taking over reefs along the southeastern U.S. and Caribbean are native to the Pacific and may have started as home aquarium fish released into the Atlantic where they have no natural predators. As a result, they threaten reef ecosystems and the fishing economy.

According to the Nature Conservancy, invasive species have contributed directly to the decline of 42 percent of the threatened and endangered species in the United States. The annual cost to the U.S. economy is estimated at $120 billion a year. On a global scale, the annual cost of efforts to deal with the impacts and try to control invasive species is equal to five percent of the world’s economy.13

Key to our survival

Noted biologist E. O. Wilson writes that “biodiversity as a whole forms a shield protecting each of the species that together compose it, ourselves included.”14 Indeed, we depend on the Earth’s rich biodiversity for crucial ecosystem services – pollination, pest control, water filtration, soil creation and climate regulation. Food, medicine and shelter are all derived from the abundant organic resources of the Earth. In 2014, the global market for plant-derived medicines was worth an estimated $24.4 billion and growing. Some of these medicines are used to treat cancer, malaria and heart disease.15

BIODIVERSITY HOTSPOTS

Reproduced courtesy of Conservation International Foundation

The Earth’s biodiversity hotspots, areas that are rich in species and seriously threatened with destruction.

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Loss of biodiversity also deprives us of tools that might help in the struggle to feed ever-increasing numbers of people. For example, only a few of the more than quarter million known plant species have been investigated for their potential as crops. Only about 150 plant species are under cultivation. According to research by the Food and Agriculture Organization, the majority of humans live on only 12 plant species.16 Genetic information from wild plants may help this limited, and therefore vulnerable, food supply withstand the effects of disease, insects or climactic change as the human population grows to an expected 11 billion by the end of the century.

Out of the vast array of species inhabiting the Earth, humanity uses only 0.1 percent. The potential for the other 99.9 percent is enormous and mostly unexplored. However, with every species that is driven to extinction, we lose some potential to cure disease, improve crop productivity and enhance our standard of living.

S.O.S. – Save our species

Given the importance of biodiversity for our survival, how can we halt the current mass extinction event? Maintaining the variety of life on Earth will require humanity to address all of the H.I.P.P.O. threats. Global conservation efforts thus far have lowered extinction rates of land-dwelling animal species by approximately 20 percent. In the United States, passage of the Endangered Species Act has saved 227 species that otherwise would have disappeared.17 Conservation efforts work but much more work will be needed to save the diversity of the natural world.

Stemming habitat loss will be most critical in protecting the widest variety of species, from the smallest plants and insects to the largest mammals. Every nation in the world already has a system of protected areas. According to the World Database on Protected Areas, these areas accounted for slightly less than 15 percent of Earth’s land and 2.8 percent of Earth’s ocean area in 2016.18 Biologists agree that land and ocean conservancy will need to increase dramatically to save a significant amount of species and entire ecosystems. In an effort to protect the largest reserves possible, E.O. Wilson recently proposed a goal of setting aside half of Earth for other species.

International cooperation is critical in addressing biodiversity loss from poaching since wildlife is

harvested for international trade. In 1973, Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) was formed. Now numbering 183 member countries, CITES has listed some 5,000 animal species and 28,000 plant species meriting protection against over-exploitation through international trade.19 These listings have led to many improvements in the management and regulation of international trade in wild species, such as eliminating markets for products such as rhino horn, ivory and tiger parts, in order to reduce illegal poaching to supply these products. International agreements on reducing greenhouse gas emissions will also benefit species’ survival.

Prevention of pollution and the spread of invasive species will take the coordinated stewardship of a range of stakeholders from farmers and industrialists to hikers and pet owners. Each of us has a role to play in maintaining biodiversity.

Birds like this male Anna’s hummingbird will unintentionally pollinate many flowers as they forage for food.

Photo Credit: freebilly/istockphoto.com

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1 Vos, J. M., Joppa, L. M., Gittleman, J. L., Stephens, P. L., & Pimm, S. L. (2014, August 26). Estimating the normal background rate of species extinction. Conservation Biology, 29 (2), 452-462. doi:10.1111/cobi.12380.

2 International Union for Conservation of Nature. (n.d.). IUCN red list of threatened species. Retrieved February 15, 2017, from http://www.iucn.org.

3 Watson, J. E., Jones, K. R., Fuller, R. A., Di Marco, M., Segan, D. B., Butchart, S. H. M., . . . Venter, O. (2016). Persistent disparities between recent rates of habitat conversion and protection and implications for future global conservation targets. Conservation Letters,9(6), 413-421. doi:10.1111/conl.12295.

4 Environmental science and conservation news. (n.d.). Retrieved February 15, 2017, from http://www.mongabay.com/.

5 Dahl, T. E. (1990). Wetlands loss in the United States, 1780s-1980s. U.S. Department of the Interior, Fish and Wildlife Service. Washington, D.C., 13 pp.; Dahl, T. E. (2011). Status and trends of wetlands in the conterminous United States 2004 to 2009. U.S. Dept. of the Interior, U.S. Fish and Wildlife Service, Fisheries and Habitat Conservation, Washington, D.C.

6 Florida Panther: Species Profile. (n.d.). Retrieved from http://www.nps.gov/ever/learn/nature/floridapanther.htm.

7 Polar Bear. (n.d.). Retrieved February 15, 2017, from http://www.worldwildlife.org/species/polar-bear.

8 Nitrogen & Phosphorus. (n.d.). Retrieved from http://www.cbf.org/about-the-bay/issues/dead-zones/nitrogen-phosphorus.

9 National Geographic Society, (2012, October 09). Dead zone. Retrieved from http://www.nationalgeographic.org/encyclopedia/dead-zone/.

10 Tiger. (n.d.). Retrieved from http://www.worldwildlife.org/species/tiger.

11 Ripple, W. J., Abernethy, K., Betts, M.G., Chapron, G., Dirzo, R., Galetti, M., . . . Young, H. (2016). Bushmeat hunting and extinction risk to the world’s mammals. Royal Society Open Science,3(10), 160498. doi:10.1098/rsos.160498.

12 Global Oceans Commission. (2014). From decline to recovery: A rescue package for the global ocean. Oxford, UK.

13 Impacts of invasive species. (n.d.). Retrieved from http://www.nature.org/ourinitiatives/habitats/forests/explore/invasives-101.xml.

14, 17 Wilson, E. O. (2017). Half-earth: our planet’s fight for life. New York: W.W. Norton and Co.

15, 16 IDRC - International Development Research Centre. (n.d.). Retrieved from http://www.idrc.ca/.

18 World Database on Protected Areas. (2017, February 14). Retrieved February 15, 2017, from https://www.iucn.org/theme/protected-areas/our-work/world-database-protected-areas.

19 CITES: A viable and working convention for conservation. (n.d.). Retrieved from World Wildlife Fund, http://wwf.panda.org/what_we_do/how_we_work/policy/conventions/cites/cites_achievements/