Causes of Extinction: HIPPO

Habitat Destruction

Habitats are destroyed everyday due to human activities like building houses, adding roads, mining, clearing trees, and generally expanding into where natural environments once existed. As a natural ecosystem shrinks, more and more species lose the resources that they need to survive.

Invasive Species

Introduced species also wipe out many indigenous species. Nearly 20% of known endangered vertebrates are threatened by introduced species. When humans bring an alien species into an ecosystem, that species may take over niches that other species had occupied. They also might change the ecosystem enough to indirectly force out native species or bring with them diseases to which the natives have no immunity. Especially on islands, where species have evolved in isolation and have not dealt with adapting to newcomers, the original inhabitants may be unable to adapt and survive. In Guam, the invasion of the brown tree snake from Papua New Guinea has resulted in the extinction of half the island's native birds and several lizard species.

Population Growth (Human)

Recent studies conclude that the underlying causes of biodiversity loss include population growth, migration to ecologically sensitive areas, poverty and inequity, policies that promote unsustainable resource consumption, and a lack of environmental awareness. In order to slow biodiversity loss, nations will need to address these root causes.

Growth in demand for food and housing, each rooted in population growth, has contributed to the loss of biodiversity. Both the conversion of species-rich forests and wetlands to cropland and the increasing intensity of fertilizer and pesticide use are major factors in the extinction of species, and they are direct responses to increases in food demand. Suburban sprawl and urban concentration also increasingly contribute to habitat loss and degradation.

Pollution

Pollution also causes extinction. Many toxic substances that are released inadvertently or in the process of waste disposal are very similar to pesticides, and have similar impacts on living systems.

The sulfur dioxide gas that is produced when coal and fuel oil are burned can cause diseases in humans. In broad-leaved and evergreen plants, sulfur oxides inhibit growth and cause cells in the leaves to collapse or become distorted. Air pollution has wiped out vegetation, and with the plants, of course, go all of the animal populations dependent on them. The oxides of sulfur and nitrogen released into the atmosphere from factories and car exhausts undergo chemical reactions that convert them into nitric and sulfuric acids. As a result, rains over large parts of North America and Europe are ten to a thousand times as acidic as rains from unpolluted skies.

In the Adirondack Mountains of North America, the rains are acidifying the water and the nitric acid is reacting with the soil to release large amounts of aluminum, which is then washed into the lakes. These acids build up during the winter, and in the spring, when the snow melts, they pour into lakes in concentrations lethal to fishes. After this initial acid water rush, a flush of aluminum pollution follows. As a result, all fish populations in three hundred Adirondack lakes are now extinct, and the Brook Trout and other species may have been wiped out over the entire area.

Over Consumption

Over-consumption of all nature’s resources contributes to extinction, and international trade further endangers certain species. In Africa, commercial hunting is responsible for putting 1/3 of the currently threatened primary forest at risk. Species populations can also shrink when local people are forced by habitat destruction to rely on a smaller area for their food needs, or when a certain species becomes popular on the international market. Such species include the ocelot, the caiman alligator and several mahogany varieties. People trap or kill animals and ship them to other countries, where they are taken as pets or used to make other products. Once a species becomes rare or protected, the profit in smuggling can increase; international illegal wildlife trade is a $2-3 billion a year business.