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Minor Causes of Extinct Animals

There are many contributing factors to extinctions. It is rare when one thing causes an entire species of animal to die out, although sometimes a single cause can be pinpointed. This is usually habitat loss, overhunting or an invasion of a nonnative species that competes with and kills the animal. More often, it is a combination of these or other, less-common factors that causes a species to become extinct.

Review of Major Causes
- Overhunting is when one species, most often humans, hunts another species until all within that species have been killed, as happened to the passenger pigeon in the United States. Habitat loss is the destruction of a species' range. This is especially dangerous in the South American rainforest, where the range can be as little as a few acres. Habitat loss is expected to be the No. 1 cause of extinction in the future. Invasion of a nonnative species is the introduction of new species to an area, with the newcomer out-competing the native species. Cane toads, Africanized honeybees and gypsy moths are all destructive animals not native to the U.S., and common rats and cats have devastating effects to island ecosystems when introduced.
Climate Change of Cooling
- Glaciation is a cause of many prehistoric extinctions but few, if any, modern ones.
  
  Glaciation is cited as a cause of extinction in studies of prehistoric animals. It is the process in which glaciers grow larger and larger as the Earth cools; they eventually cover much of the land and take up much of the Earth's water. It is one effect of global cooling. Cooling and glaciation are not common now, but they are one theory behind the extinction in the Triassic period, when plesiosaurs, or marine dinosaurs, died out.
Climate Change of Warming
- Global warming also causes changes to animals' habitats, but in the opposite way of glaciation. The glaciers melt, the Earth is warmer, and animals accustomed to cold weather are now out of place. The plants that used to feed them retreat over time, and if the animals cannot migrate farther, they die out. Global warming has been a far less common cause of extinction than cooling in the past.
Pollution
- Modern pollution can contribute to extinction. Chemicals are introduced to an area accidentally or intentionally, and animals without resistance to that chemical are poisoned. It is mostly a danger for small populations in a small range, such as some desert pupfish in the Southwest.
Extra-terrestrial Impacts
- The Gulf of Mexico may have been formed by a meteor impact that indirectly killed the dinosaurs.
  
  Children were once told that dinosaurs died out when a comet hit the Earth. Scientists have investigated this cause, and many have deemed it unlikely because evidence is scarce. However, impacts from extra-terrestrial bodies can cause changes in the environment by throwing ash, dirt and even radiation into the air. The impacts are a factor but not a direct cause of extinction.
Volcanoes
- Volcanoes also have been blamed for the disappearance of dinosaurs. They may be a factor because their emissions of dust, ash and other particles interfere with the climate. They can block sunlight, which causes cooling. The eruption itself damages a relatively confined area but can contribute to climate change if it goes on long enough or if many volcanoes erupt. Volcanoes, similar to impacts, are not a major cause of extinction but can factor in with many causes.

Animals & Science