4.2.2-.4 Causes of Extinction

EXTINCT is FOREVER!!

Non-human causes of extinction: Volcanic events Ocean temperature change Sea level changes Meteorites Glaciations Global climate change Competition/predation

Human causes of extinction/loss of biodiversity - HIPPO Habitat destruction and fragmentation Introduced species Pollution Population Over consumption

Rates of Extinction: = number of species becoming extinct per unit time. Rates of extinction are very difficult to estimate, because we don't even know within an order of magnitude how many species there are. Fossil records can reveal the average "lifetimes" of species, or how long different classes of plants and animals generally exist on the earth before going extinct.

From this information, scientists can determine a "background" rate of extinction, or the natural rate of extinction without human intervention. Because of human intervention the Earth's species are dying out at an alarming rate, up to 1,000 times faster than their natural rate of extinction.

By carefully examining fossil records and ecosystem destruction, some scientists estimate that as many as 137 species disappear from the Earth EACH DAY, which adds up to an astounding 50,000 species disappearing every year.

The Earth has experienced 5 MASS EXTINCTIONS

Mammals average species lifespan 1 million years. With ~ 5,000 mammalian species the background extinction rate = 1 every 200 years. In the past 400 years, though, 89 extinctions have been recorded, almost 45 times the natural rate. Over 50 of those extinctions have occurred in the past century, Rate = 100 times the background rate!!

Extinction Rates over geological time

Middle Cambrian age (about 540 million years ago) The locality is special because of the soft-bodied preservation of a wide diversity of fossil invertebrate animals. Period of great speciation.

Characteristics of vulnerable species Small population size - island species. Small population size - species with limited habitats. Extremely specialized species. Species with low reproductive potential. Species that require large territories. Species with limited dispersal ability.

Vulnerable species - continued Migratory species. Species that are economically valuable or hunted for sport Predators. Species that are vulnerable to pollution. Species that are incompatible with civilization.

Rainforest Tropical rainforests contain at least half of the Earth's species. Most species have evolved to inhabit very specialized niches in their environment. When humans disrupt that environment, many species cannot survive. Because species depend on each other in a complicated web of relationships, changing just one part of that web harms the entire ecosystem. This breakdown of rainforest ecosystems will likely lead to the disappearance of up to 10% of the world's species within the next 25 years.

Rainforest continued The human species depends on the rainforest's millions of life forms for its own existence - The genetic diversity found within the rainforests provides invaluable additions to the gene pool which help maintain and improve domestic crops. Without a diversity of strains, crops become overly homogenous and vulnerable to mass blight. Many medicines that we regularly use come from rainforest species.