Science 9: Unit A: Biological Diversity

Topic 7: The Sixth Extinction?

Trend for Biodiversity Traditionally new species have formed

faster than they have gone extinct leading to greater biodiversity.

In the last 65 million years, this trend has reversed. 70 species/day have been going to extinct.

Again, the closer you get to the equator, the increased the biodiversity.

Bottleneck Events=Great Extinctions

There have been five cataclysmic events that have greatly reduced the biodiversity in the world. These events affect many different species of organisms.

Some biologists refer to the arrival of humans as the Sixth extinction referring to our effect on biodiversity.

Human Impact on BiodiversityI. Pollution has made many habitats

unsuitable for the organisms living there. Acid rain, polluted streams and oceans all destroy habitats, kill off organisms, and reduce biodiversity.

II. Greenhouse Effect has forced many species adapted to colder environments to retreat further north. Arctic species may go extinct from a loss of their habitat.

Human Impact on Biodiversity III. Human Expansion – Humans have an

average ecological footprint (Grade 7) that is too large for the Earth to sustain. This means ecosystems are suffering. Also, the human population will reach 7 billion soon. Our population explosion means increased use of natural resources, clear-cutting and urban sprawl. (e.g. Amazon Rain Forest)

Bioindicator Species A species that is an indicator of the overall

health of an ecosystem. These species usually are large carnivores.

Why carnivores? Because when an ecosystem suffers, carnivores are usually the first to feel it, having trouble obtaining food.

How Long Have Humans Been Reducing Biodiversity? 30000 years ago Early Homo Sapiens wiped out

our human competitors the Neanderthals. 8000 y.a. Humans wiped out the Wooly Mammoth

and other large mammals for food. 400 y.a. Portuguese sailors killed off the Dodo

bird for food. Despite our long history, the rate of human-

caused extinction is growing now at a faster rate because of our technologies.

Extinction Versus Extirpation Extinction is the wiping out of an entire

species throughout the world Extirpation is the wiping out of an entire

population of a species from an ecosystem or area.