1. How many species are there?

2. What is the "normal" rate of extinction?

3. What is the current rate of extinction?

4. How much extinction can be directly related to human activities?

How many species are there?

1. Described species = 1.4 - 1.7 million

ca. 4,800 prokaryotes
ca. 26,900 algae
ca. 30,800 protozoa
ca. 69,000 fungi
ca. 248,400 plants
ca. 281,000 animals (non-insect)
ca. 751,000 insects

2. Estimates suggest there may be more than 30 million species

based on sampling in tropical forests

(that's a lot of undescribed species! - 85 to 99% of species unknown to science)
example: 1990 study by Norwegian scientists

estimated 4,000 different species of bacteria in 1 gram of soil from one location
there are only 4,800 known species of bacteria!

What is the "normal" rate of extinction?

Tropical forest as an example:

Estimates suggest there are 10,000,000 species in tropical forests

1. One million years is the normal life span of a species

2. Extinction rate of 10 species per year can be expected under normal conditions

- 0.0001% extinction rate

- evidence from island models and fossil histories

What is the current rate of extinction?

1. Predictable relationship between the # of spp and the area of habitat they occupy.

can estimate rate of extinction based on the amount of habitat lost each year

2. Annual species loss of about 0.27%

10,000,000 X 0.0027 = 27,000

How much can be attributed to human activities???

1. Humans are changing the face of the planet through:

deforestation
conversion of farm land to urban areas
increased emissions of greenhouse gasses (global warming)increased waste (water, soil, and air pollution)
depletion of ozone layer
increased soil erosion
economic growth
population growth

2. Background rate of extinction = 10 spp per year; estimated current rate = 27,000 spp per year

Current rate exceeds normal rate by 2,700X!!!!

3. Concept of the Ecological Footprint

a measure of the "load" imposed by a given population on nature

represents the land area necessary to sustain current levels of resource consumption and waste discharge