1. Global Biodiversity and Extinction

2. How Many Species Are there?
We have catalogued and explored every corner of Earth, but…
We still know very little about the number of different species and how many are going extinct
An estimate is around 7 million (not counting bacteria)
Only about million have been described/named
Most are terrestrial animals
(2/3) 66%! Are in the tropics
50% of tropical forests have already been cleared by humans

3. Extinction Life Span of a species (varies) Background Extinction Rate
Most mammals: ~1 million years
Some arthropods: ~10 million +
Background Extinction Rate
The natural extinction rate of all species
Should be ~1 species per million species per year
Based on fossil record
So between 10 and 100 species per year
Greater in “hotspots”
Today the rate is estimated to be 100 times larger than “usual”
Mass Extinctions
There have been 5 major ones
Most have been due to a rapid change in climate perhaps caused by a natural disaster

4. 5

5. The Sixth Mass Extinction
Humans are pushing more animals towards extinction faster than any other mass extinction
One estimate
25% of all plant and animal species have gone extinct between 1985 and 2015!
Some do well in our new human environment
“Weedy species”
Most do not
Recovery after a mass extinction takes about 5-10 million years (that would be about 200,000 generations of humans, but we have only been around for 7,500 or so generations)
Humans are the direct cause of ecosystem stress because…
1. Transform the Environment
2. Overexploit other Species
3. Introduce alien/invasive Species
4. Pollute the environment