History, Humans, & the Price of Expansion

How long have humans been impacting biodiversity?

Is there evidence that humans have caused extinctions in the past?

• What kind of evidence would you need to address this question?

Catastrophic large-animal extinctions occurred around the world not long after humans first arrived in a geographical region, in the wake of initial human colonization. Numbers indicate percentages of extinct genera during the past 100,000 years. (http://www.pbs.org/wgbh/nova/stoneage/megafauna.html )

The extinction of large mammals and flightless birds coincided closely with the arrival of humans in North America, Madagascar, and New Zealand, and less decisively earlier in Australia. In Africa, where humans and animals evolved together for millions of years, the damage was less severe.

Wilson p. 252

Human-caused extinctions in history

• Australia – 86% of genera extinct

• North & South America - ~75% of genera extinct

• Madagascar & New Zealand – 13 species of flightless birds lost

• Hawaii – 39+ species of birds alone lost

• Africa….??

What were the probable causes of these pre-historic extinctions?

• Over-hunting: humans as a new predator

OVERHUNTING: American bison skull heap. There were as few as 750 bison in 1890 due to overhunting. (http://en.wikinews.org/wiki/Largest_mass_extinction_in_65_million_years_underway,_scientists_say)

What were the probable causes of these pre-historic extinctions?

• Introduction of exotic species: new competitors & predators

A severe waterlettuce (Pistia stratiotes L.) infestation on Lake Okeechobee in southern Florida.

:

Case in Point: North America at the end of the Pleistocene

Woolly MammothSource: http://www.pbs.org/wgbh/nova/stoneage/megafauna.html

…mega-fauna that went extinct

Giant Ground Sloth

Dire Wolf

What caused these extinctions?

Human Hunting?

• Visit: http://www.museum.state.il.us/exhibits/larson/lp_extinction.html

A Change in Climate?

• What evidence would you need to support or refute either claim?