Population growth and sustainability

Outline:• Human population growth• Sustainability• Harvesting resources

– Farming– Forestry– Fisheries

Readings: Chapters 27

Human population, 1 A.D. – 2000 A.D.

Using the same starting and ending points, the figure above illustrates what human population growth would look like if it followed the logistic growth model [dN/dt = rN (K-N)/K]or the exponential growth model (dN/dt = rN).

Natural capital

• Range of natural resources provided by ecosystems: – air, water, soil, nutrients, forests,

grasslands, etc.

Simple model of resource use

The fate of non-renewable resources

Wastes, by-products

Feeding humanity: agriculture

• 30,000 edible plant species• 90% of food supply is dominated by

only 15 plant and 8 animal species• Wheat, rice and corn = 80% of all cereal

crops consumed• Two main forms: traditional vs.

industrialized

Swidden agriculture

Monoculture Farming

Phytophthora infestans, “late blight”Fungal agent that caused the Irish Potato blight of the mid-19th

Century

• Introduced to Ireland in the 1840s, where potatoes (an exotic species that had become critical to the country’s food supply) were grown in dense monocultures.

• Destroyed plants in the field (above left) and also potatoes held in storage (above right)

• Thirteen percent of the Irish population died of starvation; another 20% emigrated to the United States

Parasitic mites are a major threat to monoculture fish farms, and to nearby populations of wild fish

Number of pesticide-resistant arthropods(Known to be resistant to at least one pesticide)

Apr. 14, 1935: “Black Sunday”

During the 1930s, severe droughts resulted in crop failure, wind erosion of soil, and massive dust storms. Thousands of families emigrated from the region during the time of the Great Depression.

Algal blooms

Salinization

A “salt desert” in Tunisia

The mechanization of agriculture has greatly increased food production

Large-scale sustainable agriculture:

•Soil conservation methods

•Reduction in use of pesticides

•Alternative sources of soil nutrients

•Water conservation and protection

Permaculture

Sustainable forestry?• 35% of Earth’s surface covered by

forest ecosystems• Provide: fuel, building materials, shelter• Plantations but 90% of global forest

resources harvested from native forests

Feeding humanity: fisheries

• 80% of fish catch comes from oceans and lakes

Pacific sardine