Human Populations We are the only species able to consider and alter our rates of birth and death In nature some populations grow smoothly to a stable carrying capacity but others overshoot that density and may crash before rebuilding to a relatively stable level. A few crash to extinction.

Human growth resembles exponential growth; increasing slowly at first but later at accelerated rates showing no signs of reaching carrying capacity Referred to as a “weed” species b/c we are fast growing, rapidly dispersing, and colonizing habitats from pole to pole

Different countries show different patterns of population growth today, and history shows varying patterns of growth across time. Early Homo sapiens probably had high birth and death rates also effected by density independent factors like ice ages and volcanic eruptions

Change in carrying capacity Things changed w/ the invention of agriculture Still had disease w/ animal domestication and city living Reliable food sources; shared child care, division of labor Advances in technology

Increase Carrying Capacity With major advances in technology As humans modified the environment by irrigating land Building cities Transporting animals, plants, products

Demographic Transition Humans pass through 4 stages of growth –1 high birth and death rates; slow uneven growth –2 lower death rate (dr) but not lower birth rate (br); rate of population growth high –3 decline in br; low dr; br falls b/c of a variety of technological changes; growth rate slows –4 br declines more = death rates; growth rate falls to zero

Human population continues to grow but many scientists believe that we over- consume resources and exceed the environment’s capacity to cycle nutrients and process waste. Possible population crash is possible

Factors that can lead to crisis Agricultural system –”green revolution” depends on nonrenewable fossil fuels for fertilizers, pesticides, and irrigation Most countries depend on almost entirely on petroleum to fuel industrialization and transportation

Factors that can lead to crisis Fresh water supplies are declining due to pollution and overuse Habitat destruction due to agriculture, development, and mining Burning of fossil fuels has brought about atmospheric change

Sustainability We must consider the impact of our decisions on the next seven generations A sustainable activity or state can be maintained indefinitely, w/out compromising resources for the future.

Sustainability Sustainability of products and services considers complete life cycles – raw materials, manufacturing, transportation/distribution, use and re-use, maintenance, recycling and disposal.

Sustainability Way to estimate sustainability is your ecological footprint –The amount of land area you would need to sustain your current lifestyle –Considers resources you consume and pollution you generate then calculates the amount of land needed to produce equivalent RENEWABLE resources