Biology Ch. 6 - Humans in the Biosphere

11/14/22 - 12/1/22 Mr. Sandro

Human Population Growth

1. Little to no change for the first 200,000 years
2. Deaths rates decrease due to agriculture (1950s Green Revolution), domesticated animals, enabled permanent cities/towns, healthcare, and Industrial Revolution
3. Births rates stayed high
4. Population now growing exponentially
Population reaches 8 billion on Nov. 15th, 2022!

Demography

the study of human populations

Population growth in the US, Canada, Japan, China, and Europe, has SLOWED because of

The Demographic Transition

The Demographic Transition Phase 1:

death rates fall, birth rates don't. Pop. grows exponentially

The Demographic Transition Phase 2:

population gets wealthier, educates. Birth rates drop, pop. growth slows/stops

"The Tragedy of the Commons"

when a resource (anything with value) is free to use but unregulated, humans tend to use it up as quickly as possible until it is depleted

Resource Types

1. Nonrenewable
-coal, oil, natural gas - millions of years to form
2. Renewable
-wood, water, sun, wind, air (but are these all really renewable??)

Environmental Problems (there are 7 main ones)

1. Freshwater Depletion
2. Polar Ozone Holes
3. Desertification
4. Deforestation
5. Climate Change
6. Overfishing
7. Biological Magnification

Freshwater Depletion

a. Pollution and overuse of groundwater - hundreds of years to regenerate
b. deforestation/overfarming/grazing erodes soil, creates desert conditions (soil can't hold water)
c. 75% of US water is used for agriculture

Freshwater Delpetion Solutions

-drip irrigation
-protect the wetlands, which purify H2O and "recharge" groundwater

Polar Ozone Holes

a. Caused by aerosol can CfC's being released in atmosphere
b. Open every summer, close every winter
c. Increased UV rays harm living things
*Not to be confused with climate change

Polar Ozone Holes Solutions

-CfC's are banned --> Holes have started shrinking!

Desertification

a. Farming and overgrazing causes heavy erosion, resulting in soil losing ability to hold water

Desertification Solutions

-crop rotation
-grazing area rotation
-leave plant roots in the ground after a harvest
-Contour farming

Deforestation

a. 80% of old-growth forests (nonrenewable), have over half of the tree cover gone
b. Erosion and habitat loss, increase in CO2, decrease in watersheds

Deforestation Solutions

-selective logging
-tree farms
-faster-growing GMO trees

Climate Change

a. CO2 at highest in 650,000 years
b. Since 1880, the temperature increased nearly 1`C
c. Droughts more frequent and severe (led to more forest fires)
d. Severe hurricanes, up to 75% since 1970
e. Snow cover, sea ice, glaciers, and ice caps declining worldwide
f. Sea levels increasing worldwide (4-8 in. since 1990)
g. Ocean temps and ocean CO2 concentrations increasing
h. By 2050, global temps. will rise ~2`C

Overfishing

a. Many food fish are nearly depleted (salmon, halibut, cod, crab, etc)
b. International waters (T.O.C.)

Overfishing Solutions

-close certain areas to fishing
-aquaculture (fish farms)

Biological Magnification

a. Toxins like DDT and Mercury become more concentrated as they move up food chains
b. "rule of 10%" - energy is lost, but certain toxins are not
c. As much as ten times more toxin from one trophic level go to the level above