chapter 18

Conservation biology

Human activity can upset the balance of ecosystems, leading to the decline and extinction of many species.
- Bonobos (Pan paniscus) are a type of chimpanzee and our closest living relatives.
  As a consequence of habitat loss and their exploitation as a source of food in parts of Central Africa, they have been driven to near extinction, and are almost never seen in the wild.
- The passenger pigeon was once common and abundant in North America.
  Hunting and other human activity such as loss of habitat due to deforestation led to their extinction (death of every member of the species) by 1914.

Introduction of invasive species is a main factor in the disruption of ecosystems.

Monk parakeets have been introduced from South America, and can be a nuisance in cities such as Chicago, where they build large nests on utility poles and heat-giving transformers.
Introduced species that have negative impacts on native ecosystems are called invasive species.

Invasive species

Brown tree snake was introduced into Guam in 1952. Native birds had never experienced predation by snakes, and 8 species have been eradicated by this alien predator.	Purple loosestrife was imported to the U.S. in the 1800s from Eurasia. It has invaded wetlands with aggressive growth that overwhelms native plants, replacing diverse communities with monocultures of loosestrife.	Zebra mussels invaded the U.S. from Eurasia in the 1980s in the ballast water of cargo ships. They feed on small plankton, removing food for fish in the Great Lakes. They also clog intake pipes of water-treatment plants and factories.

Atmospheric pollution includes chlorofluorocarbons (CFCs), which can deplete the ozone layer.
- The ozone layer in the upper atmosphere absorbs harmful UV rays from the sun.
  Chlorofluorocarbons (CFCs) can accumulate in the atmosphere and deplete the layer.
  Since 1975 an ozone "hole" has appeared over the South Pole.
  CFC use began to be phased out by the Montreal Protocol in 1989.
- CFCs (chlorofluorocarbons) are chemicals that accumulate in the atmosphere as a by-product of refrigerants, aerosol propellants, and foaming agents.
  UV-B radiation breaks down the CFC molecules in the stratosphere, releasing free chlorine ions, which destroy ozone (O₃) molecules by converting them to oxygen gas (O₂).
Burning fossil fuels releases sulfur and nitrogen into the atmosphere, causing acid precipitation.
- Acid Precipitation
  Power plants send excess sulfur and nitrogen into the atmosphere, producing sulfuric acid and nitric acid when mixed with water vapor.
  The lowered pH of rain and snow result in acid precipitation that fall on soil and water far away.
  The acid can damage trees not adapted to low pH.
- Acid precipitation is concentrated in the Northeast of continental U.S.
  Higher human population densities there result in more acidic emission from burning of fossil fuels.
  - Clean rain is slightly acidic at a pH of 5.6. Why?
    - Carbon dioxide in the atmosphere mixes with water vapor to yield carbonic acid.
- Acidic environments often damages trees not adapted to low pH.
  Prolonged exposure to acid fog in mountainous areas can damage leaves, reducing photosynthesis, and eventually killing trees.
Burning fossil fuels releases carbon dioxide into the atmosphere, leading to global warming due to the greenhouse effect.
- Greenhouse effect and climate change
  Burning fossil fuels (oil, natural gas, coal) results in accumulation of carbon dioxide in the atmosphere.
  1. Energy from the sun passes through the atmosphere to warm the earth's surface.
  2. Some infrared radiation (heat) is reflected and escapes into space.
  3. Carbon dioxide acts as a greenhouse gas to absorb heat that is trapped near the surface.
  Accumulated carbon dioxide can lead to global warming, melting polar ice caps.
  Note: 2017 was the 3rd hottest year ever, and 2018 was the 4th.
  Other factors may also affect climate change.
- One consequence of global warming is melting of the Arctic Ocean ice cap.
  As solid water in the ice melts into liquid form, ocean levels will rise.
- Earth's orbit around the Sun undergo periodic Milankovitch cycles.
  - Orbit eccentricity: the shape of Earth's orbit varies between round and elliptical every 100,000 years.
  - Axial tilt: the angle of the tilt as the Earth spins on its axis varies between 22.1° and 24.5° every 41,000 years.
  - Axial precession: the tilt of the Earth's axis of rotation "wobbles" in 360° cycles of 20,000 years.