Biology 115, Lecture 25:
Even More Ecology

Spring 1999 T. Irving; revised April 2000 A. Howard

Pollution (continued)

Pollution with "synthetic organic" compounds

• Organic here means related chemically to chemicals from living organisms
• Plastics are not generally harmful, in fact remarkably non-toxic
• Tangling of animals in fishing line, ingestion of plastic bags by giant sea turtles
• Main problem is disposal; does not degrade so elements cannot be recycled in natural cycles in the biosphere.
• Uses up petroleum, a non-renewable resource
  
• If people recycle, problem may be eliminated
• Plastic recycling still not widespread
• e.g. McDonald's cannot use recyclable plastic containers for drive-thru since people won't recycle
• They use non-recyclable coated paper instead.
• Which is better?

Pollution by pesticides

These are also synthetic organic compounds; they kill weeds (herbicides), molds & fungi (fungicides), insects (insecticides)

• Herbicides: generally speaking relatively benign; but they include Agent Orange
  • A herbicide used in large amounts during the Viet Nam war
  • Long and controversial series of reports on whether it caused increased rates of cancer, birth defects ( in veterans & there children)
  • Harmful action now thought to be due to "dioxin" contamination of the herbicide and not to the herbicide itself
• Insecticides:
  • Chlorinated hydrocarbons
    • e.g. DDT are hard to break down in the environment
    • 1/2 life about 30 years
    • Somewhat toxic to mammals, more dangerous to birds
    • Exacerbated by biomagnification
    • Up to 5 ppm has been measured human breast milk
    • No longer used in US but is exported for control of malaria bearing mosquitoes
  • Organic phosphates
    • include melathion, parathion
    • break down more rapidly than chlorinated hydrocarbons but more toxic to mammals
  • Carbamates
    • e.g. sevin
    • Relatively non-toxic to humans and generally short lived
  • Natural pesticides
    • Insecticides generally can't discriminate between the 1000 or so insect pests and the 10⁶ or more benign or beneficial insects
    • Can really mess up ecosystems with indiscriminate use of insecticides.
    • More specific insecticides are coming into use:
    • Insect parasite/predators to kill other insects
    • Insect viruses pathogenic bacteria or the poisons from them
    • Insect hormones which affect specific species ("birth control for roaches")
    • Use of natural pesticides is less disrupting to the ecosystem because the ecosystem has evolved along with them.
    • Introducing "exotic" species to an area can be extremely disruptive
• Organic foods
  • Food grown only with "natural" fertilizers (compost, manure etc.) and pesticides (e.g. lady bugs to eat aphids and certain bacteria to kill grasshoppers)
  • Still controversial whether absence of synthetic herbicide, fungicide, insecticide and other chemical residues has a great affect on reducing danger of foods eaten
  • e.g. Alar is a growth regulator sprayed on apples so that they don't drop prematurely and delays ripening in cold storage
  • Can also break down into a known carcinogen
  • On the other hand, untreated apples can grow molds which produce their own but "natural" carcinogens
    
  • Many of the chemicals released into the environment by humans are mutagens which, may in turn, result in birth defects & cancer in humans
  • Most mutagens are also cancer causing
  • There is evidence that many foods naturally may contain high levels of carcinogens as normal constituents of these foods
  • Natural carcinogens may in fact dwarf any man-made chemicals in terms of danger

Pollution due to electricity generation

• Coal burning power plants
  • Coal contains variable amounts of sulfur which when burned produces S0₂ gas
  • SO₂ can be scrubbed but some always escapes and is converted to sulfuric acid in the atmosphere
  • Returns to earth as acid rain
  • Lowers pH of lakes and ponds so that natural plants and animals all die.
  • Acidifies the soils of forests so that trees die off.
  • Coal burning also releases traces of heavy metals and radioactive materials into the air.
  • Residue can be considered hazardous wastes
• Nuclear power plants
  • Well - run nuclear power plants release very little nuclear fall-out into the environment
  • Heat pollution a concern
  • Best existing plants small but significant risk of catastrophic failure. ( 1: in 10⁴ reactor years)
  • Spent reactor fuel very hazardous, difficult to store and has a very long lifetime
  • Nuclear fusion reactors would produce great amounts of power with relatively little radioactive waste but still many years away from a practical source.
• "Clean" Power Sources
  • Hydroelectric power is a relatively benign way to generate electricity
  • Sometimes the source of potential energy is natural e.g. Niagara Falls
  • Most often from dams
  • Dams can be very ecologically disruptive since can change entire nature of vast regions of a country
  • Solar and wind power slowly increasing in popularity
  • Minimal disruption to environment
  • Still not competitive with fossil fuel based electricity since coal and oil artificially cheap

Smog

Primary pollutants are NO,NO₂,N₂0 and SO₂

• come from factory emissions and automobile exhaust
• These react with sunlight and other chemicals in the air to form secondary polutants
• Nitric Acid, sulfuric acid, ozone, sulfate salts
• These combine with particulates to form hazy smog
• "Temperature inversions" can hold warm air and smog close to the ground
• EPA banned leaded gasoline and requires cleaner burning fuels in affected regions.
• Methanol or ethanol common additives
• Testing automobiles for emissions helps reduce smog
• Smog - respiratory diseases, emphyzema, asthma, bronchitis
• Indoor pollution - "sick buildings"

Human Ecology

• Humans, because of their technology, have been able to "opt out" of natural ecological principles.
• We have disrupted the biosphere time and time again by adding "unnatural" things to it or replacing "natural ecosystems" with "unnatural" ones
• Human population growth has also been uncoupled from natural ecological constraints
• Species can adopt of two major reproductive strategies
  • Produce a lot of offspring and let them "sink or swim"
  • Produce few offspring and take very good care of them
• Latter strategy adopted most birds and mammals
• How large can the human population grow?
• What are probable consequences for the earth?

Reproductive potential and carrying capacity

• Reproductive potential of any species is the theoretical reproductive capacity free of any constraints (e.g. limits food, space, shelter).
• Up to 10,000 years ago human population was probably stable at about 4 x 10⁶ (way below reproductive potential)
• Rose slowly to about 500 x 10⁶ at the beginning of the industrial revolution (18th century)
• A rapid increase to about 6 x 10⁹ today (still way below reproductive potential)
• Increases due to a many factors including:
• Switch from "hunter-gatherer" to agriculture (more stable food supply)
• Colonization of "new world" by Europeans
  
• New world was very sparsely populated so could support large numbers of immigrants and their offspring
• Mineral and other (timber, furs, sugar cane, etc.) wealth allowed populations back in Europe to increase
• Industrialization included improvements in farming
• Advances in medical care/public health resulted in a great reduction in death due to childhood diseases

Carrying Capacity

• Carrying capacity of an ecosystem (or the biosphere) is the actual population a species can reach because of limiting factors
• Availability of food, shelter, amount of predation, parasitism, disease
• Carrying capacity may vary e.g. from season to season
• In natural populations can cause steep rises and falls in populations
• Longer cycles (e.g. years) can also be identified
• Most species reach carrying capacity and oscillate close to it

Carrying capacity of biosphere for humans

• Every time in history one or more constraints have been lifted, human populations have increased
• Current world population is 6 x 10⁹ people;
  How close is this to carrying capacity?
  • It depends on which populations (countries, geographic areas) under discussion
  • In western countries carrying capacity has not been reached
    (assuming western standards of living).
  • Others (Sudan, Ethiopia) carrying capacity has been exceeded
  • (assuming less developed country (LDC) standards of living).
  • If everyone in the world lived at LDC living standards, we are not at the carrying capacity
  • If everyone had more developed country (MDC) living standards, we have already exceeded the carrying capacity

Politics of demographics

• Explosive population growth an important and serious biological issue.
• Even more important economic, political and humanitarian issue.
• Should we share our wealth with undeveloped countries?
• Should undeveloped countries try to limit their population growth?
• Do we have the right to impose our ideas on other nations?
• Difficult to separate the biological problems from the political/social ones
  • e.g. Famines in Ethiopia
  • Enough food can be donated by MDC's to feed the country
  • Warring factions have hindered the distribution of food because starvation is in effect a weapon of war

Immediate prospects for population growth

• Will the conflict between human population and carrying capacity get worse?
• In the near term, undoubtedly
• More developed countries underwent a demographic transition so that most developed nations have "zero population growth" or less
• In America fertility is about 2.1 children /female of reproductive age.
• Growth rate LDC's peaked at 2.4%/year ~1960
• Slow decline since
• Decline attributable mainly to more effective family planning
  
• Rate would be higher except that many small children in LDC's die every year
• Human population is currently increasing at about 2% a year which implies a doubling time of about 39 years
• In just 20 years world population would go to 9 x 10⁹ people.
• World will need approximately twice as much food, jobs, water, energy to maintain the same world standard of living

Biology and the Law

• People have realized that pollution is a extremely serious problem & leaders have passed laws designed to protect the environment
• Very recent phenomenon, most within last ~20 years
• Laws generally cautious, rare that a pollutant is banned outright or cleaned up right away
• E.g. cleaning up of toxic waste dumps pretty slow and deliberate
• Very powerful political forces opposing environmental legislation
• Our industries compete in a global economy and can be at a competitive disadvantage with those in LDC's with less stringent environmental laws
• Solutions will always be compromises between health and economics, perceived and likely risks

What can you do?

• Ecological problems will not go away without strenuous, concerted efforts by all nations and will effect your generation, in particular, in many important ways.
• Informed citizens will need to influence public policy with their votes
• Remember:
• Problems & solutions will be very complicated, simple one-sided proposals on either side of an issue may be worse than useless
• All proposed solutions will demand at least some understanding of biology at a level of sophistication greater than the daily newspaper.
• It is also important to take personal steps to reduce your impact on the environment
• Rethink, reduce & recycle
• Efforts of one individual may seem inconsequential but all contribute to a culture that emphasizes and eventually realizes sustainable development