Ecology and Ecosystems

Reading assignment: Chapter 4, Ecosystems and How They Work; Chapter 6, Changes in Populations, Communities, and Ecosystems

Why is ecology important?

• Ecology is the study of organisms and their surroundings
• A better understanding of how human induced changes affect organisms and their environment

How do we describe life?

• an ability to replicate, the production of offspring
• posses a genetic code such as DNA which has the ability to:
  • self replicate
  • store all information about the organism and how to construct essential functions
• utilize energy and matter from its surroundings
• maintain functionality in a hostile environment
• adapt to changes in the environment

How does earth's life adapt to changes in their surroundings?

• Mutation
  • Mutation is random changes in the genetic code (DNA) of an organism. These changes may be
    • helpful
    • harmful
    • neither
• Helpful genetic changes have a greater likelihood of being passed on to subsequent generations, the process of natural selection.
• Evolution is the change in the genetic code of a population brought about by natural selection.

What is an ecosystem?

• An ecosystem is an arbitrary group of organisms and their surroundings
• In order to be stable, an ecosystem must be diverse
• The trophic level of an organism describes its distance, in steps, from the prime energy source, the sun
• Trophic level one includes all producers: plants and algae
• Trophic level two includes those animals which consume producers (vegetarians)

The following figure illustrates the different trophic levels for an arbitrary terrestrial ecosystem

Organisms residing higher on the trophic scale have less energy available to them, as illustrated below:

What supports life on Earth?

• Life exists in only a thin layer just above and below the earth's surface, the biosphere.
• The atmosphere is composed of mostly nitrogen (78%) and oxygen (21%)
  • The lower atmosphere is the troposphere, which extends up about 11 miles.
  • The next layer of atmosphere is the stratosphere, which extends up to about 30 miles.
  • The hydrosphere is the water contained on earth, the oceans, rivers, lakes, polar caps, groundwater, atmospheric water, etc.
  • The lithosphere is the upper geologic formations which contain and support life.
• Global geochemical cycles
  • Many if not all elements and compounds are important to organisms on Earth. Many elements or compounds are present in different forms, being converted from one form to another by various chemical and biochemical processes.
  • A global geochemical cycle is the pathways, transformations, and repositories of an element or compound as it moves throughout the biosphere.
  • Some of the more important cycles are illustrated in the following:
    • The carbon cycle--carbon is a major building block of life on Earth

• Nitrogen cycle

Bioconcentration

• Bioconcentration is the accumulation or increase in concentration of a substance as it proceeds up the food chain.
  • Many high molecular weight organics are sparsely soluble in water but highly soluble in lipids (fatty tissues).
  • This unequal solubility can lead to bioconcentration if the substances are not effectively metabolized by the organism.
• The following is an actual example of the bioconcentration of DDT in an aquatic environment.

Source: Woodwell, George M., Charles F. Wurster, Jr., and Peter A. Isaacson, "DDT Residues in an East Coast Estuary: A Case of Biological Concentration of a Persistent Insecticide," Science, Vol. 156, pp. 821-824, May 1967.

How much habitat have we lost?

• Before agriculture began some 10,000 years ago about 35% of the earth's land surface was covered by forest.

• Today only about 25% is covered with forest. And, of that, only about 12% contains original ecosystems.

• Types of forests:

  • Old growth forests are forests that have not been significantly disturbed by humans. In the United States, examples are the western Douglas fir, redwoods, and giant sequoia. Such forests are wonderful habitat for many species. The standing and fallen dead trees also provide excellent habitat.

  • Secondary growth forests are forests that have grown after cutting the original trees. Most US forests are second growth. The many pine forests in the Shawnee Forest in southern Illinois are secondary growth that replaced the native hardwoods.

• Many second growth forests in tropical regions are really monoculture tree farms.

• Tropical forests cover only about 6% of the land area. As they are cut, there is a change in the climate causing conditions which no longer favor their sustainability.

• Illinois once had 22 million acres of prairie. We now have just over 2,000 acres. If you are interested in reading more about our lost prairies, see The Tallgrass Prairie in Illinois by Kenneth R. Robertson.

How fast are we losing habitat?

• Current estimates are that we are losing about 60,000 square miles of tropical forest each year. That is about two football fields per second.

• Well over 90% of Brazils east coast forests are gone.

Landsat images of the state of Rondonia Brazil 11 years apart. The photo on the right shows a significant deforestation pattern along a road built into the forest. (Photo courtesy NASA).

How does it affect the survival of species?

• During the past 100 years, habitat loss, and other factors, have reduced the range of the Indian Tiger to possibly 5 to 10% of its original range.

• The range of the Black Rhino has been reduced to only 1 to 3% of its original range due to habitat destruction and poaching.

• Habitat destruction and other factors have reduced the Florida panther to near extinction. It is estimated there are only 30 to 50 left in the wild.

What about the human population?

• The human population increased at a slow rate until 1200 to 1600 AD
• Development of agriculture, technology, industry and medicine has given humans ability to increase their numbers at a phenomenal rate
• World population is now doubling approximately each 40 years

The US population will increase by 277 people during one 60 minute summer lecture period.

The world population will increase by 9160 people during one 60 minute summer lecture period.

Current US Population

Current World Population

There will be additional lecture material on human population later in the semester.

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