Biology 100/101
Lectures 20 AND 21: Biodiversity
Text readings in Lifeby Ricki Lewis:
Information on this topic is presented in several different chapters. These chapter sections, in addition to the information contained in this WWW outline and links, will help you understand biodiversity (and prepare for the final exam).
- Chapt. 1: pg 12-14 (biodiversity, life in hot springs and thermostable enzymes, taxonomy)
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Chapt. 16: pg 338-344 (mutations: their causes and types)
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Chapt. 20: pg 404-405 (genetics of populations), p. 410 (mutation), pp. 413-414 (how species arise), pp. 416-419 (mass extinctions)
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Chap. 21: pg 426-437 (Classifying Life: taxonomy, biodiversity, and life's three domains)
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Chapt. 44: pg 890-907 (Environmental Concerns: review and biodiversity)
Web resources:
Objectives:
After studying this material you should be able to:
- Define what biodiversity is and its relationship to genes, species, and ecosystems.
- Describe the roles of sexual reproduction, meiosis, and mutation in the origin and maintenance of genetic variation in a population.
- Have a basic working knowledge of the number of species known, the estimated number in existence, and how these numbers are distributed among the major groups of organisms. You should also be aware of the three domains of life and how these domains relate to the prokaryote/eukaryote subdivision and life's major kingdoms.
- Explain how biodiversity can be lost, how rapidly it is being lost, and some of the reasons why we might be concerned about this loss.
- Discuss the value and potential value of biodiversity to humans.
What is biodiversity?
Biodiversity has to be defined at several levels, in terms of genes, species, and ecosystems.
It is a dynamic process and what we see now is the product of hundreds of millions of years of evolutionary history.
Biodiversity increases when new genetic variation is produced, a new species arises, or a novel ecosystem (or habitat) is formed.
Biodiversity decreases when the genetic variation within a species decreases, a species becomes extinct, or an ecosystem (or habitat) is lost.
1. Genetic diversity
- The variety of genetic information contained in all of the individual plants, animals, and microorganisms in the world.
- It occurs within and between populations of the same species as well as between species. Individuals belonging to the same species are usually not identical genetically.
- Differences in the amount and distribution of genetic variation within species can be attributed to the enormous variety and complexity of habitats, and the different ways organisms have adapted to these habitats.
- Genetic diversity can be measured using a variety of DNA and protein-based techniques.
- It can also (in part) be catalogued based on visible traits. For example, of the 100,000 genes in humans, 10,000 are outwardly (visibly) expressed and vary from person to person. Such phenotypic differences include differences in race, eye color, height, etc.
- By now you should be able to dicuss genetic diversity based on sexual reproduction, meiosis, mutation, and populations.
- What are the sources of genetic variation in a population?
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- How does new genetic variation arise?
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- How does genetic variation spread through a population?
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2. Species diversity
- The variety of living species.
- The question "What is a species?" is not readily answered, and many definitions exist.
- Lewis defines a species as "a group of similar individuals that interbreed in nature and are reproductively isolated from all other such groups." How can reproductive isolation be accomplished, anyway? [see pg. 413, text]
- Basically, species are the different "kinds" of living or extinct organisms.
- Systems for the classification of species go back at least 2,500 years to the Greeks (Aristotle and Plato).
- All life is grouped into three domains: Bacteria (the "prokaryotes"), Eukarya (the eukaryotes), and Archaea. The Eukarya includes the protists, plants, fungi, and animals (traditionally considered kingdoms).
- How many species are there?
Some examples from: Systematics Agenda 2000: Charting the Biosphere. Some of these numbers may differ from those shown on pg. 436 (Table 21.5) in your text.
|
Number Described |
Estimated to be Discovered |
| Viruses |
5,000 |
about 500,000 |
| Bacteria |
4,000 |
400,000-3 million |
| Fungi |
70,000 |
1-1.5 million |
| Protozoans |
40,000 |
100,000-200,000 |
| Algae |
40,000 |
200,000-10 million |
| Flowering plants |
250,000 |
300,000-500,000 |
| Vertebrates |
45,000 |
50,000 |
| Roundworms |
15,000 |
500,000-1 million |
| Mollusks |
70,000 |
200,000 |
| Crustaceans |
40,000 |
150,000 |
| Spiders and mites |
75,000 |
750,000-10 million |
| Insects |
950,000 |
8-100 million |
- An estimated 1.6 million species have been described to date.
- Estimates for the total number of species vary from 10 to 50 million (and perhaps up to 100 million).
- Species diversity is not evenly distributed across the globe. Species richness is concentrated in equatorial regions and decreases as one moves to the poles (or increases in altitude).
For additional information:
3. Ecosystem (or habitat) diversity
- The variety of habitats, biotic communities, and ecological processes (e.g., energy flow, water and nutrient cycling, succession, competition, mutualism) occurring within and between each type of ecosystem.
- Ecosystem diversity is harder to measure than species or genetic diversity, partly because ecosystems themselves are harder to define. Nevertheless, it is a precondition for
species and genetic diversity.
For additional information:
Reduction of biological diversity
How is biodiversity being lost?
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Endangered species act as a warning that something is wrong (like canaries in coal mines).
Extinction is accelerating. The number of organisms on Earth is being reduced at a rate 1,000-10,000 times higher than the time before humans evolved.
1-2% of the tropical forests are removed each year. This is equivalent to losing an area the size of Florida each year!
During the next 30 years 20% of all extant rain forest organisms (hundreds of thousands of species) will become extinct. Present estimates say we are losing 27,000 species each year. By the year 2100, half of the remaining rain forest will be gone (and over half the species).
20% all bird species have gone extinct during the last 2000 years and 11% more are endangered now. In the US over last 100 years, 2% of the amphibians, 1.2% of the fish, 1% of the plants, and 9% of the freshwater mussels have vanished. Note that these are all species easily observed and recorded. Other losses are unknown.
These losses are numerically comparable to those in the 5 mass extinctions that occurred on earth during the last 500 million years. The last one was the end of the reptiles, 65 million years ago. Most significant, however, is that humans are responsible for this one, and its rate is much faster than any prior mass extinction (a few decades to centuries vs. millions of years).
Losses of biodiversity are irreversible. Replacement of the number of species (though not the same ones) takes approximately 10 million years.
For more discussion on rates of extinctions, especially in the tropics, check out the Rainforest Action Network. Here there's lots of links to rates of rainforest destruction.
Why is biological diversity important?
1. Pharmaceuticals
- 80% of people in less-developed countries rely heavily or entirely on drugs derived from natural sources (World Health Organization estimate). More than 20,000 species have been used for medicinal purposes.
- Of the drugs used in the U.S., 25% derived from plants, 13% from microorganisms (including many antibiotics), and 3% from animals. Overall, that is 41% of our prescription drugs which are derived from living organisms!
- Many of these drugs cannot be manufactured synthetically (or, if they are, they do not work as effectively).
- Relatively few flowering plants (that is, of the ones we know) have been examined for their medicinal properties. Up to 1992, only 2% (or 5,000 species) had been examined. But a number of these have become multi-billion dollar commodities:
- Digitalis (foxglove), for the cardiac stimulant digitoxin.
- Catharanthus roseus (rosy periwinkle), for vincristine & vinblastine. These are the most effective drugs for the treatment of childhood leukemia and Hodgkin's disease. From Madagascar, this is the source of two of the most effective anticancer agents ever discovered.
- Taxus brevifolia (Pacific yew) for taxol, used to treat ovarian and breast cancer.
- Cyclosporin, a powerful immunosuppression agent used in organ transplants, was discovered in a Norwegian fungus.
- Penicillin, of course, was also first isolated from bread mold.
- Nature's Pharmacy from the National Wildlife Federation.
- A treasure trove for future generations. A discussion of the rosy periwinkle and the value of biodiversity.
Questions and Issues:
Will technological advances in the pharmaceutical industry preclude further natural-products research?
Not likely, as natural diversity is valued for the "blueprint" it provides for new synthetic drugs. Some drugs (e.g., taxol) are so unusual structurally, that they would probably have never been discovered in the laboratory.
Are rainforests really all that important for medicines, or do we just say they may provide cures for cancer and AIDS?
According to the National Cancer Institute, over 70% of the promising anti-cancer drugs come from plants in the rain forest. See bioprospecting for new pharmaceuticals.
Just who really benefits from the commercialization of biodiversity?
2. Foods
- 30,000 or more plant species have edible parts; 7,000 species are grown and used as food by humans; 20 species feed the majority (90%) of the world's population; just 3 species are the major world-wide staples (rice, wheat, and corn).
- Wild plant gene pools are important to augment the narrow genetic base of established food crops (by providing resistance to disease, improved agricultural productivity, and different environmental tolerances). Most improvements in agriculture will depend upon the survival of these "gene banks."
- Many presently underutilized food crops have the potential to become important in the future. Remember: the relatively few species currently cultivated have had lots of research and selective breeding applied to them!
- Food and biodiversity in nature's supermarket. Our future food supply depends on biodiversity.
- Genetic diversity and corn. In 1970, 15% of the US corn crop was wiped out by leaf blight. Mexican wild corn (Zea diploperennis) is resistant to a number of serious viral corn diseases that infect Zea mays. Researchers have transferred this viral resistance to corn. It may also be possible to produce perennial corn.
3. Wood and other products from biological resources
- fuel, construction, paper production
- new hybrids and varieties of ornamental plants developed and marketed
- adhesives from barnacles
- fibers from spider silk
- natural pesticides from microorganisms
- petroleum substitutes
4. Genetic resources
- Specific habitats (ecosystem diversity) are important for breeding and spawning.
- Some habitats are genetic reservoirs from which seed and other materials can be obtained.
- Biotechnological advances permit genetic engineering wizardry (i.e., the transfer of genes from one organism to another).
5. Ecosystem-level benefits
- Protection of water resources (vegetation regulates and stabilizes water runoff and increases water yield and quality).
- Soil formation and protection (helps in the formation and maintenance of soil structure and quality, the retention of moisture and nutrient levels, and the prevention of erosion). What's happening to the tropical rain forests?
- Maintance of ecosystem functioning (nutrient storage and cycling, atmospheric oxygen/carbon dioxide balance, the removal or disturbance of one part of the ecosystem could affect the functioning of many other parts--recall the intricate web of life).
- Pollution breakdown and absorption (bacteria and other organisms breakdown pollutants; wetlands can act as filters).
- Recovery from unpredictable events. Degraded ecosystems are less likely to recover from natural and man-made disasters (genetic variability is depleted and extinctions occur). Biodiversity promotes stability. See page 818, text.
Keystone species. What are they, and how are they related to biodiversity?
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6. Social benefits
- recreation, research opportunities, education
7. Ethics
The relationship of biodiversity to systematics
Much of our knowledge on biodiversity comes from the basic activities of systematic biologists, namely the discovery and description of new species, the determination of their characteristics and evolutionary (phylogenetic) relationships to other species, and the organization of this knowledge into classification systems. These classification systems are powerful predictive tools that help us to understand, maintain, and effectively utilize this great biological wealth.
and away we go!