BSCI 124 Lecture Notes

Undergraduate Program in Plant Biology, University of Maryland



I. Biodiversity

  1. Definition: [REQUIRED READING] The variety and variability of life-forms, both contemporary and extinct, including genetic and ecosystem diversity, in a defined area at and over time.
  2. Global patterns [REQUIRED READING]
    1. Approximately 90 phyla of extant organisms
    2. Most have few species and are marine
    3. Plants
      1. Bryophyta (bryophytes, mosses & hornworts): 24000 sp
      2. Polypodiophyta (ferns): 8500 sp
      3. Lycopodiophyta (club mosses): 1225 sp.
      4. Equisetophyta (horsetails): 29 sp.
      5. Psilotophyta (whisk ferns): 4 sp.
      6. Cycadophyta (cycads): 105 sp.
      7. Pinophyta (conifers): 600 sp.
      8. Ginkgoophyta (ginkgo): 1 sp.
      9. Gnetophyta (gnetops): 70 sp.
      10. Magnoliophyta (flowering plants): 245000 sp.

    Plant and animal diversity is critical to habitat preservation

  3. Concepts of biodiversity
    1. Hypotheses:
      1. "Rivet popper": Each species is important in its own small way, lose one (like a rivet in a plane) and little happens but the ecosystem weakens. Lose several species and at some point the whole system fails.
      2. "Redundancy": Most species are superfluous as only a few are critical to the survival of the ecosystem. Species are like passengers on the plane, even with only a few, the plane can still fly
    2. Evidence
      1. Crop production increases with diversity, e.g., greater production of corn if other plants are intercropped than increasing the number of corn plants per acre
      2. Increased ecosystem resilience to stress with increase species diversity
      3. Full productivity can be reached by a few select species in terms of biomass but most ecosystems have far more species than necessary, thus random loss will not cause system collapse
  4. Levels of diversity
    1. Rates of speciation [See also examples of recent speciation]
      1. Rapid speciation occurs in tropical and arid (especially desert) regions; less so in temperate regions
      2. Rate of speciation low in aquatic habitat yet individual species tend to survive for much longer periods of time; rates much higher in areas of environmental stress (desert)
      3. Individual species survive for long periods of geological time in tropical regions where more species per unit area can exist and where even marginally successful species can survive a library filled with numerous books, even those with numerous error
      4. Individual species do not survive for long periods of time in areas of environmental stress a library of only a few books, all essentially in perfect condition
    2. Species diversity
      1. About 2800 species of vascular plants (ferns, fern allies, gymnosperms and flowering plants) in Alaska; about the same number in Maryland
      2. About 5000 species in eastern United States; about 4800 species in Nevada
      3. About 22000 species in North America north of Mexico; about 25000 species in Costa Rica

    Humans can cause species extinction in small but diverse areas

  5. Threats to diversity - an essay by E.O. Wilson
    1. Humans: Current major cause of species loss and habitat degradation
      1. Human-caused habitat destruction is often wanton and thorough; widespread and often concentrated
      2. Native species often lost and habit invaded by exotic weeds
      3. Alien plants tend to be short-lived and aggressively weedy
    2. Non-random, naturally occurring species losses
      1. Selective and random; infrequent and widely scattered
      2. Native species reduced in numbers but not locally extirpated; habitat locally disrupted but not thoroughly destroyed
      3. Re-colonization is by native species even if area initially invaded by alien species
    3. Different habitats have different kinds of threat and different causes of those threats
      1. Coastal ecosystems
      2. Marine ecosystems
  6. Significance of biodiversity {REQUIRED READING]
    1. Long the study of biologists
    2. Public now aware that as a global resource, biodiversity is the underpinning of the healthy functioning of the earth's many ecosystems
    3. Persons involved with decision-making affecting the environment require knowledge of the origin and extent of biodiversity, and how it might be maintained
    4. Without a biologically viable world, humans will not exist
      1. Biodiversity provides an array of services that maintain life on earth
      2. Biodiversity provides humans with substantial economic benefits
        • 1) crops
          2) domestic animals
          3) medicines
          4) natural products: wildlife, fish, timber
          5) some 10000 species of plants and animals are exploited industrially
      3. Biodiversity provides humans with esthetic benefits

II. What is known about the biota?

Much of the tropical forest has yet to be explored meaning that as it is being destroyed,
thousands of potentially useful species are going extinct before they are even known

  1. Far more organisms to discover than have been found and studied scientifically
    1. The number of plants thought to exist now is about 350,000 of which only some 256,000 have be described
    2. Of the estimated 30 million animals, only some 1.1 million are known
    3. Mere discovery is not enough
      1. Described and classified
      2. Role in the environment evaluated
      3. Potential value
  2. Conservation critical to maintaining currently available biodiversity
    1. Critical habitat: The area required to maintain not only one species but the suite of species that make up the population structure in which the species is found
    2. Germplasm preservation: Natural populations of species critical to human survival must be preserved with their population structure to provide future germplasm for human survival in a changing environment
    3. Conservation is successful only when large areas are maintained
  3. Future of the biota
    1. Responsibility of all people
    2. Effective only at national and international level; impetus for action at local level.
    3. People make decisions to destroy the environment; people can also make the decision not to abuse the environment
    4. Maryland Natural Heritage Program: What is being done here? Check out the teaching program in California

III. Extinction

The small franklinia tree (Franklinia alatamaha), named for Benjamin Franklin in 1785,
is known today only from garden specimens, being last seen in the wild in 1803

  1. Definitions:
    1. Extinction: The loss of a species from the biota; the failure of a taxonomic group to produce direct descendants, causing its worldwide disappearance from the record at a given point.
    2. Extirpation: The loss of a species from a significant portion of its range
    3. Endemic: A species restricted to a defined geographic area
  2. Extinction as a natural process
    1. Each species has a finite lifetime probably 99% of all organisms that have existed are now extinct
    2. Most species exist 2-5 million years
    3. Extinction can result in an available ecological niche (where an organism lives and its behavior in that place) to be occupied by other species
  3. Kinds of extinction
    1. Background extinction: The continuous, low-level rate of extinction
    2. Mass extinction: A large loss of species in a brief geological period of time
      1. Cretaceous extinction when the dinosaurs disappeared some 65 million years ago (mya) -- see this site and especially the pictures
      2. Numerous major extinctions have occurred (5 or 6) each resulting in a fundamental change of the biota (e.g., rise of flowering plants at the end of the Jurassic some 130 mya)
      3. Significant extinctions occur about every 26 million years
  4. Causes of mass extinction
    1. Climate: Changes in the climate always results in changes in the biota; sudden (in geologic time) and profound changes nearly always result in mass extinction events. Gradual changes usually result in a displacement of the biota but not necessarily mass extinction
      1. Pleistocene glaciation [good but slow to load!] (over the last 2.5 my) resulted in significant extinction of grazing animals in North America and Eurasia, but not in Africa and portions of South America
      2. Eastern deciduous forests pushed into eastern Mexico so that most of the flora survived; montane forests in southern California and Arizona were extirpated during the Holocene (last 10,000 y) as the climate warmed after the glacial era
    2. Geologic events: Dramatic flooding, extensive volcanic activity, major tetonic shifts (e.g., continental drift, widespread volcanic eruptions), etc. can all resulted in global or near-global extinction events
      1. Increases or decrease in sea levels
      2. Volcanic and fire-induced high altitude air pollution
      3. Continental drift and island formation
    3. Meteorite: Impact of large or numerous meteorites. [See When the Sky Fell by Philippe Claeys, a thorough summary]
      1. Meteorite: Impact with earth can cause increase in dust at high elevations
      2. End of Cretaceous probably caused by meteorite hitting the earth near Yucatan; iridium layer found at same level all around the earth
      3. Human: The single largest cause of extinction presently [REVIEW this paper, "The Current State of Biodiversity" by E.O. Wilson]
        1. About 2400 species disappear daily
        2. About 10000 new species described annually
        3. Extinction rate now greater than that at the end of the Cretaceous Period

    Other sites of interest
    Biodiversity: An overview: An excellent and thorough review from
    Biodiversity Internet Sites
    Biodiversity Conservation Information System
    Biodiversity: The most fundamental issue a speech by Thomas Lovejoy
    Natural Heritage Network Central Server: Biodiversity sites in the New World
    The case for saving species
    Why species are important
    Extinctions past and present
    Diversity Special: By Dr. Veron Heywood - A major summary of global biodiversity efforts
    Centre for Plant Biodiversity: An example of a national biodiversity program
    Protecting biodiversity: from Greenpeace
    Greenpeace Biodiversity Page
    Teaching Biodiversity: A Unit Study for Elementary Teachers
    The Stochastic Extinction Model: Technical but interesting
    The Biophilia Hypothesis: Read the introduction by E.O. Wilson
    All about asteroids
    An excellent review of dinosaurs!

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    Last revised: 23 Aug 1998 - Reveal