U6115: Populations

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U6115 Populations Land UseTuesday July 8,
2003

• What is Biodiversity
• Importance of Biodiversity
• Levels of Biodiversity
• Threats to Biodiversity
• Patterns of Biodiversity

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• A one-acre patch of elm trees produces oxygen,
  removes carbon from the atmosphere, and captures
  at least 16 tons of airborne dirt, which rain
  then washes back to the ground as productive
  soil.
• Norman Myers 1983

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What is Biodiversity?

• The variety of different types of organisms
  present and interacting in an ecosystem.
• Often more species equals more diversity,
  although there are, in fact many more factors
  beyond a simple count of species that determine
  whether biodiversity is higher or lower in any
  given ecosystem.

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Biodiversity and global economy

• Globally agriculture, which depends on genetic
  stock from natural ecological systems, is now a
  3 trillion global
• Recreation and nature tourism generates some 12
  billion worldwide in annual revenues
• In the United States, the economic benefits from
  wild plants and animals comprise approximately
  4.5 of the Gross Domestic Product.
• Global trade in wild plants (timber and others)
  is estimated at 6 billion annually

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Biodiversity and food security

• Much of the world's major food crops, including
  corn, wheat, and soybeans, depend on new genetic
  material from the wild to remain productive and
  healthy.
• Food production from wild stocks of fish is the
  single largest source of animal protein for the
  world's 6 billion inhabitants. In the US alone
  more than 10 billion pounds of fish, valued at
  about 4 billion, were caught and sold yearly.

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Levels of Biodiversity

• Genetic Diversity
• Species Diversity
• Ecosystem Diversity

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Genetic Diversity

• Amount and variety of genetic material within
  individuals, populations or communities
• Source of biodiversity at all levels
• Knowledge of amount of genetic variability
  present within local populations essential in
  directing conservation programs.
• Amount of genetic differences among species could
  help determine rates of evolutionary change

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Species Level

• Species Richness numerical count of species
  present in an area. Richness tends to increase
  over area and sampling intensity
• Species Diversity When species are weighted by
  some measure of importance e.g. abundance,
  productivity or size.
• Measures of Diversity include
• Shannon-Wiener Index
• Simpson index

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Shannons Diversity Index

• Assume that there are n possible categories in a
  data set and that their proportions are
  pi,.....,pn. Then Shannons diversity index for
  this system is defined to be
• H -Spiln(pi)
• accounts for both abundance and evenness of the
  species present
• The proportion of species i relative to the total
  number of species (pi) is calculated, and then
  multiplied by the natural logarithm of this
  proportion (lnpi).

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Simpsons Diversity Index, D

• Simpson's diversity index (D) characterizes
  species diversity in a community.
• Simpson's diversity index (D) characterizes
  species diversity in a community.
• D 1/(Spi2)
• The proportion of species i relative to the total
  number of species (pi) is calculated and squared.
  The squared proportions for all the species are
  summed, and the reciprocal is taken.

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Ecosystem and Biome diversity

• Ecosystems are the collection of all the plants
  and animals within a particular area
• Ecosystems may differ in species composition,
  physical structure and function as a result of
  differences in physical structure and composition
• Biomes are large ecological units on the basis of
  dominant vegetation
• Preserving a variety of ecosystems and biomes are
  necessary for preserving species diversity

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Temporal Patterns of Species richness

• Fossil record indicate variation of species
  richness over time and space
• Largest number of phyla in the Cambrian and
  pre-Cambrian period
• Total number of phyla has since declined but
  overall richness has increased

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Spatial patterns of species richness

• Point Richness number of species that can be
  found in a single point in space
• Alpha (a-) richness number of species found in a
  small homogenous area
• Beta (ß-) richness rate of change in species in
  species composition across habitats
• Gamma (?-) richness change across large
  landscape gradients
• Richness is directly related to physical
  environment, productivity and structural
  complexity of communities

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Species /Area relations
Number of species
Area (sq.mi)
Relationship between area and number of
amphibian species in selected Islands in West
Indies- MacArthur Wilson 1967
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Limits of species richness

• Productivity hypothesis High productivity
  results in higher number of species
• Stability hypothesis- environments that are
  stable tend to support higher number species

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Threats to biodiversity

• habitat destruction (slash and burn agric. or
  felling of old-growth forests)
• overexploitation (fishing, hunting)
• pollution (domestic and industrial emissions)
• global climate change (the greenhouse effect and
  destruction of the ozone layer)
• invasion by introduced species (displacement of
  native species
• underlying social conditions (increased
  per-capita consumption, poverty, rapid population
  growth, unsound economic and social policies )

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Threats to Biodiversity contd

• Habitat degradation
• Some 93 of coral reefs damaged directly or
  indirectly by human activities
• During the 1990s between 130,000 and 150,000 km2
  of forest cover lost each year
• Changes in atmospheric composition.
• siltation, nutrient loading, pollution of air and
  water by toxic chemicals

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Patterns of species vulnerability

• Rare Species
• Long-lived species
• Keystone species

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Rare species

• May be the result of many factors small range,
  high habitat specificity or small population
  density
• Human-induced rarity may be more damaging

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Long-lived species

• Well-suited to long-term predictability
• Often not equipped to adapt to rapid changes
  brought by human-induced changes
• Often population declines may take many years to
  recover

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Keystone species

• A species or group of species that makes and
  unusual contribution to a community structure or
  processes
• May be predators, food source or species that
  maintains critical ecosystem processes
• A loss of a keystone species may lead to loss of
  others that depend on it.

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Biodiversity ManagementConservation vs
Preservation?

• All about management of Genetic Variation
• Aim is to allow continued evolutionary change in
  the populations and species concerned
• Since ecological systems are not static-
  management should allow for change- Conservation
  rather than preservation.
• 3 Time scales of concern extinction avoidance
  (short-term) ability to adapt or evolve (medium
  term) and potential for continued speciation
  (long-term)
• Units of conservation What are the units of
  conservation? How do we determine the most
  appropriate unit?

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Next week

• Habitat fragmentation and biological consequences
  
• Population dynamics on heterogeneous landscapes

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Todays lab

• Review of two short papers.
• Stuart Chapin III et al 2000. Consequences of
  changing biodiversity Nature Vol. 405 pp. 234
  http//www.nature.com/cgi-taf/DynaPage.taf?file/n
  ature/journal/v405/n6783/full/405234a0_fs.htmlcon
  tent_filetypepdf
• Franklin, J.F. 1993. Preserving Biodiversity
  Species, Ecosystems or Landscapes? Ecological
  Applications, 3(2), pp. 202 - 205.
  http//www.jstor.org/cgi-bin/jstor/printpage/10510
  761/di960380/96p0004u/0.pd f?userIDa027019f_at_colum
  bia.edu/01cc9933410050dc70ebbackcontexttable-ofc
  ontentsconfigjstordowhatAcrobat0.pdf