Biodiversity

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Transcript Biodiversity

U6115: Populations & Land Use
Tuesday July 8, 2003
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What is Biodiversity
Importance of Biodiversity
Levels of Biodiversity
Threats to Biodiversity
Patterns of Biodiversity
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
What is Biodiversity?
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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.
Biodiversity and global economy
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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
Biodiversity and food security
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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.
Levels of Biodiversity
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Genetic Diversity
Species Diversity
Ecosystem Diversity
Genetic Diversity
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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
Species Level
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Species Richness: numerical count of species present in an
area. Richness tends to increase over area and sampling
intensity
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Species Diversity: When species are weighted by some
measure of importance e.g. abundance, productivity or size.
Measures of Diversity include:
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Shannon-Wiener Index
Simpson index
Shannon’s Diversity Index
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Assume that there are n possible categories in a data set and
that their proportions are pi,.....,pn. Then Shannon’s diversity
index for this system is defined to be :
H’ = -Σpiln(pi)
accounts for both abundance and evenness of the species
present
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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).
Simpson’s Diversity Index, D
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Simpson's diversity index (D) characterizes species
diversity in a community.
Simpson's diversity index (D) characterizes species
diversity in a community.
D = 1/(Σpi2)
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.
Ecosystem and Biome diversity
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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
Temporal Patterns of Species richness
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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
Spatial patterns of species richness
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Point Richness: number of species that can be
found in a single point in space
Alpha (α-) richness: number of species found in a
small homogenous area
Beta (β-) richness: rate of change in species in
species composition across habitats
Gamma (γ-) richness: change across large
landscape gradients
Richness is directly related to physical environment,
productivity and structural complexity of communities
Species /Area relations
Number of species
100
Cuba
Jamaica
10
Monserrat
Saba
Redonda
10
100
1000 10000 100000
Area (sq.mi)
Relationship between area and number of amphibian
species in selected Islands in West Indies- MacArthur & Wilson 1967
Limits of species richness
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Productivity hypothesis: High productivity
results in higher number of species
Stability hypothesis- environments that are
stable tend to support higher number species
Threats to biodiversity
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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 )
Threats to Biodiversity cont’d
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Habitat degradation
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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
Patterns of species vulnerability
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Rare Species
Long-lived species
Keystone species
Rare species
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May be the result of many factors small
range, high habitat specificity or small
population density
Human-induced rarity may be more
damaging
Long-lived species
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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
Keystone species
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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.
Biodiversity Management
Conservation vs Preservation?
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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?
Next week
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Habitat fragmentation and biological
consequences
Population dynamics on heterogeneous
landscapes
Today’s lab
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Review of two short papers.
Stuart Chapin III et al 2000. Consequences of changing
biodiversity Nature Vol. 405 pp. 234 http://www.nature.com/cgitaf/DynaPage.taf?file=/nature/journal/v405/n6783/full/405234a0_fs.html&content_filetype=pdf
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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/10510761/di960380/96p0004u/0.pd
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