Transcript ENVI 30 Environmental Issues - University of San Diego Home Pages

Biodiversity – Factors
I.
E.
Exotic Species
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Species invasions may profoundly affect
ecosystems
Detrimental exotic species usually are
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Superior competitors
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Ex – Argentine ants, starlings, zebra mussels
Effective predators
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Ex – Nile perch, mongeese
Biodiversity – Factors
I.
E.
Exotic Species
1.
Zebra mussel
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Competitor in Great Lakes and elsewhere
Transported from Europe in ballast water
Fouling organism
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Restricts movement of water through intake
pipes
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Colonizes boat hulls, pier pilings, buoys, etc.
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Fouls other organisms (clams, mussels)
Filter feeder – removes larvae and particulate
material
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Outcompetes native shellfish species for food
and space
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Removes larvae from water
Biodiversity – Factors
I.
E.
Exotic Species
2.
Mongoose
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3.
Predator in Hawaii
Introduced in 1883 to combat rat population
Prey on native birds
Lionfish
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Venomous predator
Introduced in Caribbean/W Atlantic ca. early/mid
1990’s
Preys on 65+ spp. of fishes
No natural predators
Nile perch – Lake Victoria
Argentine ants - California
Brown tree snake - Guam
Caulerpa taxifolia - California
Biodiversity – Value
II.
A.
Value to Humans
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Economic
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Ex – Lomborg: $3-33 trillion annually
Biodiversity loss could lead to removal of species that benefit
humans but aren’t currently known to do so
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Ex – Chapin et al. suggested increase in frequency of Lyme disease
during 20th century may have been related to increase in abundance of
tick-bearing mice (once controlled by food competition with passenger
pigeons)
Species extinction reduces potential pool of species containing
chemical compounds with pharmaceutical or industrial
applications
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Counter – Many pharmaceutical companies now use directed design to
search for new drugs
Problem – Benefits may not be obvious
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Difficult to convince people that it’s important to preserve something
with no immediately apparent intrinsic value to them (charisma?)
Ex – Economic value of viral resistance added to commercial strains of
perennial corn through hybridization with teosinte (Mexican wild grass)
is ~ $230-300 million
Ex – Weedy tomatoes from Peru
Discovered in 1962 during search for potatoes
Seeds sent to researcher at UC Davis who used plants to breed with
other tomatoes
In 1980 after nearly 10 generations of crossing and backcrossing, new
strains were produced with larger fruit, improved pigmentation and
increased concentrations of sugars and soluble solids
Biodiversity – Value
II.
B.
Ecosystem Value
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1.
Biodiversity can have large effects on ecosystem
stability and productivity
Benefits of biodiversity
a.
b.
Productivity
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Halving species richness reduces productivity by
10-20% (Tilman)
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Average plot with one plant species is less than half
as productive as a plot with 24-32 species
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Question – Can these results be extrapolated to
other systems and time/space scales?
Nutrient retention
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Loss of nutrients through leaching is reduced when
diversity is high
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Caveat – Studies to date have focused on low
diversity communities (Why?); can those results be
generalized?
Biodiversity – Value
II.
B.
Ecosystem Value
1.
Benefits of biodiversity
c.
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Ecosystem stability
Mechanism
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Multiple species within a trophic level compete for
resources
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If abundance of one species declines due to perturbation,
competing species may increase in abundance
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Individual species abundances may vary, but community
as a whole is more stable with more species
Consequences
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High diversity doesn’t guarantee that individual
populations won’t fluctuate
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Ex – Higher diversity (unfertilized) plots of native plant
species maintained more biomass during drought than
lower diversity (fertilized) plots
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High diversity may confer greater resistance to pests and
diseases
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Ex – Higher diversity plots of native plant species had
greater resistance to fungal diseases, reduced predation
by herbivorous insects and reduced invasion by weeds
Biodiversity – Value
II.
B.
Ecosystem Value
2.
Considerations
a.
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b.
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Species richness vs. Species evenness
Simple species richness may be deceptive as an indicator of
biodiversity and ecosystem stability
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Evenness usually responds more rapidly to perturbation
than richness and may have important ecosystem
consequences
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Richness is typical focus of studies and policy decisions
Importance of individual species
Charismatic megafauna: What about non-charismatic species?
Different species affect ecosystems in different ways (keystone
species vs. non-keystone species)
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Ex – Sea otters/Sea urchins/Kelp forests in eastern Pacific
Ocean
Question: How many species are required to maintain “normal”
ecosystem function and stability?
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No magic number
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Losing one ant species in a tropical forest may have less
immediate impact than losing one species of fungus that
is crucial to nutrient cycling in the soil
Biodiversity – Management
III.
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Strategies outlined in Convention on Biological
Diversity
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Developed between 1988 and 1992
Opened for ratification at UN Conference on
Environment and Development (Rio “Earth Summit”)
Ratified by 168 nations; went into force in Dec 1992
Objectives – “…the conservation of biological
diversity, the sustainable use of its components and
the fair and equitable sharing of the benefits arising
out of the utilization of genetic resources…”
Articles 8-9 specify a combination of in situ
and ex situ conservation measures
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Primary use of in situ conservation
Use of ex situ measures as a complement
IV.
Genetic Engineering
A.
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Background
Concept based on idea that organisms share
same basic genetic material (DNA)
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Theoretically possible to transfer genes
between organisms and expect traits to be
transferred faithfully
Insertion of a foreign gene into a species’
genome creates a transgenic organism
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Inserted gene may or may not be expressed
Theoretically, no limits on what can be inserted
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Functionally similar units (genes)
Same basic mechanisms of gene expression
Ex – Insulin gene inserted into bacteria
Ex – UCSD researchers inserted bacterial
luciferin/luciferase genes into tobacco plant
Technology offers potential to create novel
organisms with unusual and potentially
beneficial attributes
IV.
Genetic Engineering
A.
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Background
Concept based on idea that organisms share
same basic genetic material (DNA)
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Theoretically possible to transfer genes
between organisms and expect traits to be
transferred faithfully
Insertion of a foreign gene into a species’
genome creates a transgenic organism
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Inserted gene may or may not be expressed
Theoretically, no limits on what can be inserted
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Functionally similar units (genes)
Same basic mechanisms of gene expression
Ex – Insulin gene inserted into bacteria
Ex – UCSD researchers inserted bacterial
luciferin/luciferase genes into tobacco plant
Technology offers potential to create novel
organisms with unusual and potentially
beneficial attributes
IV.
Genetic Engineering
B.
Purposes
1.
Accelerate and refine selection process
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2.
Create otherwise unattainable hybrids
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“Normal” hybridizing limited by
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Generation time
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Combining entire genomes, not just traits of interest
Ex – Arctic flounder and strawberry or tomato
Bottom line - Genetic engineering of organisms is
intended to benefit humans, not modified organisms
Proponents stress potential benefits to
humankind and the environment
Opponents emphasize potential risks and
concerns
Conversation with Hugh Grant