Environment 121 Lecture: Topic: Levels of Biodiversity 14 April 2009 Victoria Sork

Environment 121 Lecture:
Topic: Levels of Biodiversity
14 April 2009
Victoria Sork
1
Levels of Biodiversity
1. Genetic diversity: amount of genetic variation
within a species
2. Species diversity: number of species within a
region
3. Ecosystem diversity:
a) variation among ecosystems, communities,
landscapes
b) Variation within ecosystems
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I. Genetic diversity
1. Defn: variation in some genetic marker across
loci
2. Stuff of evolution
a) Evolutionary potential is determined by
amount of genetic variation
3. Varies across species depending on:
a) Life history
b) Life span
c) Dispersal patterns
d) Population size
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Example: Life history and Distribution on
Genetic Diversity in plants (He)
Annual
Short-lived
perennial
Long-lived
perennial
Endemic
.149
.083
.105
Narrow
.113
.148
.163
Regional
.143
.123
.190
Widespread
.200
.154
na
Methods:
1. Surveyed published studies in plant literature
2. Calculated genetic diversity using average heterozygosity
across loci
Results:
1. Variation across life history form
2. Endemics tend to have les variation and widespread more
Source: J. L. Hamrick and M. J. W. Godt. 1996 Effects of Life History Traits on
Genetic Diversity in Plant Species. Phil Trans Royal Soc: Biol Sci. 351: 1291-12974
Measures of genetic diversity
1.
Phenotype: can be used to measure genetic variation
•
Eye color, blood type, flower color
2.
Allozymes: Variant forms of an enzyme coded for by different alleles at same
locus
•
Codominant markers considered neutral; co
•
Can be influenced by natural selection
3.
Microsatellites, aka Simple Sequence Repeats (SSRs)
•
Poldymorphic loci in nuclear or organelle DNA
•
Repeating units of 1-6 bases pairs
•
Codominant markers considered neutral
4.
Single nucleotide polymorphisms (SNPs):
•
DNA sequence variation of a single nucleotide ATCG
•
Co-dominant; opportunities for thousands of loci
5.
Gene sequence
•
gene is a locatable region of genome region associated with a function
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Evolution & Biodiversity: Genetic Drift
1.
2.
3.
4.
Change in gene frequency due to chance
Can be an important evolutionary force
Small populations vs large populations
Population bottleneck: larger population
contracts to a much smaller one (e.g. Northern
elephant seal)
5. Founder events: when a small group in a
population from the original population forms a
new one (e.g. albinism among San Blas Kuna)
 Genetic drift reduces genetic variation.
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Examples of Genetic Drift
1. Pere David’s Deer
a) Major genetic bottleneck in
b) Originally from China; now extinct
c) Only known in zoos
2. Northern Elephant Seal
a) Population size reduced
significantly due to hunting
b) Less genetic variation than
southern elephant seals
3. Human examples:
a) Dutch settlers in South Africa,
Afrikaners, have high frequency
of Huntington’s disease
b) Kuna Indians of San Blas Islands
off Panama have high frequency
of albinism
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Evolution & Biodiversity: Gene flow
1. Movement of gene affects the distribution of genotypes
•
Plants: pollen or seeds
•
Animals: dispersal of young or movement of adults
2. Occurs at varying spatial and temporal scales
– Within local population—affects who mates with whom
– Among populations, also called migration
•
homogenizes populations
•
Reduces impact of natural selection and local adaptation
3. Long term gene movement:
•
Historical migration (e.g. humans)
•
phylogeography
 Gene flow maintains and distributes genetic variation.8
Migration among populations
Study of Lizards on Caribbean Islands,
where storms can elimination local
populations
Methods: sampled lizards on different
islands
• Microsatellite genetic markers
• Evaluated migration among islands
->Found that ocean currents
influenced pattern of migration.
Source: Calsbeek, R. and Smith, T.B. Ocean currents mediate gene flow in island
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lizards Nature 426: 552-555
Example: Local gene movement via pollen
movement
SDD - measured
Quercus lobata (Née)
Continuous populations in
oak savanna
 genotype seeds and adults
 paternity analysis
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Post-Pleistocene migration of oaks in Europe
Distribution of choloroplast
haplotypes
Recolonization routes
R3
Rapid recolonization of glaciated
regions, possibly due to acorn
dispersal by birds.
R1
R2
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Adaptation and genetic diversity
Natural selection can
lead to genotypic
diversity across
sites
Example: Phenotypic
variation in
Potentilla
glandulosa
(source: Clausen,
Keck, Hiesey 1940
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Evidence
Common garden and
reciprocal transplant
experiments
Clausen, Keck, Heisey
results
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II. Ecosystem Diversity
1. Ecosystem: large ecological unit including biotic
and abiotic components
2. Biome:
• largest ecological unit
• based on temperature and precipitation (see
figure)
• Defined by dominant vegetation
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Holdridge life zone figure
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Legend for previous map shows
ecosystem diversity
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Ecosystem Diversity
1. Ecosystem have different species composition
that contributes to global species diversity
2. Diversities vary in species richness
3. High diversity ecosystems
a) Tropical rainforests
b) Temperate rainforests
c) Coral reefs
d) Fynbos
4. Low diversity ecosystem
a) Arctic tundra (trophic structure)
b) Florida everglades (low nutrients)
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Figure 2.3 Biodiversity indexes for three regions,
each consisting of three separate mountains
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California Floristic Province
1. One of only five areas with a
Mediterranean-type climate in the world
-- all of which are on the hotspot list
2. Hot, dry summers and cool, wet winters.
3. The region contains a wide variety of
ecosystems, including sagebrush steppe,
prickly pear shrubland, coastal sage
scrub, chaparral, juniper-pine woodland,
upper montane-subalpine forest, alpine
forest, riparian forest, cypress forests,
mixed evergreen forests, Douglas fir
forests, sequoia forests, redwood
forests, coastal dunes, and salt marshes.
4. 24.7 % original vegetation remaining
5. High endemism
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Fynbos of western Cape, S Africa
1. Mediterranean climate
ecosystem
2. Winter rainfall
3. Shrubland or heathland
vegetation
4. Highest species diversity per
unit area
5. greater diversity than tropical
rainforests
6. Proteas and Ericas
7. Fire adapted
8. High alpha diversity
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Ecosystems: Food webs
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Ecosystems: Trophic levels
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Keystone vs dominant species
1. Keystone species has an impact on community
that is proportionally greater than its actual
relative abundance, biomass, or energy flow
2. Dominant species is the species that has the
most biomass or that determines community
structure
3. Classic examples:
a) Star fish as keystone predator and intertidal
food webs
b) Tropical figs as keystone resource
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Keystone predators
Maintain species diversity by stabilizing the food
web and preventing competition
Eagle owl
Gray wolf
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Dominant species
1. The more complex the community structure the
more likely there will be a dominant species
(e.g. coniferous forest, temperate deciduous
forest versus tropical rain forest
2. Dominant species can also promote diversity
(e.g. oaks)
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Conclusions
1. Genetic diversity is an important component of
biodiversity
a) For some species, genetic differences across
populations will be important
b) Not all individuals of a species are the same
c) Reflects the impact of evolutionary forces
2. Species diversity patterns vary geographically
a) Ecosystem affects diversity
b) Alpha, beta, gamma diversity varies
3. Ecosystem diversity varies geographically
a) The more complex the ecosystem the more
diversity
b) Rainfall and temperature influence ecosystem
diversity
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