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Environment 121 Lecture:Topic: Levels of Biodiversity

14 April 2009Victoria Sork

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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,

landscapesb) Variation within ecosystems

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I. Genetic diversity

1. Defn: variation in some genetic marker across loci

2. Stuff of evolutiona) Evolutionary potential is determined by

amount of genetic variation

3. Varies across species depending on: a) Life historyb) Life spanc) Dispersal patternsd) 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

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: 1291-1297

Methods:1. Surveyed published studies in plant literature2. Calculated genetic diversity using average heterozygosity

across loci

Results:1. Variation across life history form2. Endemics tend to have les variation and widespread more

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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 Drift1. Change in gene frequency due to chance2. Can be an important evolutionary force3. Small populations vs large populations4. 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 Deera) Major genetic bottleneck inb) Originally from China; now extinctc) Only known in zoos

2. Northern Elephant Seala) Population size reduced significantly

due to huntingb) Less genetic variation than southern

elephant seals3. 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.

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Migration among populationsStudy of Lizards on Caribbean Islands, where storms can elimination local populationsMethods: sampled lizards on different islands• Microsatellite genetic markers• Evaluated migration among islands

Source: Calsbeek, R. and Smith, T.B. Ocean currents mediate gene flow in island lizards Nature 426: 552-555

->Found that ocean currents influenced pattern of migration.

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Quercus lobata (Née)Continuous populations in oak savanna genotype seeds and adults paternity analysis

SDD - measured

Example: Local gene movement via pollen movement

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Post-Pleistocene migration of oaks in Europe

Distribution of choloroplast haplotypes

R1R2

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Recolonization routes

Rapid recolonization of glaciated regions, possibly due to acorn dispersal by birds.

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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 richness3. High diversity ecosystems

a) Tropical rainforestsb) Temperate rainforestsc) Coral reefsd) Fynbos

4. Low diversity ecosystema) 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 remaining5. High endemism

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Fynbos of western Cape, S Africa

1. Mediterranean climate ecosystem

2. Winter rainfall3. Shrubland or heathland

vegetation4. Highest species diversity per

unit area5. greater diversity than tropical

rainforests6. 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 websb) Tropical figs as keystone resource

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Keystone predatorsMaintain 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 biodiversitya) For some species, genetic differences across

populations will be importantb) Not all individuals of a species are the samec) Reflects the impact of evolutionary forces

2. Species diversity patterns vary geographicallya) Ecosystem affects diversityb) Alpha, beta, gamma diversity varies

3. Ecosystem diversity varies geographicallya) The more complex the ecosystem the more diversityb) Rainfall and temperature influence ecosystem

diversity