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 2 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 3 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 5 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. 6 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 7 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 9 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 10 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 11 12 Adaptation and genetic diversity Natural selection can lead to genotypic diversity across sites Example: Phenotypic variation in Potentilla glandulosa (source: Clausen, Keck, Hiesey 1940 13 Evidence Common garden and reciprocal transplant experiments Clausen, Keck, Heisey results 14 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 15 Holdridge life zone figure 16 17 Legend for previous map shows ecosystem diversity 18 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) 19 Figure 2.3 Biodiversity indexes for three regions, each consisting of three separate mountains 20 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 21 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 22 Ecosystems: Food webs 23 Ecosystems: Trophic levels 24 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 25 Keystone predators Maintain species diversity by stabilizing the food web and preventing competition Eagle owl Gray wolf 26 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) 27 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 28