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Ch. 6: Evolutionary Processes/Outcomes Plants and Environment • 1) Liebig (1840) – Law of the Minimum: Growth/distribution depends on environmental factor most limiting A Festive MoB CuMnZn Clapping Nicely Plants and Environment • 2) Shelford (American: early 1900s) – Upper limits for factors – Proposed “Theory of Tolerance” Plants and Environment • Phenotype: appearance • Genotype: genetic make-up • Phenotype: determined by genotype & environment Plants and the Environment • Equation: • Vp = Vg + Ve • Vp = total phenotypic • Vg = variation due • Ve = variation due Focus Vg Plants and the Environment • Adaptation: – 1) Genetically – 2) With • How determine trait adaptation? Hard! Genetic importance Plants and the Environment • Genetic basis: • Heritability (h2): resemblance between relatives due • h 2 = V g / Vp – Vg = variation due to – Vp = total Plants and the Environment • 1 approach: slope regression line (r2) y = mx + b; m is slope r2=0.52 r2=0 r2=1 Plants and the Environment • Plant height ex. (r2)=0.21 or 21% (h2)=0.21 or 21% Fig. 6.3 Genetic Variation • More better (generally) • Why? – 1) Raw material evolution (change genetic makeup) – 2) Dominant alleles mask “lethal recessives:” fatal if Finish this sentence: If you were haploid you’d be __________________ Genetic Variation • Problem: genetic drift! Loss • Small pop’ns Start: 50% mix 2 alleles Small population (9 inds.) Large population (50 inds.) Genetic Variation • Ex, Wollemi “pine” (Australia) Loss of Genetic Variability • Ex, Wollemi “Pine” (Australia) • Extinct 2 mya, 2 groups found 1994. Famous quote…… Discoverer David Noble Loss of Genetic Variability • Ex, Wollemi “Pine” (Australia) • No measurable genetic diversity! Collecting seeds by helicopter Genetic Variation • Sources new genetic variation? – 1) Mutation: Heritable . Rare: 10% of pop’n. each generation (new mutation) – 2) Immigration. Plants and the Environment • Recall: • Adaptation: – 1) Genetically determined trait – 2) With survival or reproductive benefit • How show benefit? Hard! Ex Adaptation Story • Homoblasty = same twig/leaf forms Adaptation Story • Homoblasty = same • Different twig/leaf forms (plant age) = heteroblasty – Also called “juvenile” • Ex, many Junipers (Juniperus) Adaptation Story • Young plants (0-3 m tall) “divaricate” (wide-angled) • • Older (> 3 m): normal Pennantia corymbosa normal divaricate Adaptation Story – Adaptation climate? – Adaptation herbivores (moas)? normal Plagianthus regius divaricate Moas? New Zealand’s Moas • Ratites (Order) • 11 species Giant moa leg bones Giant moa replica New Zealand’s Moas • Hunted extinct by Maori Adaptation Story • How study defense hypothesis? • Other Adaptation Story • Divaricate: 30-70% less loss • Branches resist • Divaricate Adaptation Story • Non-native mammals not affected (shearing teeth) – Heteroblastic species declining Plants and the Environment • Recall: • Adaptation: – 1) Genetically determined trait – 2) With survival or reproductive benefit • How show benefit? Hard! Variation due to Environment • Vp = Vg + Ve Variation due to Environment • Phenotypic plasticity: vary form/physiology Variation due to Environment • Ex, heterophylly: different – (“hetero”=other; “phyll”=leaf) Emergent vs. Submerged leaves Fig. 6.5 Species as ecological tool • Now: species as tool • Issues: – Species indicators – Plants adapt at – Revegetation/reforestation: does where Species • Species def’n. – Species: Populations morphologically similar & – Biological species approach – Others: cladistics, etc. Species • Good indicators: Ex, Quercus laevis (turkey oak). Dry sandy soils (sandhills) Species • Bad indicators: widespread • Differences genetic ( environmental ( • How evaluate? ?) or ?) Vp = Vg + Ve