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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 variation • Vg = variation due to genotype • Ve = variation due to environment Focus Vg Plants and the Environment • Adaptation: What is an adaptation? Plants and the Environment • Adaptation: – 1) Genetically determined trait – 2) With survival or reproductive benefit • How determine trait adaptation? Hard! Genetic importance Plants and the Environment • Genetic basis: • Heritability (h2): resemblance b/w relatives (shared genes) • h 2 = Vg / V p – Vg = variation due to genotype – Vp = total phenotypic variation 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 – 2) Dominant alleles mask “lethal recessives:” Finish this sentence: If you were haploid you’d be __________________ Genetic Variation • Problem: genetic drift! 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. 40 plants! 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 change – 2) 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 Adaptation Story • Homoblasty = • Different • = heteroblasty – Also called “juvenile” foliage • Ex, many Junipers (Juniperus) Adaptation Story • Field trip: New Zealand! • 20% trees heteroblastic Adaptation Story • Young plants (0-3 m tall) “divaricate” ( • 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 spp. Giant moa leg bones Giant moa replica New Zealand’s Moas • Hunted extinct by Maori Adaptation Story • How study defense hypothesis? Adaptation Story • Divaricate: 30-70% Adaptation Story • Non-native mammals not affected (shearing teeth) – Heteroblastic spp. 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/ Variation due to Environment • Ex, heterophylly: different leaf – (“hetero”=other; “phyll”=leaf) Emergent vs. Submerged leaves Fig. 6.5 Species as ecological tool • Now: sp. as tool • Issues: – Sp. indicators environmental conditions? – Plants adapt at sp. level? – Revegetation/reforestation: does where we obtain plants matter? Species • Species def’n. – Species: Populations – Biological species – Others: cladistics, etc. Species as ecological tool • Issues: – Sp. indicators environmental conditions? – Plants adapt at sp. level? – Revegetation/reforestation: does where we obtain plants matter? Species • Good indicators: Ex, Quercus laevis (turkey oak). Species • Bad indicators: widespread & variable • Differences • How evaluate? Vp = Vg + Ve