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

• h2 = Vg / 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

r2=0.52

r2=1

Plants and the Environment• Plant height ex.

Fig. 6.3

(r2)=0.21 or 21%

(h2)=0.21 or 21%

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

Small population (9 inds.) Large population (50 inds.)

Start: 50% mix 2 alleles

Genetic Variation• Ex, Wollemi “pine” (Australia)

Loss of Genetic Variability• Ex, Wollemi “Pine” (Australia)• Extinct 2 mya, 2 groups found 1994.

DiscovererDavidNobleFamous quote……

Loss of Genetic Variability• Ex, Wollemi “Pine” (Australia)• No measurable genetic diversity!

Collecting seedsby 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)?

Plagianthus regius

normal 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)

Fig. 6.5

Emergent vs.Submerged leaves

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 ( ?) or

environmental ( ?)• How evaluate?

Vp = Vg + Ve