Plant Ecology

1. Plant Ecology Section 1: Interactions Between Plants and Their Environment

2. Tropisms All living organism have the ability to respond to their environment. Tropism: a directional growth to an environmental stimulus • Phototropism: response to light • Stems grow toward light • How is phototropism beneficial to the plant.

3. Tropisms • Thigmotropism: Response to touch • Vines and climbing plants grow around anything that they touch. • Gravitropism: response to gravity • Roots always grow with the force of gravity • Stems always grow against the force of gravity.

4. Plant Hormones • Hormone: chemical signals produced by living organisms that affect growth and development as well as respond to the environment. • Hormone are usually created in one part of an organism and travel to different cells and tissues.

5. Plant Hormones • Charles Darwin and his son wanted to find out what causes phototropism. • Describe Darwin’s experiment? • What did Darwin learn from the experiment?

6. Auxins • The substance in Darwin’s seedlings was identified as auxin. • Produced in the apical meristem of the stem. • The effects of auxin. • Cause cell elongation (cells on the shaded side of the plant grow faster, causing phototropism) • Promotes the growth of new roots.

7. Auxins The effects of Auxin (cont.) • Auxin inhibits the growth of buds near the apical meristem. • Apical Dominance – the side branches closest to the apical meristem grow more slowly. • Why does this happen? • If you remove the apical meristem, the side branches will grow more quickly? • Why does this happen?

8. Cytokinins • The opposite of Auxins • Auxins are produced in the top of the plant and move down • Cytokinins are produced at the bottom of the plant and move up. • Produced in the roots of the plant • Effects in the plant • Promotes cell division. • Promotes the growth of new stems • Inhibits cell elongation

9. Ethylene • Ripe or wounded fruits produce more ethylene than unripe fruits • “One rotten apple spoils the whole bunch” • The only hormone that exist as a gas. • Produced in fruit tissues and aging leaves and flowers. • Effects of Ethylene • Causes unneeded plant parts to fall off (leaves in autumn, and flower petals after pollination) • Speeds up the ripening of fruit.

10. Gibberellins • Produced in the meristems of the stems, roots and seeds. • Effects of Gibberellins • Promote plant growth (especially in stems and fruits) • Promote dormant seeds to germinate.

11. Abscisic Acid • Promote seed dormancy (rain may wash away the ABA from the seed and cause it to germinate) • Closes the stomata during drought • Prevents plant growth. • Abscisic acid (ABA) has the opposite effects of gibberellins. • Produced by the seeds • Effects of ABA

12. Section 2: Interactions Between Plants and Other Organisms

13. Symbiosis Ex: Fungi help almost all plants absorb minerals from the soil. The plant provides the fungus with carbohydrates. Symbiosis: a close relationship where 2 different species live closely together. • Mutualism: both organisms benefit in the relationship.

14. Symbiosis • Commensalism: one organism benefits and the other is not affected. Ex: Epiphytes are plants that grow on larger plants Explain how the epiphyte is benefited by growing on a larger plant.

15. Symbiosis Parasitism: one organism benefits (parasite) and the other organism is harmed (host) Ex: Mistletoe grow directly on a host tree. Its roots insert into the tree’s vascular tissue and it steals water and nutrients. • Explain the difference between an epiphyte and a parasite.

16. Predation • Predation: the consumption of one organism (the prey) by another (predator) • One organism is benefited and the other is harmed. • Coevolution: predators evolve to be better at catching prey and prey evolve to be better at escaping predators. • Ex: Milkweed evolved toxins that are poisonous to almost all animals. Overtime, monarchs caterpillars evolved a tolerance to milkweed toxins.

17. Predation • Carnivorous Plants: plants that have specialized leaves to trap and digest insects. • Plants do not get energy from digesting insects • Trapping insects is an adaptation evolved for growing in mineral poor soils. Ex: Venus Flytrap – Insects land on a hinged leaf and touch the trigger hairs, which cause the leaf to suddenly close

18. Competition • Plant compete for water, light, minerals and space. • Competition harms both species that use a limited resource. Competition occurs when 2 or more individual simultaneously require a single resource that is in limited supply

19. Section 3: Interactions Between Plants and Humans

20. Agriculture • Domesticated plants appear considerably different they did in nature. • Domesticated plants are completely dependent on humans for their survival. • Humans have been on Earth for 2 million years, but have for only farmed for the last 10,000 years • 6 plant species provide 80% of human calories Wheat, rice, corn, potato, sweet potato, cassava • Domesticated plants have been change to meet our needs.

21. Agriculture • How have humans domesticated plants • Selective Breeding: allowing only plants with desired traits to reproduce. • Hybridization: using cross-pollination to breed different plant together to get the best of both plants. • Indbreeding: using self-pollination to produce plants that have the same traits as the parent plant. • How are were humans able to use selective breeding to change teosinte into modern corn?

22. Agriculture • Ex: Bt Corn has a bacteria gene that produces a toxin that is harmless to humans but kills insects. • Selective breeding requires traits already exists in a population – we can not make new traits. 2. Genetically Modified (GM) Crops: genes from other organisms have been inserted into the DNA of the crop plant.

23. Agriculture Cons of GM Crops • The spread GM pollen grains cannot be controlled Ex: Some weeds inherented genes that make them immune to pesticides. • The long-term effects GM crops have not been studied. Pros of GM Crops • Farmers use less pesticides. • Produce more food in less space

24. Loss of Biodiversity Monocultures: the practice of growing a single species over a wide area. Advantages • Allows higher crop yields • improves harvesting efficiency. • Disadvantages • Removes more nutrients from soil. (Forces farmers to use chemical fertilizers) • Pest and disease spread very rapidly. (Forcers farmers to use chemical pesticides) What is biodiversity?

25. Loss of Biodiversity Invasive Species: introduction of foreign species to new environments which out compete native species for resources. • Example:

26. Loss of Biodiversity Habitat Destruction • Deforestation: loss of forest • Forest hold soil in place • Some forest never grow back because of soil erosion • Acid Rain: Air pollutants combine with water vapor in the atmosphere to form nitric and sulfuric aid. • How does acid affect plants?

27. Ecological Succession Plants (and their habitats) will recover if they are just left alone. Ecological Succession: changes in an ecosystem over time (especially after disturbances). • Primary Succession: begins with no remnants of an older community. • Begins after a volcanic explosion or a retreating glacier. • Leaves only bare rock

28. Ecological Succession • Secondary Succession: begins after a natural disturbance that leaves soil behind. • Begins after a forest fire, deforestation and farming • Occurs much faster than primary succession. • Climax Community – fairly stable, dominant community established after succession.