Plant Ecology

Section 1: Interactions Between Plants and Their Environment

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.

• Gravitropism: response to gravity– Roots always grow with the force of gravity– Stems always grow against the force of gravity.

• Thigmotropism: Response to touch– Vines and climbing plants grow

around anything that they touch.

Tropisms

• 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.

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?

Plant Hormones

• 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.

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?

Auxins

• Produced in the roots of the plant

• Effects in the plant– Promotes cell division.– Promotes the growth of

new stems– Inhibits cell elongation

• 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.

Cytokinins

• 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. – Ripe or wounded fruits

produce more ethylene than unripe fruits

– “One rotten apple spoils the whole bunch”

Ethylene

• 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.

Gibberellins

• Abscisic acid (ABA) has the opposite effects of gibberellins.

• Produced by the seeds

• Effects of ABA

– 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

Section 2: Interactions Between Plants and Other Organisms

Symbiosis: a close relationship where 2 different species live closely together.

• Mutualism: both organisms benefit in the relationship.

Ex: Fungi help almost all plants absorb minerals from the soil. The plant provides the fungus with carbohydrates.

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.

Symbiosis

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.

• 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.

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

Predation

Competition occurs when 2 or more individual simultaneously require a single resource that is in limited supply

• Plant compete for water, light, minerals and space.

• Competition harms both species that use a limited resource.

Competition

Section 3: Interactions Between Plants and Humans

• 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.

– Domesticated plants appear considerably different they did in nature.

– Domesticated plants are completely dependent on humans for their survival.

Agriculture

• How have humans domesticated plants

1. 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?

Agriculture

– 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.

– Ex: Bt Corn has a bacteria gene that produces a toxin that is harmless to humans but kills insects.

Agriculture

Pros of GM Crops• Farmers use less pesticides.• Produce more food in less

space

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.

Agriculture

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)

Loss of Biodiversity

What is biodiversity?

Invasive Species: introduction of foreign species to new environments which out compete native species for resources.

• Example:

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?

Loss of Biodiversity

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

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.

Ecological Succession