2.7 Changes in Ecosystems: Ecological Succession

• Natural, gradual changes in the types of species that live in an area; can be primary or secondary
• The gradual replacement of one plant community by another through natural processes over time

Primary Succession

• Begins in a place without any soil
• Sides of volcanoes
• Landslides
• Flooding
• Starts with the arrival of airborne pioneer species such as lichens that do not need soil
• Soil starts to form as lichens, weather and erosion break down rock
• When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil
• Simple plants like mosses and ferns can grow in the new soil
• The simple plants die, adding more organic material
• The soil layer thickens, and grasses, wildflowers, and other plants begin to take over
• These plants die, and they add more nutrients to the soil
• Shrubs and tress can survive now
• Insects, small birds, and mammals have begun to move in
• What was once bare rock now supports a variety of life

Secondary Succession

• Begins in a place that already has soil and was once the home of living organisms
• Occurs faster and has different pioneer species than primary succession
• Example: after forest fires

Climax Community

• A stable group of plants and animals that is the end result of the succession process

^^Indicator species:^^ give early warning signs of damage or danger to a community

• Common indicator species:
• Birds
• Butterflies
• Amphibians

Why are amphibians declining?

1. Habitat loss and fragmentation: loss of wetlands, deforestation, development
2. Prolonged drought: dries up breeding pools, dehydration
3. Pollution: thin, permeable skins absorb pollutants from air, water, and soil
4. UV radiation: harms embryos
5. Parasitism: flatworms
6. Overhunting: where frogs are a delicacy
7. Nonnative species: competitors

^^Keystone species:^^ have a larger impact on the community, if removed, than other species

• Pollinators
• Apex predators
• Decomposers
• specific ex: sea otter
• feed on sea urchins, controlling their population
• urchins would deplete the habitat's kelp
• Kelp is the producer; the major source of food and shelter for the ecosystem.

What happens when you lose a keystone species?

• Food webs and nutrient cycles disrupted
• Population crashes
• Extinctions

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