19.6 - Succession

• succession

  process by which ecosystems change as species colonise an area
• where does succession happen?

  barren, inhospitable land or where an ecosystem has been disrupted after a major event

  e.g.: glacier retreating and depositing rock, volcanic eruptions
• primary succession

  happens on land that's been newly formed or exposed so there's no life or soil or organic material

  slower process
• secondary succession

  happens where an ecosystem is disrupted so there's still soil and some organic matter

  faster process
• stages of succession

  barren land

  primary colonisers - pioneer species

  secondary colonisers and tertiary colonisers - subsequent species

  scrubland

  climax community
• how can a new species alter the environment as succession happens?

  they can make it less suitable for existing species so out compete them

  or make it more suitable for existing species so are out competed by them
• common features that emerge during succession

  abiotic environment becomes less hostile

  greater number and variety of habitats and niches

  increased biodiversity as different species occupy habitats

  more complex food webs leading to increased biomass
• stages of primary succession (1) - pioneer species

  abiotic conditions are hostile so only pioneer species grow (lichen) because they are adapted to inhospitable environments

  pioneer species weather rock and decompose so humus builds up (organic matter) forming basic soil
• stages of primary succession (2) - subsequent species

  conditions are less hostile so subsequent species (mosses, ferns) grow, providing more shade so lichen dies

  soil becomes richer as more rock is weathered and more plants decompose helping retain more water so more complex species grow (grass, shrubs)
• stages of primary succession (3) - climax community

  dominant species emerge: they change the environment so it becomes less suitable for other species so out compete them

  climax community is reached: area is colonised by a dominant species and ecosystem remains stable
• primary succession for animals

  same changes which are determined by plant species and habitats available
• stages is secondary succession

  same as primary succession but happens at a later stage because soil is already present
• pioneer species in secondary succession

  larger plants like shrubs

  more complex animals
• why is secondary succession a faster process than primary succession?

  soil already exists where spores and seeds often remain alive and there's an influx of animals and plants through migration from the surrounding areas
• what happens at each stage of succession?

  different plants and animals better adapted for the improved conditions move in and out compete plants and animals already there and become the dominant species
• features of pioneer species that make them suitable for inhospitable conditions

  asexual reproduction so a single organism can rapidly multiply to build a population

  production of lots of wind-dispersed seeds or spores so they can reach isolated places

  rapid germination of seeds so they don't need a dormant period

  ability to photosynthesise as light is normally available but other resources aren't

  ability to fix nitrogen from the atmosphere because soil has little to no nutrients

  tolerance to extreme conditions
• why are climax communities different?

  because they depend on the climate of the ecosystem
• climatic climax

  the climax community for a particular climate