Stability and change

• Ecological succession


  The process of change in a particular area over a period of time
• Types of ecological succession

  • Primary
  • Secondary
• Primary succession

  • Bare rock with no existing soil is colonized for the first time (volcanic eruptions, retreating glaciers)
• Secondary succession


  • Started by a disturbance (fire, hurricane), soil intact with an established ecosystem
• Changing abiotic factors

  • Natural disturbances
  • Soil composition (Nutrient deposition, weathering, pollution)
  • Geological changes (Soil erosion, depositions of sediments)
• Changing biotic factors

  • Pioneer species - change the environment and soil fertility
  • Competition - better adapted species replace others
  • Predation and prey cycles - affects population dynamics
  • Presence of keystone species
• Arrested succession

  Human activity prevents climax
• Examples of arrested succession

  • Grazing livestock - eat vegetation that may have grown
  • Drainage of wetlands - drier soil, decreased biodiversity
• Primary succession process

  1. Pioneer species are the first to colonies (lichens, mosses)

  2. As they die, soil quality improves in depth and nitrogen content

  3. Pioneer species replaced by successive communities, leaf litter adds to quality and depth of soil

  4. Climax community - ecological community in which populations remain stable and exist in balance

  5. Changes (Plant size increases, Primary production increases biomass, Increases species diversity, Increased complexity of food web, Increased nutrient cycling)
• Cyclical succession

  Repeated cycles of secondary succession
• Plants adapted for cyclical succession

  • Lodgepole pines produce serotinous pinecones that only release seeds after exposed to heat
• Whittaker's climograph

  Predicts terrestrial biome found in a location according to mean annual temperature and precipitation
• Factors affecting sustainability of agriculture

  • Soil erosion - reduces fertility of soil
  • Leaching of nutrients - due to overuse of fertilizers, drains into nearby ecosystems
  • Supply of fertilizers - manufacturing affects the environment, mining phosphates
  • Pollution due to agrochemicals - eutrophication, pesticides are long term, biomagnification
  • Carbon footprint - amount of carbon released by individuals
  • Eutrophication (Excess nutrients enter an aquatic ecosystem, Algal bloom blocks light, Dead organisms sink and decompose, Increases BOD, Decreased oxygen availability, Decreased biodiversity, Some algae release toxins)
• Biomagnification of pollutants

  Chemical substances become concentrated in tissues
• Pesticide


  Chemical used to control organisms that are a danger to crops
• Bioaccumulation


  Build up of non-biodegradable chemicals in the body
• Biomagnification of DDT

  1. DDT stored in fat tissues

  2. Some insects survive and have DDT in tissue

  3. Insects eaten by fish, fish eaten by ospreys

  4. DDT makes egg shells weak, break during incubation, offspring die
• Biomagnification of mercury

  1. Fish and shellfish have traces

  2. Larger fish have a higher concentration

  3. Mercury is converted by bacteria to methylmercury

  4. Methylmercury is biomagnified in food chains

  5. Causes Minamata - neurological disease
• Plastics


  Range of synthetic materials that do not biodegrade
• Impacts of plastics

  • Kills the albatross after being eaten
  • Suffocates turtles or blocks their digestive tract
• Hinewai reserve


  • Reduced human impact
  • Reintroduced predators and keystone species
  • New Zealand, in situ
• Ecosystems


  Biological communities of interacting organisms and their physical environment
• Examples of stable ecosystems

  • Tropical rainforests
  • Deserts
• Requirements for ecosystem stability

  • Steady supply of energy
  • Nutrient cycling without leakages
  • Absence of disruptions
  • Tolerable climate environments
  • High genetic diversity
• Tipping point

  Critical threshold that leads to large and irreversible damage in the climate system
• Tipping point example

  • Amazon rainforest (Atmospheric water vapor for transpiration, Cooling, wind patterns, rain flow, Carbon sink, Deforestation)
• Keystone species


  Disproportionately large effect on community structure relative to its abundance, Maintain continuity and stability of ecosystem
• Keystone species example


  • Wolves in Yellowstone national park (Increase biodiversity, Keep elks moving)
• Sustainable harvesting example

  • Silver top palms harvested sustainably in the Bahamas (Leavers are removed without killing the plants)
• Maximum sustainable yield


  Max average catch a stock can sustain over a long time period, Optimum balance between reproductive and growth rate with harvesting and natural mortality
• Methods to assess fish population

  • Capture, mark, release, recapture
  • Echo sounders
  • Analysis of fish catch
• Mesocosm


  Indoor experimental system that examines the environment under controlled conditions (Pros: Control variables, Measure degree of stability, Precise impact of a disturbing factor; Cons: Unrealistic)