Food Chains and Webs

• Ecosystem


  A biological community of interacting organisms and their physical environment
• Biotic and abiotic factors

  • Biotic factor: a living organism in an ecosystem
  • Abiotic factor: a non-living organism in an ecosystem
• Organism interrelationships

  1. Mutualism: both organisms benefit

  2. Commensalism: one benefits while the other is not affected

  3. Parasitism: parasite benefits while the host is harmed

  4. Competition: organisms compete for resources

  5. Predation: predator hunts and eats prey
• Parasitism


  A relationship where one organism, the parasite, benefits from living within and harming the host
• Competition


  A relationship where organisms compete for resources within an ecosystem
• Mutualism


  A relationship where two organisms both benefit
• Commensalism

  A relationship where one organism benefits while the other is not affected
• Factors affecting population size

  • Climate, competition, water availability, pollution, greenery, current population, birth rates, fertility rates, gender ratios
• Competition limits population growth because


  The ecosystem lacks resources, leading to inadequate access without competition
• Disease limits population growth because

  It kills off organisms and can spread if contagious
• Destruction of habitat limits population growth because

  It kills off organisms and leaves remaining ones with limited resources
• Introducing species can limit population growth because

  If not capable of surviving, they die off or can be harmful to the ecosystem
• Seasonal changes can enhance population growth because

  They provide more resources like rainfall and sunlight, reducing competition
• Increased food availability can enhance population growth because

  It reduces competition for food
• Temperature changes can enhance population growth because

  They can make habitats more suitable for survival and provide more resources
• Food web
• Food chain
• Producers

  Organisms in an ecosystem that use photosynthesis to convert sunlight into chemical energy for food, with 100% energy
• Consumers


  Organisms in an ecosystem that feed off other organisms, retaining only 10% of consumed energy
• Herbivores


  Consumers that consume plants in an ecosystem to prevent overgrowth and allow repopulation
• Carnivores


  Consumers that consume other animals to prevent overpopulation and continue the life cycle
• Omnivores


  Consumers that consume both animals and plants to balance consumption in the ecosystem
• Carnivores consume other animals in an ecosystem and prevent overpopulation of animals while continuing the life cycle
• Omnivores consume both animals and plants in an ecosystem and balance the consumption of both plants and animals to ensure that there is never too much or too little
• Scavengers consume decaying biomass such as dead animals, meat and rotting plant material. Their role is to clear the dead and decaying matter from the ecosystem
• Decomposers break down dead organisms into other matter to provide nutrients for primary producers
• Energy flow in food webs

  Primary producer retains 100% of the energy, primary consumer retains 10%, secondary consumer retains 1%, tertiary consumer retains 0.1%, apex predator retains 0.01%
• Trophic levels in a food web

  • Primary producer
  • Primary consumer
  • Secondary consumer
  • Tertiary consumer
  • Apex predator
• Biodiversity is when an ecosystem is rich in different kinds of plants and organisms and contains a variety of them to maintain and sustain the ecosystem; the variety of plant and animal life in a particular habitat
• Biodiversity ensures that there is enough variety of plant and animal life to maintain food webs and the cycle of life. It also helps with food security and has economic benefits
• Natural disasters, and bushfires in particular, can be a threat to biodiversity because it can destroy and burn down the natural habitat as well as the plant and animal life in it. However, it can help plants and animals adapt to be able to prepare or even survive bushfires
• Natural disasters such as droughts can be a threat to biodiversity because it causes a lack of water resources and availability, creating competition for water and causing animals and plants to die of thirst
• Natural disasters such as floods can be a threat to biodiversity because it can drown plant and animal life and provide too much water for the organisms to handle. If the water is contaminated or polluted, it can be even more dangerous as it can pollute the habitat or spread diseases to the organisms
• Humans have a large role in the destruction of biodiversity because of the missions to clear land for cities (urban sprawl) or farming, cutting down trees for resources such as wood and paper, building dams and using river water and intentionally burning forests
• Introducing species to new habitats can be dangerous because the new species can disrupt the food webs or carry diseases and other defects that the original organisms are not immune to. They could also end up eating the other organisms in the habitat
• Chemical pesticides are chemical compounds that are used to kill pests. However, this can harm the habitat and its biodiversity by contaminating it with chemicals and killing off organisms that are essential to the habitat’s survival
• Chemical pollution can cause behavioural changes in species, physiological alterations and weakens reproduction, among other things
• Overcropping, or over farming, can strip the soil of its natural minerals and cause it to be infertile, making it extremely hard for plants to reproduce on the land
• Aboriginal and Torres Strait Islander People have many methods of preserving the natural land and habitats, such as moving to allow the plants and animals to repopulate, using fire control methods such as lighting small and controlled fires to prevent trees and shrubs from growing too thick and using fish traps
• Ecosystem


  A biological community of interacting organisms and their physical environment