Ecosystem Ecology

• Ecosystem


  A community interacting with the physical environment
• Components of an ecosystem

  • Abiotic components
  • Biotic components
• Abiotic components


  Resources, such as sunlight and inorganic nutrients, and conditions, such as type of soil, water availability
• Biotic components


  Influenced by the abiotic components, as when the force of the wind has affected the growth of a tree
• Biotic components of an ecosystem

  • Autotrophs
  • Heterotrophs
• Autotrophs


  Require only inorganic nutrients and an energy source to produce organic nutrients for their own use and for all the other members of a community. They are also called producers because they produce food.
• Photoautotrophs


  Also called photosynthetic organisms, produce most of the organic nutrients for the biosphere
• Heterotrophs


  Need a preformed source of organic nutrients. They are also called consumers because they consume food.
• Types of Heterotrophs


  • Herbivores
  • Carnivores
  • Scavengers
  • Detritivores
  • Decomposers
• Herbivores


  Animals that graze directly on plants or algae
• Carnivores


  Feed on other animals
• Scavengers


  Feed on the dead remains of animals and plants that have recently begun to decompose
• Detritivores


  Feed on detritus (organic remains in the water and soil that are in the final stages of decomposition)
• Decomposers


  Bacteria and fungi, including mushrooms that use their digestive secretions to chemically break down dead organic matter
• Food web


  A diagram that describes trophic (feeding) relationships; an interconnected food chains
• Trophic levels


  Organisms are linked to one another in a straight line, according to feeding relationships, or who eats whom

  
• Food chain


  Diagrams that show a single path of energy flow in an ecosystem
• Energy flow in the ecosystem

  • Energy flow begins when producers absorb solar energy, and chemical cycling begins when producers take in inorganic nutrients from the physical environment
  • Producers make organic nutrients (food) directly for themselves and indirectly for the other populations of the ecosystem
  • Energy flows through an ecosystem via photosynthesis because, as organic nutrients pass from one component of the ecosystem to another a portion of those nutrients is used as an energy source
  • Eventually energy dissipates into the environment as heat
  • An ecosystem survives by a combination of energy flow and matter recycling
• Food chain


  Movement of energy and nutrients from one trophic level to the next
• Food web


  Network of interconnected food chains
• Types of food webs

  • Connectedness food web
  • Energy flow food web
  • Functional food web
• Connectedness food web


  Also known as topological food web, emphasises feeding relationships among organisms, portrayed as a links in the web. It depicts only the presence or absence of a trophic interaction.
• Energy flow food web


  Also referred to as flow web or as bioenergetics web, where connections are quantified by the flux of energy between a resource and consumer.
• Functional food web


  Also known as interaction food web, identifies the feeding relationships within the topological food web that are most important to community structure.
• In a food web, connectance

  Decreases with increasing number of species
• Connectance


  Actual number of links / Potential number of links
• If there are 25 species in a tropical savanna, 49 actual links and 25 x 24/2 = 300 potential links, therefore the connectance in this community is 49/300 = 0.163
• Keystone species


  Species within a community that has a significant role out of proportion to its abundance
• Keystone species


  • Sea otter as keystone predator, predatory starfish that feeds on variety of organisms; palm nuts and figs which produce fruit during fruitless times of the year; beaver that build a dam flooding the entire river valley
• Indicator species


  Species whose status provides information on the overall health of a food web or ecosystem
• Indicator species


  • Corals are indicators of marine processes; peppered moth are indicators of pollution; polar bears for climate change
• Umbrella species


  Species whose habitat requirements are so large that protecting them would protect many other species existing in the same habitat
• Umbrella species


  • Northern spotted owl, a pair of birds need 800 ha of forest for survival and reproduction, gopher tortoises, protecting them would aid the species that use their burrows
• Flagship species


  Single large or instantly recognizable species
• Ecosystem engineers


  Species that create, modify and maintain habitats
• Ecosystem engineers


  • Gopher tortoises and beavers, African elephant, mollusks and corals
• Examples of ecosystem engineers and their effects

  • Green plants - Oxygen production
  • Soil organisms - Increase and reduce soil nitrogen and other nutrients
  • Beaver - Altered hydrology
  • Corals - Physical structure creates habitat and protection for other species
  • Trees - Physical structure creates habitat for other species
  • Gopher tortoise - Burrow used by other species
  • Woodpecker - Nest cavity used by other species
  • Termite - Provides home for other arthropods
  • Vertebrates - Their feces provide home for dung beetles
• Ecological pyramid


  Graphic representation of the number of organisms, the biomass, or the relative energy content of the various trophic levels in an ecosystem

  
• Ecological pyramids are helpful for explaining energy loss in an ecosystem, but they oversimplify energy flow
• Most likely, a pyramid based on the number of organisms in each trophic level wouldn't work. Example: Each tree would contain numerous caterpillars, so there would be more herbivores than autotrophs