Ecosystem

• Ecosystem

  A community (i.e., populations of different species) together with the non-living environment
• Example of an ecosystem

  • The community of Artic fox, Caribou, Snow geese, plants (e.g., grass & shrubs) and their non-living environment (e.g., river water and soil)
• Ecosystems

  • They range from a microcosm (e.g., an aquarium [or even a cow dung]) to a large area (e.g., lake or forest)
• Components of an ecosystem

  • Abiotic (non-living components)
  • Biotic (living components)
• Both biotic and abiotic factors influence species distribution
• Ecologists ask questions about where species occur and why species occur where they do
• Abiotic factors

  Non-living components that affect the distribution of organisms
• Abiotic factors

  • Temperature
  • Water
  • Oxygen
  • Salinity
  • Sunlight
  • Rocks and Soil
• Temperature

  An important factor in the distribution of organisms because of its effects on biological processes
• Cells may freeze and rupture below 0°C, while most proteins denature above 45°C
• Organisms adapted to extreme temperatures

  • Thick layer of fur and fat for insulation against the cold and for energy storage
  • Small ears to reduce heat loss
• Oxygen

  Certain organisms must adapt to areas of dissolved oxygen
• Adaptations for oxygen exchange in aquatic organisms

  • Use external gills for short-range exchange of nutrients, gases and wastes (through diffusion) between blood and water
• Water availability

  An important factor in species distribution
• Adaptations of desert organisms for water conservation

  • Cactus has small waxy leaves that reduce water loss
  • Camels can survive for an entire week without water, hardly sweat, and their spongy nose bones absorb any excess moisture
• Water affects oxygen availability as oxygen diffuses slowly in water
• Salinity

  Salt concentration affects the water balance of organisms through osmosis
• Adaptations to high-salinity habitats


  • Euryhaline animals like salmon can migrate between freshwater and ocean
  • White mangrove excretes excess salt through its leaves
• Sunlight

  Light intensity and quality (wavelength) affect photosynthesis
• Green plants distribution is likely to be more extensive in areas with higher light intensity
• In aquatic environments, most photosynthesis occurs near the surface (limnetic zone occupied by phytoplankton)
• In deserts, high light levels increase temperature and can stress plants and animals
• Other abiotic factors

  • pH
  • Slope/gradient
• Soil


  Many characteristics of soil limit the distribution of plants and thus the animals that feed on them
• Above the tree line, freezing temperatures, moisture deficits and strong winds restrict the growth and survival of trees
• Types of ecological interactions

  • Competition
  • Exploitation
  • Positive interactions
• Predation and herbivory are missing from the list of ecological interactions
• Interspecific interactions

  • Competition
  • Predation
  • Herbivory
  • Symbiosis
  • Facilitation
• Competition

  Interspecific competition occurs when species compete for a resource in short supply, such as food, light, space and mates
• Consequences of strong interspecific competition

  • Competitive exclusion
  • Resource partitioning
  • Character displacement
• The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place
• Resource partitioning

  Differentiation of ecological niches, enabling similar species to coexist in a community
• Ecological niche

  An organism's ecological role, the total of a species' use of biotic and abiotic resources
• Ecologically similar species can coexist in a community if there are one or more significant differences in their niches
• Interspecific competition can influence the realized (potential) niche of an organism compared to its fundamental (actual) niche
• Balanus

  A type of barnacle
• Chthamalus

  A type of barnacle
• Treatment 1: Remove Balanus

  In the absence of Balanus, Chthamalus occupies both shallow water and deep water
• Treatment 2: Remove Chthamalus


  In the absence of Chthamalus, Balanus still occupies only deep water
• Control: No treatment

  Chthamalus occupies only shallow water and Balanus occupies only deep water