Ecosystems

Ecosystems

Introduction to Ecosystems

  • Ecosystem Definition: A community of organisms and their interactions with the abiotic environment.

  • Life in Ecosystems: Involves competition for limited resources. This competition is a key aspect of natural selection.

    • Resources: Organic matter, sunlight, and nutrients.

    • Critical Factors Affecting Ecosystems: Latitude, rainfall, elevation, and presence of other species.

Types of Ecosystems

  • Three Main Categories of Ecosystems:

    • Aquatic Ecosystems

      • Marine Ecosystems:

      • Comprise over 70% of Earth's surface.

      • Three basic types:

        • Shallow ocean

        • Open ocean surface water

        • Deep ocean

      • Shallow oceans and open ocean surface water account for over 40% of all photosynthesis on Earth.

      • Freshwater Ecosystems:

      • Occupy only 1.8% of Earth's surface.

      • Include lakes, rivers, streams, and springs.

      • Very diverse systems that support a significant amount of biodiversity for their size.

      • Often referred to as biodiversity hotspots.

    • Terrestrial Ecosystems:

      • Diverse ecosystems categorized into biomes including mountains, deserts, grasslands, temperate and tropical rain forests, temperate forests, taiga, and tundra.

      • Notable Variation: Even within the same biome, ecosystems can appear very different.

Food Webs and Trophic Levels

  • Food Chains and Webs:

    • Food Chain Definition: The pathway of energy and matter being transferred from one organism to another.

    • Trophic Level: Each organism occupies a specific trophic level in a food chain.

    • Food Web Definition: A network of food chains that illustrates how organisms within a community feed on one another, demonstrating energy and nutrient flow.

Trophic Efficiency

  • Definition: The percentage of production that is transferred from one trophic level to the next.

    • Range: Typically between 5% and 20% efficiency.

    • Example:

    • Quaternary Consumers: Eagles

    • Tertiary Consumers: Snakes, Owls

    • Secondary Consumers: Rats, Sparrows, Frogs

    • Primary Consumers: Butterflies, Grasshoppers, Ants, Caterpillars, Bees

    • Producers: Trees, Grasses, Flowering Plants, Crops

  • Energy Transfer Illustration:

    • Biomass Transfer:

    • Primary Producers: 10,000 J (from sunlight)

    • Primary Consumers: 1,000 J (10% of producers)

    • Secondary Consumers: 100 J (10% of primary consumers)

    • Tertiary Consumers: 10 J (10% of secondary consumers)

Trophic Cascades

  • Concept: A trophic cascade occurs when a change in the population of one species leads to widespread effects throughout the food chain, positively or negatively impacting other species.

  • Examples of Trophic Control:

    • Top-Down Control:

    • Example: Introduction of wolves leads to a decrease in deer population, which subsequently increases grass growth due to reduced grazing.

    • Bottom-Up Control:

    • Example: If wolf populations are low, the availability of resources for lower trophic levels is restricted, which inhibits the support of a larger wolf population.

Food Web Dynamics and Biomagnification

  • Biomagnification: Refers to the increasing concentration of persistent, toxic substances in the organisms at each trophic level, from primary producers up to apex predators.

    • Examples of substances that bioaccumulate include DDT, PCBs, mercury, and cadmium.

Biogeochemical Cycling

  • Concept of Energy Flow: Energy flows through ecosystems, entering primarily as sunlight and leaving as heat during transfers between trophic levels.

  • Matter Recycling: Unlike energy, the matter that constitutes living organisms can be conserved and recycled.

  • Biogeochemical Cycle Definition: The process of recycling inorganic matter between living organisms and their environment.

  • Common Inorganic Molecules Involved in Cycling:

    • Carbon (C)

    • Nitrogen (N)

    • Hydrogen (H)

    • Oxygen (O)

    • Phosphorus (P)

    • Sulfur (S)

  • Existence: These elements can exist in various chemical forms across different environments (atmosphere, land, water, subsurface).

  • Influence of Geologic Processes: Includes weathering, erosion, water drainage, and subduction of continental plates.

Water Cycle

  • Processes in the Water Cycle:

    • Evaporation & Sublimation: Conversion of water into vapor and ice into vapor.

    • Condensation & Precipitation: Formation of clouds and precipitation returning water to Earth's surface.

    • Subsurface Water Flow: Rainwater permeates into the ground.

    • Surface Runoff/Snowmelt: Flow of freshwater from rain or melting ice.

    • Streamflow: Movement of runoff entering streams and lakes, eventually reaching the ocean.

Biological Carbon Cycle

  • Overview of Carbon Exchange: Describes the exchange of carbon among living organisms and the environment.

  • Global CO2 Emissions Data (1950-2022):

    • Notable growth of global CO2 emissions, increased six-fold since 1950, with significant contributions from regions like the U.S., China, and India.

    • Contribution Per Region (1950-2022):

    • U.S., China, and India now account for more than half of the world’s total CO2 emissions.

  • Processes Affecting Carbon Cycle:

    • Geological Activity

    • Photosynthesis

    • Human Influence through Combustion

    • Respiration and Decomposition processes are also vital.

    • Data Representation:

      • Emission figures are quantified in tonnes of CO₂ for specific years, showing significant increases over time, particularly in emerging economies.