ECO 8

ECOSYSTEMS

What is an Ecosystem?

  • Definition of ecosystem: The biological community together with its associated non-living environment.

  • Concept emphasizing the interdependent flow of energy and materials between living and non-living components.

Biotic Components of an Ecosystem

  • Consist of living things.

  • Divided into two groups based on their source of food:

    • Autotrophs: Organisms that produce their own food.

    • Heterotrophs: Organisms that consume other organisms for food (consumers).

Autotrophs

  • Types include:

    • Algae

    • Cyanobacteria

    • Photosynthetic protists

    • Plants

    • Chemosynthetic bacteria.

  • Require only inorganic nutrients to produce organic nutrients and obtain energy.

Heterotrophs

  • Require a source of preformed organic nutrients.

  • Types of heterotrophs:

    • Herbivore: Plant-eating organisms.

    • Carnivore: Flesh-eating organisms.

    • Omnivore: Organisms that eat both plants and animals.

    • Detritivore: Feed on dead organic matter.

    • Decomposer: Break down dead organisms and waste (e.g., fungi, bacteria).

Energy Flow & Chemical Cycling

  • Every ecosystem is characterized by two fundamental processes:

    • Energy Flow:

    • One-way flow of energy through the biotic community.

    • Begins with producers absorbing solar energy.

    • Chemical Cycling:

    • Cyclical flow of materials from the abiotic environment (non-living) through the biotic community (living) and back to the abiotic environment.

Energy Flow

  • Without exceptions, all ecosystems depend on solar energy as the primary energy source.

  • Primary productivity: The rate at which producers convert solar energy into biomass.

    • Influenced by sunlight, nutrient availability, and water availability.

Productivity of Ecosystems

  • Examples of productivity in various ecosystems:

    • Tropical Rain Forests: High productivity; abundant rainfall and sunlight.

    • Estuaries and Marshes: High productivity; nutrient influx from rivers and streams.

Primary Productivity of Ecosystems

  • Productivity levels demonstrate variations:

    • Tropical Forest: High, approximately 4,800extkcal/m2/extyear4,800 ext{ kcal/m}^2/ ext{year}.

    • Temperate Forest: Moderate, approximately 2,400extkcal/m2/extyear2,400 ext{ kcal/m}^2/ ext{year}.

    • Savanna: Lower, approximately 1,600extkcal/m2/extyear1,600 ext{ kcal/m}^2/ ext{year}.

    • Deserts: Very low, approximately 100extkcal/m2/extyear100 ext{ kcal/m}^2/ ext{year}.

Loss of Energy in Flow

  • Energy captured by producers is lost as heat during cellular respiration.

  • Consumers lose energy through respiration, excretion, and death.

  • About 10% of the energy is passed from one trophic level to the next.

Trophic Levels

  • Ecosystems have a trophic structure that determines energy flow and chemical cycling:

    • Primary Producers: Autotrophs (e.g., plants, algae).

    • Primary Consumers: Herbivores.

    • Secondary Consumers: Carnivores that eat herbivores.

    • Tertiary Consumers: Top carnivores.

    • Detritivores and Decomposers: Break down dead materials and recycle nutrients.

Food Webs

  • Feeding relationships in nature are complex; multiple organisms can interact at various levels:

    • Example: One primary consumer may eat several types of plants.

    • These relationships are depicted in food web diagrams.

Ecological Pyramids

  • Energy loss between trophic levels depicted as an ecological pyramid.

  • Food chains lose energy typically illustrated by 10% energy transfer:

    • Few top carnivores can be supported in ecosystems due to this loss.

    • Pyramid of Energy: Represents energy availability at each trophic level, generally stated as a surplus of 90% energy loss per level.

Example Calculations of Energy Requirements

  • Minimum primary production required to support aphid production of 28 gC·m$^{-2}$·year$^{-1}$:

    • Using the equation: Total primary production = Aphid production / 10% = 280extgC⋅m−2⋅extyear−1280 ext{ gC·m}^{-2}· ext{year}^{-1}.

  • To support cat production, where cat production is 368extgC⋅year−1368 ext{ gC·year}^{-1}:

    • Total primary production required from grass = Cat production / 10% = 3,680,000extgC/year3,680,000 ext{ gC/year}.

Grassland and Demand

  • Each category of producers affects the subsequent producers and consumers.

  • Example: If 60% of the diet of an aphid comprises roses, only 40% (or 11.2extgC⋅m−2⋅extyear−111.2 ext{ gC·m}^{-2}· ext{year}^{-1}) must come from grass. This is crucial for understanding ecosystem dynamics and compensations across species.