BIO330 Chapter 4: Ecosystems Ecology

Ecosystems and Ecology

• An ecosystem includes all living organisms (multiple communities) in a given area, as well as the abiotic factors with which they interact.
• A community consists only of living organisms in a specific area, excluding abiotic factors.
• A biome spans a large geographical area, defined by characteristic environmental conditions that determine what species can survive within it.

Trophic Structure

• Trophic structure refers to the different feeding relationships in an ecosystem that determine the route of energy flow and the pattern of chemical cycling.
• It is represented by the food chain or food web, showing the flow of material and energy among different organisms.

Energy Flows Through Ecosystems (Primary Productivity)

• Primary productivity is the amount of light energy converted to chemical energy (organic matter) by autotrophs in an ecosystem during a given time period.
• Gross primary productivity (GPP) is the total organic matter produced, including that used by autotrophs for respiration.
• Net primary productivity (NPP) is the amount of organic matter produced that is available for heterotrophs (NPP = GPP - R, where R is the energy used by autotrophs for respiration).

Productivity of Different Ecosystems

• Some ecosystems have high net primary productivity, such as swamps, marshes, and tropical rainforests (>8000 kcal/m²/year).
• Others have low net primary productivity, such as deserts (<800 kcal/m²/year) and open oceans (<1600 kcal/m²/year).

Energy Flows Through Ecosystems (Ecological Pyramids)

• Most ecosystems demonstrate a normal pyramid of biomass, with a sharp decrease in biomass at successively higher trophic levels.
• Some aquatic ecosystems demonstrate an inverted pyramid of biomass, where a small population of phytoplankton supports a large population of zooplankton.

Biogeochemical Cycles

• The movement of energy and matter through ecosystems are related, as both occur through the transfer of substances through photosynthesis, feeding relationships, and decomposition.
• Matter can be recycled within and between ecosystems, unlike energy.

The Carbon Cycle

• Photosynthesis captures carbon, while respiration returns it to the atmosphere.
• The burning of wood and fossil fuels adds CO₂ to the atmosphere.
• Dissolved CO₂ in aquatic ecosystems reacts with water to form bicarbonates.

The Nitrogen Cycle

• Plants take up nitrogen in the form of nitrate, mostly from nitrification of decomposed organic materials.
• Atmospheric nitrogen is added through nitrogen fixation, while denitrification returns nitrogen to the atmosphere.

The Phosphorus Cycle

• Phosphorus cycles within soil and water, with no atmospheric component.
• Phosphorus is lost from terrestrial ecosystems through leaching and chemical precipitation, but gained from weathering of rocks.
• Phosphorus is re-deposited in the soil when plants and animals decompose, and can become available again through geological uplifting.

This quiz covers the basics of ecosystem ecology, including trophic structure, energy flows, and bio-geochemical cycles. Students will learn about the components of an ecosystem and how they interact with each other.