Ecosystem Energy Transfer Quiz

Secondary Production in Ecosystems

• Secondary production refers to the conversion of chemical energy from food into biomass by consumers during a specific timeframe.
• Herbivores, or primary consumers, typically consume only about one-sixth of total plant production in ecosystems.

Energy Transfer and Production Efficiency

• A caterpillar utilizes only one-sixth of the energy from the leaves it eats for growth, with the rest used in respiration or lost in feces.
• Energy from feces can be temporarily retained in the ecosystem but is mostly lost as heat when consumed by decomposers.
• Production efficiency is determined by the percentage of energy from assimilated food saved for growth and reproduction rather than lost to respiration.
• Birds and mammals have low production efficiencies (around 4-30%), while fishes have efficiencies of 10-20%, and insects and microorganisms exceed 40%.

Trophic Efficiency and Energy Flow

• Trophic efficiency is the percentage of production that transfers from one trophic level to another, always lower than production efficiency due to losses at each stage.
• Average trophic efficiencies range from 5% to 20%, meaning a significant amount of energy (approximately 80%-95%) is lost between levels.
• Example: If 10% of energy is transferred from primary producers to primary consumers, only 1% of net primary production is available to secondary consumers.

Energy Flow in Salt Marsh Ecosystem

• John Teal’s study on a salt marsh showed the energy flow among producers, consumers, and decomposers, measuring solar radiation and biomass.
• Solar energy incorporated: Gross primary production at 34,580 kilocalories; Net primary production at 6,585 kilocalories.
• Detritus leaving the marsh accounted for 3,671 kilocalories; significant losses occur through respiration of both producers and consumers.

Implications of Energy Loss

• The loss of energy along the food chain limits the number of top-level carnivores an ecosystem can support, usually capping food chains at around four to five trophic levels.
• An energy pyramid visually represents these losses, showing how net production decreases at higher trophic levels.

Biomass Distribution

• Biomass pyramids typically demonstrate decreased biomass from primary producers to top-level consumers, illustrating inefficiencies in energy transfer.
• Inverted biomass pyramids may occur in aquatic systems where rapid consumption and replacement by phytoplankton support larger populations of primary consumers (zooplankton).

Human Consumption and Energy Efficiency

• Consuming meat is less efficient than obtaining energy directly from plants, highlighting food conversion inefficiencies.
• A shift towards plant-based diets could better allocate resources and require less land to support human populations globally.

Ecosystem Energy and Nutrient Cycling

• Ecosystems primarily rely on solar energy, while essential chemical elements are limited and need continuous recycling.
• Organisms regularly assimilate nutrients, releasing waste and returning atoms to the atmosphere, water, or soil upon death.
• Decomposers are key heterotrophs that break down organic matter, liberating nutrients for plants and autotrophs to utilize.

Decomposition Rates

• Decomposition rates vary with environmental factors: temperature, moisture, nutrient availability.
• In warmer ecosystems, decomposers function more efficiently, with litter decomposing significantly faster in tropical rainforests than in temperate forests.
• On average, organic material decomposes in a few months to a few years in tropical rainforests; in temperate regions, it can take four to six years.

Impact of Temperature on Decomposition

• Research conducted by the Canadian Forest Service demonstrated a fourfold increase in litter decomposition rates in warmer ecosystems compared to colder ones.
• Conditions that hinder decomposition include excessive dryness or saturation, particularly in cold, wet areas such as peatlands, leading to significant organic matter storage.

Biogeochemical Cycles

• Nutrient cycling involves both biotic (living) and abiotic (non-living) components, distinguished as global and local cycles.
• Gaseous elements like carbon, oxygen, sulfur, and nitrogen exist globally in the atmosphere; others like phosphorus and potassium cycle more locally.
• Nutrients in living organisms and detritus are transferred to other organisms through food webs and decomposition processes.

Water Cycle

• Water is essential for life, influencing ecosystem processes like primary production and decomposition.
• The oceans contain around 97% of the world's water, with glaciers and polar ice caps holding approximately 2%, and the remaining 1% found in lakes, rivers, and groundwater.
• Key processes in the water cycle include evaporation, condensation, precipitation, and plant transpiration.

Carbon Cycle

• Carbon is a vital building block in organic molecules and is cycled through processes like photosynthesis by plants, cellular respiration by consumers, and fossil fuel combustion.
• Major carbon reservoirs include fossil fuels, soils, ocean sediments, and atmospheric CO2, where geological time scales play a role in carbon storage dynamics.

Nitrogen Cycle

• Nitrogen is crucial for amino acids, proteins, and nucleic acids, with plants utilizing forms like ammonium and nitrate while animals require organic forms.
• Natural nitrogen fixation occurs through bacteria and processes such as lightning. Human activity has increased nitrogen inputs through fertilizers and agricultural practices.

Phosphorus Cycle

• Phosphorus is vital for nucleic acids, ATP, and skeletal structures; its most significant form is phosphate, which plants absorb.
• Phosphorus accumulates primarily in sedimentary rocks, with localized recycling due to soil retention and limited atmospheric movement.

Hubbard Brook Experimental Forest Case Study

• Research has been ongoing since 1963 on nutrient cycling in the Hubbard Brook Experimental Forest, focusing on how vegetation affects drainage and nutrient loss.
• After clear-cutting a watershed, water and nutrient runoff increased markedly, particularly in the concentration of nitrate, leading to concerns about drinking water safety.
• Internal cycling was found to conserve most minerals, while deforestation led to dramatic losses in nutrient retention, highlighting the role of vegetation in ecosystem productivity and nutrient control.