Ecology: Primary Production and Efficiency

Compensatory Growth and Grazing

• Moderate grazing can increase plant productivity due to compensatory growth, where plants respond to grazing by increasing their growth rate.

Species Richness and Primary Production

• Species richness of primary producers (plants, algae) influences primary production, with evidence showing that higher species richness leads to greater primary production.
• This is because a diverse range of species can exploit different resources and occupy different niches, resulting in more efficient use of resources.

Primary Production and Species Richness

• Primary production can be greater with higher species richness of primary producers because diverse species can:
  • Utilize different resources and exploit different niches
  • Increase the efficiency of resource use
  • Enhance ecosystem stability

Ecological Efficiency

• Ecological efficiency is the percentage of energy transferred from one trophic level to the next.
• It is typically low, ranging from 5-20%, due to energy losses during trophic transfers.

Secondary Productivity

• Secondary productivity is the rate of biomass production of heterotrophic organisms, such as consumers and detritivores.

Bottom-Up Control of Secondary Production

• Research has demonstrated that primary production can control secondary production through bottom-up effects, where changes in primary production influence the availability of resources for secondary producers.

Trophic Vocabulary

• Key terms:
  • Primary producer: autotroph that produces its own food through photosynthesis
  • Autotroph: organism that produces its own food through photosynthesis
  • Photosynthesis: process of converting light energy into organic compounds
  • Secondary producer: heterotroph that consumes other organisms to obtain energy
  • Consumer: heterotroph that consumes other organisms to obtain energy
  • Heterotroph: organism that obtains energy by consuming other organisms
  • Herbivore: consumer that eats plants
  • Detritivore: consumer that eats dead organic matter
  • Predator/Carnivore: consumer that eats other animals

Equations for Primary Production and Respiration

• Photosynthesis equation: 6CO2 + 6H2O + light energy → C6H12O6 (glucose) + 6O2
• Respiration equation: C6H12O6 (glucose) + 6O2 → 6CO2 + 6H2O + ATP

Ecosystem Metabolic Processes

• Gross primary productivity (GPP): total rate of photosynthesis
• Net primary productivity (NPP): GPP - Rp (autotrophic respiration)
• Autotrophic respiration (Rp): energy used by autotrophs for maintenance and growth
• Heterotrophic respiration (Rh): energy used by heterotrophs for maintenance and growth
• Ecosystem respiration (Re): total energy used by ecosystem for maintenance and growth
• Net ecosystem productivity (NEP): NPP - Re

Relations between Ecosystem Metabolic Processes

• NEP = GPP - Re
• NPP = GPP - Rp

Partitioning of GPP

• A percentage of GPP is allocated to Rp (autotrophic respiration)
• The remaining percentage is allocated to NPP

Influence of Climate on Primary Production

• Climate influences primary production, with evidence showing that changes in temperature, precipitation, and other climate factors affect primary production.

Influence of Plant Growth Form on Primary Production

• Plant growth form, such as leaf area, influences primary production, with evidence showing that variations in leaf area affect primary production.

Limiting Nutrient

• A limiting nutrient is a nutrient that restricts the growth of organisms when it is scarce.
• Research evidence, such as nutrient addition experiments, can be used to identify which nutrient is limiting in a particular ecosystem.

Nutrient Limitation in Aquatic Ecosystems

• Nitrogen (N) typically limits primary production in lakes and rivers
• Phosphorus (P) typically limits primary production in estuaries and oceans