Chapter 19 Summary

CONCEPT 19.1 Energy in ecosystems originates with primary production by autotrophs.

• Gross primary production (GPP) is the total amount of carbon fixed by the autotrophs in an ecosystem.
• The amount of GPP in an ecosystem is determined by photosynthetic rates per unit leaf area and the leaf area index.
• Net primary production is equal to gross primary production minus respiration.
• Net primary productivity changes during succession due to changes in leaf area index and in the balance between photosynthetic and nonphotosynthetic tissues.
• Researchers have developed diverse approaches to measuring net primary production at different spatial and temporal scales.

CONCEPT 19.2 Net primary productivity is constrained by both physical and biotic environmental factors.

• Variation in terrestrial net primary productivity is associated with variation in temperature and precipitation, which affects resource availability and the types and abundances of plants.
• The intrinsic growth rate of plants influences temporal variation in net primary productivity and ecosystem response to climatic variation.
• Net primary productivity in aquatic ecosystems is controlled by the supply of nutrients, particularly phosphorus and nitrogen.

CONCEPT 19.3 Global patterns of net primary production reflect climatic controls and biome types.

• Terrestrial and oceanic net primary production contribute nearly equal proportions of global net primary production
• The majority of terrestrial net primary production occurs in the tropics, including tropical forests and savannas.
• Differences in NPP among terrestrial biomes reflect differences in leaf area index and in the length of the growing season.
• Although nearshore ecosystems are the most productive per unit of area, the majority of oceanic net primary production is derived from the open ocean due to its larger area.

CONCEPT 19.4 Secondary production is generated through the consumption of organic matter by heterotrophs.

• Heterotrophs derive energy from the consumption of live or dead organic matter.
• Net secondary production is the energy ingested by heterotrophs minus the energy used in respiration and egested in feces and urine.
• Heterotroph diet can be estimated by comparing the natural abundances of C, N, or S isotopes in potential food sources with isotopic composition of the tissues of the consumer.