THINGS TO KNOW FROM CHAPTER 54: ECOSYSTEMS
Introduction
 Ecosystem: all organisms living in a community and the abiotic factors they
interact with
 Ecosystems dynamics:
o Energy flow:
 sunlight, autotrophs, heterotrophs, heat
 cannot be recycled
 energy flows through ecosystems
o Chemical cycling:
 carbon, nitrogen, etc.
 matter cycles within the ecosystem
54.1: Energy Flow and Chemical Cycling
 Ecosystems are transformers of energy and processors of matter
 Ecosystems and Physical Laws
o Energy cannot be created or destroyed; just transformed
o Energy conversion is not completely efficient; heat is lost
 Trophic Relationships
o Primary producers support all others (autotrophs mainly photosynthetic
plants, algae and prokaryotes; also chemosynthetic autotrophs)
o Heterotrophs:
 primary consumers: herbivores
 secondary consumers: carnivores that eat herbivores
 tertiary consumers: carnivores that eat carnivores
o Detritivores or decomposers
 Decomposition
o Prokaryotes, fungi and animals
o Link primary producers and consumers in ecosystem
o Make chemical elements available and bring back to soil, air, water
o Mainly prokaryotes and fungi
54.2: Primary Production is Limited by Physical and Chemical Factors
 Primary Production: amount of light energy converted to chemical energy by
autotrophs in a given time period
 Ecosystem Energy Budgets:
o Photosynthetic production sets energy budget for ecosystem
o Global Energy Budget: Only a small fraction of radiation strikes
autotrophs and only small amount is usable for photosynthesis (1%)
o Gross and Net Primary Productivity:
 GPP: Gross Primary Production; total primary production in an
ecosystem; light energy converted into chemical energy by
photosynthesis per unit time; some molecules are used by the
plant
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NPP: Net Primary Production: GPP – energy used by primary
producers for respiration; available energy in the ecosystem
NPP is not total biomass of photosynthetic autotrophs (standing
crop); NPP = new biomass at any given time
Tropical rainforests are the most productive terrestrial
ecosystems; estuaries and coral reefs are productive but cover
a small area; oceans are large but NPP per unit area is low

What limits primary production in aquatic ecosystems (marine and freshwater)
o Light Limitation: only reach photic zone; not just light limits or there
would be gradient along equator
o Nutrient Limitation:
 Limiting nutrient must be added for production in a particular
area; Nitrogen or Phosphorus
 N or P is low in photic zone and more abundant in deeper water
where it is too dark for photosynthesis
 Iron also is a limiting nutrient
 Upwelling areas: nutrient rich deep waters circulate to ocean
surface have high primary production
 Also common in freshwater lakes: eutrophication (cyanobacteria
dominate); lead to loss of fishes (phosphorus)

Primary Production in Terrestrial & Wetland Ecosystems
o Temperature and moisture are key factors in controlling primary
production in wetland and terrestrial ecosystems
o Tropical: warm and wet
o Actual evapotranspiration
o Locally: minerals in soil can be limiting factors: N and P
54.3: Energy Transfer between Trophic Levels is Usually < 20%
 Secondary production: amount of chemical energy in consumer’s food that is
converted to own biomass during a given time period
 Much of primary production is not used: don’t eat all; don’t digest all
 Production Efficiency:
o Caterpillar uses 1/6 for secondary production (growth) also uses
energy for cellular respiration (lost as heat), feces (detritivores)
o Only chemical energy stored as biomass is available for secondary
consumers
o Net Secondary Production/Assimilation of Primary Production
 NSP: energy stored as biomass
 Assimilation: energy taken in and used for growth, respiration,
and reproduction
o Production Efficiency: Not used for respiration
o Birds & Mammals are 1- 3 % (endotherms); Insects are 40%
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Trophic Efficiency and Ecological Pyramids
o Percentage of production transferred from one trophic level to the next
o Less than production efficiencies (energy lost in respiration, contained
in feces, energy not consumed by trophic level)
o Range 5 – 20%; 80 – 95% energy is not transferred to next trophic
level
o Pyramids of production
o Pyramids of biomass (phytoplankton: usually decreases but sometimes
standing crop supports larger group of consumers; production would
be bottom heavy)
o Pyramids of numbers: loss of energy limits biomass of top level
carnivores; 4 – 5 trophic levels are maximum; predators are usually
larger
o Eating meat is inefficient use of energy flow; could feed more with only
plant material
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Green World Hypothesis:
o Terrestrial herbivores are held in check and consume little plant
biomass
o Herbivores consumer 17% of NPP of plants
o Things that keep herbivores in check:
 Plants have defenses against herbivores
 Nutrients limit herbivores; not energy supply
 Abiotic factors limit herbivores
 Intraspecific competition can limit herbivore numbers
 Interspecific interactions keep densities in check
54.4: Biological and Geochemical Processes move Nutrients between
Organic and Inorganic Parts of the Ecosystem
 Chemical Elements are limited; need to be recycled
 Biogeochemical cycles: nutrients circuit in biotic and abiotic
 General Model of Chemical Cycling:
o Global and Local
o Study Picture 54.16 on page 1195
 Organic or inorganic materials
 Are materials directly available for use by organisms
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Biogeochemical Cycles (study pages 1196 – 1197)
o Water Cycle
o Carbon Cycle
o Nitrogen Cycle:
 Nitrogen fixation: conversion of Nitrogen gas by bacteria to
forms that can be used
 Ammonification: decomposes organic nitrogen to ammonium
 Nitrification: Ammonium is converted to nitrate by nitrifying
bacteria
 Denitrification: anaerobic conditions; denitrifying bacteria use
nitrate instead of oxygen and release Nitrogen gas
o Phosphorus Cycle
Decomposition and Nutrient Cycling Rates: relates to evapotranspiration
Vegetation and Nutrient Cycling
54.5: Human Population is Disrupting Chemical Cycles
 Nutrient Enrichment:
o Agriculture and Nitrogen Cycling
o Contamination of Aquatic Ecosystems: cultural eutrophication
 Acid Precipitation:
 Toxins: Biological Magnification (Mercury in Big Fishes)
 Atmospheric Carbon Dioxide: Greenhouse Effect and Global Warming
 Depleting Atmospheric Ozone
o