Sections
Some Physical Constraints on Flow
First Law of Thermodynamics
Second Law of Thermodynamics
Primary production is often measured in weight of producer (usually plants or algae, but can be bacteria in some systems) tissue added to the system
Gross Primary Production (GPP) is the amount of energy fixed by photosynthesis and chemosynthesis in an ecosystem
Net Primary Production (NPP) is GPP minus the energy lost to respiration by the producers
Net Change in Biomass (B) is NPP minus the energy lost to herbivory (G) and that lost to plant (algal) mortality (L)
DB = NPP - G - L
There are some generalities that can be made about the relationship between productivity and standing biomass
- Primary Productivity and standing crop (total biomass) are not always positively correlated
- Reefs - most productive but have a tiny standing crop because turnover is so high
- Total continental versus total marine
- Standing crop of marine producers is much smaller than terrestrial system producers with similar productivity, although the marine system supports lots of herbivores and carnivores
- This means that turnover is much greater in marine systems
Production Efficiency is the proportion of energy fixed to that available (sunlight for photosynthesis)
NPP efficiency is usually 1% or less
Terrestrial ecosystems
Aquatic Ecosystems
Question: As CO2 builds up in the atmosphere, some predict that some dry terrestrial ecosystems will become more productive and that there will be little gains in aquatic systems. What is responsible for this? I'll give you a hint - it's not the CO2 concentration, but something affected by it.
Biomass produced by producers (primary production) can only move into two other components
Measuring secondary production
Gross assimilation (amount of plant/algal material eaten) is reduced by the amount of energy (and the compounds needed to supply it) used to maintain the herbivore/detritivore
Gross Assimilation - Maintenance = Net Secondary Production
- The book refers to maintenance as respiration, but this is not correct, as respiration provides energy for both production and maintenance
- In endothermic vertebrates, maintenance is easiest to measure as the basal metabolic rate
Net production is measured as biomass increase
- Growth of individuals
- New individuals
Secondary Production Efficiency of secondary producers is the ratio of Net Secondary Production/Assimilation
Lindeman Efficiency is different from the efficiencies discussed so far
- the ratio of assimilation between trophic levels
- Maintenance is included in both the denominator and numerator, and will cancel out if it is the same proportion for each trophic level
Terrestrial ecosystems
- Often near 10% for all but decomposers
- Decomposers get what the herbivores and carnivores do not
- Total energy flow not much affected by carnivores (who produce 10% of 10%, or only 1% of primary production)
Aquatic Ecosystems
- Higher than for terrestrial systems, leading to rapid turnover in biomass
- Often as high as 40 % for aquatic herbivores
- Often as high as 80% for aquatic carnivores
Control of Secondary Production
Increase in primary production often leads to an increase in secondary production
This leads to the phenomenon that well-fertilized fields are attacked by herbivorous insects more than unfertilized fields (remember the ecosystem exploitation hypothesis)
Follows nutrients as they flow through the system
Nutrient cycles are the most thoroughly modeled ecological processes, also called Biogeochemical cycles, and are the paths of materials as they enter an ecosystem, pass through various componenets of the ecosystem, and finally exit the ecosystem
Nutrient pools - nutrients in a species, a trophic level, or in some abiotic portion of the system (such as the soil or the atmosphere)
Flux rates are the rates of flow from pool to pool
Sources - a pool that is outside of the system and is often considered to be inexhaustible, although the flow from the source may be very slow
Sinks - where materials go when they leave the system
General model
Sources
Volcanism
Pools | Flux pathways | |
Input | Output | |
Producers | photosynthesis | respiration, herbivory, death |
Consumers | herbivory | respiration, carnivory (between trophic levels), death |
Decomposers | death | respiration |
Detritus | plants, animals | consumption by decomposers |
Fossil fuels | anaerobic respiration | human-caused combustion |
Atmosphere/Water |
Ocean is generally considered to be in equilibrium with atmosphere, such that an alteration in one will inevitably lead to an alteration in the other
this needs some work
note that the role of microorganisms is key
biocides, target organisms, Primary production, Gross Primary Production, Net Primary Production, Terrestrial ecosystems, Soil Moisture, Evapotranspiration rate, Length of Growing Season, Nutrient Limitation, Eutrophication, secondary production, Gross Assimilation, net secondary production, the basal metabolic rate, Efficiency, Production Efficiency, Lindeman efficiency, Biomass, assimilation, maintenance, early and late succession communities, Nutrient Cycling, Local models, Global models, Biosphere, Biogeochemical cycles, Nutrient pools, Flux rates, Sources, Sinks, Global Carbon Cycle, Volcanism, Global Phosphorous Cycle, Global Nitrogen Cycle, Fixation, Denitrification
Last updated October 26, 2006