Lecture: Chapter 21 - Ecosystem Energetics Flashcards
Ecosystem
The term ecosystem was first used by Tansley to refer to all the components of an ecological system, biotic and abiotic, that influence the flow of energy and elements
Where does energy in ecosystems originate?
Energy in ecosystems originate with primary production by autotrophs
Primary production
the chemical energy generated by autotrophs during photosynthesis and chemosynthesis. It is the source of energy for all organisms, from bacteria to humans.
Light or chemical energy –> chemical energy
Primary productivity
Rate of primary production. The rate at which organic matter is created by photosynthesis
Describe the process from sunlight to herbivore
Solar radiation -> photosynthesis [release of energy not used in photosynthesis] -> green plant -> energy transfer [release of energy lost in respiration and as heat] -> herbivore
Gross primary production (GPP)
total amount of carbon fixed by autotrophs.
GPP depends on photosynthetic rate
Net Primary Production (NPP)
Biomass gained by the plant after respiratory losses
- NPP is the energy left over where C is allocated for plant growth, defense against herbivory, reproduction, and for consumption by detritivores and herbivores
- NPP represents input of carbon in ecosystems
- NPP = GPP -> respiration by autotrophs (Ra)
Standing Crop biomass
Amount of organic matter in an area at a given time. The accumulation of NPP over time
Trade off between root and shoot allocation
Plants compete for belowground versus aboveground resources
shoots - roots
the more allocation of C to photosynthetic shoots relative to roots increases future NPP
Higher net C gain + greater plant growth
Primary Production
Plants can respond to environmetnal conditions by allocation carbon to the sgrowth o fdifferent tissues
Net primary productivity is constrained by both physical and biotic environmental factors
NPP varies substantially over space and time. Much of the varaition is correlated with climate.
What limits net primary production?
Factors related to leaf biomass
Factors relating to photosynthetic rate
- water availability
- light temperature
Factors relating to ability to accumulate biomass
Leaf area index
The total one-sided area of leaf tissue per unit ground surface area
Measure of light use efficiency
Varies among biomes and with season
Leibig’s Law of the minimum
Growth is controlled by the scarcest recourse (limiting factor)
Many experiments indicate that nutrients, particularly nitrogen, control NPP in terrestrial ecosystems
Freshwater systems: NPP
NPP in lakes and rivers is often limited by phosphorus and nitrogen availability.
In rivers and streams NPP is often low. Most of the energy is derived from terrestrial organic matter
Terrestrial systems: NPP
Short term nutrient addition experiments suggest N limitation in Tundra and Wetland ecosystems
Marine systems: NPP
As biomass accumulates nutrients are depleted in surface water
Also lost to deeper layers or sediments
Nutrient enrichment in deep water
These lead to nutrient limitation of production in marine systems
Nitrogen in marine systems
N is more often limited in marine systems than in others
Biological uses of Fe
Energy acquisition
- Respiration
- Photosynthetic enzymes
Nitrogen cycle
- Nitrate assimilation
- Nitrogen fixation
Fe as a nutrient
General facts
- needed in trace amounts
- most abundant elemetnt in crust
Three sources
- Upwelling
- Dust
- Ships
NPP: estuaries
are usuall nutrient-rich; variation in NPP is correlated with nitrogen inputs from rivers
NPP: ocean
In the open ocean, NPP is mainly from phytoplankton, limited by nitrogen.
NPP: equatorial Pacific Ocean
But NPP in the equatorial Pacific Ocean appears to be limited by iron
Secondary Production
Secondary production is generated through the consumption ororganic matter by heterotrophs
Heterotrophs get their energy by consuming organic compounds that were produced by other organisms: Secondary production
Secondary Production: Heterotrophs
- Herbivores eat plants and algae
- Carnivores eat other live animals
- Detrivores eat dead organic matter (detrius)
- Omnivores eat both plants and animals
Bottom-up control
Primary productivity is a constraint on secondary productivity within an ecosystem
Assimilation efficiency (A/I)
Proportion of ingested food that is assimilated; how efficiently consumer extracts energy from food.
- determined by food quality and the physiology of the consumer
- lower in herbivores and detrivores than carnivores
Production efficiency (P/A)
proportion of assimilated food that goes into new consumer biomass/secondary production
Surface area to volume ration
As body size increases, the surface area-to-volume ratio decreases for same-shaped objects.
What does energy transfer on a trophic level dependent upon?
The amount of energy transferred from one trophic level to the next depends on food quality and consumer abundance and physiology
Trophic pyramid
Portrays the relative amounts of energy or biomass of each trophic level
Some of the biomass at each level is not consumed and some of the energy is dispersed to the transfer to the next level
Trophic efficiency
Amount of energy at one trophic level divided by the amount of energy at the trophic level immediately below it
Energy flow among trophic levels
Only about 10% of the energy in a trophic level is passed on to the next trophic level.
1000g-> 100g->10g->1g
This is why energy runs out after 4 or 5 trophic transfers in an ecosystem and why carnivores (especially top carnivores) are scarce, relative to herbavores
Grazing
relatively large animals feed on leaves, fruits, seeds
primary producers [plant]-> herbivore [mouse]-> carnivore [snake]
Detrital
Microorganisms and small animals consume dead remains of plants and indigestible excretes of herbivores
