Primary Production Flashcards
What does primary production do for us
Provides all food
Provides food, ecosystems and habitats for other species
Absorbs carbon
Provides goods and services for humans
Primary production
The synthesis of organic molecules from inorganic substances such as light or chemical energy
Organisms that can do this are called autotrophs or primary producers
Gross primary production
Total primary production
Measured as the conversion of energy from light to the chemical energy of organic molecules per unit time
Net primary production equation
GPP - R
R = respiration for autotrophs
Can be measured as dry biomass or carbon sequestered
Net primary production
The amount of new biomass (or carbon) added in a given time period (NOT the total biomass of autotrophs)
Why is it important to measure primary production
Understand plant growth
Improve/predict crop yields
Food available for animals
Predict climate impacts on ecosystem NPP
Model CO2 uptake by plants
How is PP measured
Carbon dioxide uptake eg eddy covariance
Annual growth
Tree circumference
Remote sensing techniques measuring photosynthetic capacity.
What percentage of NPP ends up below-ground
46%
Factors limiting pp
Light
Carbon dioxide
Temperature
Nutrients
Soil pH
Water
What has the highest level of total global net primary production per unit area
Algal beds and reefs
Most productive ecosystems per unit area
Tropical rainforests
Estuaries
Coral reefs
Marine ecosystems
Relatively unproductive per unit area but contribute much to global NPP due to their size
What determines biomes
Temperature and precipitation
Most vulnerable biomes to climate change
Temperate mixed forest
Boreal conifer
Alpine
Tundra
Climate change thresholds
The first threshold, related to a decay in vegetation productivity and photosynthetic activity, occurs when crossing an aridity level of ~0.54.
At aridity levels of ~0.7, sharp declines in soil fertility, plant nitrogen content, and biotic (plant–soil, plant–plant) interactions, and drastic compositional changes in plant and soil microbial communities are observed.
Finally, drastic reductions in plant cover, increases in soil albedo, and shifts in leaf traits toward stress avoidance were detected at an aridity level of ~0.8
Biomass - ecology
The mass of living organisms in an area
Can be measured as dry or wet weight or we can use carbon
Biomass - renewable energy
Material from organisms that can be burned eg wood and straw
Net ecosystem production
A measure of the total biomass accumulation in an ecosystem during a given period
GPP - R
R = total respiration of all organisms
Global net ecosystem production
useful to ecologists because its value determines whether an ecosystem is gaining or losing carbon over time.
For example a forest may have a positive NPP but still lose carbon if heterotrophs release it as CO2 more quickly than primary production.
NEP >0
Ecosystem is a carbon sink (absorbs more co2 than it releases)
NEP < 0
Ecosystem is a carbon source (releases more co2 than it absorbs)
Perspectives from the Anthropocene
1: Humans have now made more mass than exists in the biosphere
2: Humans now appropriate 24% of all biomass, exceeding the estimated safe planetary boundary for this
3: Human activities are impacting some autotrophs’ ability to deliver their primary production function
Functional aspect of biosphere integrity
How much of the global NOP is appropriated by humans and therefore no longer available to support ecosystems
Set the safe boundary at 10% - currently we take 24%
Efficiency of energy transfer between trophic levels
Typically only 10% efficient
Energy pyramid
Represents the loss of energy with each transfer in a food chain
Trophic efficiency
percentage of production transferred from one trophic level to the next.
Trophic efficiency equation
Net Productivity at trophic level N/Production at trophic level n-1
E.g. Net productivity of all primary consumers/Production of all plants
Applies to whole trophic levels
% of net primary production going to animal consumption varies between ecosystems
Tropical Rain Forest – 7%
Temperate Deciduous Forest – 5%
Grassland – 10%
Open Ocean – 40%
Where does most of the net primary production go
Decomposers (mostly microbial)
Production efficiency
percentage of assimilated (eaten) biomass converted into new biomass.
can apply to individual populations
Birds and mammals have efficiencies in the range of 1–3% because of the high cost of endothermy
Fish have production efficiencies of around 10%
Insects and microorganisms have efficiencies of 40% or more (lower costs of endothermy)
Production efficiency equation
Net productivity/Total food intake (assimilation)
Where does the rest of production efficiency go
Metabolized in growth, keeping warm (endotherms), behaviour
Some goes into faeces, hair that is moulted etc.
It all has to go somewhere
What is transferred between organisms in a food chain
Transfer of fixed carbon between trophic levels (provides the energy for metabolism)
There is never perfect transfer
Many other materials such as nitrogen and phosphorous travel through food webs
Contaminants can also be transferred (e.g. pesticides and heavy metals) and may accumulate as they go up the food chain
Proportions of key substances change as move between trophic levels with different metabolic needs – animals have higher proportion of nitrogen-rich compounds than plants, for instance
Trophic level definition
All organisms are the same position in the food chain
Why are food chains relatively short
Energetic hypothesis - length of the food chain is limited by the inefficiency of energy transfer along the chain
What is a food web
Shows trophic interactions, i.e. feeding relationships, by lines or arrows and can be:
Based on a particular organism which is source (e.g. oak) or sink (e.g. starfish),
Based on a functional group (e.g. tropical leaf miners, pollinators)
Community or habitat (e.g. pond, desert)
Usually selective and often miss whole segments of communities
They provide an idea of species’ roles in ecosystems – to an extent
Reflect aspects of animal learning and behaviour in making food choices
How are food webs built
Observation of feeding
Gut contents, faecal pellets
Stable isotope ratios to indicate trophic position and/or source of food
What can food webs indicate
Which species in a community are likely to depend on each other
Which species are likely to compete
Which species may be critical to the community
How a community will/does respond to invasive species or extinctions
But often we can only find out when we do an experiment (deliberate or otherwise)
Functional redundancy in the ecosystem
More than one species doing a specific job
Bottom up model
proposes a unidirectional influence from lower to higher trophic levels
In this case, the presence or absence of mineral nutrients (N) controls plant (V) numbers, which control herbivore (H) numbers, which control predator (P) numbers
Testing bottom up vs top down control of plant biomass
Control the top down factor (herbivores)
Control the bottom up factor (fertilizer, water, etc.)
Control both together
Four possible treatments
Top down model
also called the trophic cascade model, proposes that control comes from the trophic level above
In this case, predators limit herbivores, herbivores limit plants, and plants limit nutrient levels
Invasive species management
Uses top down control
Example of a trophic cascade
In a Finnish lake, blooms of cyanobacteria (primary producers) occurred when zooplankton (primary consumers) were eaten by large populations of roach (fish -secondary consumers)
The removal of roach and addition of pike (tertiary consumers) controlled roach populations, allowing zooplankton populations to increase and ending cyanobacterial blooms
Keystone species
a species that has a disproportionately large effect on its natural environment relative to its abundance.
You own 300 acres of patchy temperate forest mixed with grassy meadows. Which one of the following actions would increase the net primary productivity of the area the most?
Planting 500 new trees.
