Primary Production

Question 1

What does primary production do for us

Answer 1

Provides all food
Provides food, ecosystems and habitats for other species
Absorbs carbon
Provides goods and services for humans

Question 2

Primary production

Answer 2

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

Question 3

Gross primary production

Answer 3

Total primary production
Measured as the conversion of energy from light to the chemical energy of organic molecules per unit time

Question 4

Net primary production equation

Answer 4

GPP - R
R = respiration for autotrophs

Can be measured as dry biomass or carbon sequestered

Question 6

Net primary production

Answer 6

The amount of new biomass (or carbon) added in a given time period (NOT the total biomass of autotrophs)

Question 7

Why is it important to measure primary production

Answer 7

Understand plant growth
Improve/predict crop yields
Food available for animals
Predict climate impacts on ecosystem NPP
Model CO2 uptake by plants

Question 8

How is PP measured

Answer 8

Carbon dioxide uptake eg eddy covariance
Annual growth
Tree circumference
Remote sensing techniques measuring photosynthetic capacity.

Question 9

What percentage of NPP ends up below-ground

Answer 9

46%

Question 10

Factors limiting pp

Answer 10

Light
Carbon dioxide
Temperature
Nutrients
Soil pH
Water

Question 11

What has the highest level of total global net primary production per unit area

Answer 11

Algal beds and reefs

Question 12

Most productive ecosystems per unit area

Answer 12

Tropical rainforests
Estuaries
Coral reefs

Question 13

Marine ecosystems

Answer 13

Relatively unproductive per unit area but contribute much to global NPP due to their size

Question 14

What determines biomes

Answer 14

Temperature and precipitation

Question 15

Most vulnerable biomes to climate change

Answer 15

Temperate mixed forest
Boreal conifer
Alpine
Tundra

Question 16

Climate change thresholds

Answer 16

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

Question 17

Biomass - ecology

Answer 17

The mass of living organisms in an area
Can be measured as dry or wet weight or we can use carbon

Question 18

Biomass - renewable energy

Answer 18

Material from organisms that can be burned eg wood and straw

Question 19

Net ecosystem production

Answer 19

A measure of the total biomass accumulation in an ecosystem during a given period
GPP - R

R = total respiration of all organisms

Question 20

Global net ecosystem production

Answer 20

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.

Question 21

NEP >0

Answer 21

Ecosystem is a carbon sink (absorbs more co2 than it releases)

Question 22

NEP < 0

Answer 22

Ecosystem is a carbon source (releases more co2 than it absorbs)

Question 23

Perspectives from the Anthropocene

Answer 23

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

Question 24

Functional aspect of biosphere integrity

Answer 24

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%

Question 25

Efficiency of energy transfer between trophic levels

Answer 25

Typically only 10% efficient

Question 26

Energy pyramid

Answer 26

Represents the loss of energy with each transfer in a food chain

Question 27

Trophic efficiency

Answer 27

percentage of production transferred from one trophic level to the next.

Question 28

Trophic efficiency equation

Answer 28

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

Question 29

% of net primary production going to animal consumption varies between ecosystems

Answer 29

Tropical Rain Forest – 7% Temperate Deciduous Forest – 5% Grassland – 10% Open Ocean – 40%

Question 30

Where does most of the net primary production go

Answer 30

Decomposers (mostly microbial)

Question 31

Production efficiency

Answer 31

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)

Question 32

Production efficiency equation

Answer 32

Net productivity/Total food intake (assimilation)

Question 33

Where does the rest of production efficiency go

Answer 33

Metabolized in growth, keeping warm (endotherms), behaviour Some goes into faeces, hair that is moulted etc. It all has to go somewhere

Question 34

What is transferred between organisms in a food chain

Answer 34

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

Question 35

Trophic level definition

Answer 35

All organisms are the same position in the food chain

Question 36

Why are food chains relatively short

Answer 36

Energetic hypothesis - length of the food chain is limited by the inefficiency of energy transfer along the chain

Question 37

What is a food web

Answer 37

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

Question 38

How are food webs built

Answer 38

Observation of feeding Gut contents, faecal pellets Stable isotope ratios to indicate trophic position and/or source of food

Question 39

What can food webs indicate

Answer 39

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)

Question 40

Functional redundancy in the ecosystem

Answer 40

More than one species doing a specific job

Question 41

Bottom up model

Answer 41

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

Question 42

Testing bottom up vs top down control of plant biomass

Answer 42

Control the top down factor (herbivores) Control the bottom up factor (fertilizer, water, etc.) Control both together Four possible treatments

Question 43

Top down model

Answer 43

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

Question 44

Invasive species management

Answer 44

Uses top down control

Question 45

Example of a trophic cascade

Answer 45

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

Question 46

Keystone species

Answer 46

a species that has a disproportionately large effect on its natural environment relative to its abundance.

Question 47

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?

Answer 47

Planting 500 new trees.