Chapter 11 - the flux of energy and matter through ecosystems (CHAPTER + SLIDES)

Question 1

What is Assimilation Efficiency (AE)?

Answer 1

The percentage of consumed energy that is actually assimilated across the gut wall by an organism; the remainder is lost in feces.

AE is crucial for understanding energy transfer in ecosystems.

Question 2

Define Atmospheric Deposition.

Answer 2

The net flux of materials from the atmosphere to an ecosystem, including both dryfall and wetfall.

This process is significant for nutrient cycling.

Question 3

What does Biomass refer to?

Answer 3

The mass of organisms per unit area of ground (or water), usually expressed in units such as g carbon m⁻² or tonnes dry weight ha⁻¹.

Biomass is an important indicator of ecosystem health.

Question 4

What are Biogeochemical Cycles?

Answer 4

The pathways by which chemical elements move through the biotic and abiotic components of an ecosystem.

These cycles are essential for nutrient availability.

Question 5

Define Colimitation.

Answer 5

A phenomenon where two or more nutrients are simultaneously limiting to primary productivity.

Understanding colimitation helps in managing ecosystems.

Question 6

What is Consumption Efficiency (CE)?

Answer 6

The percentage of the total production of a trophic level that is consumed by the trophic level above it.

CE is important for assessing energy flow in food webs.

Question 7

Explain Decomposition.

Answer 7

The process by which dead organic matter is broken down into simpler inorganic substances.

Decomposition is vital for nutrient recycling.

Question 8

What is Denitrification?

Answer 8

The conversion of nitrate into molecular nitrogen gas (N₂) by bacteria, typically occurring in environments lacking oxygen.

Denitrification is a critical process in the nitrogen cycle.

Question 9

Who are Detritivores?

Answer 9

Organisms that consume dead organic matter (detritus).

Detritivores play an essential role in decomposition and nutrient cycling.

Question 10

Define Dryfall.

Answer 10

The settling of particles from the atmosphere during periods without rain.

Dryfall contributes to atmospheric deposition.

Question 11

What is an Endorheic Basin?

Answer 11

A watershed from which there is no outflow of water, either on the surface as rivers or underground by flow or diffusion through rock or permeable material.

Also called a terminal or closed basin.

Question 12

Explain Eutrophication.

Answer 12

The enrichment of a water body with nutrients, often leading to excessive primary production and subsequent oxygen depletion.

Eutrophication can result in harmful algal blooms.

Question 13

What is Gross Primary Productivity (GPP)?

Answer 13

The total rate at which autotrophs convert light energy into chemical energy through photosynthesis.

GPP is a measure of the energy available to an ecosystem.

Question 14

Define Human Appropriation of Net Primary Productivity (HANPP).

Answer 14

The portion of the world’s NPP that is used or controlled by humans.

HANPP reflects human impact on ecosystems.

Question 15

What does Immobilization mean?

Answer 15

The incorporation of inorganic nutrients into organic forms within the biomass of organisms or detritus.

This process is crucial for nutrient cycling.

Question 16

What is Liebig’s Law of the Minimum?

Answer 16

States that plant growth is limited by the nutrient in shortest supply relative to the plant’s needs.

This law highlights the importance of nutrient balance.

Question 17

Define Mineralization.

Answer 17

The conversion of elements from organic forms to inorganic forms during decomposition.

Mineralization is a key step in nutrient recycling.

Question 18

What is Net Primary Productivity (NPP)?

Answer 18

The rate at which biomass is produced by autotrophs; calculated as Gross Primary Productivity minus the energy lost through respiration by the autotrophs.

NPP is a critical measure of ecosystem productivity.

Question 19

Explain Nitrogen Fixation.

Answer 19

The conversion of molecular nitrogen gas (N₂) from the atmosphere into biologically available forms like ammonium by certain microorganisms.

Nitrogen fixation is essential for plant growth.

Question 20

What is a Nutrient Budget?

Answer 20

An accounting of the inputs, outputs, and internal cycling of a nutrient within an ecosystem.

Nutrient budgets help in ecosystem management.

Question 21

Define Primary Productivity.

Answer 21

The rate of production of organic carbon by autotrophic organisms (producers) per unit area.

Primary productivity is fundamental to food webs.

Question 22

What is Production Efficiency (PE)?

Answer 22

The percentage of assimilated energy that is converted into new biomass by an organism or trophic level.

PE indicates how efficiently energy is converted into biomass.

Question 23

Explain Recycling in ecosystems.

Answer 23

The repeated uptake and release of nutrient elements within an ecosystem as they pass through food chains and decomposition pathways.

Recycling is vital for sustainability in ecosystems.

Question 24

What is the Redfield Ratio?

Answer 24

The relatively fixed ratio of dissolved nitrogen to phosphorus (approximately 15:1 by moles) found in much of the world’s oceans and in marine phytoplankton tissues.

The Redfield Ratio is important for understanding nutrient dynamics in aquatic systems.

Question 25

Define Secondary Productivity.

Answer 25

The rate of production of biomass by heterotrophs (consumers and decomposers). ## Footnote Secondary productivity is essential for energy transfer in ecosystems.

Question 26

What is Standing Crop (or Standing Stock)?

Answer 26

The total biomass of living organisms within a unit area. ## Footnote Standing crop reflects the current state of biomass in an ecosystem.

Question 27

Explain Stoichiometry in ecosystems.

Answer 27

The relationship between the abundances of different elements in organisms and their environment. ## Footnote Stoichiometry plays a role in nutrient availability and biological processes.

Question 28

What is Turnover Rate?

Answer 28

Primary productivity per unit biomass. ## Footnote Turnover rate is an important metric for understanding ecosystem dynamics.

Question 29

Define Weathering.

Answer 29

The physical and chemical breakdown of rocks and soil, which can release nutrients into the ecosystem. ## Footnote Weathering contributes to soil fertility.

Question 30

What is Wetfall?

Answer 30

The flux of materials dissolved in rain and snow to an ecosystem. ## Footnote Wetfall is a component of atmospheric deposition.

Question 31

Define standing crop and how it is typically measured.

Answer 31

Standing crop refers to the total biomass of living organisms within a unit area. It is typically measured as mass of organisms per unit area (or water), often expressed as g carbon m⁻² or tonnes dry weight ha⁻¹.

Question 32

What is the difference between gross primary productivity and net primary productivity?

Answer 32

Gross primary productivity (GPP) is the total rate of carbon production by autotrophs through photosynthesis. Net primary productivity (NPP) is GPP minus the energy lost through respiration by the autotrophs themselves.

Question 33

Explain Liebig's Law of the Minimum in the context of plant growth.

Answer 33

Liebig's Law of the Minimum states that the growth of a plant is limited primarily by the single nutrient that is in the shortest supply relative to the plant's needs. This means that increasing the supply of other nutrients will not significantly increase growth until the limiting nutrient is also increased.

Question 34

Why is phosphorus limitation common in tropical forests with old soils?

Answer 34

Phosphorus limitation is common in tropical forests with old soils because weathering over geological time scales leaches phosphorus away or binds it in unavailable mineral forms. Younger soils often have higher levels of available phosphorus.

Question 35

Describe the Redfield ratio and its significance in marine ecosystems.

Answer 35

The Redfield ratio is an N:P ratio by moles of approximately 15:1, often observed in both dissolved nutrient concentrations in ocean water and in phytoplankton biomass. It suggests a stoichiometric balance between nitrogen and phosphorus requirements for phytoplankton growth in much of the world's oceans.

Question 36

Why is nitrogen fixation by planktonic cyanobacteria uncommon in most estuaries?

Answer 36

Nitrogen fixation by planktonic cyanobacteria is uncommon in most estuaries due to an interaction between a physiological constraint and zooplankton grazing. High sulfate concentrations in seawater interfere with molybdenum uptake, which is essential for nitrogen fixation, slowing cyanobacterial growth and making them vulnerable to grazing.

Question 37

What is the main source of iron limitation in some ocean regions?

Answer 37

Iron limitation in some ocean regions, such as the Southern Ocean and equatorial Pacific, occurs despite abundant nitrogen and phosphorus. This is because iron is required for photosynthesis, and its supply to these surface waters from atmospheric deposition or deep ocean mixing is low.

Question 38

How does the consumption efficiency (CE) of herbivores differ between forests and phytoplankton communities?

Answer 38

The consumption efficiency (CE) of herbivores is typically much lower in forests (estimated at 5%) compared to phytoplankton communities (estimated at 50%). This is because only a fraction of the total plant biomass in a forest is consumed by herbivores, while phytoplankton are much more readily grazed.

Question 39

What is mineralization in the context of decomposition?

Answer 39

Mineralization is the conversion of elements from organic forms (contained within dead organisms or detritus) back into inorganic forms that can be assimilated by primary producers. This process is carried out by decomposers like bacteria and fungi.

Question 40

Explain how vegetation influences nutrient retention in terrestrial ecosystems.

Answer 40

Vegetation influences nutrient retention through two main mechanisms: transpiration and uptake. Transpiration draws water and dissolved nutrients up from the soil, keeping them within the ecosystem. Plants also directly assimilate nutrients into their biomass, preventing them from being lost through leaching or erosion.