Week 8: Flux of Energy & Matter

Question 1

Standing crop

Answer 1

The bodies of the living organisms within a unit area constitute a standing crop of
biomass.

Question 2

Biomass

Answer 2

The mass of organisms per unit area of ground (or water), usually expressed
in units of energy (such as joules per square meter),
dry organic matter (grams per square meter), or mass of carbon (grams of carbon per square meter).

Question 3

Primary productivity

Answer 3

The rate at which biomass is produced per unit area or volume through photosynthesis. Like biomass, it can be expressed in many different units, including energy (such as joules per square meter per day, or per year), dry organic matter (grams per square meter per day), or mass of carbon (grams carbon per square meter per day). Ecologists consider both gross primary pro- ductivity and net primary productivity.

Question 4

Gross primary productivity

Answer 4

The total fixation of energy by photosynthesis. A proportion of this, however, is respired away by the primary producer organisms (the autotrophs) themselves and is lost from the ecosystem as respiratory heat (R_auto)

Question 5

Respiratory heat (R_auto)

Answer 5

The production portion of carbon dioxide in an ecosystem’s carbon flux, while photosynthesis typically accounts for the majority of the ecosystem’s carbon consumption.

Question 6

Net Primary Productivity

Answer 6

This is the difference between GPP and R_auto. It represents the actual rate of production of new biomass that is available for consumption by heterotrophic organisms (bacteria, fungi, and animals).

Question 7

Secondary productivity

Answer 7

The rate of production of biomass by heterotrophs.

Question 8

Net ecosystem productivity

Answer 8

Net ecosystem
productivity is the difference between GPP and the respiration of all organisms in an ecosystem (R auto)- It measures the net rate of accumulation or loss of
organic matter, energy, or organic carbon from the ecosystem and is equivalent to the rate of NPP minus the respiration of all heterotrophic organisms (R het).

Question 9

Live consumer system

Answer 9

A proportion of primary
production is consumed by herbivores, which, in turn, are consumed by carnivores.

Question 10

Decomposer system

Answer 10

The fraction of NPP that is not eaten by herbivores

Question 11

Decomposer

Answer 11

Fungi, bacteria, invertebrates such as worms and insects have the ability to break down dead organisms into smaller particles and create new compounds.

Question 12

Detritivore

Answer 12

Nnimals that consume dead matter

Question 13

Colimitation

Answer 13

In some ecosystems, both nitrogen and phosphorus are limiting to production.

Question 14

Eutrophication

Answer 14

The process of excess nutrient enrichment.

Question 15

Positive feedback

Answer 15

Occurs to increase the change or output.

Question 16

Transfer efficiencies

Answer 16

The proportions of net primary production flowing along
each of the possible energy pathways.

Question 17

Consumption efficiency (CE)

Answer 17

The percentage of total productivity available at one trophic level that is consumed (‘ingested’) by the trophic level above. For primary consumers, CE is the percentage of joules (or organic carbon, which is the source of the potential energy) produced per unit time and area as NPP that finds its way into the guts of herbivores. In the case of secondary consumers, it is the percentage of herbivore productivity eaten by carnivores. The remainder dies without being eaten and enters the decomposer system. Reasonable average values for CE by herbivores are approximately 5% in forests, 25% in grasslands, and 50% in phytoplankton-dominated communities. For carnivores, CE varies from 25% to almost 100%.

Question 18

Production efficiency (PE)

Answer 18

The percentage of assimilated energy incorporated into new biomass; the remainder is entirely lost to the community as respira- tory heat. PE varies according to the taxonomic class of the organisms concerned. Invertebrates in general have high efficiencies (30-50%), losing relatively lit- tle energy in respiratory heat. Among the vertebrates, ectotherms (whose body temperature varies accord- ing to environmental temperature; see Chapter 3) have intermediate values for PE (around 10%), while endotherms, which expend considerable energy to maintain a constant temperature, convert only 1% to 5% of assimilated energy at most into production. Microorganisms, including protozoa, tend to have very high PEs, 50% or greater.

Question 19

Trophic transfer efficiency

Answer 19

One trophic level to the next is simply CE x AE x PE. This represents the percentage of energy (or organic matter)
at one trophic level that is transferred to the next.

Question 20

Assimilation efficiency (AE)

Answer 20

The percentage of food energy taken into the guts of consumers in a tro- phic level that is assimilated across the gut wall and becomes available for incorporation into growth or to do work. The remainder is lost as feces and enters the decomposer system. It is harder for us to ascribe an assimilation efficiency to microorganisms, in which food does not pass through a gut and feces are not pro- duced. Bacteria and fungi digest dead organic matter externally and, between them, typically absorb almost all the product: they are often said to have AEs of 100%. AEs are typically low for terrestrial herbivores, detritivores, and microbivores (20-50%), somewhat higher for aquatic herbivores, and high for carnivores (around 80% and sometimes higher). The way plants allocate production to roots, wood, leaves, seeds, and fruits also influences their usefulness to herbivores. Seeds and fruits may be assimilated with efficiencies as high as 60-70% and leaves with about 50% efficiency, while the AE for wood may be as low as 15%.

Question 21

Immobilization

Answer 21

Occurs when
an inorganic element is incorporated into organic form, often during primary production, for example, when carbon dioxide becomes incorporated into a plant’s carbohydrates.

Question 22

Mineralization

Answer 22

Chemical nutrients—the conversion of elements from organic back to an inorganic form.

Question 23

Decomposition

Answer 23

The gradual disintegration of dead organic matter (dead bodies, shed parts of bodies, feces) and is brought about by both physical and biological agencies.

Question 24

Microbivore

Answer 24

A group of animals that
operate alongside the detritivores and can be difficult to distinguish from them.

Question 25

Shredder

Answer 25

Detritivores that feed on coarse particulate
organic matter, such as tree leaves fallen into a river; these animals fragment the material into finer particles.

Question 26

Collecter-filterer

Answer 26

Such as larvae of blackflies in rivers, consume the fine particulate organic matter that otherwise would be carried downstream.

Question 27

Cellulase

Answer 27

Enzymes that break down the cellulose found in plant cell walls into simple sugars that can serve as the raw materials for biofuels, as well as many of the biobased chemicals, plastics, and other materials

Question 28

Nitrogen cycle

Answer 28

The continuing transformation of nitrogen including assimilation into biomass and mineralization back to ammonium.

Question 29

Nitrogen fixation

Answer 29

Any natural or industrial process that causes free nitrogen

Question 30

(De)Nitrification

Answer 30

Denitrification occurs in environments largely devoid of oxygen and is a type of respiration in which the bacteria use nitrate instead of oxygen as an electron acceptor.

Question 31

Closed system

Answer 31

Ecosystems that do not rely on matter exchange with any part outside the system.

Question 32

Open system

Answer 32

One in which energy can be transferred between the system and its surroundings.

Question 33

Weathering

Answer 33

The breaking down or dissolving of rocks and minerals on the surface of the Earth

Question 34

Deposistion

Answer 34

The net flux of materials from the atmosphere to the ecosystem.