Lecture: Chapter 21 - Ecosystem Energetics

Question 1

Ecosystem

Answer 1

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

Question 2

Where does energy in ecosystems originate?

Answer 2

Energy in ecosystems originate with primary production by autotrophs

Question 3

Primary production

Answer 3

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

Question 4

Primary productivity

Answer 4

Rate of primary production. The rate at which organic matter is created by photosynthesis

Question 5

Describe the process from sunlight to herbivore

Answer 5

Solar radiation -> photosynthesis [release of energy not used in photosynthesis] -> green plant -> energy transfer [release of energy lost in respiration and as heat] -> herbivore

Question 6

Gross primary production (GPP)

Answer 6

total amount of carbon fixed by autotrophs.

GPP depends on photosynthetic rate

Question 7

Net Primary Production (NPP)

Answer 7

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)

Question 8

Standing Crop biomass

Answer 8

Amount of organic matter in an area at a given time. The accumulation of NPP over time

Question 9

Trade off between root and shoot allocation

Answer 9

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

Question 10

Primary Production

Answer 10

Plants can respond to environmetnal conditions by allocation carbon to the sgrowth o fdifferent tissues

Question 11

Net primary productivity is constrained by both physical and biotic environmental factors

Answer 11

NPP varies substantially over space and time. Much of the varaition is correlated with climate.

Question 12

What limits net primary production?

Answer 12

Factors related to leaf biomass

Factors relating to photosynthetic rate

• water availability
• light temperature

Factors relating to ability to accumulate biomass

Question 13

Leaf area index

Answer 13

The total one-sided area of leaf tissue per unit ground surface area

Measure of light use efficiency

Varies among biomes and with season

Question 14

Leibig’s Law of the minimum

Answer 14

Growth is controlled by the scarcest recourse (limiting factor)

Many experiments indicate that nutrients, particularly nitrogen, control NPP in terrestrial ecosystems

Question 15

Freshwater systems: NPP

Answer 15

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

Question 16

Terrestrial systems: NPP

Answer 16

Short term nutrient addition experiments suggest N limitation in Tundra and Wetland ecosystems

Question 17

Marine systems: NPP

Answer 17

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

Question 18

Nitrogen in marine systems

Answer 18

N is more often limited in marine systems than in others

Question 19

Biological uses of Fe

Answer 19

Energy acquisition

• Respiration
• Photosynthetic enzymes

Nitrogen cycle

• Nitrate assimilation
• Nitrogen fixation

Question 20

Fe as a nutrient

Answer 20

General facts

• needed in trace amounts
• most abundant elemetnt in crust

Three sources

• Upwelling
• Dust
• Ships

Question 21

NPP: estuaries

Answer 21

are usuall nutrient-rich; variation in NPP is correlated with nitrogen inputs from rivers

Question 22

NPP: ocean

Answer 22

In the open ocean, NPP is mainly from phytoplankton, limited by nitrogen.

Question 23

NPP: equatorial Pacific Ocean

Answer 23

But NPP in the equatorial Pacific Ocean appears to be limited by iron

Question 24

Secondary Production

Answer 24

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

Question 25

Secondary Production: Heterotrophs

Answer 25

• Herbivores eat plants and algae
• Carnivores eat other live animals
• Detrivores eat dead organic matter (detrius)
• Omnivores eat both plants and animals

Question 26

Bottom-up control

Answer 26

Primary productivity is a constraint on secondary productivity within an ecosystem

Question 27

Assimilation efficiency (A/I)

Answer 27

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

Question 28

Production efficiency (P/A)

Answer 28

proportion of assimilated food that goes into new consumer biomass/secondary production

Question 29

Surface area to volume ration

Answer 29

As body size increases, the surface area-to-volume ratio decreases for same-shaped objects.

Question 30

What does energy transfer on a trophic level dependent upon?

Answer 30

The amount of energy transferred from one trophic level to the next depends on food quality and consumer abundance and physiology

Question 31

Trophic pyramid

Answer 31

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

Question 32

Trophic efficiency

Answer 32

Amount of energy at one trophic level divided by the amount of energy at the trophic level immediately below it

Question 33

Energy flow among trophic levels

Answer 33

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

Question 34

Grazing

Answer 34

relatively large animals feed on leaves, fruits, seeds

primary producers [plant]-> herbivore [mouse]-> carnivore [snake]

Question 35

Detrital

Answer 35

Microorganisms and small animals consume dead remains of plants and indigestible excretes of herbivores