Lecture 17 + 18

Question 1

Which of the following are variables that determine the relative importance of energy pathways? (you may select one or more answers)
- consumption efficiencies
- production efficiencies
- stimulation efficiencies
- assimilation efficiencies

Answer 1

consumption efficiencies
production efficiencies
assimilation efficiencies

Question 2

All the primary producer biomass produced is not consumed alive by herbivores. That which dies supports a community of _________?

Answer 2

Decomposers

Question 3

True or false: during the process of mineralization chemicals are converted from an organic form to an inorganic form.

Answer 3

True

Question 4

Aquatic trophic level transfer efficiencies are on average…

Answer 4

10%

Question 5

DOM

Answer 5

Dead organic matter

Question 6

Grazer food chains

Answer 6

NPP consumed by herbivores

Question 7

Two major ways to think about food webs

Answer 7

• relation to community structure
• energy flow

Question 8

Efficiency

Answer 8

No process in nature occurs with 100% efficiencies
- always a loss of useful energy when energy is transferred (i.e., when food is eaten)
- 10% rule

Question 9

Trophic efficiencies in 48 phytoplankton-based ecosystems

Answer 9

High productivity ecosystems (including productive lakes, with upwelling ecosystems as an example)

Question 10

Aquatic ecosystems with high nutrients select for

Answer 10

Large phytoplankton
- low surface to volume ratio (less need for enzymes to take up nutrients)
- short food chains (efficient, so high production of fish per unit of primary production)
ex. 800 -> 80 -> 8 -> 0.8

Question 11

Upwelling systems comprise

Answer 11

5% of the world’s oceans, and produce 25% of total ocean fish catch

Question 12

Small phytoplankton have

Answer 12

high surface to volume ratio (lots of sites for enzymes to take up nutrients relative to mass of chlorophyll)
- long food chains (inefficient, so less production of top predator fish per unit of primary production
ex. 50 -> 5- > 0.5 -> 0.05 -> 0.005 -> 0.0005 (compared to 0.8 for yellowfin tuna in upwelling ecosystem)

Question 13

Food chain magnification

Answer 13

Fish do not produce fatty acids, but rather bioconcentrate them from their foods
- wild caught fish are rich in omega-3 fatty acids (produced by algae -> healthy for humans!)
- farm-raised fish fed just on corn and soybean are high in omega-6 fatty acids (unhealthy for humans!)

Question 14

Trophic transfer efficiency chart; production at one trophic level

Answer 14

1. consumption efficiency (waste: not consumed)
2. assimilation efficiency (waste: excreted)
3. production efficiency (waste: respired)
   -> production at next trophic level
   trophic transfer efficiency covers the entire thing

Question 15

ex. component efficiencies behind the trophic transfer 10% efficiency for aquatic ecosystems

Answer 15

phytoplankton to zooplankton
net primary production
CE: 55%
AE: 50%
PE: 40%
herbivore production

trophic transfer efficiency = CE * AE * PE = 11%

Question 16

ex. zooplankton to fish

Answer 16

CE: 100% (no consumption waste)
AE: 80%
PE: 10%
CE * AE * PE = 8%

Question 17

Which of the following best characterizes the production efficiency for fish?
a) Fish have more advanced physiological adaptations, which allow them to use their food more efficiently, with a production efficiency of 60% or greater.
b) Fish spend more energy than zooplankton in searching for their food, which gives them a somewhat lower production efficiency (25% rather than 40% for zooplankton)
c) Fish spend more energy than zooplankton in searching for their food, which gives them a far lower production efficiency (10% rather than 40% for zooplankton)
d) Because of the high quality of their food, fish have a very high productive efficiency (90%)
e) Most aquatic animals have similar production efficiencies = 40%

Answer 17

c) Fish spend more energy than zooplankton in searching for their food, which gives them a far lower production efficiency (10% rather than 40% for zooplankton)

Question 18

Consumption efficiencies for herbivores
plankton systems = 50%
grasslands = ?
forests = ?

Which of the following best characterizes the consumption efficiencies in terrestrial ecosystems?
a) As with aquatic ecosystems, consumption efficiencies are in the range of 50%
b) Efficiencies in terrestrial ecosystems tend to be higher than in aquatic ecosystems (less “messy eating”)
c) Efficiencies are higher in grasslands than in aquatic ecosystems (think of zebras and buffalo) but much lower in forests (few grazers)
d) Consumption efficiencies in all terrestrial ecosystems are quite low (lot of defecation)
e) Consumption efficiencies are 50% for aquatic ecosystems, only half of this amount in grasslands, and lower yet in forests.

Answer 18

e) Consumption efficiencies are 50% for aquatic ecosystems, only half of this amount in grasslands, and lower yet in forests.

plankton systems = 50%
grasslands = 25%
forests = 5%

Question 19

ex. grass to zebra (savannah ecosystem)

Answer 19

CE: 25%
AE: 20%
PE: 3%
-> zooplankton and fish are 40% and 10%
trophic transfer efficiency = 0.15%

Question 20

Food quality (C/N moles)
Tree trunks and roots: 600 (200 -1,000)
Tree leaves: 35 (25 – 50)
Grasses: 35 (25 – 50)
Algae: 7 (5 – 10)
Animals: 7 (6 – 8)

Answer 20

• high C means hard to digest structure
• high N (low C/N) means protein

Question 21

Which of the following best characterizes the production efficiency for zebras?
a) Zebras and other warm-blooded animals use a lot of energy for thermoregulation, giving them a very low production efficiency (~ 3%)
b) Because of thermoregulation, warm-blooded animals such as zebra can use their food very effectively (efficiency production = 75%)
c) Zebras are slow moving and do not need to search for food (grasses), which gives them a very high efficiency production (75%)
d) All vertebrates (fish, zebras, whales, lions, etc.) have production efficiencies near 10%
e) Production efficiencies for zebras vary seasonally, and are ~ 40% during the wet season when they have plenty of water but fall to 10% in the dry season, as zebras expend more energy searching for and retaining water.

Answer 21

a) Zebras and other warm-blooded animals use a lot of energy for thermoregulation, giving them a very low production efficiency (~ 3%)

Question 22

Production efficiencies for herbivores: invertebrates, warm-blooded animals, and cold-blooded animals

Answer 22

invertebrates = 30-50%
warm-blooded animals = 1-5%
cold-blooded vertebrates = 10%

Question 23

ex. zebras to cheetahs

Answer 23

CE: 60%
AE: 80%
PE: 3%
Trophic transfer efficiency: CE * AE * PE = 1.5%

Question 24

Trophic energy transfer efficiencies vary from far less than 1% to 20% or so

Answer 24

In aquatic ecosystems, the average is indeed approximately 10%, on average
- generally far lower in terrestrial ecosystems, usually less than 2%, and often far less

Question 25

Two critical points

Answer 25

1. primary producers in aquatic systems have better food quality (more protein, less hard to digest structural material) 2. warm blooded animals are inefficient, and invertebrates are the most efficient

Question 26

Primary production general ranking

Answer 26

wetlands algal bed & reef tropical forest estuaries

Question 27

We can think about primary production in terms of nitrogen (protein)

Answer 27

g C m-2 yr-1 | g N m-2 yr-1 Tropical forest: 810, 10 Temperate grassland: 250, 5 Subtropical ocean gyres: 50, 7 Estuaries: 800, 115

Question 28

What is the fate of NPP not consumed by herbivores?

Answer 28

Non-living organic material - obvious particles (dead leaves, feces, etc.) - dissolved substances in water and soil solution - very fine organic materials distributed in soils and sediments

Question 29

Microorganisms (bacteria, fungi, archaea) play a major role in decomposing organic matter

Answer 29

Animals can be important, partly by breaking up large particles into smaller pieces more easily attacked by microorganisms (shredding leaves, eating woods, etc.) Animals can also be important by feeding on the microorganisms, which can further stimulate growth of the microorganisms and decomposition of the organic matter.

Question 30

Decomposers (bacteria & fungi) often have efficiencies of 40-50%

Answer 30

Not investing any energy in temperature control, or searching for food - although may produce a lot of enzymes released to the environment to help get food

Question 31

Decomposers (bacteria & fungi):

Answer 31

dead leaves or wood -50%> decomposers -20%> detritivore

Question 32

As organic matter is decomposed, carbon is respired and released to atmosphere as CO2

Answer 32

The nitrogen and phosphorus (and potassium, calcium, iron, etc.) in the organic matter is released to the environment. - this "mineralization" is essential in supplying nutrients for net primary production

Question 33

True or false: In line with the second law of thermodynamics some energy is always lost as heat when being transferred from one form to another.

Answer 33

True

Question 34

True or false: Trophic transfer efficiencies tend to be ~10% in aquatic and terrestrial system.

Answer 34

False: trophic energy transfer efficiencies vary from far less than 1% to 20% or so - in aquatic ecosystems, the average is indeed approximately 10%, on average - generally far lower in terrestrial ecosystems, usually less than 2%, and often far less

Question 35

In which of these aquatic biomes should we expect to find the longest food chains: - Continental shelf waters - Eutrophic lakes - Productive estuaries - Subtropical gyres - Upwelling regions

Answer 35

Subtropical gyres - large phytoplankton, low SA:V ratio, shorter food chains, more efficient - small phytoplankton have high SA:V ratio, long food chains, inefficient

Question 36

Consumption efficiency of an organism is 0.25, assimilation efficiency 0.25, production efficiency 0.45, and ratio equaled 0.01. Which of these terms would you use to calculate the trophic transfer efficiency of this organism? (you may select one or more answers) - consumption efficiency - ratio - assimilation efficiency - production efficiency

Answer 36

consumption efficiency assimilation efficiency production efficiency

Question 37

If consumption efficiency of an organism was 25%, assimilation efficiency 25% and production efficiency 45% what would the trophic transfer efficiency of this organism be?

Answer 37

2.8%

Question 38

In which of the following systems do we expect biomagnification of a toxic compound to be the biggest problem for a top predator? - A system with 1 trophic level - A system with 2 trophic levels - A system with 3 trophic levels - A system with 4 trophic levels - A system with 5 trophic levels

Answer 38

A system with 5 trophic levels - this principle can also be applied to positive compounds like fatty acids - food-chain magnification

Question 39

For each of the following pairs of items select the one that would be associated with higher trophic transfer efficiency (select 5 answers one per pair). 1. ectotherm 1. endotherm 2. an organism eats bark 2. an organism eats leaves 3. a grassland in which 20% of the grass is grazed 3. a grassland in which 30% of the grass is grazed 4. an animal has feces that supports numerous decomposers 4. an animal has feces that supports few decomposers 5. a system with a short food chain 5. a system with a long food chain

Answer 39

1. ectotherms have lower rates of respiration (higher PE) 2. leaves are more calorie rich (higher AE) 3. more consumption = higher CE 4. if a great deal of energy is excreted in feces, such that it can support many decomposers, it means there was lower AE 5. longer food chains have more trophic transfers and so more energy is lost

Question 40

Which 3 organisms would most likely be early colonists of newly dead material? - bacteria - fungi - grazers - archaea

Answer 40

- bacteria - fungi - archaea

Question 41

__________ occurs when an inorganic element is incorporated into an organic form.

Answer 41

Immobilization

Question 42

_____________ occurs when elements are converted from organic form back to an inorganic form.

Answer 42

Mineralization

Question 43

______________ is a process whereby dead bodies, shed parts of bodies, or feces gradually disintegrate.

Answer 43

Decomposition

Question 44

Energy flows through the food chain

Answer 44

energy that is respired is dissipated to the environment - it is gone, in terms of useful energy energy flow in the food web is carried as the embodied energy in organic matter (we think of this as "food") as the matter is respired, organic C becomes CO2 - the CO2 can be used again in primary production ENERGY FLOWS, MATTER CYCLES

Question 45

ENERGY FLOWS, MATTER CYCLES

Answer 45

as organic matter is respired, all elements in organic matter are released as inorganic forms - not just CO2, but inorganic N, P, K, S, Ca, etc. And these too can be used again in primary production

Question 46

As this dead organic matter is decomposed by microbes, the organic carbon is respired away as carbon dioxide

Answer 46

And organic nitrogen becomes inorganic nitrogen, organic phosphorus becomes inorganic phosphorus, organic potassium becomes inorganic potassium, etc. -> "mineralization"

Question 47

Excretion of feces also is

Answer 47

organic matter, which is decomposed by microbes (after assimilation efficiency)

Question 48

When studying element cycles, ecologists often focus on nitrogen and phosphorus. Why?

Answer 48

Elements most likely to be limiting to net primary productivity.

Question 49

External inputs

Answer 49

Deposition of dust from the atmosphere, inputs from upstream waters, mixing from deep ocean waters, plus N fixation)

Question 50

Exports

Answer 50

In waters flowing downstream, sinking out of surface ocean etc., plus loss of N gases

Question 51

The phosphorus cycle

Answer 51

dissolved inorganic phosphate -> organic P in plants and algae (uptake by primary producers) -> organic P in animals and microbes (mineralization) -> dissolved inorganic phosphate <- (weathering) <--> inorganic phosphate absorbed to soils and sediments

Question 52

A "geologic" cycle

Answer 52

no gas phase transfers; phosphorus stays in same oxidation-reduction state

Question 53

New inputs (terrestrial systems): weathering can be important

Answer 53

- Rock-derived nutrients are supplied by weathering, or the physical and chemical breakdown of rock minerals - Dominant input route for: P, Mg, Ca - Rate of nutrient input depends on: -> composition of initial parent material (limestone? shale? granite?) -> extent of past weathering (intensity, duration)

Question 54

Supplies of P decrease over geological time

Answer 54

and are low in old, highly weathered soils

Question 55

Dust storms in the Sahel Desert can place considerable phosphorus into the atmosphere

Answer 55

with some of this reaching as far as the Amazon rainforest over 5,000 km away

Question 56

In most ecosystems, the rate of recycling through

Answer 56

mineralization far exceeds weathering and rates of external inputs

Question 57

In many types of ecosystems, most of the demand for nutrients for primary production is suppled by

Answer 57

recycling (not new inputs)

Question 58

Nitrification

Answer 58

NH4+ -> NO3- results in N2O, NO, NO2

Question 59

Denitrification

Answer 59

NO3- -> N2 results in N2O, NO, NO2

Question 60

Bacterial N fixation

Answer 60

N2 -> organic N in plants and algae

Question 61

The nitrogen cycle

Answer 61

NO3- -> N2, NO3-, NH4+ -> organic N in plants and algae -> organic N in animals and microbes -> NH4+

Question 62

The nitrogen cycle has much more biology involved than for the phosphorus cycle

Answer 62

Many complicated bacterial process (hugely simplified here); gas fluxes important; weathering less important

Question 63

Denitrification only occurs in absence of oxygen, when bacteria switch to use nitrate instead in their respiration

Answer 63

Globally important for removing biologically available nitrogen NO3- -> N2 results in N2O, NO, NO2

Question 64

Internal recycling of nitrogen always greater than

Answer 64

the rate of N fixation (and usually greater than other external inputs)

Question 65

Although N fixation is always small relatively to the rate of N recycling in any ecosystem

Answer 65

N fixation is important for providing some new N, to balance supply of P to primary producers Bacterial N fixation N2 -> organic N in plants and algae

Question 66

Lake 227, experimental lakes area

Answer 66

- phosphorus added at same rate in all years - planktonic, N-fixing cyanobacteria were virtually absent in 1972-1974 but dominated the plankton in the summer of 1975

Question 67

Internal recycling of nitrogen always

Answer 67

greater than the rate of N fixation

Question 68

Also, nitrogen fixation absolutely critical at global scale in replenishing nitrogen lost through denitrification.

Answer 68

Without nitrogen fixation, there would be no life on Earth.

Question 69

Case study: How should we manage nutrients to reduce eutrophication in Chesapeake Bay? A coastal marine ecosystem, very sensitive to excess nutrient inputs, which lead to eutrophication (excessive net primary production). Nitrogen limited ecosystem

Answer 69

Chesapeake Bay watershed - Keep in mind: most of the nutrient inputs to the Bay come from agriculture and atmospheric deposition of nutrients onto the landscape, with subsequent runoff to rivers and then the Bay (sewage inputs are small). - Export of P downstream largely by erosion of particle-bound P (since P is so easily absorbed..."sticky") - Export of N downstream largely as nitrate dissolved in water (nitrate much less absorbed on soils than is inorganic phosphate; nitrate can flow in groundwater)

Question 70

Effectiveness of management practices for reducing N and P:

Answer 70

Phosphorus | Nitrogen No-till agriculture: very effective, not effective Winter cover crops: effective, very effective Perennial cropping systems: effective, very effective Buffer strips along streams: effective, variable

Question 71

From 1985 to 2010, environmental management for eutrophication of Chesapeake Bay used the P-control strategies that had worked so successfully for lake eutrophication since the early 1970s.

Answer 71

Lack of recognition that the problem was from nitrogen, or that management practices develop for phosphorus may not work for nitrogen.

Question 72

Chesapeake Bay – what has happened?

Answer 72

- water quality degraded through 1970s and 80s - agreement in 1985 for 40% reduction in N by 2000 and again by 2010 - little or no measurable improvement in water quality by 2010 - management practices were not effective (for nitrogen) - more improvement since 2010, due to less nitrogen deposition (Clean Air Act) and use of winter cover crops

Question 73

How does disturbance affect nutrient cycles and nutrient retention by ecosystems: a forest example

Answer 73

Whole ecosystem experiment at Hubbard Brook (NH) - watershed #2 clearcut in 1965 - watershed #6 left as undisturbed control -> export of nutrients in streams measured at weirs in subsequent years

Question 74

How does clear cutting influence the amount of nutrients leaving the system? - the amount of nutrients leaving the system will decrease - there will be no change in the amount of nutrients leaving the system - the amount of nutrients leaving the system will increase

Answer 74

The amount of nutrients leaving the system will increase

Question 75

Before the trees were cut down, the loss of biologically important materials such as calcium, potassium, and nitrate was small in both the experimental watershed and a reference one.

Answer 75

After the cut, the export of materials increased dramatically in the experimental watershed - paired catchments (small watersheds), which had similar exports in streams before the cutting

Question 76

Uptake by plants stops, but mineralization continues, so inorganic N

Answer 76

builds up as nitrate is exported in the stream NO3- -> organic N in plants and algae stopped

Question 77

In many types of ecosystems, most of the demand for nutrients for primary production is

Answer 77

supplied by recycling (not new inputs)

Question 78

Closed ecosystem

Answer 78

ex. subtropical gyre - input to ecosystem of 0.5mg nitrogen per square metre per day - uptake by primary producers of 30mg nitrogen per square metre per day -> input to ecosystem of 90mg nitrogen per square metre per day -> open ecosystem

Question 79

Open ecosystem

Answer 79

ex. salt marsh - uptake by primary producers of 80mg nitrogen per square metre per day

Question 80

Is recycling more prominent in open or closed systems?

Answer 80

Closed systems

Question 81

Liebig's law of the minimum

Answer 81

Open ecosystems because they're being fertilized - external nutrients is high, developed in the context of agriculture (very open ecosystems)

Question 82

A more nuanced view of nutrient limitation in ecosystems such as the subtropical gyres, which are relatively CLOSED (recycling particularly important)

Answer 82

Nitrogen and phosphorus co-limiting (or nearly so) - biology acts over geological time scales to accommodate the nutrient cycles - contrast with most coastal marine ecosystems, which are far more OPEN, with large external inputs of nutrients, making limitation by one particular nutrient (N) more likely

Question 83

Why does energy flow and matter cycle?

Answer 83

Energy is lost as heat and matter is not created or destroyed

Question 84

The main original source of nutrients such as calcium, iron, magnesium, phosphorous, and potassium in many terrestrial ecosystems is _______.

Answer 84

The weathering of parent bedrock and soil

Question 85

The most substantial pathway of loss of elements in an ecosystem is through streamflow. A system such as a stream moves phosphorous and iron mostly attached to particles, while nitrogen is mostly dissolved. Thus, a stream carries the load of nutrients _______________.

Answer 85

As both dissolved and particulate

Question 86

You conduct an experiment where you add nitrogen to 5 plots that are at the top of 5 hills. At the bottom of each of these hills you measure the output of nitrogen from the system after year. All the plots are the same except for the noted detail. In which of these plots would you expect to find the greatest nitrogen output? - A plot that was clear-cut 3 years ago - A plot that was burned 5 year ago - A plot that is bedrock - A plot that is at a climax community - A plot that has a very high density of trees - A plot that has a very low density of trees

Answer 86

The plot that is bedrock would not hold the nitrogen, it would just wash away out of the system.

Question 87

N2O, NO, NO2

Answer 87

other nitrogen gasses

Question 88

N2

Answer 88

Nitrogen gas (dinitrogen)

Question 89

NO3

Answer 89

Nitrate

Question 90

NH4

Answer 90

Ammonium

Question 91

Nitrification

Answer 91

Bacteria convert ammonium to nitrate

Question 92

Denitrification

Answer 92

Bacteria convert nitrate to inorganic N2

Question 93

N Fixation

Answer 93

Bacteria convert N2 into organic N

Question 94

Mineralization

Answer 94

General term for converting organic matter into inorganic matter

Question 95

Which of the following 2 world views concerning ecosystems is likely to give you a more complete understanding of nutrient limitation? - Liebig - Redfield

Answer 95

Redfield built on the work of Liebig. Not only do his views account for nutrient limitation but it accounts for nutrient limitation with respect to the needs of organisms.