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Ecology and the Environment > Lecture 17 + 18 > Flashcards

Lecture 17 + 18 Flashcards

1
Q

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

A

consumption efficiencies
production efficiencies
assimilation efficiencies

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2
Q

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

A

Decomposers

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3
Q

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

A

True

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4
Q

Aquatic trophic level transfer efficiencies are on average…

A

10%

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5
Q

DOM

A

Dead organic matter

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6
Q

Grazer food chains

A

NPP consumed by herbivores

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7
Q

Two major ways to think about food webs

A
  • relation to community structure
  • energy flow
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8
Q

Efficiency

A

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

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9
Q

Trophic efficiencies in 48 phytoplankton-based ecosystems

A

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

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10
Q

Aquatic ecosystems with high nutrients select for

A

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

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11
Q

Upwelling systems comprise

A

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

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12
Q

Small phytoplankton have

A

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)

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13
Q

Food chain magnification

A

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!)

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14
Q

Trophic transfer efficiency chart; production at one trophic level

A
  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
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15
Q

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

A

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

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

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16
Q

ex. zooplankton to fish

A

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

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17
Q

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%

A

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)

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18
Q

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.

A

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%

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19
Q

ex. grass to zebra (savannah ecosystem)

A

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

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20
Q

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)

A
  • high C means hard to digest structure
  • high N (low C/N) means protein
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21
Q

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.

A

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

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22
Q

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

A

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

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23
Q

ex. zebras to cheetahs

A

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

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24
Q

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

A

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

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25
Q

Two critical points

A
  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
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26
Q

Primary production general ranking

A

wetlands
algal bed & reef
tropical forest
estuaries

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27
Q

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

A

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

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28
Q

What is the fate of NPP not consumed by herbivores?

A

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

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29
Q

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

A

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.

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30
Q

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

A

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

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31
Q

Decomposers (bacteria & fungi):

A

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

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32
Q

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

A

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

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33
Q

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.

A

True

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34
Q

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

A

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

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35
Q

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

A

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

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36
Q

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

A

consumption efficiency
assimilation efficiency
production efficiency

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37
Q

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?

A

2.8%

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38
Q

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

A

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

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39
Q

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

A
  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
40
Q

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

A
  • bacteria
  • fungi
  • archaea
41
Q

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

A

Immobilization

42
Q

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

A

Mineralization

43
Q

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

A

Decomposition

44
Q

Energy flows through the food chain

A

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

45
Q

ENERGY FLOWS, MATTER CYCLES

A

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

46
Q

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

A

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

47
Q

Excretion of feces also is

A

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

48
Q

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

A

Elements most likely to be limiting to net primary productivity.

49
Q

External inputs

A

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

50
Q

Exports

A

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

51
Q

The phosphorus cycle

A

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

52
Q

A “geologic” cycle

A

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

53
Q

New inputs (terrestrial systems): weathering can be important

A
  • 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)
54
Q

Supplies of P decrease over geological time

A

and are low in old, highly weathered soils

55
Q

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

A

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

56
Q

In most ecosystems, the rate of recycling through

A

mineralization far exceeds weathering and rates of external inputs

57
Q

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

A

recycling (not new inputs)

58
Q

Nitrification

A

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

59
Q

Denitrification

A

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

60
Q

Bacterial N fixation

A

N2 -> organic N in plants and algae

61
Q

The nitrogen cycle

A

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

62
Q

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

A

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

63
Q

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

A

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

64
Q

Internal recycling of nitrogen always greater than

A

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

65
Q

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

A

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

66
Q

Lake 227, experimental lakes area

A
  • 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
67
Q

Internal recycling of nitrogen always

A

greater than the rate of N fixation

68
Q

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

A

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

69
Q

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

A

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)

70
Q

Effectiveness of management practices for reducing N and P:

A

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

71
Q

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.

A

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

72
Q

Chesapeake Bay –what has happened?

A
  • 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
73
Q

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

A

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

74
Q

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

A

The amount of nutrients leaving the system will increase

75
Q

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.

A

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

76
Q

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

A

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

77
Q

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

A

supplied by recycling (not new inputs)

78
Q

Closed ecosystem

A

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

79
Q

Open ecosystem

A

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

80
Q

Is recycling more prominent in open or closed systems?

A

Closed systems

81
Q

Liebig’s law of the minimum

A

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

82
Q

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

A

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

83
Q

Why does energy flow and matter cycle?

A

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

84
Q

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

A

The weathering of parent bedrock and soil

85
Q

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 _______________.

A

As both dissolved and particulate

86
Q

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

A

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

87
Q

N2O, NO, NO2

A

other nitrogen gasses

88
Q

N2

A

Nitrogen gas (dinitrogen)

89
Q

NO3

A

Nitrate

90
Q

NH4

A

Ammonium

91
Q

Nitrification

A

Bacteria convert ammonium to nitrate

92
Q

Denitrification

A

Bacteria convert nitrate to inorganic N2

93
Q

N Fixation

A

Bacteria convert N2 into organic N

94
Q

Mineralization

A

General term for converting organic matter into inorganic matter

95
Q

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

A

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.

Ecology and the Environment (13 decks)

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