Lecture 17 + 18 Flashcards
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
consumption efficiencies
production efficiencies
assimilation efficiencies
All the primary producer biomass produced is not consumed alive by herbivores. That which dies supports a community of _________?
Decomposers
True or false: during the process of mineralization chemicals are converted from an organic form to an inorganic form.
True
Aquatic trophic level transfer efficiencies are on average…
10%
DOM
Dead organic matter
Grazer food chains
NPP consumed by herbivores
Two major ways to think about food webs
- relation to community structure
- energy flow
Efficiency
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
Trophic efficiencies in 48 phytoplankton-based ecosystems
High productivity ecosystems (including productive lakes, with upwelling ecosystems as an example)
Aquatic ecosystems with high nutrients select for
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
Upwelling systems comprise
5% of the world’s oceans, and produce 25% of total ocean fish catch
Small phytoplankton have
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)
Food chain magnification
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!)
Trophic transfer efficiency chart; production at one trophic level
- consumption efficiency (waste: not consumed)
- assimilation efficiency (waste: excreted)
- production efficiency (waste: respired)
-> production at next trophic level
trophic transfer efficiency covers the entire thing
ex. component efficiencies behind the trophic transfer 10% efficiency for aquatic ecosystems
phytoplankton to zooplankton
net primary production
CE: 55%
AE: 50%
PE: 40%
herbivore production
trophic transfer efficiency = CE * AE * PE = 11%
ex. zooplankton to fish
CE: 100% (no consumption waste)
AE: 80%
PE: 10%
CE * AE * PE = 8%
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%
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)
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.
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%
ex. grass to zebra (savannah ecosystem)
CE: 25%
AE: 20%
PE: 3%
-> zooplankton and fish are 40% and 10%
trophic transfer efficiency = 0.15%
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)
- high C means hard to digest structure
- high N (low C/N) means protein
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) Zebras and other warm-blooded animals use a lot of energy for thermoregulation, giving them a very low production efficiency (~ 3%)
Production efficiencies for herbivores: invertebrates, warm-blooded animals, and cold-blooded animals
invertebrates = 30-50%
warm-blooded animals = 1-5%
cold-blooded vertebrates = 10%
ex. zebras to cheetahs
CE: 60%
AE: 80%
PE: 3%
Trophic transfer efficiency: CE * AE * PE = 1.5%
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
Two critical points
- primary producers in aquatic systems have better food quality (more protein, less hard to digest structural material)
- warm blooded animals are inefficient, and invertebrates are the most efficient
Primary production general ranking
wetlands
algal bed & reef
tropical forest
estuaries
We can think about primary production in terms of nitrogen (protein)
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
What is the fate of NPP not consumed by herbivores?
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
Microorganisms (bacteria, fungi, archaea) play a major role in decomposing organic matter
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.
Decomposers (bacteria & fungi) often have efficiencies of 40-50%
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
Decomposers (bacteria & fungi):
dead leaves or wood -50%> decomposers -20%> detritivore
As organic matter is decomposed, carbon is respired and released to atmosphere as CO2
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
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.
True
True or false: Trophic transfer efficiencies tend to be ~10% in aquatic and terrestrial system.
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
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
Subtropical gyres
- large phytoplankton, low SA:V ratio, shorter food chains, more efficient
- small phytoplankton have high SA:V ratio, long food chains, inefficient
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
consumption efficiency
assimilation efficiency
production efficiency
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?
2.8%
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 system with 5 trophic levels
- this principle can also be applied to positive compounds like fatty acids
- food-chain magnification
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
- ectotherms have lower rates of respiration (higher PE)
- leaves are more calorie rich (higher AE)
- more consumption = higher CE
- if a great deal of energy is excreted in feces, such that it can support many decomposers, it means there was lower AE
- longer food chains have more trophic transfers and so more energy is lost
Which 3 organisms would most likely be early colonists of newly dead material?
- bacteria
- fungi
- grazers
- archaea
- bacteria
- fungi
- archaea
__________ occurs when an inorganic element is incorporated into an organic form.
Immobilization
_____________ occurs when elements are converted from organic form back to an inorganic form.
Mineralization
______________ is a process whereby dead bodies, shed parts of bodies, or feces gradually disintegrate.
Decomposition
Energy flows through the food chain
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
ENERGY FLOWS, MATTER CYCLES
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
As this dead organic matter is decomposed by microbes, the organic carbon is respired away as carbon dioxide
And organic nitrogen becomes inorganic nitrogen, organic phosphorus becomes inorganic phosphorus, organic potassium becomes inorganic potassium, etc.
-> “mineralization”
Excretion of feces also is
organic matter, which is decomposed by microbes (after assimilation efficiency)
When studying element cycles, ecologists often focus on nitrogen and phosphorus. Why?
Elements most likely to be limiting to net primary productivity.
External inputs
Deposition of dust from the atmosphere, inputs from upstream waters, mixing from deep ocean waters, plus N fixation)
Exports
In waters flowing downstream, sinking out of surface ocean etc., plus loss of N gases
The phosphorus cycle
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
A “geologic” cycle
no gas phase transfers; phosphorus stays in same oxidation-reduction state
New inputs (terrestrial systems): weathering can be important
- 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)
Supplies of P decrease over geological time
and are low in old, highly weathered soils
Dust storms in the Sahel Desert can place considerable phosphorus into the atmosphere
with some of this reaching as far as the Amazon rainforest over 5,000 km away
In most ecosystems, the rate of recycling through
mineralization far exceeds weathering and rates of external inputs
In many types of ecosystems, most of the demand for nutrients for primary production is suppled by
recycling (not new inputs)
Nitrification
NH4+ -> NO3-
results in N2O, NO, NO2
Denitrification
NO3- -> N2
results in N2O, NO, NO2
Bacterial N fixation
N2 -> organic N in plants and algae
The nitrogen cycle
NO3- -> N2, NO3-, NH4+ -> organic N in plants and algae -> organic N in animals and microbes -> NH4+
The nitrogen cycle has much more biology involved than for the phosphorus cycle
Many complicated bacterial process (hugely simplified here); gas fluxes important; weathering less important
Denitrification only occurs in absence of oxygen, when bacteria switch to use nitrate instead in their respiration
Globally important for removing biologically available nitrogen
NO3- -> N2
results in N2O, NO, NO2
Internal recycling of nitrogen always greater than
the rate of N fixation (and usually greater than other external inputs)
Although N fixation is always small relatively to the rate of N recycling in any ecosystem
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
Lake 227, experimental lakes area
- 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
Internal recycling of nitrogen always
greater than the rate of N fixation
Also, nitrogen fixation absolutely critical at global scale in replenishing nitrogen lost through denitrification.
Without nitrogen fixation, there would be no life on Earth.
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
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)
Effectiveness of management practices for reducing N and P:
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
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.
Lack of recognition that the problem was from nitrogen, or that management practices develop for phosphorus may not work for nitrogen.
Chesapeake Bay –what has happened?
- 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
How does disturbance affect nutrient cycles and nutrient retention by ecosystems: a forest example
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
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
The amount of nutrients leaving the system will increase
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.
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
Uptake by plants stops, but mineralization continues, so inorganic N
builds up as nitrate is exported in the stream
NO3- -> organic N in plants and algae stopped
In many types of ecosystems, most of the demand for nutrients for primary production is
supplied by recycling (not new inputs)
Closed ecosystem
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
Open ecosystem
ex. salt marsh
- uptake by primary producers of 80mg nitrogen per square metre per day
Is recycling more prominent in open or closed systems?
Closed systems
Liebig’s law of the minimum
Open ecosystems because they’re being fertilized
- external nutrients is high, developed in the context of agriculture (very open ecosystems)
A more nuanced view of nutrient limitation in ecosystems such as the subtropical gyres, which are relatively CLOSED (recycling particularly important)
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
Why does energy flow and matter cycle?
Energy is lost as heat and matter is not created or destroyed
The main original source of nutrients such as calcium, iron, magnesium, phosphorous, and potassium in many terrestrial ecosystems is _______.
The weathering of parent bedrock and soil
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 _______________.
As both dissolved and particulate
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
The plot that is bedrock would not hold the nitrogen, it would just wash away out of the system.
N2O, NO, NO2
other nitrogen gasses
N2
Nitrogen gas (dinitrogen)
NO3
Nitrate
NH4
Ammonium
Nitrification
Bacteria convert ammonium to nitrate
Denitrification
Bacteria convert nitrate to inorganic N2
N Fixation
Bacteria convert N2 into organic N
Mineralization
General term for converting organic matter into inorganic matter
Which of the following 2 world views concerning ecosystems is likely to give you a more complete understanding of nutrient limitation?
- Liebig
- Redfield
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.
