Chapter 7 - Ecological Energetics and Nutrient Cycling Flashcards
1
Q
In what ways are the organisms belonging to the populations that make up the community in any ecosystem interrelated at many levels?
A
- The organisms belonging to the populations that make up the community in any ecosystem are usually interrelated at many levels.
- The the previous chapter we reviewed how the organisms associated with one sere modify the environment making it more suitable for the organisms in the subsequent sere.
- The feeding relationships that exist within an ecosystem are another very obvious, and important, example of the links between the different individuals, and species, within an ecosystem.
2
Q
Feeding Defintion
A
Feeding involves the transfer of energy between living things.
3
Q
Producers
Consumers
The above are key terms relating to what phenomena?
A
The feeding relationships and transfer of energy in ecosystems.
4
Q
Producers defintion
A
Producers are organisms that manufacture organic substances from inorganic substances using energy.
5
Q
Producers are organisms that manufacture organic substances from inorganic substances using energy.
What type of energy do producers utilise in order to manufacture organic substances from inorganic substances?
A
- Almost all producers (plants) use light energy to produce organic compounds by photosynthesis.
- A very small number of producer species, the chemoautotrophs, use chemical energy (rather than light) to produce organic compounds from inorganic materials.
- Examples include some species of prokaryotes that live in deep cave systems far from available light (and with no possibility of organic content seeping into the system from above).
- These prokaryotes are able to make organic substances using the minerals in the rock as a source of chemical energy.
- Communities in these ecosystems have only been able to develop and survive as the producers have evolved an energy source other than light.
- Nitrifying bacteria are chemoautotrophs.
6
Q
Consumers definition
A
Consumers are organisms that obtain their energy by feeding on other organisms.
7
Q
Give an example of a consumer
A
Animals
8
Q
Primary consumers Defintion
A
Primary consumers are organisms that obtain their energy by feeding on producers (plants).
9
Q
Secondary consumers defintion
A
Secondary consumers are organisms that obtain their energy by feeding on primary consumers.
10
Q
Tertiary consumers defintion
A
Tertiary consumers are organisms that obtain their energy by feeding on secondary consumers.
11
Q
What are primary consumers often referred to as?
A
Herbivores (plant feeders).
12
Q
What are secondary and tertiary consumers often referred to as?
A
Carnivores, as they feed on other animals.
13
Q
What groups of organisms are involved in decay and decomposition?
A
Decomposers and detritivores
14
Q
What is the role of decomposers and detritivores in ecological energetics?
A
They are involved in decay and decomposition.
15
Q
Why does energy flow through an ecosystem?
A
As a consequence of photosynthesis by producers and the subsequent feeding relationships involved, alongside the flow of energy through the detritus pathway.
16
Q
Give some examples of decomposers
A
Bacteria and fungi
17
Q
Give some examples of detritivores
A
Small animals such as earthworms, millipedes and woodlice.
18
Q
What is a food chain?
A
- A food chain shows the link between a producer, a primary consumer, a secondary consumer and possibly a tertiary consumer.
- Each stage is referred to as a trophic level with producers being at the first trophic level, primary consumers at the second trophic level and so on.
19
Q
What is each stage in a food chain referred to as?
A
A trophic level
20
Q
Draw a simple food chain with four trophic levels
A
Textbook page 117
21
Q
Why, in reality, are food chains usually not a realistic representation of the feeding relationships that exist in an ecosystem?
A
As most animals do not rely on a singe food source - this would be far too risky in most ecosystems.
22
Q
What is a food web?
A
- A food web is the pattern of interrelated ‘food chains’ that operate in an ecosystem.
- In complex ecosystems, such as the climax community stage, food webs tend to be very complex involving many different species.
23
Q
- The quantitative relationships between trophic levels
What are some of the advantages and disadvantages of food chains and food webs?
A
- Advantages
• Food chains and food webs are useful in that they show the path of energy flow. - Disadvantages
• They do not provide any information concerning the number, or biomass, of organisms at each trophic level, ie the quantitative relationships.
24
Q
- The quantitative relationships between trophic levels
Food chains and food webs are useful in that they show the path of energy flow but they do not provide any information concerning the number, or biomass, of organisms at each trophic level, ie the quantitative relationships.
How can these quantitative relationships therefore be displayed graphically?
A
The relative number, biomass, or even energy of the organisms involved can be represented through the display of ecological pyramids.
25
Name some of the ecological pyramids used by ecologists when studying ecological energetics
Pyramids of numbers
Pyramids of biomass
Pyramids of energy (productivity)
26
What is a pyramid of numbers?
* A pyramid of numbers represents the total number of organisms at each trophic level in a food chain or web.
* Normally as there will be more organisms at the producer level than there are primary consumers, and so on, this gives a pyramid shape, hence the term pyramid of numbers.
27
What do the length of the bars on a pyramid of numbers represent?
The length of the bars in a pyramid of numbers is usually drawn proportional to the number at each level (the depth of bars should be the same for each level).
28
Draw a simple pyramid of numbers
Textbook page 117
29
Comment on how effective a pyramid of numbers is in terms of representing the quantitative relationships between trophic levels
* Pyramids of numbers are often a very simplified or inaccurate picture of the energy flow between trophic levels.
* They do not take account of the size of the organism, often resulting in inverted pyramids of numbers (see textbook page 118).
* When very large numbers are involved at any trophic level it is very difficult, or impossible, to scale the bars accurately. For example, one large oak tree may have several million insects operating as primary consumers.
30
What are pyramids of biomass?
* Pyramids of biomass represent the biomass of the organisms at a particular trophic level in a food chain or food web.
* Biomass can be measured as fresh mass or dry mass.
31
What can biomass be measured as?
* Biomass can be measured as fresh mass or dry mass.
* Fresh mass is more variable but will still normally give an accurate representation.
* Dry mass (drying the organism(s) until constant mass is achieved) is more accurate but time consuming and also means that the organisms are killed in the process.
32
Why can inverted pyramids of biomass result?
* With a pyramid of biomass (as with a pyramid of numbers), only the organisms present at any one time (the standing crop) are considered.
* Consequently, inverted pyramids of biomass can result, but often for different reasons than pyramids of numbers.
* Inverted pyramids of biomass for food webs are much less common than inverted pyramids of numbers.
33
Give an example of an ecosystem which often produces inverted pyramids of biomass
* Commonly used examples include some marine or aquatic pyramids of biomass as they do not take into account the biomass over the whole year but only represent an instantaneous value.
* In early spring the biomass of zooplankton (protoctistans and small animals that feed on phytoplankton) may exceed that of the phytoplankton.
* The food web is only sustainable because the phytoplankton reproduce at such a rapid rate that their numbers are quickly replenished.
34
Draw a diagram of an inverted pyramid of biomass
Textbook page 118, diagram b)
35
Why are inverted pyramids of biomass for food chains very uncommon?
* While inverted pyramids of biomass for food webs are very uncommon, inverted pyramids of biomass in a particular food chain are much more common.
* This can be explained by the consumer(s) having a number of different food sources (ie other sources outside a particular food chain).
* Inverted pyramids of numbers in food chains can also arise for the same reason.
36
What are some of the advantages and disadvantages of pyramids of biomass?
* Pyramids of biomass are more representative than pyramids of number but their disadvantages include problems with obtaining the data required - we have already noted the problems associated with dry mass but how do you obtain even the fresh mass of an oak tree?
* Additionally, pyramids of biomass can sometimes give a false picture of the amount of energy available to be transferred.
* A single oak tree can provide food for millions of leaf-eating insects but should the value represented in the pyramid be the mass of the entire tree or just the edible leaves?
37
What is a pyramid of energy (productivity)?
* The term productivity means how much new material is produced.
* Pyramids of energy reflect the new material produced (productivity) over a period of time.
* The data may be represented as kJ m^-2 yr^-1 (kilojoules per square metre per year) and this indicates how much new material, represented as the energy it contains, is produced in a square metre of ecosystem over the period of one year.
* Stable ecosystems will always represent energy flow as a pyramid.
38
What are some of the advantages and disadvantages of a pyramid of energy (productivity)?
* Pyramids of energy give the most accurate representation of the energy at a particular level but the values are more difficult to obtain as values need to be obtained over a time period to compare the before and after.
* Pyramids of energy are particularly useful in comparing ecosystems (including agricultural ecosystems).
39
What is the energy source for all ecosystems?
The Sun is the ultimate energy sources for all ecosystems.
40
What is the principle route by which energy is made available to the communities within an ecosystem?
As the Sun is the ultimate energy source for all ecosystems, photosynthesis is the principle route by which energy is made available to the communities within the ecosystem.
41
Why can energy flow be relatively inefficient?
Only a very small percentage of the energy reaching the Earth's atmosphere is used by producers to make organic compounds in the process of photosynthesis and even less is available to consumers.
42
How can energy loss occur between the Sun and the plants?
* Less than 1% of the Sun's energy reaching the atmosphere is available to plants for a number of reasons, as over 90% of the energy us reflected back into space by dust particles or clouds, or is absorbed by water vapour or dust in the atmosphere and then re-radiated as heat energy.
* Of the small percentage of the Sun's energy reaching the surface of the Earth, only a small proportion of this is used as most will fall on bare ground and will therefore miss the leaves of the plant. As much as 99.9% of the light reaching the Earth's surface will not be available to plants for this reason.
43
How is some of the light energy that strikes the leaf surface lost?
Of the Sun's energy that actually strikes a leaf, most is lost through:
* Being reflected from the surface of leaves - this process is often exacerbated by the presence of a thick waxy cuticle (a necessary compromise between maximising light harvesting and reducing water loss).
* Some energy is used in the evaporation of water (on the leaf surface).
* Missing the chloroplasts within the leaf. Although the chloroplasts are arranged in the cells of the palisade layer to trap as much light as possible, the volume of the chloroplasts in a palisade cell is very small.
* Over half of the light reaching the leaves is of the wrong wavelength. Most plants have pigments that absorb the blue and red parts of the visible spectrum with the green part of the spectrum being reflected.
* The photosynthetic (photochemical) reactions are inefficient, with much of the energy being lost as heat.
44
How much of the incident light energy that reaches the leaf surface will be converted into chemical energy via photosynthesis?
Between 0.5 and 1% of the incident light that reaches the leaf surface will be converted into chemical energy (organic compounds) as a result of photosynthesis.
45
Draw a diagram of a leaf illustrating the fate of light energy reaching the leaf surface
Textbook page 120
46
What is the name given to the energy in the organic compounds produced by plants in photosynthesis?
The gross primary production (GPP)
47
What is the gross primary production (GPP)?
The energy in the organic compounds produced by plants in photosynthesis.
48
How much of the growth primary production (GPP) do plants use in respiration (R)?
Plants use up to 50% of the GPP in respiration.
49
State the formula for the net primary production (NPP)
NPP = GPP - R
50
What is the net primary production (NPP)?
The energy in the organic compounds produced by plants in photosynthesis is called the gross primary production (GPP). However, plants use up to 50% of the GPP in respiration (R). The remainder, the net primary production (NPP), is available for plant growth, or for the other trophic levels in the ecosystem should the plant die or be eaten.
51
What are the units for GPP and NPP?
• GPP or NPP is often represented as kilojoules per square metre per year (kJ m^-2 yr^-1) as it is usually taken to represent the energy in the ecosystem as opposed to being a calculation based on individual plants.
52
What are GPP and NPP indicators of?
GPP and NPP are indicators of the productivity of an ecosystem.
53
In terrestrial (land based) ecosystems what factor(s) generally limit the GPP (and NPP)?
* In terrestrial (land based) ecosystems, the GPP (and NPP) is generally limited by temperature and moisture - the most productive natural ecosystems are tropical swamps and tropical forests where both temperature and moisture availability are approaching optimum levels.
* In aquatic and marine ecosystems, nutrient (mineral) availability is often the limiting resource.
54
Draw a flow diagram illustrating the relationship between gross primary production, net primary production and respiration
Textbook page 120
55
- Energy transfer between producers and consumers
Comment on the efficiency of energy transfer between producers and primary consumers and among consumers relative to the conversion of solar energy into organic compounds
* The transfer of energy between producers and primary consumers and among consumers is much more efficient than the conversion of solar energy into organic compounds.
* Nonetheless, it is still relatively inefficient.
56
Excluding the conversion of solar energy into organic compounds, what is the least efficient stage in energy flow through the different trophic levels of a food chain?
The least efficient stage is between producers and primary consumers (typically between 5-10%).
57
Excluding the conversion of solar energy into organic compounds, the least efficient stage in energy flow through the different trophic levels of a food chain is between producers and primary consumers (typically between 5-10%). Why is this the case?
* Much plant material cannot be accessed, for example, plant roots and tree trunks are not grazed to the extent that succulent and accessible leaves are.
* Much plant material is very difficult to digest - very few species have the enzymes necessary to digest cellulose and lignin.
* Therefore, herbivores typically can only assimilate a small percentage of the plant material they eat with considerable quantities of indigested material being egested.
* Excretory losses also contribute to energy losses - metabolic waste, for example, urea, is excreted and this represents energy that is not available to be transferred to the next trophic level.
* Much of the organic content that is eaten by primary consumers is used in respiration to generate ATP.
* The energy 'lost' through respiration is lost as 'heat' - heat is produced as a byproduct of the respiratory process.
* Respiratory losses are particularly high in mammals and birds (endotherms).
* The maintenance of a high and constant body temperature requires high metabolic activity and consequently high levels of respiration and unavoidable heat loss.
* Additionally, some plants (or plant parts, for example, leaves from deciduous trees in Autumn) enter the decomposer food chain and are not available to primary consumers.
58
How efficient is energy transfer between animals (consumers)?
10-20%
59
Why is energy transfer between animals (consumers) more efficient (typically between 10-20%) than between plants and herbivores?
* Generally, more of an animal can be eaten and digested.
* However, again only a small proportion of the energy in any animal will be built up into organic compounds in the next trophic level due to excretory losses, uneaten structures, or being used in respiration or through death and entry into the decomposer food chain.
60
Draw a flow diagram illustrating energy flow through the different trophic levels of a food chain
Textbook page 121
61
Why are the efficiency values used in energy flow diagrams of food chains often approximated?
The actual amount of energy that flows (and is lost) in a particular ecosystem depends on the species involved and may vary considerably from the 'typical' values used here.
62
Why are there typically no more than three steps in a food chain?
There are typically no more than three steps in a food chain (and very seldom more than four or five) due to the inefficiency of energy transfer and the huge efficiency losses that take place at each step.
63
Why does energy need to continually enter an ecosystem from the sun?
As the transfer of energy through trophic levels is energy flow. It is not a cycle - energy needs to continually enter the system from the Sun.
64
Where are agricultural ecosystems particularly important?
Northern Ireland
65
What are the two types of agricultural ecosystem?
Crop based agricultural ecosystems
| Animal (livestock) based agricultural ecosystems
66
For both crop and livestock systems, what are the key aims?
The key aims are the increased efficiency of energy transfer into the crops (and animals) and the reduction of losses through unwanted consumption by consumers, through respiration or losses through the decomposer pathway.
67
What aspect of agriculture receives large investment?
There is much investment in increasing agricultural productivity.
68
- Increasing primary productivity in plants
How can plant (crop) growth be increased?
By removing or reducing the limiting factors affecting growth.
69
Increasing primary productivity in plants - Plant (crop) growth can be increased by removing or reducing the limiting factors affecting growth. How can this be achieved?
* This can be done artificially in, for example, glasshouses by providing extra light, heat and carbon dioxide.
* However, most crops are grown outside and the most realistic way of increasing productivity is through the use of fertiliser, reducing the effect of pests and appropriate spacing of crops.
70
How can productivity be enhanced through the appropriate spacing of crops?
Sowing seeds at the optimum density ensures that competition among adjacent crop plants is reduced yet allows the crop to maximise coverage of the land used - another delicate balancing act.
71
What is the general principle for increasing the productivity of farming of domestic livestock?
The general principle is that by making energy conversion more efficient and restricting energy losses, where possible, more energy (meat products) will be available to humans.
72
How can the productivity of farming of domestic livestock be increased?
* Intensive farming of domestic livestock often involves the confinement of the animals to very specific areas - this can be cattle in a fenced-off section of a field or pigs in an outhouse, ensuring that less energy is used in movement.
* Keeping cattle in a small section of field also ensures that less land is utilised at any one time and that manure from the animals is more evenly spread over the land.
* Keeping animals indoors in warm conditions (much of the warmth, in all but the coldest conditions, is often produced by the animals themselves) reduces the energy required to produce heat and maintain body temperature.
* The use of high energy foods such as silage and high protein foods (for example, soya meal) are other measures geared to increasing productivity.
73
What is silage?
Silage is cut grass or maize that is chopped into small pieces and stored in anaerobic conditions.
74
Silage is cut grass or maize that is chopped into small pieces and stored in anaerobic conditions.
How can the anaerobic conditions required be produced?
The anaerobic conditions can be produced through covering the silage by large sheets of plastic (often held in place by old tyres) or through producing plastic covered bales.
75
Describe the sequence of events that lead to the production of silage
* Silage is cut grass or maize that is chopped into small pieces and stored in anaerobic conditions.
* Microorganisms respire in the anaerobic conditions created and produce lactic acid.
* The low pH, as a consequence of the lactic acid buildup, restricts other (decomposing) microbial growth thus preserving the high nutrient status of the grass throughout the winter.
* The grass can be cut several times during the growing period and preserved as silage at the time when it is most productive and nutritious, and therefore provides a highly nutritious winter fodder (at a time when other sources are in short supply).
76
What are some of the issues surrounding intensive farming of domestic livestock?
The intensive farming of domestic livestock raises many ethical and management issues.
77
What are some of the ethical issues surrounding intensive farming of domestic livestock?
Intensively farmed animals suffer high stress levels and often bone and joint damage; the hooves of cattle did not evolve for movement on concrete, especially slats).
78
What are some of the management issues surrounding intensive farming of domestic livestock?
* Disease is much more likely to spread rapidly when animals are confined in close proximity.
* The overuse of antibiotics to control (and often prevent) disease has been significant in the spread of antibiotic resistance in bacteria.
* Reduced genetic diversity results through the selective breeding of the most productive and profitable varieties.
* Increased pollution from the increased use of fossil fuels or general farmland waste is another consequence.
79
Comment on energy efficiency and the human diet
* The production of animal products is much less efficient than using crops.
* The inefficiency of energy transfer through food chains means that much more energy is available to humans through eating plant products rather than animal products.
80
Energy efficiency and the human diet - The production of animal products is much less efficient than using crops. The inefficiency of energy transfer through food chains means that much more energy is available to humans through eating plant products rather than animal products.
What does this mean for someone who eats meat as a significant part of their diet?
In effect, each human who eats meat as a significant part of his/her diet requires much more land to produce the food required than does a vegetarian.
81
Why do some Asian countries have human populations that have a staple diet of plant products?
* The production of animal products is much less efficient than using crops.
* The inefficiency of energy transfer through food chains means that much more energy is available to humans though eating plant products rather than animals products.
* In effect, each human who eats meat as a significant part of his/her diet requires much more land to produce the food required than does a vegetarian.
* For this reason very highly populated countries, such as some of those found in parts of Asia, have human populations that have a staple diet of plant products (for example rice) with meat being an uncommon luxury.
82
Why in much of Europe and North America are meat products more commonly used compared with some Asian countries?
• Due to the inefficiency of eating meat products, this is possible only through the relatively low population densities involved (for example, in France) or through importing meat from other countries (for example, as happens in Britain).
83
What is the energy used in the production of new tissue in animals referred to as?
Secondary productivity
84
Productivity in animals (secondary productivity) definition
The energy used in the production of new tissue in animals is referred to as secondary productivity.
85
What type(s) of productivity are crop farmers concerned with?
Crop farmers are concerned with increasing primary productivity (crop growth).
86
What type(s) of productivity are farmers of livestock concerned with?
Farmers of livestock are concerned with both primary productivity (if producing own animal feeds) and secondary productivity in the animals themselves.
87
How can the efficiency of secondary productivity be worked out?
Using energy budgets
88
Give the energy budget formula used to calculate the net secondary productivity, stating what each variable represents
```
P = C - (R + F+ U)
P = C - R - F - U
```
```
P = Net secondary productivity
C = Energy consumed
R = Energy lost through respiration
F = Energy lost through faeces
U = Energy lost through urine
```
89
In intensive farming, which variables in the energy budget formula for the efficiency of secondary productivity should increased/decreased in order to maximise growth and profit?
In intensive farming, maximising P (by using high energy foods) and reducing any of R, U and/or F (most easily done with R by, for example, confinement) can lead to increases in growth and profit.
90
Complete the energy budget of a bullock worked example on page 124 of the textbook
Values in arbitrary units
91
State a key factor in the flow of energy in ecosystems
The process requires the input of energy from the Sun.
92
Comment briefly on nutrient cycling through ecosystems
* There is no input of nutrients from another source into the Earth, therefore the finite supply we have on Earth is recycled through ecosystems.
* The recycling of nutrients can be considered in terms of the recycling of the elements they contain, for example, carbon and nitrogen.
93
Describe some of the similarities and differences between energy flow through ecosystems and nutrient cycling through ecosystems
Similarities
• The recycling of nutrients and the flow of energy both involve transfer from producer to consumer, between consumers, and through the decomposer chain.
Differences
• Nutrients enter the producer from within the ecosystem (for example, plants absorbing carbon dioxide from the atmosphere for photosynthesis), whereas the input of energy is required from an external source (the Sun).
94
Why is carbon so important?
Carbon is an essential component of all the major macromolecules found in living organisms - essentially the 'building block of life'.
95
In simple terms, how is carbon recycled through the ecosystem?
Carbon is recycled through the processes of photosynthesis and respiration, the two key biochemical processes in the evolution of life.
96
What are the two key biochemical processes in the evolution of life?
Photosynthesis and respiration
97
Describe briefly the process of photosynthesis with reference to carbon
In photosynthesis, producers (plants) are able to fix inorganic carbon dioxide and incorporate it into a range of organic products.
98
Describe briefly the process of respiration with reference to carbon
In respiration, organic products such as carbohydrates, fats and occasionally proteins (all containing carbon) are broken down to produce ATP, with carbon dioxide being released as a waste product.
99
How do consumers gain carbon?
Through feeding
100
Consumers gain carbon through feeding. How is this possible?
As both plant and animal tissue are rich in carbon, and complex organic compounds are broken down and built up in the ongoing cycle of feeding, digestion and the assimilation of food products in animals.
101
What role do decomposers play in the carbon cycle?
Saprobiotic microorganisms (decomposers) break down the organic molecules 'trapped' in urine, faeces and dead organisms during decay and decomposition, and release the carbon as carbon dioxide, again in the process of respiration.
102
How are fossil fuels formed?
* At certain stages of the Earth's history some dead organisms have been preserved in environments hostile to decay (fossilisation).
* Fossil fuels such as coal and peat contain 'locked in' carbon that has not been released as the process of decay and decomposition could not take place.
* This carbon is released (often many millions of years later) by the process of combustion.
103
Draw a flow diagram summarising the carbon cycle
Textbook page 125
