2.3 Ecosystems and Sustainability Flashcards
1
Q
What is an ecosystem?
A
All the living organisms and all the non-living components in a specific habitat, and their interactions
2
Q
Definition of habitat
A
The place where an organism lives
3
Q
Definition of population
A
A collection of individuals of the same species in a defined area
4
Q
Definition of community
A
All of the populations of different species who live in the same place at the same time, and can interact with each other
5
Q
What are biotic factors?
A
Living factors that influence organisms
6
Q
Give 2 examples of biotic factors
A
Predation, disease, food supply
7
Q
What are abiotic factors?
A
Non-living factors that influence organisms
8
Q
Give 2 examples of abiotic factors
A
pH, temperature, soil type
9
Q
What are producers?
A
Plants and photosynthetic organisms (e.g. algae and bacteria) that supply chemical energy to all other organisms
10
Q
What are primary consumers?
A
Organisms such as animals and fungi who feed on plants (herbivores)
11
Q
What are secondary consumers?
A
Organisms that eat primary consumers
12
Q
What are tertiary consumers?
A
Carnivorous organisms that eat secondary consumers
13
Q
What are decomposers?
A
Organisms (such as bacteria, fungi and some animals) that feed on waste material or dead organisms
14
Q
How do living organisms release energy?
A
Via respiration
15
Q
Where does the energy that organisms release come from?
A
Sunlight - light energy is captured through photosynthesis and converted to chemical energy stored in molecules like glucose
16
Q
What is a trophic level?
A
The level at which an organism feeds in a food chain
17
Q
What do the arrows in a food chain represent?
A
The transfer of energy
18
Q
Why is some energy lost from the food chain between trophic levels?
A
- Living organisms need energy to carry out living processes. Some of this energy is eventually converted to heat
- Energy remains stored in dead organisms and waste material. This energy is only available to decomposers.
19
Q
What is the result of losing energy from a food chain?
A
Less energy is available to sustain living tissue at higher levels of the food chain
- This means that less living tissue can be kept alive
- So there are fewer consumers at higher levels
20
Q
Definition of succession
A
A directional change in a community of organisms over time
21
Q
How does a community develop from bare ground?
A
By primary succession:
- Algae and liches begin to live on the bare rock (pioneer community)
- Erosion of the rock, and a build up of dead and rotting organisms, produces enough soil for larger plants like mosses and ferns to grow. These replace, or succeed, the algae and lichens
- Larger plants can then succeed these smaller plants in a similar way, until a final, stable community is reached. This is called a climax community
22
Q
What is secondary succession?
A
Succession that takes place on previously colonised, but disturbed or damaged, habitat
23
Q
What is the first stage in the succession of sand dunes?
A
- Pioneer plants such as sea rocket and prickly sandwort colonise the sand just above the high water mark
- These can tolerate salt water spray, lack of fresh water and unstable sand
24
Q
What is the second stage in the succession of sand dunes?
A
- Wind-blown sand builds up around the base of these plants, forming a ‘mini’ sand dune
- As plants die and decay, nutrients accumulate in this mini dune
- As the dune gets bigger, plants like sea sandwort and sea couch grass colonise it
- Because sea crouch grass has underground stems, it helps to stabilise the sand
25
What is the third stage in the succession of sand dunes?
- With more stability and accumulation of more nutrients, plants like sea spurge and marram grass start to grow
- Marram grass is special; its shoots trap wind-blown sand and, as the sand accumulates, the shoots grow taller to stay above the growing dune
- This traps more sand
26
What is the fourth (and final) stage in the succession of sand dunes?
- As the sand dune and nutrients build up, other plants colonise the sand
- Many, such as hare's-foot clover and bird's-foot trefoil, are members of the bean family
- Bacteria in their root nodules convert nitrogen into nitrates
- With nitrates available, more species, like sand fescue and viper's bugloss, colonise the dunes
- This stabilises them further
- Eventually, a dune's community may develop into grassland, and then into woodland
27
Why do ecologists usually study ecosystems?
To find out whether the abundance and distribution of a species is related to that of other species, or to environmental factors
28
What is a quadrat?
A square frame that defines the sample area, used for sampling ecosystems
29
What types of data can you collect from a quadrat?
- Distribution: presence or absence of each species
| - Abundance: estimate or count the number of individuals
30
What are the disadvantages to estimating percentage cover?
- Difficult
| - Inaccurate
31
How can you improve the percentage cover method?
By using a point frame
32
How does a point frame work?
- Stand the point quadrat firmly on the ground
- Lower each needle downwards
- Record the species that the tip touches on the way down
- The number of needles that touch each species is proportional to the percentage cover of that species
33
Why is it important to decide where to place the quadrats before starting to sample?
- You may bias the sample
- E.g. Sampling from only one corner of the area may not be representative of the whole area due to abiotic or biotic factors
34
How can you avoid biasing a sample and provide a sample that is representative of the whole habitat?
- Randomly position the quadrats across the habitat (e.g. by using a random number able to create coordinates)
- Take samples at regular distances across the habitat
35
How can ecologists work out how many quadrats they need?
- Ecologists carry out a pilot study
- They take random samples across the habitat and make a cumulative frequency table
- They then plot cumulative frequency against quadrat number
- The point where the curve levels off tells them the minimum number of quadrats to use
- Ecologists often double this number
36
How can you work out how big your quadrats should be?
- Count the number of species you find in larger and larger quadrats
- Plot quadrat area on the x-axis, against the number of species you find in each one
- Read the optimal quadrat size at the point where the curve starts to level off
37
What is a transect?
A line taken across a habitat
38
How is a line transect taken?
At regular intervals, make a note of which species are touching the tape
39
How is an interrupted belt transect taken?
At regular intervals, place a quadrat next to the line
40
How is a continuous belt transect taken?
Place a quadrat next to the line, moving it along the line after looking at each quadrat
41
When does competition between organisms occur?
When resources are not present in adequate amounts to satisfy the needs of all the individuals who depend on those resources
42
What happens when the intensity of competition increases?
- The rate of reproduction decreases
| - The death rate increases
43
What is intraspecific competition?
Competition between members of the same species
44
What is interspecific competition?
Competition between members of different species
45
How does intraspecific competition allow the population to remain fairly stable?
- If the population size drops, competition reduces, and the population size then increases
- If the population size increases, competition increases, and the population size then drops
46
What can interspecific competition affect?
Both the population size of a species and the distribution of a species in an ecosystem
47
What is the competitive exclusive principle?
If 2 species have exactly the same niche, 1 would be outcompeted by the other and would die out of become extinct in that habitat
48
Why does the competitive exclusive principle not always apply in natural ecosystems?
- Sometimes, interspecific competition could simply result in 1 population being much smaller than the other, with both population sizes remaining fairly constant
- In the lab it is easy to exclude the effects of other variables, so the habitat of the 2 species remains very stable. In the wild, however, a wide range of variables may act as limiting factors for the growth of different populations
49
What methods are there for managing small-scale timber production and maintaining sustainability?
- Coppicing
- Pollarding
- Rotational coppicing
50
What is coppicing?
- It involves cutting the trunk of a deciduous tree close to the ground
- Once cut, several new shoots will grow from the cut surface, and eventually mature into stems of quite narrow diameter
- These can be cut and used for fencing, firewood or furniture
- After cutting, new shoots start to grow again and the coppice cycle continues
51
What is a deciduous tree?
A tree that loses its leaves in winter
52
What is pollarding?
- Similar to coppicing
| - But the trunk is cut higher up
53
When is pollarding useful?
When the deer population is high:
- They like to eat the emerging shoots from a coppiced stem
- But if cut higher up, the deer cannot reach the shoots
54
What is rotational coppicing?
- Woodland managers divide the wood into sections
- They cut 1 section a year until they've all been cut
- By the time they want to coppice the first section again, the new stems have matured and are ready to be cut
55
What does the length of rotation for rotational coppicing depend on?
- The time taken for stems to mature (depends on the species)
- The dimensions of wood required
56
What are standards? (In rotational coppicing)
- Trees that are left to grow larger without being coppiced
| - Supply larger pieces of timber
57
Why is rotational coppicing good?
It is good for biodiversity:
- Left unmanaged, woodland goes through a process of succession
- Trees can block out light to the floor of the woodland and reduce the number of species that can grow there
- By using rotational coppicing, different areas of woodland provide different types of habitat, letting more light in and increasing the number and diversity of species
58
What methods are there for managing small-scale timber production and maintaining sustainability?
- Clear-felling
| - Selective cutting
59
What is clear-felling?
Cutting down all the trees in 1 area
60
What are the disadvantages to clear-felling?
- It can destroy habitats on a large scale
- Can reduce soil-mineral levels
- Leaves soil susceptible to erosion
- Soil may run off into waterways, polluting them
61
Why may soil run off into waterways because of clear-felling?
Because trees usually:
- Remove water from the soil and stop soil being washed away by rain
- Maintain soil nutrient levels through the trees' role in the carbon and nitrogen cycles
62
What is an advantage and disadvantage of leaving each section of woodland to mature for 50-100 years before clear-felling?
- Allows biodiversity to increase
| - The timescale is not cost-effective
63
What principles does modern sustainable forestry work on?
- Any tree which is harvested is replaced by another tree, either grown naturally or planted
- Even with extraction of timber, the forest as a whole must maintain its ecological function regarding biodiversity, climate and mineral and water cycles
- Local people should derive benefit from the forest
64
What is selective cutting?
You remove only the largest, most valuable trees
65
What is the advantage to selective cutting?
The habitat is broadly unaffected
66
How do foresters manage woodlands sustainably?
- Control pests and pathogens
- Only plant particular tree species where they know they will grow well
- Position trees an optimal distance apart. If trees are too close, this will cause too much competition for light, and they will grow tall and thin, producing poor quality timber
67
How is a pyramid of biomass made?
- All the organisms are collected
- They are put in an oven at 80°C until all the water in them has been evaporated
- A pyramid is then drawn, with the area of the bars is proportional to the dry mass of all the organisms at that trophic level
68
What is a disadvantage to drawing pyramids of biomass and how can this be overcome?
- Destructive to the ecosystem being studied
- Different species may release different amounts of energy per unit mass
- Ecologists measure the wet mass of the organism and calculate the dry mass on the basis of previously published data
69
Why are pyramids of biomass used?
Provides a more accurate picture about how much living tissue exists at each level than counting the number of organisms
70
How are pyramids of energy drawn?
- Organisms are burned in a calorimeter
| - The heat energy released per gram is calculated
71
What are the disadvantages to pyramids of energy?
- Destructive
- Time-consuming
- Have limitations:
- Only take a snapshot of an ecosystem at 1 moment in time
- Because population sizes can fluctuate over time, this may provide a distorted idea of the efficiency of energy transfer
72
What are pyramids of productivity?
- A pyramid of energy flow (the rate at which energy passes through each trophic level: productivity)
- Gives an idea of how much energy is available to the organisms at a particular trophic level, per unit area, in a given amount of time
73
What is primary productivity?
The productivity of plants at the base of the food chain
74
What is the gross primary productivity?
The rate at which plants convert light energy into chemical energy
75
What is the net primary productivity? (NPP)
- The remaining energy after energy has been lost when the plant respires
- The rate at which carbohydrate accumulates in the tissue of plants of an ecosystem and is measured in dry organic mass
76
How can humans increase the net primary productivity?
- Crops are planted early to provide a longer growing season to harvest more light. Some are grown under light banks
- Irrigating crops or breeding drought-resistant strains
- Greenhouses to produce a warmer temp. Planting field crops early to provide a longer growing season to avoid the impact of temp
- Crop rotation, fertiliser, including a nitrogen-fixing plant (provide nutrients)
- Spraying with pesticide, breeding pest-resistant plants
- Spraying with fungicides
- Use herbicides to remove weeds
77
How can humans improve secondary productivity?
- Harvesting animals just before adulthood minimises loss of energy (young animals use more energy for growth than adults)
- Treat farm animals with steroids (more energy used for growth)
- Selective breeding
- Treat animals with antibiotics (avoids loss of energy to pathogens)
- Zero grazing for animals (maximises energy for muscle production) - supply them with food, keep temp constant
78
How do bacteria and fungi feed?
Saprotrophically:
- They secrete enzymes onto dead and waste materials
- These enzymes digest the material into small molecules, which are then absorbed into the organisms body
- Having been absorbed, the molecules are stored or respired to release energy
79
Why are saprotrophs important?
They recycle trapped energy and nutrients from the dead organisms
80
What is nitrogen fixation?
Nitrogen gas is very unreactive, so plants cannot use it directly
Instead, they use a supply of 'fixed' nitrogen such as ammonium ions or nitrate ions.
Nitrogen fixation can occur when lightning strikes, through the Haber process or through nitrogen-fixing bacteria
81
What are nitrogen-fixing bacteria?
Bacteria that live freely in the soil
- They fix nitrogen gas, which is in the air within the soil
- They then use it to manufacture amino acids
Can also live inside the root nodules of certain plants
- They have a mutualistic relationship with the plant: the bacteria provide the plant with fixed nitrogen and receive carbon compounds, such as glucose, in return
- Proteins in the nodules absorb oxygen and keep the conditions anaerobic. Under these conditions the bacteria use an enzyme, nitrogen reductase, to reduce nitrogen gas to ammonium ions
82
When does nitrification occur?
When chemoautotrophic bacteria in the soil absorb ammonium ions
83
How does nitrification occur?
- Ammonium ions are released by bacteria involved in putrefaction of proteins found in dead or waste organic matter
- Chemoautotrophic bacteria obtain energy by oxidising nitrites to nitrates
- Because this oxidation requires oxygen, these reactions only happen in well-aerated soils
- Nitrates can be absorbed from the soil by plants and used to make nucleotide bases and amino acids
84
What is denitrification?
The conversion of nitrates back to nitrogen gas by bacteria
- When the bacteria involved are growing under anaerobic conditions, they use nitrates as a source of oxygen for their respiration and produce nitrogen gas and nitrous oxide
85
How can the steadily increasing human population threaten biodiversity?
- Over-exploitation of wild populations for food, for sport and for commerce: species are harvested faster than they can replenish themselves
- Habitat disruption and fragmentation as a result of more intensive agricultural practices, increased pollution, or widespread building
- Species introduced to an ecosystem by humans, deliberately or accidentally. These may out-compete native species, which may become extinct.
86
What are the ethics of conservation?
- Every species has value in its own right, irrespective of whether it has financial value to humans
- Every living thing has a right to survive
- Humans have an ethical responsibility to look after them
87
What are the economic and social reasons for conservation being important?
- Many species provide a valuable food source, and were originally domesticated from wild species. Genetic diversity in wild strains may be needed in the future to breed for disease resistance, drought tolerance or improved yield. so new species may be domesticated for food use
- Natural environments are a valuable source of potentially beneficial resources (e.g. Drugs)
- Natural predators of pests can act as biological control agents, which can have advantages over the use of synthetic chemicals
- Many species have indirect economic value (e.g. Wild insect species are responsible for pollinating crop plants)
- Some communities maintain water quality, protect soil and break down waste products
- Ecotourism and recreation in the countryside also have significant social and financial value, thanks to the aesthetic value
88
What management strategies are there for maintaining biodiversity in a dynamic ecosystem?
- Raise carrying capacity by providing extra food
- Move individuals to enlarge populations, or encourage natural dispersion of individuals between fragmented habitats by developing dispersal corridors of appropriate habitat
- Restrict dispersal of individuals by fencing
- Control predators and poachers
- Vaccinate individuals against disease
- Preserve habitats by preventing pollution or disruption, or intervene to restrict the progress of succession
89
What does the size of a population depend on?
The balance between the death rate (mortality) and the rate of reproduction
90
What is the lag phase?
The phase during which there may only a few individuals, still acclimatising to their habitat. At this point, the rate of reproduction is low and the growth in population size is low
91
What is the log phase?
- When resources are plentiful and conditions are good
- The rate of reproduction is fast and exceeds mortality
- The population size increases rapidly
92
What is the stationary phase?
- The population size has levelled out at the carrying capacity of the habitat
- The habitat itself cannot support a larger population
- The rates of reproduction and mortality are equal
- The population size therefore stays stable or fluctuates very slightly up and down in response to small variations in environmental conditions each year
93
What is the carrying capacity?
The maximum population size that can be maintained over a period of time in a particular habitat
- The habitat cannot support a larger population due to limiting factors
94
How can predation act as a limiting factor on a prey's population size, which in its turn can affect the predator's population size?
- When the predator population gets bigger, more prey are eaten
- The prey population then gets smaller, leaving less food for the predators
- With less food, fewer predators can survive and their population size reduces
- With fewer predators, fewer prey are eaten, and their population size increases
- With more prey, the predator population gets bigger, and the cycle starts again
95
What allows the Galápagos Islands to have rapid evolutionary change?
The Islands' isolation
Small population sizes
- These provide optimal conditions
96
Why has the population of the Galapagos grown?
- In response to a developing tourist trade
- Expanding demand for marine products like sea cucumbers and lobster
- Economic problems in mainland Ecuador (1990s)
97
What effect has the increase in population size had on the Galápagos Islands?
- It has placed huge demands on water, energy and sanitation services
- More waste and pollution have been produced
- Demand for oil has increased
- Oil spill in 2001 had an adverse effect on marine and coastal ecosystems
- Increased pollution, building and conversion of land for agriculture have caused destruction and fragmentation of habitats
98
What effect has whaling and fur-trade had on the Galápagos Islands?
- Whales and seals were harvested from the Galápagos Islands during the nineteenth century, to be sold internationally
- Species were harvested faster than they could replenish themselves
- Giant tortoises were taken because they could survive on little food in the hold of a ship for a long time, before being killed and eaten
- This had a catastrophic effect on tortoise populations
99
What other effects have marine-related industries had on the Galápagos Islands?
- The boom in fishing for exotic species in the 1990s had left populations seriously depleted
- Depletion of sea cucumber populations has a drastic effect on under-water ecology
- The international market for shark fin has led to the deaths of 150000 sharks each year around the islands (14 species are now listed as endangered)
100
What effect can alien species have on native species?
- They can out-compete native species
- They can eat native species
- Destroy native species' habitats
- Bring diseases
101
What effect has the red quinine tree had on the Galápagos Islands?
It is an aggressively invasive species
- Occupied the highlands on Santa Cruz Island
- Spreads rapidly (wind dispersed seeds)
- The ecosystem in the highlands has changed from low scrub and grassland to a closed forest canopy
- Because of this the native Cacaotillo shrub has been almost eradicated from Santa Cruz
- The Galápagos petrel has lost its nesting sites
- The red quinine also successfully out-competes native Scalesia trees
102
What effects have cats had on the Galápagos Islands?
They hunt a number of species, including the lava lizard and young iguanas
103
What effects have goats had on the Galápagos Islands?
- They eat Galápagos rock purslane, a species unique to the island
- They out-compete the giant tortoise for grazing
- They trample and feed on the tortoises' food supply
- They change the habitat to reduce the huber of tortoise nesting sites
- On Northern Isabella Island, they have also transformed forest into grassland, leading to soil erosion
104
What strategies have been adopted to prevent the introduction and dispersion of introduced species and to treat the problems caused by such species?
- Culling has been successful against feral goats on Isabella Island and pigs on Santiago Island
- Natural populations have been exploited to reduce the damage caused to ecosystems by pest populations
- A quarantine system has been instigated, where arriving boats and tourists are searched for foreign species
105
What pest control methods are there?
- Providing suitable habitats for natural predators
- Removing the pests mechanically
- Using biological agents
- Using pesticides (as a last resort)
- Preventative measures such as crop rotation and intercropping
106
What are the advantages and disadvantages of pesticides?
Advantages: act quickly; easy to apply
Disadvantages: can affect other, non-target species; organisms develop resistance,
107
What are the advantages and disadvantages of zero grazing?
Advantages: efficient energy conversion, produces low cost food, uses less space, easier to prevent disease being introduced, easier to isolate ill animals
Disadvantages: animals vulnerable to rapid spread of disease, use of drugs can lead to antibiotic resistance, unnatural conditions may affect the animal, restricted movement may cause osteoporosis and joint pain
