Populations and Ecosystems Flashcards
(146 cards)
1
Q
What are ecosystems described as?
A
Dynamic and are all subject to change (energy flow, biological cycles, succession, species composition, population size)
2
Q
What factors cause populations to fluctuate?
A
Birth Rate
Death Rate
Immigration
Emigration
3
Q
Which factors increase the population size?
A
Birth rate and immigration
4
Q
Which factors decrease the population size?
A
Death rate and emigration
5
Q
When will the population increase
A
BR and Immigration > DR and Emigration
6
Q
Which term do you use for bacteria, yeast and plants instead of birth rate?
A
Reproductive rate
7
Q
What are fugitive species?
A
They are species which rely on a large capacity for reproduction and dispersal to increase numbers due to being poor at competition. They invade a new environment rapidly e.g algae colonising bare rock.
8
Q
What are equilibrium species?
A
They control the population by competition in a stable habitat, shown by a sigmoid population growth curve.
9
Q
What are the phases?
A
- Lag Phase
- Log/exponential phase
- Stationary phase
- Death/decline phase
10
Q
What is the lag phase?
A
Its a period of slow growth due to a shortage of reproducing individuals or adaption to the environment. Last a few minutes to several days.
11
Q
Whats the exponential phase?
A
It’s when the fastest population of growth occurs where the birth rate exceeds the death rate as more reproductive species are available. The numbers will increase as long as there is no limiting factors. Bacterial cells divide at a constant rate and their population doubles per unit time (exponential growth)
12
Q
What is the stationary phase?
A
BR and DR are at equilibrium, rate of growth slows due to competition. The CARRYING CAPACITY has been reached. The number at the stationary phase depends on the availability of resources e.g more food increases the carrying capacity. The population fluctuates around the carrying capacity.
13
Q
What is carrying capacity?
A
It is the maximum population size that a particular environment can maintain over a period of time.
14
Q
What is the death phase?
A
DR> rate of production. It could cause a population crash ie if all plants are eaten. The factors which slows down the lag phase are more significant.
15
Q
What sort of graph would be used for a population graph?
A
log 10 which means each interval is 10x
16
Q
What environmental resistance slows down population?
A
Competition for food and space.
Concentration of waste products becomes increasingly toxic.
Predation.
Paratism and disease – increase population density allows infection to spread more easily.
Temperature and light intensity
17
Q
How is the predator and prey relationship regulated by negative feedback?
A
Predators are normally larger than their prey they abundance of prey limits the number of predators and the number of predators controls on numbers of prey this causes the populations to oscillate.
18
Q
What is density dependent factors?
A
Factors in which the effect is greater when the population is larger in a given area. BIOTIC FACTORS
19
Q
What are the density dependent factors?
A
Disease Paratism Accumulation of toxic waste Food availability Predation Availability of shelter
Leads to a slow down in growth
20
Q
What is density independent factors?
A
Factors in which the effect doesn’t depend on the population size. All species are equally affected.
ABIOTIC FACTORS
21
Q
What are the density independent factors?
A
Temperature: freezing, fire, water
Soil pH
Mineral availability
Light availability
22
Q
How is population sizes regulated?
A
Negative feedback
23
Q
Describe the population fluctuations?
A
If the population increases above the set point a density dependent factors increases mortality or reduces breeding so the population declines. If the population falls below a set point environmental resistance is temporarily relieved and the population rises again.
24
Q
What do plants compete for?
A
Light
Water
Space
Nutrients
25
What do animals compete for?
Food/water
Space
Shelter
Reproductive partners
26
What is intraspecific competition?
Competition between individuals of the SAME species. This limits population size and is important in natural selection.
27
What is interspecific competition?
Competition between individuals of different species. In which two species can't obtain the same niche, so the more the niche overlaps the more competition present.
28
What physical features are assessed when looking at a new habitat?
Soil type – soil which is made with granite bedrock is more acidic than soil derived from chalk.
Rainfall – tree ferns are found in high rainfall regions and cacti in low water regions.
Climate- cold habitats can only support a few plants wears warm habitat support a vast number
29
What is abundance?
The abundance of the species is a measure of how many individuals exist in the habitat.
30
How can animal abundance be assessed?
Capture- mark recapture using Lincoln index calculations.
| Kick sampling in the stream and counting aquatic invertebrates.
31
What assumptions are made when measuring abundance in animals?
No immigration or emigration.
No births or deaths in the experimental period.
Marked individuals are marked and distributed evenly.
The marking process is non-toxic and doesn't make them susceptible to predation.
32
Describe the kick sampling method?
Stand in a river with a net down stream.
Kick the river bottom and collect animal species. Repeat 3x at each position.
Fill a white tray with their contents and identify each species a number.
33
What considerations and limitations are there with measuring animal abundance?
Difficult to identify some as they look so similar.
Difficult to count total number of small species.
Many count the species more than once.
Gives a snapshot of the population it needs to be repeated throughout the year.
34
How can plan abundance be assessed?
Using a quadrat to calculate the mean number of individuals in several quadrat of an area to find the density.
Estimated percentage cover of a plant.
Estimating percentage frequency.
35
What is distribution?
Distribution of a species describes the area or volume in which its found.
36
What can be used to measure distribution?
It can be measured using a line transect which shows the variety of species along the line measured intervals, it shows a correlation with changing abiotic factors.
37
How is a belt transect used?
The belt transact:
- Involves using a tape through a studded area with quadrat positioned at regular intervals alongside.
- It provides readings for density of chosen species,
% frequency and % cover of chosen species
38
How is animal distribution measured?
Via direct observation of individuals, nests, faecal deposits or markings on vegetation
39
What makes an ecosystem function?
The sequences of energy changes in which energy flows throughout the components of the ecosystem.
40
How did nonliving systems transfer energy to living systems?
From the energy derived from unequal distribution of protons allowed the nonliving systems in the cavities of alkaline hydrothermal vents to make a transfer into living systems.
41
What energy did early organisms use?
They used chemosynthesis (energy released by chemical reactions to make carbohydrates). Electrons needed to reduce carbon dioxide or methane to sugar are derived from the oxidisation of inorganic molecules i.e. hydrogen or hydrogen sulphide.
42
What is the main source of energy from?
The Sun in which light energy is trapped by photosynthesis as chemical energy.
43
What is a trophic level?
The position of the organism in a food chain. The feeding level is a number of times energy has been transferred between the Sun and successive organisms along the food chain.
44
What is T1?
Producer (Plant)
45
What is T2?
Primary consumer (herbivore)
46
What is T3?
Secondary consumer (carnivore)
47
What are producers?
Green plants, cyanobacteria and some protoctists
48
What do producers do?
They convert light energy into carbohydrates (the energy source for the successive organisms in the chain). Solar energy is trapped and sugars are synthesised from inorganic compounds by photosynthesis. Only a small proportion of the total light energy reached is incorporated into the tissues.
49
Energy lost at the trophic levels are lost as?
heat
50
What happens at decomposition?
Producers and consumers die with the energy made from organic compounds remaining. In which detritivores and decomposers feed on these organisms as saprobionts.
51
How do detritivores derive their energy?
From small fragments of organic debris
52
What are decomposers?
Microbes obtain nutrients from dead organisms and animal waste.
53
What is detritus?
Remains of dead organisms and fallen leaves.
54
Show the flow chart of the decomposition?
Detritus --> Detritivore --> Decomposer
55
What is the food chain?
A diagram which shows a feeding relationship of an organism at each level. They don't show:
All species at each trophic level – efficiency of energy transfer is low.
Detritivores and decomposers often have a greater biomass in other consumers.
Omnivores can feed at several levels
56
What is a food web?
It shows how organisms in a community interact with one another through the food they eat
57
What does the actual length of the food chain depend on?
If more energy is inputted the chain would be longer. Predator and prey populations fluctuate which affect the length.
Large ecosystem supports longer food chains.
3-D environments have longer chains and 2-D habitats.
58
Why is light energy not absorbed by the photosynthetic pigments?
Wrong wavelength.
Reflected.
Transmitted through the leaf.
59
What is photosynthetic efficiency?
The measure of the plants ability to trap light energy.
60
What is the equation needed for photosynthetic efficiency?
PE= Quantity of light energy incorporated into the product/ Quantity of energy falling on the plant
Typical value = 1-2%
61
What is the gross ecological efficiency?
% transfer of energy from one trophic to the next
62
What is gross primary productivity (GPP)?
The rate of production of chemical energy in organic chemicals by photosynthesis (KJm-2year-1). A large proportion of GPP is released by respiration of the plant to fuel e.g. protein synthesis.
Typical value - 0.2%
63
What is net primary productivity (NPP)?
Represents the potential food available to primary consumers/heterotrophs in an ecosystem.
Typical value - 0.1%
64
How is NPP worked out?
NPP= GPP - Respiration
65
What is primary productivity?
The rate at which produces convert energy into biomass.
66
What is secondary productivity?
The rate at which consumers accumulate energy from a simulated food and biomass in their cells or tissues. Occurs in heterotrophs i.e. animals, fungi, bacteria and some protoctists
67
How is energy loss at each level?
Not all tissue is eaten (bones).
Not all is digestible so will be egested as faeces.
Respiration – provides energy needed for active transport, muscle contraction, keeping warm this is lost as heat energy.
Excretory products.
68
Why are herbivores less efficient than carnivores?
As cellulose and ligin is more difficult to digest than protein. Therefore:
More energy is left in the faeces and
More energy is required in the digestive process i.e. cows feed on plant material which is digested by mutualistic bacteria.
69
Calculate efficiency of energy transfer
Energy incorporated into biomass after transfer/ Energy available in biomass before transfer
70
What is an ecological pyramid?
A diagram which shows a particular feature of each trophic level in an ecosystem where the producers are at the bottom and successful trophic levels are above. The number of organisms, the energy or biomass at each level is represented as a bar with the area being proportional to this. However they don't take into account some species can operate at more than one level at the same time.
71
Describe pyramid of numbers?
- Shows n.o of organisms
- Easy to construct
- Don't take into account organism size
- Doesn't recognise the difference between juvenile and adult form
- A large range can make it difficult to draw to scale
- Can be inverted if there are more organisms at one level than another
72
Describe pyramid of energy?
- Shows energy transferred from one level to the next
- Most accurate at showing the feeding relationship
- The bars decrease as material passes up the chain
- Cant be inverted
- Easy to compare with different communities
73
Describe the pyramid of biomass?
- Energy incorporated into the macromolecules which make up the biomass of an organism
- If energy is greater more biomass is supported
- Relates to energy passing through the ecosystem
- Hard to measure accurately (all parts of the root must be calculated)
- Doesnt indicate productivity and energy flowing through
- May be inverted
- Doesn't take into account lifespan
- The biomass at each level seems to contribute more energy than it actually does.
- Many organism contains structures which won't transfer energy ie bones, beaks
74
What is standing crop?
The mass of an individual at one time, can be lower than biomass of the trophic level above if the organism reproduces quickly. E.g. zooplankton reproduces quickly with some getting eaten immediately any leaving enough to support the population. Their standing crop is lower than the mass of the zooplankton.
75
What is carbon a major component of?
All organic molecules ie carbohydrates, fats and proteins. In the day CO2 is converted into carbohydrates by photosynthesis or organisms return it to the air in respiration.
76
What are the key processes which use carbon?
```
Respiration
Fossilisation
Decomposition
Combustion
Photosynthesis
```
77
Describe what happens to CO2 in respiration?
CO2 is added to the air by respiration of animals, plants and microorganisms. Its return to the carbon stores in the air and oceans.
78
Describe what happens to CO2 in photosynthesis ?
CO2 is removed from the atmosphere carbon store by terrestrial plants and from oceanic stores by aquatic plants to form biosphere carbon stores: cellulose and carbohydrates.
79
Describe what happens to CO2 in decomposition?
CO2 is released from dead organisms by saprobionts
80
Describe what happens to CO2 in fossilisation?
Fossil fuel formation from dead organisms which haven't decayed and the formation of limestone and shells. If exposed to the atmosphere they erode and CO2 is released.
81
Describe what happens to CO2 in combustion?
Carbon from fossil fuels returns to the carbon store in the atmosphere.
82
What happens to the radiation emitted (UV Visible and IR energy)?
Absorbed by ozone and other atmospheric gases. Absorbed by earth.
Reflected by earth.
Radiated by the atmosphere is heat.
83
What are the greenhouse gases?
CO2, CH4, CFC's, nitrous oxide, ozone and water vapour
84
What is the greenhouse effect?
It is a natural process in which greenhouse gases allow shorter and higher wavelength solar radiation to pass through the earths atmosphere. A lot of energy is absorbed by Earth and is reradiated at lower energy, longer IR wavelength radiation.
Some radiation reaches the earth and is reflected back into space. Energy is reradiated in all directions and the re-radiated energy is absorbed back into the Earth surface.
85
What has increased greenhouse effect?
Burning fossil feels, deforestation, methane, CFCs
86
How has burning fossil fuels increased the greenhouse effect?
Industrialisation and global transport has contributed to a steep and recent increase in greenhouse emissions. Burning fossil fuels releases CO2 locked in the atmosphere.
87
How has deforestation increased the greenhouse effect?
CO2 concentration increases as the rate of CO2 removal is reduced by photosynthesis contributing to global warming. The trees cut down could be burned or left to decay releasing CO2 in the atmosphere. Forest help maintain the CO2 and oxygen balance in the atmosphere.
88
How has methane increased the greenhouse effect?
It is released in many sources:
Rice crops - anaerobic conditions in paddy fields
Cattle - CH4 belched out the castles stomach
Rotting material at landfill sites
89
What has climate change caused?
Changes in average temperature, wind patterns and rainfall.
An enhanced greenhouse effect (caused by high conc of greenhouse gases)
Habitat changes – changes species distribution leading to new colonisations and new species breeding. Colder climate animals have to move north or up in altitude.
90
What are the consequences of global warming?
- Melting of polar ice caps and then expansion of
water – flooding in lowland areas, coastal erosion.
- Increased frequency of extreme weather conditions e.g. drought hurricanes.
- Increased frequency of forest fires.
- Decreased water availability leading to desertification. - Animals must move to suitable environments and plants can only move as fast as they are dispersed leading to extinction. As animals are dependent on plants a whole ecosystem could collapse.
- Fishing areas and crop greenbelt may move. Increase crop yield (more photosynthesis) but pest populations will increase.
- Decrease in food production.
- Decrease in pH in oceans threatening organisms e.g. fish secrete mucus to protect their girls and unable to perform gas exchange. Coral reefs have external skeleton is made from calcium carbonate which is soluble in acid.
91
How has CO2 levels been improved in farming?
Improve soil quality by:
- conservation tillage: leaves crop residues on the soil surface to reduce erosion, improve water use and add organic matter to the topsoil.
- Cover crop use: enhances soil structure and add organic matter to the topsoil.
- crop rotation reduces pest numbers and mineral depletion.
92
How has CFC's increased the greenhouse effect?
They are more active than CO2 as a greenhouse gas. Used in propellants, coolants
93
How has CH4 levels been improved in farming?
- Reduction in meat and dairy intake.
- Higher high sugar grasses: oats: rapeseed and maize silage in cows diets reduce the methane they release.
- Use rice varieties grown in dry conditions
- Select varieties that have a higher yield.
- ammonium sulphate can favour non-methane producing microorganisms in paddy fields.
94
How has nitric oxide and nitrous oxide levels been improved in farming?
Improve drainage to remove water and aerate soil.
95
How has low fluctuating water supply altered farming?
Drought tolerant crops
96
How has raised sea levels altered farming?
Salt tolerant crops
97
What is the carbon footprint?
The total amount of CO2 attributable to the actions of an individual or a product or service over a period of one year.
98
Individual carbon footprint can be:
- Direct emission (energy from home or transport)
- Indirect emission (goods and services consumed i.e. production of farming tools, production of herbicides, pesticides, farm machinery powered by fossil fuels and transport of produce)
99
How can you reduce the carbon footprint?
```
Three R's (reduce, reuse, recycle).
Drive less.
Less air-conditioning and heat used.
A diet with reduced animal protein.
Avoid food waste so convert into compost.
A forestation in deforested areas.
```
100
What is the nitrogen cycle?
It's the flow of nitrogen atoms between organic and inorganic nitrogen compounds and atmospheric nitrogen gas.
101
Why is nitrogen needed?
To make amino acid which build into proteins in protein protein synthesis. Build organic bases (ATCTU) which then build nuclear tides (ATP) and nucleic acid (RNA and DNA). It also makes chlorophyll
(Amino acids can be made by from small carbohydrates compounds and then joined into proteins)
102
What form is nitrogen in when used in plants?
Nitrogen gas can't be used so they absorb nitrogen in the form of ammonium ions or nitrates by active transport and facilitated diffusion.
103
How is nitrogen in a cycle?
The organic nitrogen compounds are passed through the food chain, the decomposition of plants and animals after death and excreted/suggested products released the minerals back into the soil.
104
What are the four groups of bacteria?
Putrefying bacteria
Nitrifying bacteria
N- fixing bacteria
Denitrifying bacteria
105
What is the role of Putrefying bacteria and fungi
Decompose proteins found in dead animals and plants. These proteins are digested into amino acids which are then delaminated to produce NH2 which is reduced to produce ammonium ions.
106
What is the role of Nitrifying bacteria
They convert ammonium ions into nitrates the conditioning is needed are aerobic and need aerated soil.
Nitrosomonous convert NH4 > NO2
Nitrobacter convert NO2 > NO3
107
What is the role of N- fixing bacteria
Azotobacter is free-living nitrogen fixing bacteria in the soil which absorbs nitrogen gas to produce ammonium ions. These can leach into the soil or can be used to synthesise amino acids.
108
What is the role of Denitrifying bacteria
Pseudomonus - found in buggy waterlogged soil which converts nitrate ions into nitrogen gas so few plants can grow in the soils.
109
What are the 4 biological processes in the nitrogen cycle?
AMMONIFICATION
NITRIFICATION
DENITRIFCATION
NITROGEN FIXATION
110
Describe the process of ammonification?
Decomposers secrete enzymes which decay organisms and animal products.
Proteases digest proteins into amino acids.
Deaminases removes NH2 from amino acids and reduces them to ammonium ions.
111
Describe the process of nitrification?
Ammonium ions are converted into nitrites and then nitrates. Aerobic conditions are needed. An oxidation reaction occurs as ammonium loses H atoms and gains O atoms.
112
Describe the process of nitrogen fixation?
Nitrogen atoms are reduced to ammonium ions by prokaryotes.
Azotobacter – free-living nitrogen fixing bacteria in the soil.
Rhizobium ( symbiotic – the bacteria benefits by having food and shelter and plants get amino acids produced by the bacteria) – found in a root nodules in the fabaceae family
113
Describe nitrogen fixation in rhizobium?
Nitrogen diffuses in the nodules and nitrogenase catalyses nitrogen gas into ammonium ions using energy from ATP. This is often aerobic. Root nodules contain leg haemoglobin which binds to oxygen in the nodules and protects from oxidation. Ammonium ions are converted into organic acids than amino acids to produce bacterial proteins. It obtains nitrogen for its own metabolism with some amino acids diverted into the phloem.
114
Show using a chart of rhizobium n-fixation?
N2 (reduction by nitrogenase) NH4+ --> organic acids
| --> amino acids
115
What are the non biological processes which impact the nitrogen cycle?
Agricultural fertilisers adds nitrogen to the soil. Lightning adds a small amount of nitrogen to the soil. Leeching removes minerals from the soil
116
What improvements have been made for nitrogen circulation?
- Ploughing fields aerates the soil which favours aerobic organisms enhancing ammonium ion formation and nitrifying bacteria which enhances ammonium ion conversion into nitrites and nitrates.
- Plant roots respire aerobically and generate ATP which fuels mineral uptake.
- Ploughing increases oxygen content of soil.
- Installing drainage systems reduces waterlogged soil as it allows natural aeration.
- Draining land allows air to enter reducing anaerobic conditions which favoured denitrification which removes nitrates.
- Fertilisers containing ammonium and nitrate ions.
- Large amount of animal wastes – nitrogen and other nutrients are essential in plant growth which improves soil structure allowing it to hold more water and nutrients. Encourages microbial activity which promotes mineral supply improving plant nutrition. Manure releases nitrogen gradually over a prolonged period of time.
- Slurry (mix of water and manure) is injected into the soil.
- Treated sewage sludge instead of inorganic fertilisers. - Planting legumes when it dies it's ploughed back into the soil as 'green manure' with a high nitrogen content.
117
What does high nitrogen content in fertilisers cause?
Eutrophication. As water flows over the rocks the mineral concentration increases as more is dissolved. When the mineral concentration is too high organisms die (the water is dystophic). Eutrophication is the process of artificially increasing the mineral content of water due to leaching from land which contained nitrogen fertilisers.
118
What are problems when there is excess nitrate in the soil?
Reduce biodiversity on grassland.
| Fertilisers encourage growth of grasses and plants which shade smaller plants.
119
What are the problems when there is excess nitrates in the river?
Eutrophication of lakes and rivers.
120
What does nitrogen in water produce and cause?
As nitrate is highly soluble it readily leeches into rivers from surrounding land. Heavy rainfall increases the rate of leaching and the concentration of nitrate in bodies of water.
Nitrate in the fertiliser causes algal bloom which prevents light from penetrating to any depth of water.
High nutrient content causes rapid algae growth as nitrate isn't a limiting factor. Plants in deeper regions can't photosynthesise so die. It causes a general decrease in animal biodiversity as they rely on plants for food and shelter. Short lived algae decomposes which uses up all dissolved oxygen giving water a high biological water demand. Water becomes deoxygenated so fish die as well as other species. Nitrites and nitrates have a toxic effect against the water supply.
121
In order to avoid high nitrogen concentrations what must farmers do?
Restrict the amount of fertiliser applied to the soil.
Only apply fertiliser when crops are actively growing. Leave a 10+ m wide strip next to water sources so nitrates can't directly into the water and if they do it's over a long period of time.
Dig drainage ditches so minerals are concentrated in these area which undergo eutrophication protecting natural water sources.
Water slowly flows into the ditch and accumulate landfill. This causes a reduction in low call invertebrate biodiversity as well as reducing biodiversity of adjacent grassland however rest species have been found.
122
What is succession?
A series of predictable changes that occurred in a community over time. The replacement of one species with another overtime as the environment changes or better adapted species arrive. Succession helps an ecosystem recover and return to a state of equilibrium after a fire, flood or other disturbance.
123
What are the stages of succession called?
Seral
124
What is primary succession?
Succession of a habitat which has never previously been colonised (no established soil) e.g. Baroque, volcanic eruption, uncovered rock by retreating glaciers.
125
What is the first stage of primary succession?
A new island is formed from many volcanic eruptions were no life has ever existed. Living organisms can be carried five oceans or wind currents (spores, seeds, small plants and animals) as well as birds flying over.
126
What are pioneer species?
The first plants to grow in a new habitat often highly adapted to harsh environments. They break down the rocks into soil. Small plants are the first to colonise the bare rock i.e. mosses, algae and lichens
127
What are lichens?
Slow growing plants. They have a symbiotic relationship between fungi and algae. They are able to tolerate desiccation and low nutrients. Algae photosynthesise and fungal hyphae grip the rock and trap soil fragments/nutrients from weathering.
128
What are mosses?
They are pioneer species which are able to root in the first soil (decompose lichen) they can't survive on bare rock alone but it can tolerate desiccation.
129
Describe the grassland community stage?
Mosses and lichen can decompose establishing soil for low growing herbaceous plants and grasses. Seeds blown by the wind, established the grassland.
130
How has weathering progressed succession?
Weathering continues as more plants growth the roots break down the route the rock further producing richer and more abundant soil this continues and a lot of larger plants have the ability to survive and grow. Ferns can now grow.
131
What happens to the plants as succession progresses?
Shrubs (more woody plants), outcompete grasses and block sunlight from reaching them preventing growth. Overtime larger more complex plants grow as the type of produces very different animals can survive. So continues to get deeper increasing mineral and Hummus (more water can be held efficiently). Over time trees outcompete shrubs and small trees these large plants provide food shelter and nesting places for a variety of animals.
132
What does the climax community hold?
A great species diversity. A complex food web. Large plants dominating.
133
What does happened to plant diversity at the end of primary succession?
It does decrease slightly as the tree canopy limits light from reaching the woodland floor.
134
What is the new ecosystem now varied in?
Micro organisms, producers, consumers
135
What is the climax community?
A stable, self perpetrating community which has reached equilibrium with its environment so no further change.
136
The ecosystem has reached climax community when equilibrium has been reached between:
- GPP and total respiration
- Energy used from sunlight and released by decomposition
- Nutrient uptake from the soil and returned by decayed plants/animals
- Quantity of humus is constant (new growth and decomposition)
137
What are the gradual changes that have occurred in primary succession?
Soil gets deeper and humus/mineral content increases
n.o of woody plants increases
organisms living at a greater range of vertical levels
biodiversity and stability of a community increases
pioneer plants die and perennials occupy the space
138
What has seen increases in the primary succession?
- Soil thickness, water availability, humus and mineral content
- Biomass
- Biodiversity
- Resistance to invasion by new species
- Stability to disruption by environmental challenges
139
What is secondary succession?
A series of community changes which take place on a previously colonised but disturbed or damaged habitat e.g. felling or fire.
140
Why does secondary succession occur quicker than primary?
- If no soil is lost plants can grow quicker.
- Already suitable existing seed banks for the soil.
- Undisturbed root systems, stumps and other plants from previous plants can regenerate.
- Soil fertility and structure has already been substantially modified from previous organisms making it more suitable for growth and colonisation.
- Pioneer plants are established until climax community is reached.
- Grasses grow on existing soil.
- Ferns fill the bare soil areas.
- Complex plants enter.
141
What does the new ecosystem have?
Microorganisms, producers, consumers (heterotrophs) which live successfully together. It has now reached equilibrium.
142
How has human activity affected succession and development of the climax community?
Grazing animals maintains grassland but prevents shrubs and trees from growing.
Farming – remove species and excludes others. Deforestation.
143
What are the three factors affecting succession?
Migration, competition, facilitation
144
How has migration affected succession?
Arrival of spores, seeds and animals is vital for succession. Immigrating non-native species may spread themselves widely altering the community and soil.
145
How has competition affected succession?
Intraspecific – when the population is greater a greater proportion fails to survive. The numbers regulate as some organisms produce more offspring than a habitat can support. Organisms with more environmental suitable alleles survive.
Interspecific – each has its own niche in an ecosystem i.e. it occupies a particular place with a particular role in the community with the niche being the organisms way of life.
Give me competition occurs at all several stages. Two species can't occupy the same niche in a specific habitat, so the one with the advantage will survive
146
How has facilitation affected succession?
The association between two species is called symbiosis.
Positive interactions are important and becomes significant as succession produces communities which become more complex.
Facilitation is an ecological community which provides available sources and refuge from physical stress, predation and competition.
MUTUALISM- interaction where both species develop
COMMENSALISM- interaction between organisms of two species in which one benefits and one in unaffected e.g squirrel and an oak tree.
