Applied ecology

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Energy and food production

AGRICULTURAL ecosystems are made up largely of domesticated animals and plants used to produce food for humans. These have a HIGH productivity whereas in NATURAL ecosystems productivity is relatively LOW.

INTENSIVE FARMING is designed to maximise PRODUCTIVITY and YIELD by making use of the appropriate technology to ensure that as much of the available energy from the Sun as possible is transferred to humans.

Intensive farming increases producitivty there is a cost. Many of these methods require ENERGY INPUT FROM THE FARMER. Building livestock sheds, heating buildings, running farming machinery and producinbg fertiliser all require energy, usually in the form of BURNING FOSSIL FUELS. The farmer has to maake sure that the gains in producitiy outweigh the extra costs.

Some strategies increase NET PRIMARY PRODUCTIVITY by INCREASING GROSS PRODUCTIVITY of the crop plants (e.g. fertilisers and glasshouses)

Others do it by DECREASING RESPIRATORY LOSS (E.g. battery farming) thereby INCREASING NET SECONDARY PRODUCTION.

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Intensive farming practices

Fertilisers. Advantages: Increases the amount of mineral ions in the soil, increasing manufacture of organic compounds and growth rate.

Glasshouses (Growing crops under glass or polythene). Advantages: Optiminises light intensity, carbon dioxide concentration and temperature, preventing them from limiting the rate of photosynthesis.

Pest control. Advantages: Reduces damage to the crop or, in the case of removing weeds, reduces competition with the crop.

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Intensive farming practices

Battery farming

  • Keeping animals in small restricted areas: less energy wasted in MOVEMENT so more energy available to produce tissue and growth.
  • Controlling temperature, e.g. by keeping cages warm: Less HEAT LOSS so more energy used for growth/producing tissue.
  • Fed on a controlled diet of food that is easy to digest and absorb: High proportion of food absorbed - less is lost in FAECES.
  • Slaughtering animals while still young: Animals still growing so more energy transferred to biomass.
  • Genetically selected: Selected for high productivity.
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Other farming practices used to increase productiv

Selective breeding/genetic modification of crops. Allows particular characteristics and varieties to be chosen.

Ploughing. Aerates soil and improves drainage. Aeration provides oxygen, increasing the ACTIVITY OF AEROBICALLY RESPIRING MICROBES involved in the carbon and nitrogen cycles (e.g. nitrifying bacteria)

Crop rotation. Improves SOIL FERTILITY by:

  • Growing legumes with nitrogen fixing bateria in their root nodules, then ploughing them into the soil and allowing them to decay. INCREASES content of nitrogen-containing compounds in the soil. E.g. nitrates/ammonium ions.
  • Growing crops with different mineral requirements.

Irrigation. Prevents water from being a limiting factor of photosynthesis.

Netting. Covers crops to protect them from birds/pests/frost.

Other practices using in IF include: monoculture, mechanisation and hydroponic (growing crops in a solution of mineral ions instead of soil)

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Other farming practices used to increase productiv

Selective breeding/genetic modification of crops. Allows particular characteristics and varieties to be chosen.

Ploughing. Aerates soil and improves drainage. Aeration provides oxygen, increasing the ACTIVITY OF AEROBICALLY RESPIRING MICROBES involved in the carbon and nitrogen cycles (e.g. nitrifying bacteria)

Crop rotation. Improves SOIL FERTILITY by:

  • Growing legumes with nitrogen fixing bateria in their root nodules, then ploughing them into the soil and allowing them to decay. INCREASES content of nitrogen-containing compounds in the soil. E.g. nitrates/ammonium ions.
  • Growing crops with different mineral requirements.

Irrigation. Prevents water from being a limiting factor of photosynthesis.

Netting. Covers crops to protect them from birds/pests/frost.

Other practices using in IF include: monoculture, mechanisation and hydroponic (growing crops in a solution of mineral ions instead of soil)

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Environmental+Ethical issues with Intensive farmin

Environmental issues:

  • Contribution to the greenhouse effect associated with the increased use of fossil fuels
  •  Eutrophication associated with the use of chemical fertilisers.

Ethical issues:

  • Animal welfare issues (Small cages)
  • Use of antibiotics in animal feed may lead to/encourage antibiotic resistance to develop in bacteria.
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Fertilisers

Put mineral ions into the soil.

Nitrogen is absorbed by plants in the form of NITRATES.

The carbohydrates produced in photosynthesis can be used to make other organic compounds such as proteins, as long as there is a supply of INORGANIC MINERAL IONS that agricultural crops take up from the soil by their roots.

The most important INORGANIC ions are NITRATES, PHOSPHATES and POTASSIUM, containing the elements NITROGEN, PHOSPHOROUS and POTASSIUM. These are needed in large amounts by the PLANTS. Other elements are only required in small amounts, e.g. iron and magnesium. Different plant species require different proportions of each of these elements.

IONS needed to produce:

  • PROTEINS: NITRATES
  • NUCLEIC ACIDS: NITRATE + PHOSPHATE
  • PHOSPHOLIPIDS: PHOSPHATE
  • ATP: PHOSPHATE + NITRATE
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Fertilisers

Normally, these ions are recycled by DECOMPOSITION of dead matter and waste products in the soil. Saprobiotic organisms carry out this process. (Bacteria and fungi).

In cultivated soils this recycling is greatly reduced, this is because crops are harvested and removed - there's a lack of plant material for decomposition.

Farmers need to keep adding fertiliser to their crops to replace mineral ions that have been removed by the crops.

2 types of fertilisers, both which provide the chemical elements required for healthy plant growth.

NATURAL fertilisers consist of ORGANIC plant or animal matter (cow poo), containing complex ORGANIC compounds, e.g. urea which releases mineral ions as it decays.

ARTIFICIAL fertilisers are MANUFACTURED and contain concentrated mineral ions (Especially NPK compounds) in an INORGANIC, soluble and ready-to-use form.

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Types of fertiliser

Natural/organic (e.g. farmyard manure)

Advantages:

  • Slow, long lasting release of nutrients
  • Useful, cheap means of disposal of farm waste
  • Adds humus to soil - improves structure and drainage
  • Nutrients not readily leached

Disadvantages:

  • May be difficult/require heavy machinery to spread
  • Unknown quantities/concentration of nutrients
  • Minerals may be released too slowly
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Types of fertiliser

Artificial/organic.

Advantages

  • Nutrients released rapidly into soil
  • Clean chemicals that lack odour
  • Nutrients in concentrated form - can be applied in smaller forms (cost effective)

Disadvantages

  • Readily leached from soil, so can damage the ecosystem of ponds and lakes
  • Risk of fertiliser spray spreading to other crops
  • Expensive to buy/manufacture

Above a certain point there's no point of adding more fertiliser. This is because above this the higher concentration of ions in the soil can REDUCE the WATER POTENTIAL of the soil causing plants to LOSE water by OSMOSIS. Also high concentrations of ions in the soil can prove TOXIC to roots.

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Environmental consequenes of using artificial fert

Fertilisers in excess can have widespread environemental effects such as:

Leaching - nutrients such as NITRATES are removed from the soil.

  • INORGANIC FERTILISERS ARE VERY SOLUBLE IN WATER.
  • Rain water will DISSOLVE any soluble nutrients, such as nitrates, and wash them out of the soil.
  • The leacher nitrates find their way into watercourses, such as streams and rivers, which in turn may drain into freshwater lakes. This can then cause EUTROPHICATION.

Eutorophication

  • In most lakes and rivers there's a naturally very little nitrate meaning NITRATE IS A LIMITING FACTOR for plant and algal growth. Once nitrate leachers into the watercourse, it CEASES TO BE A LIMITING FACTOR and plants and algae grow exponentially, resulting in the following course of events:
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Eutrophication course of events

  • An 'ALGAL BLOOM' occurs (rapid algal growth)
  • A dense layer of algae forms on the surface of the water, absorbing LIGHT and preventing it from penetrating lower depths, so PLANTS below the surface CANNOT PHOTOSYNTHESISE and therefore DIE.
  • Increased COMPETITION between algae results in DEATH OF ALGAE too.
  • When the algae and plants die, they are DECOMPOSED by BACTERIA and other SAPROBIOTIC ORGANISMS, whose populations suddenly INCREASE.
  • The increase in AEROBIC RESPIRATION by BACTERIA USES up OXYGEN.
  • The dissolved oxygen in the water becomes DEPLETED, causing many species of INVERTEBRATES and FISH to DIE.

Pollution of a river can also cause eutrophication because the organic material in sewage is fed upon by bacteria, which will respire aerobically, using up the oxygen in the river. If detergents are present, these contain phosphates which will encourage algal growth.

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Pest control

Pest: Any organism, plant or animal that causes nuisance or harm to humans.

In the UK arable farming is based on monoculture where large areas of land are given over to produce a single crop. Because they're grown so closely together pests and disease can spread rapidly, thus it is important to control these in order to obtain a high yielding good quality crop.

Weeds growing amongst crop plants and insects that feed on the different parts of a crop plant are classified as pests because they REDUCE THE RATE OF PHOTOSYNTHESIS and so then the YIELD and ECONOMIC VALUE of the crop.

Crop pests are commonly:

  • Insects - eat the crop plant, so REDUCING THE AMOUNT OF PHOTOSYNTHESIS e.g. by eating leaves, roots, sugars from the stem.
  • Fungi - cause disease and so REDUCE THE CAPACITY FOR PHOTOSYNTHESIS/GROWTH.
  • Weeds - compete with crop plants for Carbon Dioxide, Light, Water & Temperature.

Wheat plants grown closer together have a lower yield than those grown further apart. This is due to more intraspecific competition as they're competing for the same resources.

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Pesticides

These are CHEMICALS that are used to kill pests. The different chemicals are sprayed onto crops or the soil. They include HERBICIDES to kill weeds, INSECTICIDES to kill unwanted insects and FUNGICIDES to destroy fungi which are damaging the crop. 

Benefits of using pesticides as a method of pest control:

  • Application can be LOCALISED to precise areas
  • A pest species can be completely eradicated from the area
  • Works QUICKLY

Why each feature is an advantage for a good pesticide:

  • Specific - no detrimental effect on other non-pest species or useful organisms
  • Biodegradable - Doesn't remain in the environment (non-persistent) and will prevent bioaccumulation. However, it should be chemically stable so it's able to work
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Problems with pesticides

  • Many are toxic to other species as well as the target pest. They are NON-SELECTIVE. This may be a problem as predator(s) of the pest may also be harmed/killed and also could harm/kill other beneficial organisms (e.g. pollinating species).
  • Many older insecticides and some in use today are PERSISTENT. i.e. they remain in a stable and active form for long periods, and ACCUMULATE IN THE FATTY TISSUES without being broken down or excreted. This means that they will remain in the bodies of insects for a long time after they are applied. When an animal further up the food chain eats these insectens then the pesticide will pass into that animal and with each step in the food chain they will become more concentrated and may reach a lethal concentration. This is BIOACCUMULATION.
  • Pesticides may need to be REAPPLIED.
  • The target species may develop RESISTANCE to the pesticide (like antibiotic resistance in bacteria).
  • May contaminate humans (directly via application or indirectly via crops).
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Problems with pesticides

  • Many are toxic to other species as well as the target pest. They are NON-SELECTIVE. This may be a problem as predator(s) of the pest may also be harmed/killed and also could harm/kill other beneficial organisms (e.g. pollinating species).
  • Many older insecticides and some in use today are PERSISTENT. i.e. they remain in a stable and active form for long periods, and ACCUMULATE IN THE FATTY TISSUES without being broken down or excreted. This means that they will remain in the bodies of insects for a long time after they are applied. When an animal further up the food chain eats these insectens then the pesticide will pass into that animal and with each step in the food chain they will become more concentrated and may reach a lethal concentration. This is BIOACCUMULATION.
  • Pesticides may need to be REAPPLIED.
  • The target species may develop RESISTANCE to the pesticide (like antibiotic resistance in bacteria).
  • May contaminate humans (directly via application or indirectly via crops).
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Biological control

This is the use of NATURAL PARASITES or PREDATORS of the pest to REDUCE THE NUMBERS of the pest population. These organisms are referred to as BIOLOGICAL AGENTS.

Stages in setting up a biological control programme:

  • Find a suitable organism as the control agent. Often the pest will only have become a pest because it has been put in an area where it has no natural predators. The control agent will often be found in the native environment of the pest. 
  • Carry out trials to ensure that the agent: 
  • is specific to the pest - does not attack indigenous species (Species that have always lived in the specific area)
  • Can establish itself in the new environment and maintain its population at a low level
  • Doesn't carry diseases that may spread to the indigenous population
  • Does not become a pest itself
  • Breed large numbers of the agent and release them into the affected area
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+&- of biological control as method of pest contro

Advantages:

  • Specific to 1 pest species
  • Only 1 application (because it reproduces) so effective in long term
  • Maintains a low population size
  • No resistance develops
  • No bioaccumulation
  • Can be used in organic farming
  • Low management and cost involved when up and running

Disadvantages:

  • Doesn't get rid of pest completely; just keeps population at a low level
  • Slow acting. Takes time for the pest population to reduce
  • Predator species may become a pest itself (e.g. cane toads)
  • Difficult to control exactly where the predator will go
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Integrated pest management systems

Involves combining the use of PESTICIDES with BIOLOGICAL CONTROL in order to achieve the most effective economic outcome. Fewer chemicals are used and only when pest populations surge.

Close monitoring of pest populations is needed in order to determine when a population has reached an economically damaging level. When the predicted loss of crop yield (and so income) as a result of pest damage is greater than the cost of treatment this is called the ECONOMIC DAMAGE THRESHOLD and this is when the crop grower needs to act and use pest control techniques. 

Advantages of using integrated system (rather than just pesticides)

  • Reduce the amount of pesticide that needs to be sprayed
  • Reduce the risk of pests developing resistance to the pesticide
  • Minimises risk to both humans and the environment
  • Increases crop productivity and limits economic damage to the agricultural industry

Other strategies used in IPM incl. physical controls, such as CROP ROTATION, and genetic controls such as GENETICALLY MODIFIED CROPS

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