I) General Nature of Agro-Ecosystems

Eco-AgroEcosystem. P.1

Eco_Agro-Ecosystem

I) General nature of Agro-ecosystems

gro-Ecosystem are those agricultural systems which are managed by m__ for the maximum output of c___ production. They are characterized by a 'm__-made' physical h_____ Acreated by methods of 'cultivation' eg. tillage, planting, fertilizing, draining, irrigation, weeding, harvesting, etc.

The dominant components are plants (and animals) sel_____, prop______, and har______by humans for a particular purpose, their composition and structure are si_____.

The plant biomass is usually dominated by one major c____, there is normally only one l____ or strata fromed by the crop itself. Only eleven plant species account for about 80% of the world food supply. Among these, the cer___ provide over 50% of the world's production of protein and energy. The number of species which have been selected as 'crop' plants is remarkably few (a result of mono______).given the diversity of the world's plant species

II) Crop plants

General Characteristics

A high proportion of crop plants are annuals and are also l____-demanding.

They are also characterized by high y_____ of that part of the plant human wish to use, which can be seeds, leaves, stem, roots or fruit.

Most crop plants have undergone very long period of dom______, some may have no known wild counterparts.

Many are so well-adapted to the man-made environment in agro-ecosystem that they cannot s______in the wild. Some could not even propagate themselves without human aid.

Crop breeding

Crop br______has been directed primarily towards the production of varieties and strains which will give max_____ yield under the prevailing conditions. eg. high yielding hybrid varieties of rice in ‘Green revolution’.

Q. What are some of the objectives of plant breeding programme? And are the possible consequences? Eco-AgroEcosystem. P.2 III) Industrialized agriculture and Green Revolution

Crop production is increased either by cultivating more land or by getting higher yields from existing cropland. Since 1950, most of the increase in world food production has come from increasing yield in what is called a Green revolution. Essentially, this involved :

 Mono______.

 plant varieties that have been sci______bred for desirable qualities

 applying large amounts of inorganic f______, ir______water

 extensive use of p______.

Between 1950 and 1970, this approach led to dramatic i______in yield in the U.S and other industrialized countries -- the First green revolution.

In 1967, after 30 years of genetic research, a modified version of the first green revolution began spreading to many LDCs. High y____, fast gr______, dw___ varieties of rice and wheat, specially bred for tropical and subtropical countries were introduced into several LDCs----the Second Green revolution.

The sh______, stronger, and stiffer stalk of the new varieties allow them to support larger heads of grain without toppling over. With large inputs of fertilizer, water, and pesticides, the wheat and rice yields can be two to five times those of traditional crops. The fast growing varieties allow farmers to grow two, and even three crops a year. Nearly 90% of the increase in world grain output in the 1960s were the result of the second Green revolution.

These increases, however, depend heavily on f -fuel inputs to run machinery, produce and apply inorganic fertilizers and pesticides, pump water for irrigation.

These high inputs of energy, water and pesticides can increase yields dramatically for a while. Experience has shown that yields is reducing because of :

 increased soil e______,  loss of soil f______,  sali______, n  waterl______,  des______,  depl____ and poll______of surface water and under______water sources,  and genetic r______of pests to pesticides.

Despite the apparent success of industrialized agriculture, its impressive productivity is at the mercy of o___ prices. Projected increases in the price of oil, changes in global climate, or both could disrupt agricultural production, cause sharp rises in food price, and lead to mass star______and disease. Eco-AgroEcosystem. P.3

Harmful Environmental Impacts_ Industrialized vs Traditional agriculture

Industrialized Agriculture Traditional Agriculture 1. Soil degradation

· Soil erosion and loss of fertility through poor · Soil erosion and rapid loss of soil fertility land use, failure to practice soil conservation caused by clearing steep mountain techniques, and too little of organic fertilizers highlands without terracing, shifting cultivation in tropical forests without · Salinization and waterlogging of heavily irrigated leaving the land fallow long enough to soils restore fertility, overgrazing

· Reduction of nutrient-recycling soil microbes · increased frequency and severity of from heavy use of pesticides and commercial flooding in lowlands when fertilizers and soil compaction by large farm mountainsides are deforested machinery

2. Air pollution

· Air pollution caused by dust blown off cropland · Air pollution caused by dust blown from that is not kept covered with vegetation. cropland not kept covered with vegetation and from overgrazed · Air pollution from droplets of pesticide sprayed rangeland from planes

· Air pollution caused by extraction, processing, transportation, and combustion of huge amount of fossil fuels used in industrial farming.

3. Water Pollution

· Pollution of stream, lakes, and estuaries and killing · Sediment pollution of water caused by of fish and shellfish from pesticide runoff. erosion and runoff from farmland, overgrazed rangeland, and deforested  Depletion of underground aquifers by excessive land. withdrawal for irrigation

 Pollution of groundwater caused by leaching of water soluble pesticides, nitrates from commercial fertilizers.

4 Ecological disruption

· Loss of genetic diversity of plants by clearing · Endangerment and extinction of biologically diverse grasslands and forests and animal wildlife caused by loss of habitat replacing them with monocultures of single crop. when grasslands and forests are cleared for farming · Endangerment and extinction of animal wildlife from loss of habitat when grasslands and forests are cleared and wetlands are drained.

· Depletion and extinction of commercially important species of fish caused by overfishing

5 Threat to human health

· Threat to health from nitrates in drinking water and · Threat to human from flooding pesticides in food and atmosphere. intensified by poor land use and from human and animal wastes discharged into irrigation and drinking water, and from improper use of agricultural chemicals. Eco-AgroEcosystem. P.4 IV) Weeds, pests and diseases

A) Weeds In creating agro-ecosystem human also provided hab____ for other organisms, which are often refer as 'weeds' or pests.

Weeds are particularly adapted to open, exposed, nutrient deficient conditions. They are characterized by high s___ production, successful germ______, ability to spread veg______, and tol______to a wide range of environmental conditions.

A considerable number of weeds are virtually cosmopolitan. Their dispersal is sometimes a direct result of hu___ activities.

Weeds com____ with crop plants for space, water, light and nutrients, some produce toxic substances, they might also be host for pests and diseases.

B) Pests and diseases The most important group causing plant di______is the par_____ fungi. Pests are the animal counterpart of weeds.

Q. What are the contributing factors to increase in pest population in agriculture?

IV) Pests and Pest Control

What is a Pest ?

We describe as a pest any organism which we find annoying, or which damages our in .

In a sense, the control or eradication of pests is related to interactions between competitors . In this case, humans try to kill or control the population of his com______- the pests by various means (phy____, chem____, bio______and inte______approach). For instance:

1) Many such species are really quite harmless, some just find them annoying. e.g.______.

2) On the other hand, many invertebrate species, and especially i______, cause enormous damage to crops of all kinds. Perhaps 30% of all food plants would be destroyed by pests, in the absence of control measures.

3) Some micro-organisms are______-causing agents, eg.______is caused by bacteria, ______is caused by a fungus and ______is caused by ______a virus and ______is caused by a protozoan.

4)Some pests are carriers of ______to plants, animals and ourselves. M______and y______fever are carried by m______, plague by fl___. Malaria presently kills millions of people every year.

Organisms, especially insects, have often been accidentally tr______by humans from one place to another. These 'foreign' pests are often the most dangerous, why? Eco-AgroEcosystem. P.5

Q. 'Foreign' pests are often the most dangerous, why?

Insects are particularly difficult to control, owing to their rapid ______rate and great m______which enables them to move long distances in search of new food sources.

Q. How does the life cycle of mosquito make it a difficult animal to eradicate?

Chemical and Biological Control

There are two classic methods of pest control. The most general method of control involves the use of chemicals called pesticides (such as insecticides, fungicides, herbicides, etc). Biological control involves the use of natural en______of the pest species. These may be pred____, para____ or disease-causing micro-organisms.

A) Chemical control a) Advantages of Chemical Control The philosophy of chemical control is very simple: achieve the maxi___ possible percentage k___ among the pests. This is what sells pesticides.

The effect of chemicals in controlling pests has been dramatic and millions of human lives have undoubtedly been saved through the use of chemicals. Their effectiveness has led to their widespread use all over the world.

Q. What are the advantages of pesticides that led to their widespread use?

b) Disadvantages of Pesticides Unfortunately, early successes have led to the abus___ use of chemicals in many instances, leading to severe problems of various kinds. Experiments to study the s___-effects of pesticides on harmless and ben_____ organisms have often been inadequately carried out.

I) Death due to Accidental Misuse The most direct problem concerns tox_____ to humans, domestic animals and pets due to accidental misuse. There are approximately 150 human deaths per year in the USA from insecticides. ii) Disruption to Ecosystem Pesticides, or residues derived from them, may cause serious disr______to ecological systems. Residues may be quite long-l in soil or fresh water. Pesticides may significantly affect decom______processes in soil.

Some residues remain active long enough (per______) to enter food chains. As they pass along food chains, they are con , especially in fat deposits. Top carnivores, usually vertebrates, may be unable to break down the residues which become increasingly and dangerously concentrated. Over the last 40 years, insecticides have entered f_____ chains in all parts of the world, terrestrial, freshwater and marine. Eco-AgroEcosystem. P.6

iii) Pest Resurgence Many pest species are capable of r____ increase in numbers. Pesticides kill b ___ pests & their predators.

Q. If a pesticide kills most of the predators as well as the pests, what might happen to the remaining small population of pests once the effect of the pesticide has worn off ?

Q. Study the diagrams; you can see that insecticide, if carelessly used, is a recipe for increasing the number of pests. Explain the phenomenon. Eco-AgroEcosystem. P.7 iv) Outbreak of a New Pest Species

A similar, but more complicated problem, involves outbreak by new pest species after treatment against a familiar one. The problem is caused by the fact that insecticides are more deadly to some species than others.

Q. Explain how aplication of pesticide can lead to outbreak of a new pest species

v) Pest Resistance

The most serious problem is pest resistance. Members of a pest species are not equally vul______/res______to a particular pesticide. Some individuals, gen ______different from the majority, may be less susceptible, and may survive to pass on their re to future pest generations.

Any mutation providing extra resistance will be highly fav and passed on. So humans, by applying pesticides, cause natural sel for the very thing we wish to avoid.

This is a serious problem. In 1950, less than 20 pest species were known to be pesticide-resistant, but by 1975 about 250 resistant species had been recorded. These include some populations of malarial mosquito, rats, lice, and many food-destroying species.

Q. Figure on the left shows how resistance has increased in a larval insect pest called the tobacco budworm. Approximately how much insecticide achieved a 50% kill in (a) 1968 and (b) 1970?

Q. In trying to develop a new pesticide what properties would you ideally want it to have?

So, even with 'ideal' pesticides, which kill only the pest and nothing else, and which rapidly become harmless, there will always be a problem of resistance. This leads to a race between scientists developing new in______and pests developing new forms of re______. Eco-AgroEcosystem. P.8

S tudy Item : Concentration effects in food chains

Since the Second World War there has been a dramatic increase in the number of man-made chemicals released into the environment. These include herbicides and pesticides designed to kill those organisms, particularly weeds and insects, that are harmful to crops, livestock and Man himself.

Among the first of the successful pesticides was a group of chlorinated hydrocarbons (organochlorines) which included DDT (dichlorodiphenyltrichloroethane), dieldrin and aldrin. These chemicals are toxic to a broad spectrum of animal species, including Man, although birds, fish and invertebrates are worse affected. To the surprise of many scientists, it was reported in the 1960s that DDT had been detected in the livers of penguins in the Antarctic, a habitat very remote from areas DDT might have been used.

Pesticide poisoning has had devastating effects on some top carnivores, most notably birds. The peregrine falcon, for example, has disappeared completely from the eastern USA as a result of DDT poisoning. Birds are especially vulnerable because DDT induces hormonal changes that affect calcium metabolism and result in the production of thinner egg shells with a consequently high loss of eggs through breakage. Levels of DDT in human body fat are 12-16 ppm in the USA, where the upper legal limit of DDT content for sale of food is 7 ppm.

In more recent years. some powerful but non-persistent pesticides have been developed, such as organophosphates (for example malathion), and the use of DDT has been severely reduced. However. DDT is relatively cheap to produce and continues to be more suitable for certain tasks, such as malaria control. When considering whether to use pesticides it is often a case of choosing the lesser of two evils. DDT has completely eradicated malaria in many parts of the world. In Mauritius, for example, although the birth rate has not changed significantly since 1900, a population explosion has occurred because far fewer babies are dying from malaria. Infant mortality fell from 150 per 1000 to 50 per 1000 in 10 years as a result of post-war spraying with DDT.

Q. The figure shows the amount of DDT at different levels in a food chain in the USA. a) If the concentration of DDT in the water surrounding the water plant was 0.02 ppm, what was the final concentration factor for DDT in passing from water into (i) primary producers, (ii) smallfish, (iii) large fish, (iv) the top carnivore

b) What conclusions can you draw from your answer to a) ? c) At which trophic level (i) is DDT likely to have the most marked effect, (ii) would DDT be most easily detected, (iii) are insect pests of crops found (a typical target of DDT)? d) Suggest ways in which the penguins might have come to contain DDT. e) Clear Lake, California, is a large lake used for recreational activities such as fishing. Disturbance of the natural ecosystem by eutrophication (nutrient enrichment) led to increased populations of midges during the 1940s and these were treated by spraying with DDD, a close relative of DDT, in 1949, 1954 and 1957. The first and second applications killed about 99% of the midges but they recovered quickly and the third application had little effect on the population.

Analysis of small fish from the lake showed levels of 1-200 ppm of DDD in the flesh eaten by Man, and 40- 2500ppm in fatty tissues. A population of 1 000 western grebes that bred at the lake died out and levels of 1600 ppm of DDD were found in their fatty tissues.

I) Suggest a reason why the DDD did not succeed in eradicating the midges and why they recovered so quickly after the third application.

ii) It has been observed that many animals die from DDT poisoning in times of food shortage. Suggest a reason for this based on the data given so far.

f) In Great Britain, the winters of 1946-7 and 1962-3 were particularly severe. The death toll of birds was high in both winters, but much higher in 1962-3. Suggest a possible reason for this in the light of the data given about DDT. Eco-AgroEcosystem. P.9

B) Biological Control

Biological control is most likely to succeed for pests that are acc______tran_____ to a new hab____--where there is no natural en____ for its control.

Unlike chemical control which aims at a short term highest possible k__, biological control wants to achieve a l____-term con___ of pest populations below a level that is econ______damaging.

Ideally, a certain bal_____ between the pest & control agent population will be established so that they regulate each other’s population in a homeo______manner.

Some successful examples of biological control Place Crop Pest Control agent USA citrus scale insects parasitic wasps Hawaii fruit Oriental fruit fly " Canada timber winter moth " Australia fruit and vegetable green vegetables bug " USA walnut walnut aphid " Australia -- prickly pear herbivorous moth USA -- klamath weed (poisonous to cattle) herbivorous beetle

A Biological Control programme consists of the following stages.  A search to find the ori___ of an accidentally imported pest species.  A search for natural en______of the pest.  A careful quar______programme when these natural enemies or control agents are imported. This is to make sure that no diseases are imported with the control agent, and that it does not itself become a p____ by preying upon other beneficial species.  Pilot Exper______to establish whether the control likely to succeed on a large scale.  If these are successful, mass cult____ and final rel______of control agent.  Eval______of the programme.

Q.1 Why do you think the numbers of pests fluctuate, both before and after the introduction of control measures?

Q.2 What step is taken to ensure that the control agents do not become pests themselves?

P______wasps are particularly successful in biological control. Other insects which have proved successful include predatory species of beetle (such as the ladybird beetle), bugs and flies. Bacteria that cause disease in pest species (Bacillus thuringiensis –BT1) are now being produced in commercial quantities. Successful control agents are those which thrive in the conditions into which they are introduced and which are sp_____ to pest species.

Q.3 Why is it important that the control agent be specific to the pest?

Q.4 Summarise below some of the features of chemical and biological control.

Chemical Control Biological Control 11 The BT toxin can also be introduced into a plant through genetic engineering e.g. BT corn, BT cotton, BT potato, etc. http://www.ca.uky.edu/entomology/entfacts/ef130.asp Eco-AgroEcosystem. P.10

C) Integrated Pest Management

An account of a Pest control programme with DDT

In 1949, Peruvian cotton farmers began using large quantities of DDT and other synthetic chemicals to control pests. Cotton production immedi- ately soared as populations a serious insect pest (a worm)fell, but after the third year of spraying, the insects evolved resistance: Individuals that happened to have pesticide-resistance mutations survived the insecticide treatment multiplied, and soon larger and larger doses of pesticide were required. By 1956, despite immense doses of toxic insecticides, resistant worms were again chewing away the cotton crops, accompanied by six new cotton predators with resistance to the poisons. That year, the cotton farmers suffered their worst losses ever: Insects ate half their crops.

Q.1 Identify the type of pest problems facing the Peruvian farmers following application of DDT.

Faced with the diastrous loss, the Peruvian farmers change their strategy, they

 re_____ use of synthetic pesticides and return to mineral insecticides (such as sulphur dust).  careful t______in application of several insecticides at the stage of the life cycle at which the insects are most vulnerable  they imported 130 million w____ that attack the eggs of the worm,  a short season var_____ of cotton plant was chosen (which mature before pest populations can build up),  specific cultural pract____ (tilling, irrigation, fertilizing) that discour____ pests and en______their natural enemies,

As a result of the change in strategy, small numbers of the worm continued to survive in their fields, but cotton yields reached new highs.

The experience of the Peruvian cotton farmers led to the first success of Integrated pest management, a system based on the ecological principles and aimed at keeping pest populations below economically harm ful levels with a minimum of chemical pesticides.

Integrated pest management requires a broad view of all inter______between the crop and other species : Eco-AgroEcosystem. P.11

Q. What should be included in this ‘broad view’ of the agro-ecosystem include in an integrated pest management programme?

 What are the insects that eat the crop, what are the potential pests? What are their roles in the ecosystem? What are the effects their removal on the ecosystem?  What are the natural enemies of the pests? predators and competitors?.  Animals that might be beneficial to the crops or the environment. e.g. those pollinate the crop; and other wildlife living in the area.  The possible effects of varying cultural paractices on the balance between pests and their natural enemies

Q. What are the major principles of integrated pest management?

 an understanding of the roles played by various biotic components of the agro-ecosystem including the crop, the pests, their natural enemies and the other wildlife.  carefully timing, spacing, and intermixing of crops so as to enhance the activities of natural predators of crop pests.  introduce biological control agents from other regions that feed exclusively on the pest, such as wasps.  integrated pest managers use chemical controls only when insects appear to do damage above some preestablished level of economic injury. And when spraying is necessary, they choose and apply compounds to hit target species, leaving "innocent bystanders" alone.

Integrated pest management could be difficult to apply because it usually involves a full ecological study of the situation and a variety of practices to ensure the success of the program, but because it avoids a whole host of problems, such as pests evolving resistance, it offers an ecologically and economically acceptable alternative to losing much of a crop to pests.

Reference reading : "Parasite Versus Host: Coevolution observed"

In 1859, twenty-four European rabbits were imported into Australia and released on a sheep ranch. "Rabbit drives" held on that ranch in the following six years resulted in the killing of some 6000 rabbits. This was not enough to exterminate the rapidly expanding population of rabbits. The size of a European rabbit population can increase by as much as twelve times in a single year when conditions are ideal, that is, when population pressure is low. The descendants of the original twenty- four rabbits reproduced at such a rapid rate that large numbers of rabbits migrated to new areas. By the 1880s the borderof the geographical areas occupied by the rabbits was moving outward in some places seventy miles in a single year.

The European rabbit soon became a dominant species in Australia, competing with both wild and domesticated animals (for example, kangaroos and sheep) for available vegetation. Desperately, the Australians attempted to stem the tide of the rabbit advance by building thousands of miles of rabbit-- proof fencing. A single segment, the "No. 1 rabbit fence" completed in 1907 in Western Australia, stretched 1100 miles. Fencing failed to stop the spread of the rabbits because it was impractical to maintain the fencing at perfect efficiency--and anything less was useless.

Australians were unable to control the European rabbit until 1950. In that year Australian scientists infected a number of European rabbits with a virus that causes myxomatosis (a tumorlike skin Eco-AgroEcosystem. P.12 infection that is often lethal). The infected rabbits were released. The Australians hoped to start an epidemic that would reduce the size of the rabbit populations and possibly even extinguish the pest in Australia.

In the epidemic that followed, 99 % of the rabbits in some areas died. The rapid recovery of the vegetation was quite extraordinary--the ranchers were able to raise more sheep than ever before.

The Australians thought they were on the verge of total victory over the rabbit. However, biological control of one species by another creates a system that selects for its own failure. Some biologists predicted that the selective system established by introducing the virus would bring about the evolution of virus-resistant rabbits and less lethal viruses. The predicted "Coevolution", the joint evolution of two different species brought about by their ecological interactions, is exactly what happened.

The rabbits that survived the first epidemic were not a random sample of the original rabbit population. Rather, a higher proportion of these surviving rabbits carried genes that enabled them to survive the viral infections. These rabbits, selected for their resistance to myxomatosis, produced offspring that in their turn were exposed to the same selection process. Consequently the proportion of rabbits that had some genetic resistance to myxomatosis increased from year to year.

The populations of myxomatosis viruses also evolved. In Australia these viruses are normally transmitted from one rabbit to another by a mosquito. However, mosquitoes are abundant only during certain seasons of the year. Consequently, for long periods each year there is no way that the virus can be transmitted from the skin of one rabbit to another. Thus the mode of transmission selects viruses that allow their hosts to survive long enough for the mosquitoes to bite the virus-containing skin tumors and transmit the viruses to another rabbit.

The coevolution of these two species prevented the Australians from bringing about the extinction of the European rabbit in Australia, although they did succeed in drastically reducing the number of rabbits.

Q.1 Which organism is the pest ? How did it become a pest in Australia ?

Q.2 What is the control agent ? What is the kind of pest control method employed here ?

Q.3 To what degree do you think the program is successful ?

Q.4 Bearing in mind the concept of co-evolution between the rabbit and the virus, what would you predict about the future population of the rabbit ?

Sugested Answers:

P.1 Q. What are some of the objectives of plant breeding programme? And are the possible consequences?

Plant breeding is also directed towards production of 'mac_____ crops', those adapted by reason of unif____ height, flowering, fruiting to mechanized cultivation, harvesting and packaging. Eco-AgroEcosystem. P.13 being responsive to fertlizers, faster growth rate, shorter life cycles, resistant to pests, drought,etc

Varieties are so often highly inbred as to be genetically un iform. They may be equ ally cold, drought or disease resistant, or tolerant to environmental stress, rendering them vulnerable to attack by pests

P.4 Q. What are the contributing factors to increase in pest population in agriculture?

Contributing factors to increase in pest population :

 Large scale mon______of crops on which pests depend as hosts.  Accidental t______of pests with the absence of natural predators or parasites.  Large-scale mechanized agriculture resulted in destruction of n______habitats, number of natural predators that originally keep pest down has been reduced.  Use of chemical p______also resulted in destruction of predatory populations (concentration effects).  Failure of pesticides to achieve l_____ term pest control. eg. pest resistance, pest resurgence, etc.

P.5 Q. 'Foreign' pests are often the most dangerous, why?

It is because in the absence of their natural enemies, they may reach enormous numbers.

P.5 Q. How does the life cycle of mosquito make it a difficult animal to eradicate?

It has a short life cycle, can breed from eggs to adult in just 7-14 days. It is not particular with breeding ground, any collection of standing water will do. The larve feed on planktons, no shortage in water bodies.

P.5 Q. What are the advantages of pesticides that led to their widespread use?

They are fast and efficient. It can be applied by most without a requirement of understanding of how it works.

P.6 Pest resurgence

Q. The pest population may be able to increase rapidly in number again due to its high reproductive rate.

Q. Pesticides remove natural predators / enemies as well as the pest. In the absence of predators & natural enemies, because of its innate higher reproductive potential, explode in population--- often before predators can re-establish an effective control.

P.7 Outbreak of a new pest species

There ae often complicated interaction between pests and their predators even in simplified ecosystems such as a cropland. A crop might be fed on by a number of insect, but just a few are considered pests because the other are not causing significant loss because they are kept in check by their natural predators and enemies.

Application of pesticides might remove the targeted pest as desired, but it might also remove natural enemies of other species that were not considered pest before. These insects (eg. herbivore B) might be less susceptible to the effect of pesticides than others, they may now multiply and explode into a pest population due to less competition and absence of predators.

P.7 Pest Resistence

Q. a) 0.05 kg/ha b) 0.55 kg/ha

Q. Maximum possible specificity so that minimal effects on species other than pests. Inexpensive to make non-persistence Eco-AgroEcosystem. P.14

P.8 Study item_Concentration effects in food chains --DDT

(a) (i) x2 (ii) x500 (iii) x2500 (iv) x3750¶

(b) DDT is subject to progressive concentration as it passes along the food chain. This suggests that it is a persistent chemical, not easily broken down and that it is stored rather than metabolized in living organisms. (In fact, it remains active for 10-15 years in soil.)¶

(c) (i) and (ii) 4th trophic level (top carnivore)

(iii) 2nd trophic level (herbivore)¶

(d) DDT has spread all over the world as a result of two factors.

First, it is carried at very low concentrations in water. If it is washed off agricultural land and into rivers some of it reaches the sea and becomes concentrated in marine food chains. Penguins feed on fish and are part of these food chains.

Secondly, DDT can be carried in the atmospheres, both because it is volatile and because it is sprayed as a dust which can be carried by wind systems over large distances.

(e) (i) A small proportion of the original midges were resistant to DDT and these were not killed by the spraying proccdure. Between sprays their numbers increased and after successivc sprays they continued to breed and eventually constituted the greater part of the population. In other words the population had undergone intensive selection pressure. ¶

(ii) The data given suggest that DDD (and therefore DDT) is stored predominantly in fatty tissues. (This is because DDD and DDT are soluble in fat rather than water.) During times of food shortage, fat is mobilised and used so that the DDD or DDT accumulated over a long period is released into the bloodstream in relatively high concentrations.¶

(f) It has been suggested that the high death toll of birds in the winter of 1962-3 compared with 1946-7 was due to the additional effects of DDT mobilisation from fatty tissues. In 1946-7 the use of DDT was limited, in the late 1950s and early 1960s its use was widespread.

P.9 Biological Control

Q1Because there are factors affecting the population of pests. eg. density dependent factors such as availability of foods; density independent factors such as fluctuating weather.

Q2A quarantine program & a small scale pilot scheme to be carried out before actual large scale production and release of the control agent.

Q.3 Tpo avoid the control agent from becoming a pest itself.

P.10 Q. What should be included in this ‘broad view’ of the agro-ecosystem include in an integrated pest management programme?

 What are the insects that eat the crop, what are the potential pests? What are their roles in the ecosystem? What are the effects their removal on the ecosystem?  What are the natural enemies of the pests? predators and competitors?.  Animals that might be beneficial to the crops or the environment. e.g. those pollinate the crop; and other wildlife living in the area.  The possible effects of varying cultural paractices on the balance between pests and their natural enemies

P.10 Q. What are the major principles of integrated pest management? Eco-AgroEcosystem. P.15

 an understanding of the roles played by various biotic components of the agro-ecosystem including the crop, the pests, their natural enemies and the other wildlife.  carefully timing, spacing, and intermixing of crops so as to enhance the activities of natural predators of crop pests.  introduce biological control agents from other regions that feed exclusively on the pest, such as wasps.  integrated pest managers use chemical controls only when insects appear to do damage above some preestablished level of economic injury. And when spraying is necessary, they choose and apply compounds to hit target species, leaving "innocent bystanders" alone.

P.12 Parasite verse host : co-evolution observed

Q1European rabbit. It was introduced into Australia where it found little natural enemies but plenty of empty niches.

Q2The myxomytosis virus. Biological control

Q3Quite successful. The rabbit population was brought down to an acceptable level.

Q4It would increase, since co-evolution enhance the survival of both species. It would bring about less harmful effect of the viruses on the rabbit which gradually become more resistant to the viral infection.

Harmful Environmental Impacts of Industrialized and Traditional agriculture

Industrialized Agriculture Traditional Agriculture 1. Soil degradation

· Soil erosion and loss of fertility through poor · Soil erosion and rapid loss of soil fertility land use, failure to practice soil conservation caused by clearing and cultivating techniques, and too little of organic fertilizers steep mountain highlands (marginal lands) without terracing, using shifting · Salinization and waterlogging of heavily irrigated cultivation in tropical forests without Eco-AgroEcosystem. P.16

soils leaving the land fallow long enough to restore fertility, overgrazing of · Reduction of nutrient-recycling soil rangeland and deforestation to provide microorganisms from heavy use of pesticides cropland or fuelwood and commercial fertilizers and soil compaction by large farm machinery · increased frequency and severity of flooding in lowlands when mountainsides are deforested

2. Air pollution

· Air pollution caused by dust blown off cropland · Air pollution caused by dust blown from that is not kept covered with vegetation. cropland not kept covered with vegetation and from overgrazed · Air pollution from droplets of pesticide sprayed rangeland from planes

· Air pollution caused by extraction, processing, transportation, and combustion of huge amount of fossil fuels used in industrial farming.

3. Water Pollution

· Pollution of stream, lakes, and estuaries and killing · Sediment pollution of water caused by of fish and shellfish from pesticide runoff. erosion and runoff from farmland, overgrazed rangeland, and deforested  Depletion of underground aquifers by excessive land. withdrawal for irrigation

 Pollution of groundwater caused by leaching of water soluble pesticides, nitrates from commercial fertilizers, salts from irrigation water.

4 Ecological disruption

· Loss of genetic diversity of plants by clearing · Endangerment and extinction of biologically diverse grasslands and forests and animal wildlife caused by loss of habitat replacing them with monocultures of single crop. when grasslands and forests are cleared for farming · Endangerment and extinction of animal wildlife from loss of habitat when grasslands and forests are cleared and wetlands are drained.

· Depletion and extinction of commercially important species of fish caused by overfishing

5 Threat to human health

· Threat to health from nitrates in drinking water and · Threat to human from flooding pesticides in food and atmosphere. intensified by poor land use and from human and animal wastes discharged into irrigation and drinking water, and from improper use of agricultural chemicals.