Lesson Notes By Weeks and Term - Senior Secondary School 2

SUBJECT: BIOLOGY

CLASS:� SS2

DATE:

TERM: 3RD TERM

REFERENCES

• Modern Biology for Senior Secondary Schools by S.T. Ramalingam
• Essential Biology by M.C Michael�
• New School Biology by H. Stone and Cozen
• SSCE Past Questions and Answers
• New System Biology by Lam and Kwan�
• College Biology by IdodoUmeh
• UTME and Cambridge Past Questions and Answers�
• Biology Practical Textbook

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WEEK EIGHT

OVERCROWDING AND FOOD SHORTAGE

CONTENT

• Overcrowding
• Factors Causing Overcrowding
• Effects of Overcrowding
• Adaptation to Overcrowding
• Food Shortage

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OVERCROWDING

This is a situation in which a population increases beyond a point called the carrying capacity where the resources (e.g. food and space) are not enough to support all the individuals in thepopulation. Therefore, overcrowding reduces the food and space available for individual�

species in the population.

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FACTORS CAUSING OVERCROWDING

1. Natality:� An increase in the rate at which a particular species gives birth in a restricted area results in overcrowding.
2. Increase in food supply
3. Decrease in mortality: Overcrowding results when the rate of death of organisms in a habitat is lower than the rate of birth.
4. Immigration: Inflow of individuals into a habitat increases the population which later causes overcrowding.
5. Lack of dispersal of fruits or seeds of plants.
6. Social habits of animals like termites, ants and bees lead to their multiplication in the colony.
7. Inadequate space

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EFFECTS OF OVERCROWDING

These include:

1. Shortage of food since the available food in the habitat in the habitat is rapidly eaten up due to overcrowding.
2. Shortage of space due to increasing population of species.
3. Competition occurs as the organisms struggle for scarce resources e.g. food, space. The stronger ones get the resources while the weaker ones are deprived i.e. survival of the fittest.
4. Anti-social behaviours like fighting or cannibalism can result from the stress of overcrowding.
5. Easy spread of diseases e.g. tuberculosis in human (air-borne).
6. Preying or feeding on each other when food is in short supply.
7. Death of organisms as weaker organisms in overcrowding area easily dies off due to lack of food and space.

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ADAPTATION TO AVOID OVERCROWDING

In order to survive overcrowding, plants and animals have developed the following adaptive features:

1. TERRITORIAL BEHAVIOUR

Animals like mammals, lizards, birds etc establish territories which they are possessive of. They fight for and defend the territories against any intruders. A successful claim of the territory ensures sufficient food, space mating partners and parental care for the organisms.

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• SWARMING

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This is exhibited by some social animals such as termite and bees when some of them move out from an old colony to a new one. Hence, overcrowding is avoided.

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• EMIGRATION�

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This is the outward movement of animals out of their locality to anther place of settlement. This prevent overcrowding.

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• DISPERSAL OF SEEDS AND FRUITS�

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This could be by water, wind, animals, insects and explosive mechanism. The seeds and fruits are carried far away from the parent plants. Hence, overcrowding is prevented.

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• FORMATION OF CANOPIES

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This is an attribute of forest trees. This helps the plants to trap enough sunlight and also prevent the shorter plants below from getting the light. The lower plants�

eventually die off and overcrowding is avoided.

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• PRODUCTION OF CHEMICALS

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Roots of some plants produce chemicals which prevent the growth of other plants close to them. Therefore, overcrowding is avoided.

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FOOD SHORTAGE

In a well established habitat, population sizes of various species are adjusted to the quantity of food that is available in the habitat. Factors that can decrease the food supply to the habitat thereby causing food shortage are as follows;

• Natural disaster like flood, drought
• Diseases of plants and animals
• Pests such as locust, grasshoppers, weevils
• Lack of or inadequate storage facilities
• Bush burning which destroys soil organisms reduces soil fertility and exposed the soil to erosion.

All these result in poor yield and eventual food shortage

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EFFECT OF FOOD SHORTAGE ON POPULATION SIZE

1. Competition: - Scarcity of food leads to struggling among organisms for any available food. This results in the survival of the fittest. This can result in fighting and cannibalism (animals feeding on themselves e.g. man)
2. Emigration: - Animals also move from an area of food shortage to where sufficient food is available.
3. Decrease in the rate of reproduction: - Many human beings and marriage due to lack of or inadequate food supply may engage in family planning to reduce the number of children to be catered for.

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GENERAL EVALUATION

1. What is food shortage?
2. Outline four factors that cause food shortage.
3. State three causes of food shortage.
4. State two outcomes of succession.
5. Discuss five adaptive features of organisms used to survive overcrowding.

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READNG ASSIGNMENT

College Biology, chapter 23, pages 541-544

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WEEKEND ASSIGNMENT

SECTION A

1. The following except one results from food shortage A. Competition B. Reduced mortality rate C. Emigration D. Increased mortality rate.�
2. Food shortage makes the population size A. increase B. decrease C. stabilize D. fluctuate��
3. Food storage results in A. stability of price B. Natural disaster C. high natality rate D. overpopulation�
4. These are methods of storing and preserving food except A. Silos B.� barns C.� refrigeration D. Marketing.
5. These are forms of adaptation to avoid overcrowding except A. Pairing B.Territoriality C. Swarming D. Canopy

SECTION B

1. (a) What is overcrowding?

(b) State five effects of overcrowding.

2. State five ways of improving crop yield.