To Get this chapter, you must activate this app
Version: 1.0.2
Verification Number:
TT
Enter the Activation Number below:

To Get your activation number
Contact:

08033527655
+2348033527655
or
New Senior School Biology Practical Activity & Work Book 3
Chapter
4
ECOLOGY OF POPULATIONS/
BALANCE IN NATURE
Notable Concepts

Background Information

Ecological Succession

Agiven biotic community undergoes changes. Such changes can be seasonal which follows the same pattern each year. But there is another kind of change, which is a change in species due to changing habitatic conditions and competition for resources. This change is a progressive change in which earlier community are replaced by latter ones. After many years, the community becomes a forest, savannah or any biotic community as the case may be. When the vegetation reaches its highest development; the same species of organism appear or exist from year to year.Such a community becomes a climax community. A climax community is a community that remains the same or stable in its composition and size over a long period of time. It is a maximum community which a given habitat can support.
The sequential and gradual replacement of communities which leads to a climax community is called succession.
Two types of succession are recognized by ecologists
(i)Primary Succession and
(ii) Secondary Succession.

Primary succession:

Primary succession occurs where there is no prior existence of a community and it can begin on a new soil, an aquatic environment or rock. The first settlers are refered to as primary colonizers. Green microscopic algae, lichens etc. can be primary colonizers on a heap of sub soil.

Secondary succession:

Secondary succession occurs when an existing community is interfered with or disturbed by human activities or other factors such as floods, droughts and fire. In this case, already existing organisms may still be present in such habitat.

Over crowding

Overcrowding is an effect of population growth.
Population is the total number of organisms of a given species in a habitat at as given time. The average number of organisms of a species per unit area of a habitat is called population density.
Increase in population beyond a certain point results to overcrowding. Over crowding occurs when the available space per individual organism is too small for its well being. Overcrowding can be caused by the following factors:
  1. Increase in growth of population in a restricted area.
  2. Increase in population of organisms with social habit within their colonies
  3. Lack of proper dispersal
  4. When there are no predators
  5. Immigration

Effects of overcrowding:

  1. Food shortage
  2. Restlessness
  3. Aggression and other anti social behaviours
  4. Reduction in reproduction rate due to the unfavourable environmental conditions.

Adaptations to avoid overcrowding

  1. Territorial behavior as in lizards and baboons
  2. Proper dispersal of seeds, fruits and even animals
  3. Swarming to form a new colony as in bees and termites.

Food Shortage

Food shortage is an effect of overcrowding and certain other factors such as drought, disease, crop pests, floods and natural disaster, improper and inadequate means of food storage and preservation.

Effects of food shortage

  1. Competition
  2. Emigration
  3. Reduction in reproduction rate
  4. Increased motality rate

Balance in nature

Biotic and abiotic factors which affect population such as natural disaster like flood, availability of food, water, space, light, temperature, competition, parasites, predators etc do so through their effects on mortality and natality.
The population sizes of species of organism in a habitat, depending on available resources at a given time, tends towards a state of dynamic equilibrium which is called Balance in nature.
It happens that if any factor affects the population size of any of the species in dynamic equilibrium, a compensating change will occur in the population size of other species. For instance carnivores( which are predators) regulate the size of their prey by feeding on them while the prey in turn regulate the size of the carnivores through their availability for food.

Human Population Growth

A factor, which limits population growth, is called a limiting factor. The summation of all the limiting factors in referred to as environmental resistance.
In nature, population of living things grow exponentially until they stabilize due to environmental resistance. Human populations owing to their ability to control their environmental factors are an exception to this usual trend.
Human beings can control their population sizes in various ways such as:
  1. Increasing their mortality through improved hygiene
  2. Increased food production.
  3. Improved natality rate and fertility
  4. Reduction in infant mortality rate etc.

Human population Control

Among humans the only universally acceptable means of population control is by decreasing birth rate through family planning.
Natural birth control methods include:
Rhythm method and withdrawal method. Use of spermicidal creams; contraceptive pills; intra- uterine device and sterilization are artificial means of birth control in family planning.

General Questions

1. A stable community which has same kind of species in appearance and composition is called a
2. Atype of succession which takes place when an existing community is disturbed due to human activities or natural disaster is referred as
3. Perennial herbs, shrubs and trees and annual weeds can exist in a given habitat of abandoned farmland at different time. Arrange the community in order of progression that will be followed to attain a climax community.
4. On a heap of subsoil, green microorganisms(algae) and lichen which may be observed the first year constitutes the first settler called
5. In a given habitat, the average number of individuals of a species per unit area of habitat is called
6. Absence of proper dispersal can cause population growth problem called
7. Write down two effects of overcrowding
Food security; growth
food suplus; percking order
restlessness; aggression
8. One adaptation in agama lizards to avoid overcrowding is territorial behavior while in bees and termites can be adaptation to avoid overcrowding.
9. _________ , _________ and _________ are causes of food shortage.
Drought; diseases, natural disaster
Mortality rate; extinction; territoral behaviour
Aggresive behaviour; presence of predators swarming
10. All factors such as availability of food, environmental factors etc that affect population do so through their effects on _________ and _________
Mortality(death rate) and natality(birth rate)
Environmental resistance and migration
aggresive behaviuor and restlessness
11. A factor which limits population growth is called a limiting factor while the sum of all limiting factors is called
12. Write down three natural birth control methods

Expression Exercises

1. Write four general characteristics of succession
2. Write five causes of food shortage

Practical Activities

1. Investigation what happens to a cleared patch of land left till several years in a building sight.
    Procedure
  1. Clear a small area of land near your house or school compound. Clear it to the point of removingevery existing community that is noticeable there
  2. Leave the ground for months without doing anything there, but observe it periodically.
  3. Record and identify plants that grow there periodically and study succession from yourobservations.

Questions

(i) What type of succession have you observed in your investigation?
(ii) Write down the type of plants that are first found there
(iii) From your observations, when did you begin to see the same species of plants and animalsconsistently in that place. Try to write down such plants and animals

2. Studying overcrowding

Material required:
Tomatoes seeds, 2 plants pots, water, soil
    Procedure
  1. Put some amount of soil in each of the two plants pots.
  2. Plant just very few( about four seeds) tomatoes seed in one pot and plenty of it up to fifty seedsin other pot.
  3. Water the planted seeds and continue to water them until they germinate and grow intoseedlings, continue the watering till one month while you observe the seedlings every day.
  4. Observe with comparism, the two seedlings in the different pots.

Answer the following questions

(i) From your observation write two effects of overcrowding on growing seedlings in the second pot
(ii) Write down four factors that may cause overcrowding in a given habitat.

Test of practical work

State four factors that can result to secondary succession in a forest habitat

ECOLOGY OF POPULATIONSPAST SSCE QUESTION

November 1990 Q8
1. List three factors that can affect population growth

June 2007 WASSCE BIOLOGY 1 PRATICAL-QUESTION

2. Specimen B is a Lizard, specimen C is a grasshopper, specimen D is a grass, specimen E is garden soil and specimen F is a branch of cactus plant.
(a)(i) Mention the habitats of specimens B,C and F. [3marks]
(ii) state three observable features which adapt specimen F to its environment. [6marks]
(iii) Construct a food chain using at least three of the given specimens.[2marks]
(b)(i) Classify specimen B,C,D,E and F into biotic and abiotic factors. [2marks]
(ii) What is the significance of specimen E in the ecosystem? [3marks]
(e) Make a drawing 8 to 10cm long of the lateral view of specimen C and label fully. (9marks)
« Previous
≡
Next »