Basic Ecological Systems III SS1 Biology Lesson Note

POPULATION CHARACTERISTICS

These include population size, density, frequency, percentage cover and distribution.

1. Population size: – this is the number of organisms of the same species living together in a given area at a particular time. 

2. Population density: – this is the number of a particular species per unit area or volume of the habitat. Therefore 

3. Population density :- population size/area of habitat. 

4. Population frequency: – this is the number of times an organism occurs within a given area or habitat.

5. Percentage cover: – this refers to how much space or area an organism occupies in its habitat.

6. Population growth rate: – this refers to the net result of the influence of natality (birth rate) and mortality (death rate) of organisms in a given habitat.  

7. Population distribution: – this refers to how individuals of the same species are arranged in a given habitat, either randomly, evenly or clumped.

POPULATION STUDIES

1. Choose the habitat.
2. Select the sampling method to be used.
3. Collect, count and record the different types of organisms present. Sampling using a quadrant or transcent using a tape can be adopted.
4. Identify the dominant species i. e. the species that has greater influence on the other members of the community.
5. Repeat the population studies at intervals.
6. Determine the population characteristics.

FACTORS AFFECTING POPULATION  

1. Natality: Ability of organisms to reproduce to increase their population 

2. Mortality: Death rate.

3. Immigration: Movement of organisms from different habitats into a new habitat and this increases the population of the new area, decreasing the population of the former habitat.

4. Emigration: Movement of organisms out of their habitat due to unfavorable conditions e.g. food scarcity etc. This reduces the population of the habitat.

5. Availability of food: Animals tend to migrate to where there is plenty of food, thereby increasing the population of such places.

6. Seasonal Climatic Changes: Whether the change is favorable or not determines the stay or migration of organisms into or out of a habitat. 

7. Breeding Season: Some organisms move out of their habitats during this season (e.g. fishes); hence the population drops.

8. Natural Disasters: Fire, drought, floods, earthquakes etc lead to a decrease in population through the death of organisms out of such habitat

MEASUREMENT OF ECOLOGICAL FACTORS

These factors can be measured using some instruments as shown below.

ASSIGNMENT

1. Climatic factors in an ecosystem include the following except A. light B. wind C. temperature   D. Oxygen.

2. The organic part of the abiotic component of an ecosystem includes the following except  A.water B. carbohydrate C. Protein d) Lipids

3. The ratio of population size to the area of the habitat is called      A.population size         B. population density      C. population frequency     D. population cover.

4. Habitat factors include all the following except A.biotic B. abiotic C. edaphic D. nature.

5. The total number of organisms of the same species in a habitat at a particular time is called    A. Population     B. community     C. census    D. all of the above
6. List five ecological instruments and state their uses.

7. State five factors affecting a population size.