Population: Characteristics, Factors and measurement of Ecological factors

CONTENT

• Population Characteristics
• Population Studies
• Factors that Affect Population
• Simple Measurement of Ecological Factors.

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

Population density = population size / area of habitat.

• Population frequency: – this is the number of times an organism occurs within a given area or habitat.
• Percentage cover: – this refers to how much space or area an organism occupies its habitat.
• Population growth rate: – this refers to the net result of the influence of natality (birth rate) and mortality (death rate) of organism in a given habitat. 
• Population distribution: – this refers to the ways in which individuals of the same species are arranged in a given habitat, either randomly, evenly or clumped.

EVALUATION

1. Define the following terms:  (i) Percentage cover (ii) Population size (iii) Population frequency (iv) Population density.
2. Mention two methods of determining population size.

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.

EVALUATION

1. How do you determine the population density of insect on a piece of land?
2. How do you determine the population of grasses in a piece of land?

FACTORS AFFECTING POPULATION 

1. Natality; Ability of organisms to reproduce to increase its 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 a habitat due to unfavourable 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 favourable 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; Like 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.

	INSTRUMENTS	USES
a.	Photometer	Light intensity
b.	Hydrometer	Light intensity in water
c.	Wind vane	Direction of wind
d.	Anemometer	Speed of wind
e.	Rainguage	Amount of rainfall
f.	Hygrometer	Relative humidity
g.	Barometer	Pressure
h.	Glass thermometer	Temperature
i.	Colorimeter or pH scale	Acidity / Alkalinity
j.	Secchi disc	Turbidity
k.	Sweep insect net	Catching insects

EVALUATION

1. State three factors that: a) increase the population of a habitat b) decrease the population of a habitat.
2. Explain the effect of bush burning on the population.
3. List five ecological instruments and their uses

GENERAL EVALUATION/REVISIONAL QUESTIONS

1. State the two components of an ecosystem
   1. With two examples each, discuss the various biotic components in an ecosystem
   1. State three factors that: a) increase the population of a habitat b) decrease the population of a habitat.
   1. State five effects of over population in a community                                                                                                                                                                                                                                                                                                                          
   1. State two Abiotic factors unique to: a) aquatic habitat b) terrestrial habitat.
   1. List five measurable ecological factors.
   1. State the ecological instruments used in measuring the factors listed above.

READING ASSIGNMENT

College Biology, chapter 23, page 530 – 532

WEEKEND ASSIGNMENT

1. Climatic factors in an ecosystem include the following except

A. light B. wind C. temperature   D. Oxygen.

• Organic part of abiotic component of an ecosystem includes the following except                A. water B. carbohydrate C. Protein d) Lipids
• 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.
• Habitat factors include all the following except A. biotic B. abiotic C. edaphic D. nature.
• 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

THEORY

1. List five ecological instruments and state their uses.

State five factors affecting a population size.