POPULATION

POPULATION A population is a group of organism of the same species (able to breed among themselves) and occupy the same area. Characteristics of a Population i. It must have a specified number of organisms (population size) which can be expressed as; – Total Population: Includes number of all organisms e.g. 1200 elephants in queen Elizabeth National park. Population density: Number of organisms per unit space i.e. area (sq. units), volume (cubic units) 1200 Elephants in 40 km2 Therefore; population density = 1200/ 40 = 30 Elephants per km2 The population size can be determined using various methods; a) Direct method. Drive and count. Used on big mammals in a par, here animals are counted from a moving track/ land rover using binoculars; you can also use a light craft and keep counting in a sample. Total: average no. per same x number of samples in the area. Challenges / weatness • This method is very expensive and tiresome • Its risky especially working with dangerous animals • The animals may tend to run away from noisy items like an aircraft. • Method work best in an open area. b) Capture, Mark, release and recapture method. It cab be used for rodents, birds, fish and insects. These organisms must have a confined movement i.e there should be minimum movement in animals into and out of the population. There is little change in the population i.e. few are born and few die. Steps i. Capture by trapping without killing by various evenly distributed traps. ii. Mark using ink that can be rubbed, tag / ring and count. iii. Release and allow them to freely mix with other organisms iv. Recapture by trapping and record, i.e. Total recapture = N2 Marked among N2 = N3 Apply Lincoln index. Where, Population in an area = N1 x N2 N3 e.g.  40 in an area 20 captured = N1 Marked and recaptured = 08 – N3 Total recapture = 18 – N2 Therefore, N1 x N2 = 20 x 18 N3 8 = 45 Flying insects: use light traps mainly carried out at night  The light is suspended at night  A large white sheet of cloth spread underneath. The sheet attracts large number of them which fall on the cloth. c) Collect and count Crawling insects – use a water trap – use a pit fall trap Water trap is mainly used for aphid  Water is placed in large trough  The trough is placed under a plant so that the insects keep falling in the water where they bare then counted. Pit fall trap is mainly used for insects like ants and termites.  Dig a pit in the path of insects  Put a beaker into the pit. The top of the beaker should be at the same level and count them

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