Organisms and Populations — Part 2: Population growth: visual lesson, CBSE Class 12 Biology

Lesson

Population growth

Part 2 — how fast can a population grow, and what stops it?

In this lesson you will

Explain how natality, mortality, immigration and emigration change population density
Compare exponential and logistic growth models
Explain carrying capacity
Describe life history variation

Diagram

Four processes change density

Density changes through natality (B) and immigration (I), which add individuals, and mortality (D) and emigration (E), which remove them.

N_{t+1} = N_t + \left[(B + I) - (D + E)\right]

Worked example

Worked example 1: next year’s population

A deer population of 500 had 60 births, 15 immigrants, 40 deaths and 25 emigrants in a year. Find the population at the end of the year.

$N_{t+1} = 500 + \left[(60 + 15) - (40 + 25)\right]$ .
$= 500 + (75 - 65) = 510$ .
Additions exceeded losses, so the population grew.

Worked table: population rises from 500 to 510
Process	Number	Effect
Births (B)	60	Add
Immigration (I)	15	Add
Deaths (D)	40	Remove
Emigration (E)	25	Remove
New population	510

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