Chapter 8, Problem 2STP

Summary Introduction

To determine:

The part of the graph that indicates exponential growth.

Introduction:

A population can be defined as a group of individuals of the same species living in the same geographic area. A population has certain attributes that an individual organism does not have, such as, birth rate, death rate and sex ratio.

Population growth curve is a graphical representation of how populationincreases, becomes stable or decreases.

Answer to Problem 2STP

In the given graph, the number 1 indicates J-shaped graph which is exponential growth.

Explanation of Solution

The density of population fluctuates due to following reasons:

Natality (B): It refers to the number of births in a given period of time that are added to the initial density.

Mortality (D): It refers to the number of deaths that are deleted from the initial density.

Immigration (I): It refers to the number of individuals who have come into the habitat from somewhere else and are added to the population.

Emigration (E): It refers to the number of individuals who left the population and migrated somewhere else.

So, if N is the population density at time t, then population density at time t+1 can be shown as:

N_t+1 = N_t+ ( B+I ) − ( D+E )

B = Birth rate

I = Immigrants

D = Death rate

E = Emigrants

There are two modes of population growth.

1. Exponential growth: This type of growth curve occurs when resources are limited. Population continues to grow as there is no shortage of resources, and it results in J-shaped curve.The expression which defines exponential growth is given as dN/dt = rN where r = (b-d) and dN/dt is change in population density in time t.

2. Logistic growth:This type of growth curve occurs when resources are limited. The population expansion decreases as the resources become limited or scarce. It levels off when the carrying capacity of the environment is reached, and results in S-shaped curve. The expression which defines exponential growth is given as dN/dt = rN(1-N/K) where r = (b-d) and dN/dt is change in population density in time t and K is carrying capacity (nature’s limit)