49 population growth
key question: what factors are responsible for changes in population number?
the number of individuals in a population (n) is calculated by knowing the gains and losses to the population. births, deaths, immigrations (movements into the population) and emigrations (movements out of the population) are that together determine the number of individuals in a population. scientists usually measure the rate of events, which are influenced by the resources available and the biotic potential, which varies among species.
births, deaths, immigration (movements into the population) and emigration (movements out of the population) are events that determine the population size. population growth depends on the number of individuals added to the population from births and immigration, minus the number lost through deaths and emigration. this is expressed as:
population growth = (births + immigration) - (deaths + emigration) (b + i - d + e)
the difference between immigration and emigration gives net migration. ecologists usually measure the rate of these events. these rates are influenced by limiting factors in the environment (e.g., availability of food, water, or habitat) and by the characteristics of the organism itself (their biotic potential or natural capacity to increase, r).
rates in population studies are commonly expressed in one of two ways:
• numbers per unit time: e.g., 20, 150 live births per year. the birth rate is termed the natality, whereas the death rate is mortality.
• per capita rate (number per head of population), e.g., 122 live births per 1000 individuals per year (12.2%).
the human population is estimated to peak at around 9 billion by 2050 as a result of multiple factors, including falling birth rates. humans have the technology and production efficiency to solve many resource problems and so might appear exempt from the direct influence of limiting factors. however, declining availability of water and land for food production are limiting factors likely to constrain population growth, at least regionally.
1. define the following terms used to describe changes in population numbers:
(a) death rate (mortality):
(b) birth rate (natality):
(c) net migration rate:
2. explain how the concept of limiting factors applies to population biology:
3. using the terms b, d, i, and e (above), construct equations to express the following:
(a) a population in equilibrium:
(b) a declining population:
(c) an increasing population:
4. a population started with a total number of 100 individuals. over the following year, population data were collected. calculate birth rates, death rates, net migration rate, and rate of population change for the data below (as percentages):
(a) births = 14: birth rate =
(b) net migration = +2: net migration rate =
(c) deaths = 20: death rate =
(d) rate of population change =
(e) state whether the population is increasing or declining:

Question

Accepted Answer

# 1.
## (a) Death rate (mortality)
# Brief Explanations:
The number of deaths per unit time in a population.
# Answer:
The number of deaths per unit time in a population.

## (b) Birth rate (natality)
# Brief Explanations:
The number of births per unit time in a population.
# Answer:
The number of births per unit time in a population.

## (c) Net migration rate
# Brief Explanations:
The difference between the rate of immigration and the rate of emigration (immigration rate - emigration rate) in a population.
# Answer:
The difference between the rate of immigration and the rate of emigration (immigration rate - emigration rate) in a population.

# 2.
# Brief Explanations:
Limiting factors (e.g., food, water, habitat) in the environment restrict population growth. They can be density - dependent (e.g., competition for resources) or density - independent (e.g., natural disasters). They influence the biotic potential (the maximum reproductive capacity of a species) and determine the carrying capacity (the maximum number of individuals an environment can support).
# Answer:
Limiting factors (e.g., food, water, habitat) in the environment restrict population growth. They can be density - dependent (e.g., competition for resources) or density - independent (e.g., natural disasters). They influence the biotic potential (the maximum reproductive capacity of a species) and determine the carrying capacity (the maximum number of individuals an environment can support).

# 3.
## (a) A population in equilibrium
# Brief Explanations:
When the population is in equilibrium, the number of individuals added (births + immigration) is equal to the number of individuals lost (deaths + emigration).
# Answer:
$B + I=D + E$

## (b) A declining population
# Brief Explanations:
A declining population means that the number of individuals lost (deaths + emigration) is greater than the number of individuals added (births + immigration).
# Answer:
$B + I<D + E$

## (c) An increasing population
# Brief Explanations:
An increasing population implies that the number of individuals added (births + immigration) is more than the number of individuals lost (deaths + emigration).
# Answer:
$B + I>D + E$

# 4.
## (a) Birth rate
# Explanation:
## Step1: Calculate birth rate formula
Birth rate $=\frac{\text{Number of births}}{\text{Initial population}}\times100\%$
## Step2: Substitute values
Given births $B = 14$ and initial population $N=100$, birth rate $=\frac{14}{100}\times 100\% = 14\%$
# Answer:
$14\%$

## (b) Net migration rate
# Explanation:
## Step1: Calculate net migration rate formula
Net migration rate $=\frac{\text{Net migration}}{\text{Initial population}}\times100\%$
## Step2: Substitute values
Given net migration $= + 2$ and initial population $N = 100$, net migration rate $=\frac{2}{100}\times100\%=2\%$
# Answer:
$2\%$

## (c) Death rate
# Explanation:
## Step1: Calculate death rate formula
Death rate $=\frac{\text{Number of deaths}}{\text{Initial population}}\times100\%$
## Step2: Substitute values
Given deaths $D = 20$ and initial population $N=100$, death rate $=\frac{20}{100}\times100\% = 20\%$
# Answer:
$20\%$

## (d) Rate of population change
# Explanation:
## Step1: Calculate population change formula
Population change $=(B + I)-(D + E)$. Here $I - E=\text{Net migration}=+2$, $B = 14$, $D = 20$. So population change $=14 + 2-20=-4$
## Step2: Calculate rate of population change formula
Rate of population change $=\frac{\text{Population change}}{\text{Initial population}}\times100\%=\frac{- 4}{100}\times100\%=-4\%$
# Answer:
$-4\%$

## (e) State whether the population is increasing or declining
# Brief Explanations:
Since the rate of population change is negative ($-4\%$), the population is losing individuals over the year.
# Answer:
Declining.

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QUESTION IMAGE

Question

Explanation:

1.

(a) Death rate (mortality)

Answer:

(b) Birth rate (natality)