Understanding Fruit Fly Population Dynamics: Calculating Death Rate

Population dynamics is the study of how populations change in size and structure over time. Key factors influencing population size include birth rates, death rates, immigration, and emigration. In this problem, we are asked to calculate the death rate of a fruit fly population.

The death rate, also known as the mortality rate, is typically expressed as the number of deaths per unit of population size per unit of time. It tells us how quickly individuals are dying within a population.

Calculating Fruit Fly Death Rate

To calculate the death rate, we use the following formula:

\(\text{Death Rate} = \frac{\text{Number of deaths}}{\text{Initial population size} \times \text{Time period}}\)

Alternatively, and more commonly in population studies, it's calculated as the number of deaths per individual per unit of time:

\(\text{Death Rate (per capita)} = \frac{\text{Number of deaths}}{\text{Initial population size}}\) per unit time

Let's identify the given information from the problem:

• Initial population size = 80 fruit flies
• Number of deaths in one week = 8 individuals
• Time period = 1 week

Now, we can plug these values into the formula to calculate the per capita death rate:

\(\text{Death Rate} = \frac{8 \text{ individuals}}{80 \text{ individuals}}\) per week

\(\text{Death Rate} = \frac{8}{80}\) per fruit fly per week

\(\text{Death Rate} = 0.1\) per fruit fly per week

The unit "per fruit fly" refers to "per individual in the population". So the death rate is 0.1 individuals per fruit fly per week.

Let's look at the options provided:

• 0.3 individuals per fruit fly per week
• 0.2 individuals per fruit fly per week
• 0.1 individuals per fruit fly per week
• 0.01 individuals per fruit fly per week

Our calculated death rate is 0.1 individuals per fruit fly per week, which matches one of the options.

The death rate indicates that, on average, for every fruit fly in the population, 0.1 individuals died during that week. This is a standard way to express vital rates in population ecology.

Revision Table: Population Dynamics Terms

Additional Information: Population Change

Understanding death rates is crucial for predicting how a population size might change. Population change is also affected by birth rates, as well as movement like immigration (individuals entering the population) and emigration (individuals leaving the population).

• Birth Rate: Similar to death rate, it's the number of births per individual per unit time.
• Population Growth: The overall change in population size over time. If the birth rate is higher than the death rate, the population will likely grow (assuming no migration). If the death rate is higher, it will likely decline.
• Population Density: The number of individuals per unit area or volume. Death rates can sometimes be density-dependent (higher when the population is crowded) or density-independent (affected by external factors like weather).

In this specific problem about fruit flies in a laboratory, migration might be negligible, simplifying the factors influencing population change to just birth and death rates.