Question

the overall population of a species decreased. what could have occurred to make this happen?
the immigration rate increased, while the death rate decreased.
the birth rate decreased, while the death rate increased.
the carrying capacity increased, while the immigration increased.
the emigration increased, while the birth rate increased.

Explanation:

To determine what causes a species' population to decrease, we analyze each option:

• Option 1: Increased immigration (more individuals coming in) and decreased death rate (fewer individuals dying) would likely increase or at least not decrease the population.
• Option 2: Decreased birth rate (fewer new individuals) and increased death rate (more individuals dying) means the number of individuals being added is less than those being lost, leading to a population decrease.
• Option 3: Increased carrying capacity (environment can support more) and increased immigration (more individuals coming in) would tend to increase the population.
• Option 4: Increased emigration (more individuals leaving) and increased birth rate (more new individuals) – the impact of these two might offset, but an increased birth rate would work against a population decrease, so this is less likely to cause a decrease compared to Option 2.

Answer:

B. The birth rate decreased, while the death rate increased.