Questions: Population Ecology: Abundance, Distribution, and Demography

Question 1

Which of the following is NOT one of the four BIDE factors that directly determine change in population size?

• A. Birth rate
• B. Immigration rate
• C. Disease prevalence
• D. Death rate

Answer: (C)

Population change = Births + Immigration - Deaths - Emigration. Disease can indirectly affect death rate, but it is not itself one of the four BIDE terms. Confusing a cause of mortality with the demographic parameter itself is a common error.

Question 2

A population with higher density than another population should also have a larger total number of individuals.

• T. True
• F. False

Answer: False

Density is individuals per unit area, not total count. A small forest patch with 50 mice in 0.1 hectares (500/ha) is far denser than a meadow with 1,000 mice across 100 hectares (10/ha), even though the meadow has more individuals. Many ecological processes scale with density, not total abundance.

Question 3

What does a Type III survivorship curve tell us about the life history of a species?

Model answer: Most individuals die very young, but those that survive early life have high long-term survival.

Type III organisms (e.g., most fish, trees, many invertebrates) produce enormous numbers of offspring with minimal parental investment. Mortality is extremely high at early life stages due to predation, competition, and environmental hazards. The few individuals that survive the vulnerable juvenile phase then experience low mortality rates — the opposite pattern from Type I organisms like humans.