USABO - USA Biology Olympiad Population Ecology and Dynamics Questions and Answers

Question 1

An age-structure diagram for a developing country shows a classic pyramid shape, with a very broad base that narrows progressively toward the top. Which of the following is the most accurate long-term prediction for this population, assuming current trends continue?

Accepted Answer

The population will experience rapid growth due to a large proportion of individuals in pre-reproductive and reproductive age groups.

Answer

A pyramid-shaped age-structure diagram indicates that a large percentage of the population is young (pre-reproductive) and in their reproductive years. [23, 24] This large cohort of young individuals will mature and have children, leading to a significant increase in population size over time, characteristic of rapid population growth. [25]

Question 2

A species of marine invertebrate releases millions of eggs into the water, of which very few survive to maturity. However, those that do survive the initial larval stages have a high probability of living for a long time. Which type of survivorship curve would this species most likely exhibit?

Accepted Answer

Type III

Answer

This life history strategy is characteristic of a Type III survivorship curve. [8, 9] This curve represents high mortality rates for the very young, followed by a much lower, constant death rate for the few individuals that survive to older age. [6, 14] This is common in species that produce a large number of offspring with little to no parental care. [8, 15]

Question 3

In the logistic growth model, represented by the equation dN/dt = rN((K-N)/K), what happens to the population growth rate (dN/dt) as the population size (N) approaches the carrying capacity (K)?

Accepted Answer

The growth rate approaches zero.

Answer

In the logistic growth equation, the term (K-N)/K represents environmental resistance. As the population size (N) gets closer to the carrying capacity (K), the numerator (K-N) approaches zero. [3, 4] This causes the entire expression for the growth rate (dN/dt) to approach zero, meaning the population size stabilizes. [26]

Question 4

Which of the following describes a key characteristic of a K-selected species compared to an r-selected species?

Accepted Answer

Extensive parental care and few offspring

Answer

K-selected species are adapted to stable environments and tend to exist near their carrying capacity (K). [7, 10] Their life history strategy involves investing heavily in a small number of offspring to maximize their survival chances. This includes traits like long gestation periods, extensive parental care, and a long lifespan. [1, 13] In contrast, r-selected species produce many offspring with little care. [2]

Question 5

A sudden, severe frost kills a large portion of a monarch butterfly population overwintering in Mexico. This event is an example of:

Accepted Answer

A density-independent limiting factor.

Answer

A density-independent limiting factor is one that affects a population regardless of its density. Natural disasters and severe weather events, like a frost, are classic examples. [5, 17] The frost kills butterflies irrespective of how many are clustered together. In contrast, density-dependent factors, such as disease or competition, have a greater effect as population density increases. [16, 21]

USABO - USA Biology Olympiad Practice Test

USABO - USA Biology Olympiad Practice Test

USABO - USA Biology Olympiad Population Ecology and Dynamics Questions and Answers