Case Study
Passage with linked questions
Case Set 1
Case AnalysisPassage
A biology student visited a pond and observed various organisms living together. She noticed that the lotus plants, fish, frogs, and insects were all part of the pond ecosystem. She recorded the number of lotus plants over two years: in the first year there were 20 plants, and by the end of the second year there were 28 plants. She also noted that 4 out of every 40 fruitflies in a nearby lab culture died each week. Her teacher explained that these statistics represent important population attributes. The student also observed that the age distribution of frogs in the pond could be represented graphically. Through her observations, she began to understand that populations have certain measurable characteristics that individual organisms do not possess, and these characteristics help ecologists understand the health and future trajectory of a given population in its habitat.
Question 1: What is the birth rate of the lotus population in the pond described?
- Birth rate = number of new individuals / initial population size
- Birth rate = 8/20 = 0.4 offspring per lotus per year
Question 2: What is the death rate in the fruitfly laboratory population, and what does it indicate about the population?
- Death rate = 4/40 = 0.1 individuals per fruitfly per week
- It indicates that 10% of the fruitfly population dies per week, which contributes to a decline in population density if not offset by births or immigration
Question 3: List and explain three population attributes that the student could study in the pond ecosystem that an individual organism cannot possess.
- Birth rate and death rate: These are per capita rates applicable to a population, not an individual. E.g., 0.4 offspring per lotus per year.
- Sex ratio: A population has a definable ratio of males to females (e.g., 60% females and 40% males), which is meaningless for a single individual.
- Age pyramid / Age distribution: The proportion of individuals of different age groups can be plotted for a population, reflecting whether the population is growing, stable, or declining — a concept inapplicable to a single organism.