Evaluate Population Explanations Practice Test

A lake is monitored for 5 years. Two explanations are offered for a decline in small fish (minnows).

Explanation 1: The minnow population declined because a new predator fish (bass) was introduced and ate more minnows. Explanation 2: The minnow population declined because a plant disease reduced aquatic plants, lowering shelter and food for minnows.

Use the population evidence below to evaluate the explanations using evidence fit and completeness (how well each explanation accounts for all the data). Which explanation is best supported by the evidence?

Population evidence (counts per survey):

• Year 1: minnows 1200, bass 40, aquatic plant cover 80%
• Year 2: minnows 1100, bass 45, aquatic plant cover 78%
• Year 3: minnows 700, bass 90, aquatic plant cover 76%
• Year 4: minnows 500, bass 130, aquatic plant cover 75%
• Year 5: minnows 480, bass 140, aquatic plant cover 74%

A coral reef site is monitored for 5 years. The number of herbivorous fish decreases. Two explanations are offered.

Explanation 1: Herbivorous fish decreased because a disease affected the fish. Explanation 2: Herbivorous fish decreased because fishing pressure increased.

Use the shared evidence below and evaluate the explanations using evidence fit and completeness. Which statement correctly evaluates the explanations?

Evidence:

• Year 1: herbivorous fish 800, fishing boats per week 2, disease signs: none
• Year 2: herbivorous fish 780, fishing boats per week 2, disease signs: none
• Year 3: herbivorous fish 500, fishing boats per week 6, disease signs: none
• Year 4: herbivorous fish 320, fishing boats per week 7, disease signs: none
• Year 5: herbivorous fish 300, fishing boats per week 7, disease signs: none