Question

Exit Ticket Scenario: Population Change & Ecosystem Impact
A group of rabbits lives in a grassland ecosystem where grass is their main food source. Over several years, the rabbit population increases rapidly due to mild winters and fewer predators. As the rabbit population grows, the grass population begins to decline. Eventually, the rabbits struggle to find enough food, and their population starts to decrease.

Constructed‑Response Prompt
Explain how a change in population size impacts an ecosystem.
Support your answer with evidence from the scenario

Answer 1

A change in population size alters how organisms use resources and interact, which in turn changes the rest of the ecosystem. When a population grows, it increases demand for its food and other resources; if that demand exceeds what the habitat can supply, resources decline and the growing population will eventually be limited. Conversely, if a population falls, its prey or food resources can recover and other species that depend on it may be affected.

Evidence from the rabbit scenario:
- Cause of change: Mild winters and fewer predators allowed the rabbit population to increase rapidly. Those are factors that reduced mortality and raised population size.
- Effect on resources: As rabbits became more numerous they ate more grass, so the grass population began to decline. Grass here is a limiting resource for rabbits.
- Feedback regulation: With less grass available, individual rabbits struggled to get enough food; starvation and lower reproduction followed, and the rabbit population decreased. This is an example of density-dependent regulation moving the population back toward the habitat’s carrying capacity.
- Wider ecosystem impact: The boom-and-bust in rabbits could produce further effects—reduced grass cover can change soil stability and plant community composition, and later changes in predator numbers or disease could follow as rabbit numbers fall or rise.

In short, population increases can deplete resources and trigger negative feedbacks that reduce that population, while those fluctuations can cascade to affect other species and ecosystem processes. The scenario illustrates carrying capacity, limiting resources, and density-dependent control in a real-world context.