Practice a College Board-style free response question on Populations. Write your response, then reveal the model answer to see exactly what earns each point.
A herd of deer is introduced onto a 500-hectare island with no natural predators and abundant vegetation. Researchers track the deer population every five years.
| Year | Deer population |
|---|---|
| 0 | 20 |
| 5 | 80 |
| 10 | 310 |
| 15 | 540 |
| 20 | 560 |
| 25 | 555 |
Between Year 0 and Year 10, the deer population shows exponential growth — the population nearly quadruples in the first five years and continues accelerating. This is possible because the island has abundant vegetation and no natural predators, removing the limiting factors that would otherwise slow growth, so the population grows at close to its maximum biological rate.
The island's carrying capacity is approximately 555–560 deer, the level the population stabilizes around. Between Year 15 and Year 25, growth has clearly slowed and leveled off — the population grew only slightly from 540 to 560 and then slightly declined to 555. This pattern is consistent with logistic growth: as the population approached the island's carrying capacity, limiting factors (likely food availability, since there are no predators) slowed growth until births and deaths roughly balanced.
The deer population would most likely decline sharply, potentially below the previous carrying capacity. A 40% reduction in vegetation would lower the island's carrying capacity for deer, since food (a density-dependent limiting factor) would now support fewer individuals. With the population already near its previous (higher) carrying capacity, the sudden drop in available food would cause a population overshoot followed by a crash — die-off from starvation and possibly increased competition — until the population reached a new, lower equilibrium matching the reduced resource base.