A scientist raised the same species of beetle in three containers for 4 weeks. The only difference was the amount of food provided each week. Data: Container 1 (low food): 18 beetles after 4 weeks; Container 2 (medium food): 44 beetles after 4 weeks; Container 3 (high food): 79 beetles after 4 weeks. Which explanation best describes the relationship between resources (food) and population size, using evidence of cause and effect? (Remember: resources can limit population size.)
- Food cannot limit population size because populations always grow without limits over time.
- The beetle population increased with more food because food is a resource needed for survival and reproduction; the containers with more food had larger populations (79 > 44 > 18). (correct answer)
- The beetles in the high-food container had different genes that caused a larger population, so food level was not the cause.
- The beetle population size changed randomly; the different food amounts did not cause the differences in population size.
Explanation: The core skill is understanding how resources influence population size in ecosystems. Resources such as food directly affect population size by providing the energy needed for organisms to survive, grow, and reproduce. Evidence shows cause-and-effect when controlled experiments vary only the resource amount and measure resulting population differences, like more beetles with higher food levels. To check understanding, compare population sizes across different resource levels and ensure other variables are constant. A common misconception is that populations grow indefinitely regardless of resources, but limits exist when resources are scarce. In general, population size increases with abundant resources but stabilizes or decreases when resources are limited. Overall, the availability of key resources determines the maximum population an environment can support.