Question

describe how the threespine stickleback population changed over this time period. use the theory of natural selection to construct a possible explanation for this change. the percentage of sticklebacks with long pelvic spines dropdown in the population. this suggests that sticklebacks with short spines were dropdown likely to survive and reproduce than sticklebacks with long spines. this may have occurred because there were significantly dropdown large fish after the populations environment changed. so sticklebacks with long spines were dropdown likely to be caught by predators than sticklebacks with short spines.

Explanation:

1. First blank: From the pie charts, the percentage of fish with long pelvic spines decreases (e.g., left chart has a very high percentage, right has 37%). So "decreased".
2. Second blank: If long - spine fish decreased, short - spine fish were more likely to survive/reproduce. So "more".
3. Third blank: After environment change, there were more large fish (predators? Or a change that favors short spines). Wait, the context is about natural selection. If long - spine fish are being caught more, maybe there are more large fish (predators) that can catch long - spine fish. So "more".
4. Fourth blank: Long - spine fish are more likely to be caught by predators (since their percentage decreased), so "more".

For the description of population change: The population of three - spine sticklebacks with long pelvic spines decreased over time, while those with short pelvic spines increased.

using natural selection: In the environment, there were selective pressures (e.g., presence of predators that can more easily catch long - spined sticklebacks). Sticklebacks with short pelvic spines had a survival advantage (maybe they were less likely to be caught by predators). So, over time, more short - spined sticklebacks survived and reproduced, passing on their genes for short spines, while long - spined sticklebacks were less likely to survive and reproduce, leading to a decrease in their proportion in the population.

via natural selection: Selective pressures (e.g., predators) favored short - spined sticklebacks. Short - spined sticklebacks had higher survival and reproductive rates (were more likely to survive and reproduce) as they were less likely to be caught by predators. Long - spined sticklebacks were more likely to be caught by predators, so they had lower survival and reproductive rates. Over time, the genes for short spines became more common, and those for long spines less common, changing the population's trait distribution.

Answer:

First blank: decreased
Second blank: more
Third blank: more
Fourth blank: more

Description of population change: The proportion of three - spine sticklebacks with long pelvic spines decreased, and the proportion with short pelvic spines increased over the time period.