Question

read this passage about two inherited traits in garter snakes.
garter snakes eat slugs, fish, and other small animals. some snakes eat certain types of prey more often than other types. the prey preference trait determines what type of prey a garter snake usually eats. for example, a snake with a slug preference will eat mostly slugs, but a snake with a fish preference will eat mostly fish.
garter snakes are less likely to hunt prey that they do not have a preference for. so if a snake cannot find the type of prey it has a preference for, the snake will be less likely to get food.
the graph below describes prey preference in an isolated population of garter snakes at the start and end of a time period long enough for natural selection to occur. at the start of this time period, the garter snakes’ environment changed.
describe how the garter snake population changed over this time period. use the theory of natural selection to construct a possible explanation for this change.
the percentage of snakes with a fish preference in the population. this suggests that snakes with a fish preference were likely to survive and reproduce than snakes with a slug preference. this may have occurred because there were significantly fish after the population’s environment changed. so snakes with a fish preference were likely to get enough food.

Explanation:

Step1: Analyze fish preference percentage change

At start, fish - preference snakes (blue bar) are ~80%, at end ~30%. So the percentage of snakes with a fish preference decreased in the population.

Step2: Relate to survival/reproduction likelihood

Since fish - preference snakes' percentage decreased, they were less likely to survive and reproduce than slug - preference snakes (red bar: start ~20%, end ~70%).

Step3: Explain environmental change impact on prey

For fish - preference snakes to be less successful, there were significantly fewer fish after the environment changed (so they struggled to get food).

Step4: Conclude food - getting likelihood

With fewer fish, snakes with a fish preference were less likely to get enough food (hence lower survival/reproduction, leading to lower percentage).

Answer:

The percentage of snakes with a fish preference \(\boldsymbol{\text{decreased}}\) in the population. This suggests that snakes with a fish preference were \(\boldsymbol{\text{less}}\) likely to survive and reproduce than snakes with a slug preference. This may have occurred because there were significantly \(\boldsymbol{\text{fewer}}\) fish after the population’s environment changed. So snakes with a fish preference were \(\boldsymbol{\text{less}}\) likely to get enough food.