Learn Polish: Drapieżnik poluje pośród krzaków. - The predator is hunting amidst the bushes.

Not really! Both mean "among" or "amidst" and they are practically interchangeable. Wśród is slightly more common, while pośród can sound a tiny bit more literary or emphasize being right in the middle of something (like the bushes here), but in everyday Polish, you can use either one. Both always require the Genitive case.

Why does krzak (bush) become krzaków here?

Because the preposition pośród (just like wśród) always forces the noun that follows it into the Genitive case. Since there are multiple bushes, we need the Genitive plural. For most masculine nouns like krzak, the Genitive plural ending is -ów, giving us krzaków.

I remember verbs ending in -ować change their stems. How does poluje fit into that?

You remembered correctly! The infinitive is polować (to hunt). When conjugating verbs that end in -ować, you drop the -ować and add -uj- before the personal endings in the present tense. For the third-person singular ("he/she/it hunts"), the ending is -e, which gives us poluje.

Is the word drapieżnik (predator) related to other common words?