Learn Swedish: Vi måste skydda den av tjuvskytten hotade arten. - We must protect the species threatened by the poacher.

This is a complex pre-modifying participial attribute. In Swedish, a descriptive phrase built around a participle (like hotade, meaning 'threatened') can be placed directly before the noun it modifies, acting like one long adjective. English usually puts this after the noun ('the species threatened by the poacher'), but Swedish often brackets it between the standalone definite article (den) and the noun (arten).

Why does the participle hotade end in an -e here instead of being just hotad?

It is acting as an adjective inside a definite noun phrase. When a noun phrase uses the freestanding definite article (den), the adjectives and participles inside it must take their definite form. For past participles of regular verbs, that form ends in -a or -e. Here, hotade matches the definite setup of den ... arten.

Why do we need the word den when arten is already in the definite form ('the species')?

This is the standard Swedish 'double definite' rule. Whenever you put an adjective—or in this case, a whole participle phrase like av tjuvskytten hotade—in front of a definite noun, you must add the freestanding definite article (den, det, or de) before the modifier.

Could I phrase this more like English, putting the description after the noun?