It's not about positive or negative - it's about active or passive, and what the underlying subject of the sentence is. In the first example, we need a past participle because the construction is a kind of passive. The tiger isn't actively positioning itself at the top of the food chain - it simply is positioned there. This is similar to saying, for example, 'Located in a sheltered bay, the harbour is ideal for fishing.' The harbour isn't locating itself - it is located. This is another passive construction. In the second example, the subject of the verb 'resemble' is the teledu itself - the teledu resembles a skunk. This is an active sentence, so we need a present participle - 'Resembling a skunk, the teledu....'. It's the same as saying, for example, 'Living in the mountains of Sumatra, the teledu ...' . It's the teledu which is doing the action of 'living', so we need a present participle. By the way, note that you need a definite article before the name of the animal because you are referring to the whole species in general, and also note that 'Sumatra' doesn't have an 'e' in it. I hope that all makes sense. In the second example