How does scientists collecting species they are studying impact the environment?

i actually asked my ecology lecturer this myself actually.

his reply was something along the lines of, if the species is believed to be indangered, people wont try to remove them for analysis, and will try to desterb them as little as possible. as a general rule of thumb though, any ecological survey should be carried out with as little disruption as possible, not just to ensure as little damage is done to the species as possible, but also so that you can be sure that all your observations are valid, and not because you've desturbed them.