See the sister comment by a_bonobo for a better insight than I have, since I'm primarily focused on biomedicine rather than ecology. My guess is that ecology (w

See the sister comment by a_bonobo for a better insight than I have, since I'm primarily focused on biomedicine rather than ecology. My guess is that ecology (which I was peripherally involved in grad school) is one of the areas where amateurs could have the biggest impact, largely because the field is so woefully underfunded and fieldwork requires more dedication and time than money, other than living expenses! Collaborating on an existing academic project might be a great way to get started, both for training and learning about the open questions in the field.