I am guessing the mods, although they can get advice on that from the advanced members themselves. There should be a sticky in that subsection informing members what should and shouldn't be posted (sometimes that doesn't work too well as we all know). Any inappropriate or misplaced threads/posts will be moved to their appropriate locations or removed.who would determine whats advanced?
My hope is that noobs will glance over the subsection and just post in the main "scorpions in general section" while more experienced members will go to the specified subsection to converse with one another, make more advanced threads/posts, etc.
Heck, the mods can filter out newcomers by the number of posts (although not the best method) in which members that have for instance about 100 or more posts can contribute while the rest (noobies) are limited to only being able to read/observe. If they want "in", they can request access from the mods. As for the experienced members who don't post very often, they can be given VIP access to the subsection by the moderators.
Moderation is essential for this. Feel free to expand on these ideas as they are still very basic and have qualities of elitism although that is not the goal.