Daniel-
This is most definitely not a fork of Wikipedia. Wikispecies is more about collecting data than writing articles. This data will be saved in a way that allows all Wikipedias, not just the English one, to use the data. As a project, Wikispecies has different aims to Wikipedia. It is aimed at the needs of scientific users rather than general users. Integrating Wikispecies into Wikimedia prevents a fork.
*That* is what the Commons is for. Fork.
Mav is correct, in my opinion. It doesn't make much sense to have separate "data projects". Instead, we should pursue developing the Commons into a single such repository from which other projects can dynamically transclude their content. With one such project, it is very clear to every participant that the sole purpose is to store data. With many specialized projects, we risk that people come across something like Wikispecies and start treating it like it is Wikipedia.
I suggest supending species.wikimedia.org until it is clearer what direction this project needs to take. If no consensus can be found, a vote on Meta seems like a good idea (apologies if there already was one and I missed it).
Regards,
Erik