Wishing for long hard hours in the field, followed by long, hard hours in a lab? If you're thinking of translating your interest in invasive species into a higher degree, check out this web page from invasivespecies.gov. It lists U.S. universities and corresponding departments where you might consider applying.
If you are new to the grad school thing, keep in mind that getting in is typically not easy, and your chances are much better if you target your potential advisors beforehand, read up on their most recent publications, and contact them directly (other grads and former grads, feel free to pipe in here!). Also, note that the link above is definitely not a complete list - I can see my alma mater UMass Boston is missing, though I know of several invasive species projects currently going on in the Biology Department. So if you don't find someone that matches your interests through that list, just try searching Google.
Thanks to Thomas D. for sending in the link. A tip of the virtual hat must also go to the excellent online comic PhD for making my labmates and me smile when it seemed like we would never dig ourselves out of graditude.