Odds of Hanging On
Your odds of advancing your career depend on a lot of different things. One, you'll have to get advanced degrees. Don't expect to move up the ranks without an MS and, eventually, a PhD. All the higher paying jobs are going to require these degrees, so just suck it up and do it. You'll need them if you want to land a promotion at your lab, tenure at a university, and—the holy grail of zoology—a chance to do fieldwork.
Also, the more you publish articles, lecture, and even get your face on screen, the more you're likely to increase your reputation and thus secure your place in the wild world of zoology. If you have ideas, get them out there, and you'll increase your odds of hanging on.
Unfortunately, not everything is in your control. When the economy dips, government and corporate money for wildlife research dips as well. It might seem like a swell idea to give cash to researching the migration patterns of bees when the economy is booming, but when the money buzzes away, zoologists are among the first to feel the sting.