When I give a talk about extinction, there are usually two questions I am asked:
I'll deal with the first question in a moment, but let's ponder the second one for now. The data presented in the first set of notes for this course shows pretty convincingly that human beings have an enormous impact on the earth and its inhabitants, an impact so large that we can't avoid having an impact on patterns and rates of species extinctions. Thus, we may or may not be smart enough to manage well, but one thing's for sure. We will have an impact. We cannot choose not to have an impact. We can only choose what kind of impact we'll have. This observation reinforces a point you'll hear me make again and again this semester: conservation biologists have to make decisions in the face of incomplete data. We don't have any choice about whether or not to make a decision, and we don't have any choice about whether we're going to manage. We can only make the decisions and choose to manage in a way that we hope will produce the outcome we want (compare ).1 In some cases that may amount to ``letting nature take its course.'' In others it will involve more active, hands-on managing.
Take the case of the Greater Sage-Grouse for example. After spending the next couple of weeks looking over the information presented in Manier et al.  you may feel as if you need more data in order to decide whether a listing as endangered or threatened is justified. It might feel as if there's too much uncertainty associated with the questions I asked to provide an answer now. Now suppose you answer the question ``Do the data suggest that the Greater Sage Grouse will go extinct if current trends continue?'' by writing ``The data currently available do not allow me to answer that question. We should continue to monitor populations for another 10 years before making a decision.'' There's no question that you'd have more data and be more likely to answer the question correctly. But suppose that the populations really are declining by about 5% per year. Then in 10 years, they will be about 40% smaller than they are now. Writing ``I need more data before I can make a decision'' is equivalent to writing ``If populations are declining now, they're declining slowly enough we can wait until we gather more data to take any actions that would reverse the decline.''
In short, the implication of the question ``What makes us think that we're smart enough to manage species and prevent their extinction?'' is that we're not smart enough to do anything, so we should keep our fingers out of the pot. The problem is that our fingers are in the pot, and there's no way to take them out as long as we're on the planet. Not only do we have to make decisions now, even before we have all of the facts we'd like to have, but we also have to accept that there's no way for us not to have an impact. Supporting 7 billion people now and 9 billion (or more) by the middle of this century means that we will have an impact. The question isn't whether or not to have an impact. It's what kind of impact to have. Given that, if we're concerned about loss of individual species or of biodiversity more broadly, we have no choice but to do something about it. Doing nothing is equivalent to saying that we don't care about loss of species or biodiversity.