Introduction

When I give a talk about extinction, there are usually two questions I am asked:

• Isn't extinction a natural process?

• What makes us think we're so smart that we can manage species to prevent they're extinction?

I'll deal with the first question in a bit later, but let's ponder the second one for now. The data I just finished presenting shows pretty convincingly, I think, that human beings have an enormous impact on the earth and its inhabitants. 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 avoid having an impact. We can only choose what kind of impact we'll have. This observation is related to my earlier point that 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 choose to manage in a way that we hope will produce the outcome we want (compare [14]).¹ In some cases that may amount to ``letting nature take its course.'' In others it will involve more active, hands-on managing.

So what about the first question? Isn't extinction a natural process? There are two components to my answer:

1. Contemporary rates of extinction are vastly greater than they are typical of the geological past, and they are projected to get worse.

2. The pattern of extinction is non-random, and the species that survive may not be those that make the world an appealing place to live.

To start, let's take a look at what the Millenium Ecosystem Report has to say about extinction rates (Figure 1). Notice the scale on the vertical axis. It's a logarithmic scale. So our best guess about the current extinction rate is that it's 100-1000 times higher than the background extinction rate in the fossil record, and the projected future extinction rate 10-100 times greater than the current rate. Numbers like that are why you often hear it said that we are living through the sixth great mass extinction in the history of life.

Figure 1: Past, present, and projected extinction rates [1].