It’s not news that humans are having an astonishing and unprecedented impact on global ecosystems, or that we consume other species at a voracious and unsustainable rate. But analyses of humans’ roles in ecosystems tend to look only at how much we do kill, and how much we should kill. But there are other important questions to answer. Specifically, how are we different from other predators, and what does this mean for sustainability?
According to a paper in this month's issue of Science, one of the most important differences is the age of the animals we prey on. Non-human predators tend to catch mainly juveniles, which tend to be smaller, weaker, slower, and easier to catch. Humans, in contrast, go for the grown-ups. This makes sense: they’re meatier—or, in the case of trophy hunting, more impressive mounted on a wall. But it has important repercussions for the populations being hunted.
The effect is that fewer adults survive to reproduce and replenish the population. If we think of sustainable ecosystems as being a bit like an investment, reproductively fit adults are the capital, and babies are the interest. As any wise retiree could explain, it’s safer to dip into the interest and keep the capital stable, than it is to start eating into the capital.
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