[T]he loss, or even reduction in numbers, of predators in an ecosystem can set off something caused a “trophic cascade” in which the change in predator population has effects across the food web and ecosystem. For example, when wolves were eliminated from the American West, there were changes in the elk population and the vegetation the elk ate.We need to integrate our knowledge and think through things inductively — we need to look at the big picture, make all necessary connections in thought, consider layers of causal connections, and make sure our ideas are tied to reality instead of convention or authority — or we will suffer.
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But changes to the food web aren’t the primary problem for human populations; the effects on ecosystem processes are often more dangerous. And many of these processes are big enough that even people in industrialized nations cannot protect themselves. The changes in vegetation that occur when the herbivore population is allowed to rise unchecked can change the frequency and intensity of wildfires. Infectious diseases can become more common; for example, in some parts of Africa where lions and leopards have become scare, populations of olive baboons have changed their behavior patterns, increasing their contacts with the humans nearby. Intestinal parasites have become more common in both the baboons and the people.
We need to think about causal relationships, not act on fear or short-term, ill-informed “economic incentive.”
To add to one point Sarah Zielinski makes: killing off predators kills off our natural biological defenses to diseases like Lyme.