Footage of a pride of lions hunting a defenseless baby zebra may be enough to tug at the heartstrings of the toughest among us. But as barbaric as this may seem, the killing of baby animals plays a fundamental role in the circle of life. However, when it comes to humans, a new study suggests that the practice of hunting adult animals, particularly predators, has had seriously negative effect on the planet’s ecosystems.

In nature, many top predators display a clear preference for hunting young and weak prey over the more mature and robust prey. There are many reasons for this, including the fact that young prey are not only easier to catch but also less likely to cause serious physical harm to the predator when fighting back. Armed with guns, other weapons, and hunting techniques, humans are exempt from this natural rule and, when given the choice, are more likely to hunt mature adult prey over their defenseless young. The new study, published in the journal Science, explored this phenomenon and found just how much more of an effect these behaviors have on the animal kingdom when compared to letting nature take its course.

For the study, a team of Canadian researchers conducted a survey of 2,125 marine and land predators around the world, and found that, on average, humans preyed on adults of other species up to 14 times more often than other predators. The study revealed that this exploitation of adult predator populations, for both farming and sport, was especially profound when it came to hunting carnivorous species. According to the press release, overfishing of adult predators was significantly most pronounced in the Atlantic Ocean, serving as a sad reminder that as economically valuable populations of predatory fish dwindle, demand rises, and more aggressive fishing ensues.

Although hunting young defenseless prey may sound horrible, it’s completely natural, according to the research. Its humans’ preference to seek out adult prey that is unnatural, and it has led to serious consequences for our ecosystem. The study explains that over-hunting sexually mature animals can modify the reproductive potential for these populations and in turn change their role in the food web. For example, hunting tuna, a predatory fish, can negatively affect their ability to reproduce, and lead to population increases in the fish they prey on — thus disrupting the food chain.

Along with upsetting the food chain, hunting large numbers of adult prey can also affect other delicate systems, affecting how we manage diseases and contain wildfires. This has been seen in sub-Saharan Africa, where a reduction in lion and leopard populations has caused the baboon population to swell. As a result, more baboons began foraging closer to humans, causing a higher risk of transmitting intestinal parasites. Declining populations of wildebeests in Africa have also led to an increase in dry vegetation being left on the ground, leading to a higher frequency of wildfires in the Serengeti.

Though the findings may be devastating, it’s not too late to turn the situation around. The researchers said that reversing these effects would involve “imposing limits of humanity’s own design.” This would involve cultural, economic, and institutional changes, such as “cultivating tolerance for carnivores, designing catch-share programs, and supporting community leadership in fisheries.” However, the most significant way to preserve carnivorous populations may be to mimic their behavior by targeting younger prey.

Source: Darimont CT, Fox CH, Bryan HM, Reimchen TE. The unique ecology of human predators. Human Impacts. 2015.

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