Human Activity Is Causing Wildlife to Shrink

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In a world increasingly dominated by humans, it seems there's less and less room for just about everything else -- so to cope, animals and plants across the globe are gradually getting smaller. For centuries, human activities such as hunting and encroachment have made life difficult for the largest species, from mammals and fish to insects and trees, leading to an evolutionary trend towards the miniature. And researchers suggest that unless countermeasures are taken to ensure 'big' makes a comeback -- we may be heading towards a world of tinier and tinier creatures.
While research into the diminution of non-human life on Earth has been steeped in academic study, the logic behind the phenomena is actually quite simple. The largest animal specimens, like deer, are typically the most targeted by hunters -- which results in fewer big deer to pass their largeness genes to a new generation. Naturally, such a selective process would dictate deers grow smaller over time, or else face a greater threat to the species itself.

Humans' love of the biggest of the bunch, of course, doesn't stop at deer. In fact, few of the largest animals on Earth, megafuana, have not been impacted by us. A report from Australia's ABC sums up our rich history of wiping-out our big animal brethren:

More than 25,000 years ago, one megafaunal species -- we humans -- began to spread rapidly around the globe and in the process helped to wipe out about half of all land mammals weighing more than 44 kilograms.
"More than 101 genera perished," Anthony Barnosky, an ecologist at University of California, Berkeley, reported in a 2008 study in Proceedings of the National Academy of Sciences (PNAS). Among the victims were whole groups of mammoths, mastodons, saber-toothed tigers, giant ground sloths, and big beavers. Many vanished in just a 4,000 year span that ended about 11,000 years ago. By then, Australia had lost roughly 88 per cent of its big mammal groups, South America 83 per cent, and North America 72 per cent. Africa did better during what is now called the Quaternary Megafauna Extinction (QME), losing about one-fifth of its big species, while Eurasia lost one-third.

Even species that aren't directly targeted by humans seem to be shifting towards a smaller frame. Shrinking or altered habitats, due to human development, tend to signal smaller inhabitants. Biologists have observed Europe's green clock beetle trending towards a lesser size over the last fifty years as increases in soil disturbances caused by humans reduce its larvae development stage, favoring faster growing, but notably smaller beetles.

Some pants also may be feeling the effect of human-selection. Historically, the biggest trees are often the first to be cut down -- a fact which may have inadvertently worked to weed-out the gene for big growth.

"Size matters," biologist Chris Darimont of the University of California, Santa Cruz, tells ABC. "A larger body size makes a species more vulnerable to all kinds of problems, from getting hunted by humans to habitat change."

Reversing this trend towards smaller wildlife will likely be slow, if it's possible at all. Researchers have noted a shortage of big fish species as fisheries target the meatiest specimens while returning the leanest. The Head of the Ocean Sciences program at the U.S. National Science Foundation, Chris Conover, says "it was going to take at least 12 generations for the fish to recover," referring to a species of fish he and his team 'overharvested' in a laboratory experiment to test the evolutionary process.

As of late, the effect of climate change on body-size of wildlife isn't well documented, but the specter looms as experts anticipate dramatic changes to Earth's ecosystems in a warmer world. Researchers say that smaller creatures tend to be the most resilient to many habitat changes, and that the loss of their larger predators may actually be a boon to them -- but this may matter little if changes in weather patterns come about as climatologists have warned.

In light of a future which may hold smaller wildlife than we know today, it is important to note that the opposite is likely true for us -- and the two factors are hardly unrelated. Obesity rates in humans continue to skyrocket as our lives become more sedentary in carbon-spewing motor vehicles, our food sources become more remote, and as it takes more encroachment into natural areas to accommodate us and all of our stuff.