There's an ongoing biodiversity loss around the globe, with some animal species going extinct and many more on the brink, and if we want to know that cause we just have to look in a mirror, researchers say.
We are in the initial days of a new mass extinction occurrence, the sixth in the Earth's history, and this time it's human activity and burgeoning human populations, not a catastrophe such as an asteroid impact or an ice age, that's leading the decline in animals life, they say.
One of several studies published in the current issue of the journal Science shows as human population doubled during the past three decades the numbers of invertebrate animals --butterflies, beetles, worms and spiders, for example -- has declined by 45 percent percent in the same period.
"We were shocked to find similar losses in invertebrates as with larger animals, as we previously thought invertebrates to be more resilient." says Ben Collen of University College London, one of the study's authors.
While larger species such as pandas, tigers and elephants that make for warm and fuzzy photos on the Internet may get more attention, the various ecosystems humans depend on can be deeply impacted by the loss of even the tiniest of species, the researchers say.
"We tend to think about extinction as loss of a species from the face of Earth, and that's very important, but there's a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well," says the study's lead author Rodolfo Dirzo of Stanford University.
Many of those ecosystems have felt the heavy hand of humans, they say, such as tropical rainforests that are being cleared at a rapid pace and marine ecosystems that are consistently overfished.
"We live amid a global wave of anthropogenically driven biodiversity loss," Dirzo and his colleagues warn, citing 322 species that have become extinct in the last 500 years.
That clear mass extinction has been given a name by scientists, "anthropocene defaunation," or a decline in animal species caused by humans and human activities.
There have been five previous mass extinctions on Earth, the most well-known -- at least to the public -- being the killing off of the dinosaurs by a massive asteroid impact 65 million years ago.
Around 252 million years ago an even more extreme event, dubbed the "Great Dying," killed off more than 90 percent of the Earth's species.
The current extinction may be in its early days, the researchers say, but its cause is become increasingly -- and worryingly -- clear.
"The underlying driving force for this is not a meteorite or a mega-volcanic eruption; it is one species -- homo sapiens," says Dirzo.