Viewed As Near-Indestructible, These Critters Have Declined Almost 50%

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December 16, 2014 | 18,206 views

Story at-a-glance

  • Since the year 1500, 322 species have become extinct
  • Anywhere from 16 percent to 33 percent of vertebrate species are currently globally threatened or endangered
  • Invertebrates, such as beetles, butterflies, spiders, and worms, are also threatened, with declines of nearly 50 percent in the past 35 years
  • Researchers believe we are in the early stages of the planet’s 6th mass extinction event, caused by human activity

By Dr. Becker

Since the year 1500, 322 species have become extinct and the remaining species are quickly (relatively speaking) declining in numbers too. On average, populations of vertebrates on earth have declined by 25 percent while 67 percent of invertebrate species have declined by 45 percent.

"Such animal declines will cascade onto ecosystem functioning and human well-being," researchers reported in the journal Science.1 The somber finding comes from Stanford University researchers, who suggest we are now in the midst of "anthrocpocene defaunation."

Defaunation is a term similar to deforestation, except "fauna" refers to the total collection of animals in a given area.2 Defaunation is the loss or decline of animals. It's happened before, but this was typically the result of a catastrophic asteroid strike or other planetary anomaly. The current die-off, on the other hand, has a more sinister cause – human activity.3

The Early Stages of Earth's 6th Mass Extinction Event?

Stanford biology professor Rodolfo Dirzo and colleagues believe we are in the early stages of the planet's 6th mass extinction event. It's estimated that 16 percent to 33 percent of vertebrate species are currently globally threatened or endangered. Large animals, which produce fewer offspring, require larger habitat, and make more attractive hunting targets, are facing the highest rate of decline.4

The western black rhinoceros, for instance, was recently declared extinct, and the West African lion may be close behind (with fewer than 250 adult lions still in existence). Habitat loss, along with overexploitation, is among the major threats to vertebrates.

Invertebrates, such as beetles, butterflies, spiders, and worms, are also threatened, with declines of nearly 50 percent in the past 35 years. As with larger animals, habitat loss is a major factor in their declines.

The analysis included data on only 452 such species – out of an estimated 1.4 million that have so far been described. So less than 1 percent of invertebrate species have been studied for potential declining numbers.

Still, the finding suggests the problem may extend much further than was ever expected. Ben Collen with University College London, who co-authored the review, stated:5

"We were shocked to find similar losses in invertebrates as with larger animals, as we previously thought invertebrates to be more resilient …

While we don't fully understand what the long-term impact of these declining numbers will be, currently we are in the potentially dangerous position of losing integral parts of ecosystems without knowing what roles they play within it."

This Is About More Than the Loss of a Species; It's a Loss of Ecosystem Functioning

When a large species becomes extinct, it gathers attention (and rightfully so), but what is much less highlighted is the trickle down effect of that loss. For instance, according to Dirzo:6

"Consider the case of heavy defaunation of large wildlife in Africa… When that happens, according to our own research, the abundance of rodents increases; this implies more vectors and host of diseases, many of which are of great... significance to humans.

We recently published another study showing that such differential defaunation in African savannas explains the increase in abundance of rodents and doubles the risk of Bartonellosis—a nasty disease in humans."

Beyond diseases in humans, animal species are responsible for pollinating plants and dispersing seeds. Insects pollinate about 75 percent of the global food supply, which contributes to nutrient cycling and decomposing organic materials, which helps ecosystems flourish.7

"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," Dirzo said.8

Researchers Call for 'Decreasing Per Capita Human Footprint'

You may feel powerless to stop animal extinctions, but each of us can help. Dirzo and colleagues recommend large-scale changes to stop defaunation, including:9

  • Decreasing the per capita human footprint
  • Developing and implementing carbon-neutral technologies
  • Producing food and goods more efficiently
  • Consuming less
  • Wasting less

You can adopt many of these changes on a smaller scale in your own life, as well as get involved with conservation efforts that appeal to you. For me, I had the honor of working with endangered black rhinos early in my career, so they hold a special place in my heart. If you'd like to learn more about rhinoceros conservations efforts and what you can do to help, visit the Save the Rhino Get Involved page.

[+]Sources and References [-]Sources and References

  • 1 Science July 25, 2014
  • 2 MongaBay.com July 24, 2014
  • 3 Stanford News Service July 24, 2014
  • 4 See Stanford News Service July 24, 2014
  • 5 See MongaBay.com July 24, 2014
  • 6 See MongaBay.com July 24, 2014
  • 7 See Stanford News Service July 24, 2014
  • 8 See Stanford News Service July 24, 2014
  • 9 Discovery News July 24, 2014