Ecosystems Benefit from Predator Presence

We are entering the middle stages of the 6th mass extinction event of the world.

That line certainly grabbed my attention when I read “Trophic Downgrading of Planet Earth” by James Estes, et al.  While mass extinctions are a natural phenomenon and are expected to continue, the upcoming 6th is considered different from previous events; scientists believe that 1) humans will be responsible for the next world-wide extinction, and 2) the next extinction will be characterized by the loss of apex consumers (those at the top of the food chain).  Why is this of particular interest to carnivore biologists?  The loss of important apex consumers results in trophic downgrading.  The theory of trophic downgrading suggests that predators ultimately control the health of their ecosystem: remove them, and a habitat’s flora and fauna will eventually fall out of balance and swing wildly from one extreme to the other, often resulting in ecosystem damage.

The downgrading process rests on the premise of another ecological phenomenon called trophic cascading.  Cascades are triggered by adding or removing predators from an ecosystem and result in changes to the predator/prey relationships within the food web.  The cascade process has been shown in every biome of the world, including highly managed ecosystems like Yellowstone National Park.  Studies have shown that the absence and presence of wolves in Yellowstone have had direct effects on the park’s plant and animal processes.  During 70 years of wolf absence from Yellowstone National park, a number of deciduous tree species quickly died out, which had a direct effect on soils, beaver and other ecosystem conditions.  Without wolves present to maintain their numbers, ungulates essentially overgrazed their environment.  Once wolves were reintroduced, ecosystem slowly found rebalance and changed ungulate feeding habits, decline in elk and coyote numbers, and an increase in beaver populations.

While very aware of the challenges ahead and the seemingly desperate state of parts of our biospheres, I am encouraged when I hear about increases in carnivore populations in some western states, like Washington’s recent wolf pack increases and recent Northern Cascade grizzly bear sighting.  Perhaps with a little assistance from their human neighbors, these and other important apex consumers can begin to refill their ecosystem niche.  If we can begin to accept predators’ necessary role in our ecosystem, we can then be more mindful of responsible and safe co-habitation with the animals upon which, we’re beginning to realize, we and our world greatly depend.

Read more on the Grizzly Bear Outreach Project’s website about how trophic downgrading influences human-caused impacts on nature such as climate change, habitat loss and more.  Watch a fun remote camera video showing how many different species (including humans!) utilize one piece of land over the course of one year – a great example of the basis for trophic cascading.

2 thoughts on “Ecosystems Benefit from Predator Presence

  1. Your last sentence of first paragraph talks of a balance. You do realize don’t you that the ballance of nature falllacy hasn’t been taught to environmental science students in 15 years. Nature exists in a state of flux.

    Second paragraph has been completely rejected by the National Park Service’s latest report on Yellowstone.

    Might want to take a look in the interest of providing accurate scientifically valid info for your readers.

    • Thanks for taking the time to respond to this post.

      Flux and balance are not mutually exclusive. Predators and prey have constantly shifting population numbers, often changing on predictable cycles.

      The classic, often-cited ecological example of this is lynx and snowshoe hare. When vegetation is abundant, showshoe hare numbers increase, which allows for an increase in lynx. Eventually the hares deplete their food sources, which weakens them and makes it easier for the lynx to kill them, bringing their population back down and allowing the vegetation to regrow. The following year the lynx population crashes due to the shortage of hares, which allows the hare population to increase again once the vegetation has reestablished itself. And the cycle goes on.

      Obviously there are other factors, and ongoing debate about top-down vs. bottom-up population drivers. Regardless, it is in constant flux, but it is also in balance. Once you remove the lynx, however, the balance is off and the flux continues in one direction until the hares have permanently changed the vegetation of an area.

      Regarding the recent Yellowstone study, I assume you are referring to Kaufmann’s paper for the USGS arguing against the “Ecology of Fear” concept. In that paper, while the researchers stated that fear was not enough of a mechanism to alter elk behavior, they still named wolves and other predators as critical for restoring aspen and other vegetation – “A landscape-level aspen recovery is likely only to occur if wolves, in combination with other predators and climate factors, further reduce the elk population.”

      If that is the paper you are referring to, you might also be interested in the response to it by Robert Beschta and William Ripple, two of the most prominent researchers in the Yellowstone Ecosystem. They found a number of flaws in Kaufmann’s methods. You can read the unpublished manuscript that has been accepted by the Ecological Society of America.

      If you are referring to a study other than Kaufmann’s, please let us know the source. We do try to stay current, and our work depends on presenting scientifically accurate information.

      Thank you again for your comment.

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