Loss of Top Predators

James A. Estes, et al. 15 Jul 2011.  Trophic Downgrading of Planet Earth. Science vol 333.

Before men, large predators and herbivores had huge influences on nature across land, ocean, and fresh water ecosystems.  Their loss has a “trophic cascade” effect across ecosystems that increases disease, wildfire, invasive species, and decreases carbon sequestration and biodiversity.

We are at the beginning of a 6th major extinction caused by homo sapiens, especially characterized by the loss of larger animals, globally.  These losses are permanent and their disappearance will have far-reaching effects.  It is our most “pervasive influence on nature”.  Some examples:

  • The loss of wolves, bison, sharks, whales, and big cats (for example) has had effects such as:
  • Sub-Saharan African baboon populations have increased due to fewer lions and leopards. Baboons are full of intestinal parasites which are now spreading to people as baboons forage near villages.
  • The recovery of large ungulate populations in the Serengeti in Africa reduced the number of wildfires
  • Whales consume lots of plankton and consequently expel a lot of feces, which sink to the ocean bottom, sequestering carbon.  The loss of whales from industrial whaling caused an extra 105 million tons of carbon to be released from oceans into the air, adding to climate change.
  • Sea otters keep underwater kelp forests abundant because they eat the urchins that consume kelp.  Sea otter populations crashed, and consequently kelp disappeared too, which led to fewer mussels, Glaucous winged-gulls, less kelp forest fish which led to bald eagles needing to eat more seabirds to make up for that less fish.
  • Willowy plants were suppressed by elk browsing in Yellowstone until wolves were introduced.  Increased riparian trees and shrubs shaded and cooled nearby streams, reduced bank erosion, and increased the number of fish and other aquatic life.

We are just beginning to learn how removal of large animals affects ecosystems and the food web.

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