Lions, tigers, and bears, oh my! What is a keystone species and how can conservationists use them?

Lion (Panthera leo)

tiger cub

Tiger (Panthera tigris)

Grizzly bear (Ursus arctos horribilis)

Grizzly bear (Ursus arctos horribilis)

What do these three animals have in common?  No, it’s not that they’re all featured in a popular film.  It’s not even that they’re all at the top of the food chain, although that’s closer.  Lions, tigers, and bears are all keystone species.

In architecture, the keystone at the top of an arch holds the arch together.  Without the keystone, the whole arch and building surrounding it will collapse.  Similarly, “keystone species” are animals that have a disproportionately large effect on the ecosystems they live in.

For example, Robert T. Paine first tested the keystone species hypothesis empirically (scientifically) by removing a species of starfish (Pisaster) from its intertidal habitat and observing the dramatic changes this removal wrought on the starfish’s prey, mussels (Mytilus) and the ecosystem as a whole.  It turns out that the starfish helped to keep the mussels’ numbers in check, and without the starfish to eat the mussels, the mussel population exploded and took over the habitat, crowding out other species and decreasing biodiversity (the numbers of different species in an ecosystem).

Keystone species can fall under several different categories.  Top predators, like the starfish, are often keystone species because of the inherent role they play by eating lots of smaller animals.  That’s why it’s so important to conserve large mammalian carnivores like lions, tigers, and bears – all endangered species – which unfortunately attract a lot of poaching due to their magnificent furs and sought-after meat.

arch1

Another category of keystone species are mutualists, which are animals that help many other species for something in return (in a mutually beneficial relationship).  For example, fruit trees are keystone mutualists because they provide shelter and food for many animals like monkeys and birds, which repay the tree by dispersing their seeds far and wide.

Finally, ecosystem engineers are keystone species because they are animals that change the physical landscape in which they live.  Beavers, elephants, and prairie dogs are all examples of ecosystem engineers because they build dams, destroy trees, and make burrows, respectively.

Prairie_Dog_closeup

Prairie dog (Cynomys)

Learning about these concepts helps scientists and environmentalists define categories in which to place animals and know which animals to target in conservation efforts.  It is far easier to conserve a whole ecosystem by protecting one species than by trying to protect the entire community of animals.  In this way, scientists use keystone species to protect Mother Nature, one animal at a time!

————————————————————————————————-

References:

See No Ordinary World’s post on sea otters, another important keystone species:  https://thisisnoordinaryworld.wordpress.com/2013/03/06/sea-otters-adorable-endangered-and-a-keystone-species/.

Keystone species definition: http://animals.about.com/od/animalswildlife101/f/keystonespecies.htm.

“Keystone.”  Wikipedia.org.  http://en.wikipedia.org/wiki/Keystone_(architecture).

“Keystone Species.” Marietta.edu.  http://www.marietta.edu/~biol/biomes/keystone.htm.

“Keystone Species.”  Wikipedia.org.  http://en.wikipedia.org/wiki/Keystone_species.

“Mutualism.”  Wikipedia.org.  http://en.wikipedia.org/wiki/Mutualism_(biology).

Advertisements

Sea Otters: Adorable, Endangered, and A Keystone Species

Here_I_am.. sea otter baby sea otter

This cuddly creature is a sea otter, or Enhydra lutris, a well-known marine mammal native to the coasts of the northern and eastern North Pacific Ocean.  This furry, playful fellow is more than just adorable, however.  Otters are a keystone species.

In architecture, the keystone at the top of an arch holds the arch together.  Without the keystone, the whole arch and building surrounding it will collapse.  Similarly, some species of animals are called “keystone species,” meaning that a whole ecosystem, or interplay between living organisms and their surroundings, depends on that particular species to keep it running smoothly.

tumblr_ma95mbDj261rt5smro1_500

Sea otters play a crucial role in their watery home.  How do we know?  Here’s the story:

In the 1700s, sea otters along the coast of California were hunted nearly to extinction for their furs and killed by fishermen who thought they were eating too much of the fish they wanted to catch.  When the otters disappeared, the animals they normally eat, sea urchins, enjoyed a large population boom.  Soon, there were so many sea urchins that they ate all of the kelp, a type of seaweed, at the bottom of the ocean, and caused an “urchin barren” to form, which means that the ocean floor is scraped clean and becomes an “ocean desert” in the ocean that is essentially devoid of life.  This is bad!  Fish raise their young in the protection of the kelp and other animals hide it in to avoid prey, and all those animals began to flee the scene as well. The fishermen now had less fish to catch, not more.  It turns out the otter was playing a much more crucial role in this ecosystem than people previously knew.

What happened to the otters?  In 1911, a treaty was passed to protect the sea otters from being hunted.  In some places, the populations of sea otters recovered, and eventually so did the kelp and fish.  But there are still some areas that have suffered near-permanent damage from the removal of just one type of animal – the sea otter – from its home.

Now, the sea otter is globally an endangered species, meaning that its numbers are so low that it is under imminent threat of becoming extinct, or dying out entirely.  The sea otter’s story shows us that if we take action we can achieve a remarkable success story that seems daunting, if not impossible, at first.

Sources:

“Here I am..” Top left photograph.  Photograph taken by Alan  Wolf and distributed under a Creative Commons License: CC BY-NC-SA 2.0

Baby sea otter photograph: sflo1822 on tumblr.

Three otters photograph: jamoore52 on tumblr.

Seat otter:  http://en.wikipedia.org/wiki/Sea_otter

Keystone species (definition): http://animals.about.com/od/animalswildlife101/f/keystonespecies.htm

Keystone species hypothesis: http://www.washington.edu/research/pathbreakers/1969g.html

Keystone species empirical evidence:  http://rspb.royalsocietypublishing.org/content/early/2012/07/03/rspb.2012.0856.full