An Isle Royale Story

  • no royalty on this island chain
  • just lots of fascinating interactions between living things
  • Isle Royale is located in the Northwestern part of Lake Superior
  • it is an archipelago composed of over 430 different islands
  • the main island is about 9 miles wide and 14 miles long
  • it houses a suite of organisms
  • from beavers to balsam firs
  • but arguably the most notable creatures on this island have been the wolves, the moose, and the aspen trees
  • let’s start from the beginning
  • Isle Royale went undisturbed by humans for quite some time
  • then we came in in the 1840s and mined the place for copper until 1900
  • swaths of forest were cut down to support mining operations
  • and even more swaths were burned to expose the copper ore
  • the most recent natural fires on this island occurred in 1936 and 1948
  • singing about 20% of the total land area of the mainland
  • in 1912
  • white tailed deer were introduced to the island
  • a new herbivore on the scene
  • but the last deer was recorded in the 1930s and the Isle Royale population has since gone extinct
  • there have also been beavers here
  • there were about 150 colonies of beavers at their peak population
  • their presence had a profound impact on plants
  • both terrestrial and aquatic
  • the main herbivore on the island are moose
  • they arrived in the early 1900s
  • within the past 50 years
  • moose populations have been anywhere between 500 and 2,000 moose in total
  • that’s a sizable number of large herbivores
  • so sizable that their presence on the island was degrading the forest habitat
  • moose will browse on a wide variety of trees
  • from quaking aspen to balsam firs
  • and there were many of them
  • so it is easy to see how moose presence could lead to defoliation
  • lucky for the trees
  • a chance immigration of a breeding pair of wolves occurred in 1949
  • the wolves arrived via a winter ice bridge
  • and found themselves stranded once the ice melted in the spring
  • the study of the interactions between the subsequent wolf population and the moose population
  • is one of the most famous predator-prey data studies
  • there were many discoveries made by observing the proceedings of Isle Royale events
  • and one of specific note is the top down terrestrial food chain control
  • it was stated earlier that wolves and aspens interact, right?
  • and that’s true
  • they interact via top down terrestrial food chain control
  • this is just a fancy way of saying that the presence of a wolf population of the island caused cascading effects that changed life for organisms lower down on the food chain
  • so when the wolves arrived
  • they preyed upon the moose
  • and when there are fewer moose
  • there are fewer herbivores
  • and when there are fewer herbivores
  • trees get to keep their leaves and the forest is healthier

Because of the chance introduction of wolves, the forest flora benefitted. But the story does not end there. Ecology is not so simple that you can call it quits after delineating one simple cause and effect relationship. Ecosystems are far too complex for that to be the case. What happened to the wolves? What happened to the moose? Those are dynamic stories for another time. For those curious to see how the stories end, take a look at the source material.

Source

“Are Isle Royale’s Wolves Chasing Extinction?” Science. N.p., n.d. Web. 19 Apr. 2016. <http://science.sciencemag.org/content/340/6135/919>.

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