Tuesday, June 2, 2015
Note: This program first aired on May 30, 2015.
Today we hear more about Iceland, that mysterious high latitude island formed from volcanos, covered in sheep, and home to elves and other hardy folk. It takes a while to sink in while you are driving around, that you aren’t going to see any animals in the road, unless they are domestic sheep. Iceland has only one native terrestrial mammal, the arctic fox, and while the population is considered viable, they aren’t especially common.
So why no other native mammals? Reindeer were introduced on purpose, and mink accidentally, escaping from fur farms. Mice and rats accompany people wherever they migrate, but only the arctic fox, and humans, got to Iceland on their own. Why, for that matter, such low terrestrial biological diversity overall? Iceland has the distinction of having no amphibians or reptiles. Of the 1100 species of insect, the flies are the most numerous, followed by beetles and bees, while there are no ants or butterflies.
In the plant kingdom things are similar, there is relatively low diversity in vascular plants and bryophytes. The only native trees are a birch, a willow and the rowan tree, a species in the same genus as mountain ash. Only 10 species of passerines, perching birds, nest in Iceland. Even if you know very little about birds you could probably name 10 passerines without much trouble. The freshwater systems on the island host only 5 species of fish.
The answer of course is that Iceland is very isolated, and only recently unglaciated. The same ice age that covered much of North America, including Maine, covered Iceland as well. The difference is that once the glaciers retreated from Maine, Maine was connected to an entire continent populated by organisms ready to move in as climate allowed. Iceland found itself in the middle of the high latitude North Atlantic Ocean, and while the ice that connected it to Greenland and northern Europe allowed the hardy little Arctic Fox to tip toe its way across the ocean, nothing else made the icy crossing.
Only things that can travel by air, water, or animal can get to Iceland. Spores and very light seeds can be blown there if they get carried very high into the atmosphere. Other seeds can float and survive the ocean crossing if they are tough enough. The only animals seen on land that are found in relative abundance in Iceland are birds, and mostly sea birds at that. Which should be no surprise, as these animals routinely migrate thousands of miles, and are not stopped by air or water. The very lack of a land bridge for terrestrial migration is the reason they fly to Iceland. Essentially no land mammals means no predators; Iceland is an excellent place to lay some eggs right on the ground and call it a nest.
What Iceland does have in spades is marine biodiversity, hundreds of species of fish are found on its continental shelf, and over 100 species of algae grace its coastline. 15 or more species of marine mammals are found in its waters. What makes Iceland such a hard place to colonize, its location and latitude, make it a perfect spot for marine productivity. It lies right on the boundary between the polar and subpolar ocean currents, warmer water from the Gulf Stream and North Atlantic current especially warm the southern coast, while colder arctic water cools the north east.
The interplay between these two, combined with the large continental shelf extending out away from Iceland, mix the ocean and distribute the nutrients that drive productivity.
Humans have been exploiting this productivity for over 1100 years, Iceland was first settled by Vikings in 870 AD. Humans have been impacting the landscape ever since. The most significant environmental impact during Iceland’s 1100 year history has been soil erosion, primarily due to changes in vegetation that result from grazing. The shrubby forests found on the island retreated, and currently the vast majority of the island is used as open range land for the thousands of sheep that are raised there. The erosion impedes recovery of native vegetation, and the mild climate and short growing season don’t help either.
All of this dawns on you as you drive around the island, seeing birds everywhere, sheep and fences, but nothing else. There are vast stretches of land inhabited only by moss. After several days of just grass and stone I felt an explosion of sweet relief when we drove through some trees. Iceland is surrounded by hundreds of kilometers of water, and just kisses the Arctic circle. Biology has cobbled together an entirely respectable community of organisms to live on this chunk of rock in the middle of nowhere. I encourage you to check it out.
The biological diversity of Iceland https://www.cbd.int/doc/world/is/is-nr-01-en.pdf