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.
References:
The biological diversity of Iceland https://www.cbd.int/doc/world/is/is-nr-01-en.pdf
