Wednesday, July 17, 2013

A Linnaeus For The Biomes

Biology concepts – ecosystem, biome, naming systems, climate, chaparral, taiga, pyrophyte

Clint Eastwood was already a minor film star when he made the spaghetti westerns 
for director Sergio Leone. It is a genre he would return to as a director, with the
Oscar winning, Unforgiven. Notice the sparse landscape behind him. This was 
probably in Spain even though the film had an Italian director 
and crew. Chaparral biome is found throughout the Mediterranean region.
Clint Eastwood made a series of westerns in the mid-1960’s; nothing surprising about that. The Good The Bad, and The Ugly, For A Few Dollars More, A Fistful of Dollars; these were all directed by Sergio Leone, an Italian director.

Filmed on location, the landscapes were barren. There were rocks and dirt, bushes and the rare tree, buttes and canyons, coyotes and lizards – typical American southwest. But the movies were filmed in Italy and Spain! These were the spaghetti westerns.

The stories took place in the American southwest and northwestern Mexico, but they were actually half a world away. How can the countryside around the Mediterranean Sea look like the desert southwest in America? The climate, flora, and fauna of very different places can look very similar because they are the same biome, sooo…..

Question of the Day: What makes biomes the same or different and who decides which biome it is?

First of all, some of the desert southwest isn’t desert. It is a biome called chaparral (chapa = scrub in Spanish). Chaparral is the smallest of all the world’s biomes. A biome is a major ecosystem with a single climate, but perhaps more than one habitat or community. It’s a huge ecosystem, which in turn is made up of several smaller habitats. The major idea is that it is housed within a single climatic region.

In North America, the chaparral is found in California and maybe Arizona, at about 40˚ North latitude. In Spain and Italy, chaparral is found at just about the same latitude. In fact, all around the edge of the Mediterranean is very chaparral-like, including North Africa and much of Israel.

The distance from the equator with the tilt of the Earth means that 40˚ South latitude might have much the same climate, and we see that the Chilean chaparral, as well as similar biomes in South Africa and Australia are close to 40˚S.

Also called a Mediterranean scrub biome, chaparral is hot, dry, and liable to catch fire. Many of it plants depend on fire to disperse or activate their seeds (pyrophytes = fire-loving). Others have below ground growth that sprouts after a fire. We will have to do some posts on pyrophytes soon. However, lots of fire doesn’t mean chaparral is lifeless; it has 20% of the world’s plant species and many are endemic (only found in that climate).

A 2013 study in PNAS shows that fire is essential for regrowth
of habitats. The study found that a chemical is produced by
plants when they catch fire, called karrikins. This signaling
molecule settles in the soil after the fire and binds to the seeds
that are there. The binding protein was discovered to be KA12,
which then alters its shape and promotes germination of the
seeds right after the fire is over. Amazing.
One exception to the endemic nature of chaparral flora is the tumbleweed. Tumbleweed is known as any small round shrub that, when sufficiently tall, will be caught by the wind, torn off its roots and blown across the forbidding landscape. You can hardly watch a western without encountering at least one rolling tumbleweed.

But it’s all a lie! The tumbleweed proper is known as Russian thistle (Salsola tragus, probably several species). It doesn’t roll along because of the harsh and destructive nature of the chaparral; this is how it disperses it seeds. After flowering, the plant dries up and disengages from its roots on purpose. As it rolls, it drops seeds, like a trail of breadcrumbs never to be used to find a way home.

Heck, Russian thistle isn’t even from the chaparral biome. It's native to the steppe grasslands of Russia, a different biome altogether. Russian steppe is cold, and is wet, but it is windy, so it’s mechanism of seed dispersal works in chaparral. Therefore, it can survive in California, and Spain, and Italy, and Morocco, and Israel. Here we have a plant that is identified closely with one climate that comes from another.

Indecision and overlap abound when it comes to naming and defining biomes. For instance, what makes a chaparral a chaparral and not a desert? What makes it a chaparral and not a grassland?

For many ecologists, the difference is precipitation. Deserts get less rain, snow, fog, or humidity than chaparrals, which in turn get less of these things than grasslands. But others divide grasslands into tall and moist versus short and wet. So does the dry grassland still get more rain than the chaparral?

In the chaparral of Israel, different biomes can come as close together as different slopes of a canyon. A 2012 study has proposed that these canyon faces with completely different flora and climate should be used as “evolution canyons” where global warming can be monitored and changes in many different ecosystems can be tracked in a small place. And this is all supposed to be within the world's smallest biome?

This is one of the proposed “evolution canyons” in the Israeli
chaparral. Notice the different vegetation on one slope as
compared to the other. There are differences in rain,
temperature, and animal life – and yet it is all supposed to
be chaparral?
At the other extreme, the taiga is the world’s largest terrestrial biome (11% of land) and is quite wet. In North America, taiga is found north of 50˚ N latitude, and tundra begins as far south as 60˚ N. England and Scotland are situated at 50-58˚ N latitude, but they are nothing like taiga or tundra. Even though they are located at similar points on the Earth, they have a different climate because they benefit from the Atlantic Conveyor, an extension of the Gulfstream. This current pulls warm air up from the tropics and keeps Great Britain warmer than it would otherwise be.

At 50-60˚ S latitude, there is very little land. Almost all the way around the Earth at those latitudes there is nothing but ocean. So latitude isn’t everything when it comes to defining biomes. Tierra del Fuego and the southern part of Patagonia are located south of 50˚ S, but they are defined as neither taiga nor tundra.

As water travels around the world through the upper and lower
currents of the ocean, it picks up and releases heat. When it is
shallow and in the tropics, it arms and travels close to the
surface. As it cools and releases its heat to the atmosphere, it
drops deeper. The gulfstream ends in the Atlantic conveyor,
which keeps Great Britain warm. The warm water moves
faster, which is why it takes less time to sail from the US to
Europe but longer to go west.
You can tell by the descriptions above that many places around the world share general descriptions, so where does one biome end and a different one begin? This is a serious point of vagueness for me. Many people publish maps showing the biomes of the Earth, and no two of them agree fully. Look at the pictures published just below.

The major terrestrial biomes of the world include desert, tundra, taiga, deciduous forest, grassland, and tropical rainforest. But these lists are often incomplete or vague. Chaparral is often left off the list; it has climate very similar to desert, plants able to deal with desert-like heat, and plants that come from grassland biomes. What is even weirder, it is the only biome where the wet season is the same as the winter season. Overall, it’s an in between biome and muddies the waters, so it often falls through the cracks.

Biomes may be classified by climate (Holdridge scheme), which generally equates to latitude, but we have already seen exceptions to that. Another scheme, Whittaker’s biome-typing, works to classify regions based on temperature and precipitation. Other systems are based on some combination of these factors, but if they are using the same factors, why don’t they agree better?

This is a busy picture, but the different colors represent different biomes,
and vary from map to map. The thing to notice is the pattern is different
in each map; no one can agree on what biomes are where.
For these schemes, the discriminating factors are abiotic (non-living influences), so they do not take in the periodic movements of animals or the invasiveness of some species in defining their boundaries. But some abiotic factors are changing quickly; like temperature, while others take much more time to change (geography). Therefore, as conditions change, these biome designations will either diverge, or will come to represent a different flora and fauna. No naming system has got these sets of problems licked.

Another problem is in the naming itself. Who decides on the name, and what does it mean in different areas of the world? The World Wide Fund For Nature (WWF) has a naming system that tries to be specific and generic at the same time. What is often called rainforest is designated by WWF as either “tropical and subtropical moist broadleaf forest” or “tropical and subtropical dry broadleaf forest” depending on the amount of precipitation. Don’t really roll off the tongue, do they?

Locality plays a role in the naming problem. Mediterranean scrub biome - is it by the sea, not always. Is it only scrub brush, not always. So that name isn’t so good. But even around the Med it’s called different things – maquis in Italy, garrigue in France, phyrygana in Greece and batha in Spain. In America, it’s the high chaparral – like the TV show. But in Chile, it’s called matorral (mata = shrub in Spanish). In South Africa, it’s the renosterveld or fynbos, but Australians know it as mallee scrub or Kwongan heath.

Carolus Linnaeus (1707-1778) developed a binomial system for naming in botany and zoology, specifically to alleviate the locality and organizational naming problems. But a system such of this was never developed for ecology. Why not?

All of this imprecise naming and description, and we’ve only touched on the terrestrial biomes. There's a whole set of problems attached to the aquatic biomes as well. Some definitions list only one biome in water, with different freshwater regions (ponds, lakes and such), and marine regions (oceans, reefs, estuaries).

The Tollund Man was found in a sphagnum peat bog in Denmark. The highly 
acidic peat tans the skin and the low oxygen condition preserves 
the clothes and hair. Only the phosphate in the bones is lost, so bones remain
in place, but not rigidly. You can see the rope around his neck. Autopsies in 
1950 and 2002 confirmed that he was hung rather than strangled. Tollund Man 
was most likely a sacrifice to the bog gods.
Other systems define each of the regions as a biome. This can also cause problems. One freshwater biome is a wetland – but what kind of wetland? There are bogs, swamps, marshes, fens (as in Fenway Park in Boston) and carrs (fens overgrown with trees). Each has a different type of feeder system, different majority floral and fauna, and even a different acidity. How could those all be the same biome?

Most bogs are found in boreal forests (taiga) in Great Britain and Scandinavia. They were thought of as sacred places where the gods lived, and where human sacrifices were often made. This is why you may find bog bodies, mummies of people who lived thousands of years ago. The acidic conditions and low oxygen preserved the tissues (but dissolved the bones usually).

So - are the bogs considered part of the taiga, or just habitats within a biome? Or are they their own biome within a biome? Not easy to decide. Biomes are essential for organizing the life on Earth, but the learning would be easier if we could find a Linnaeus for ecology.

Next week, can you have mold without mildew? Just what are they anyway?



Nevo, E. (2012). "Evolution Canyon," a potential microscale monitor of global warming across life Proceedings of the National Academy of Sciences, 109 (8), 2960-2965 DOI: 10.1073/pnas.1120633109
 
Guo, Y., Zheng, Z., La Clair, J., Chory, J., & Noel, J. (2013). Smoke-derived karrikin perception by the / -hydrolase KAI2 from Arabidopsis Proceedings of the National Academy of Sciences, 110 (20), 8284-8289 DOI: 10.1073/pnas.1306265110