Life System Proxies: Top Predator Health

All ecosystems include food webs, and many of those webs contain a predator this is a dominant member.  Early conceptualizations of predator / prey relations characterized the system as a chain with bigger things eating smaller things in a more or less linear relationship.  We now know that the image of a chain is too simple as many species are prey in multiple food relationships and similarly those same species may eat across several of what we formerly referred to as chains.

But I digress.  The point is that in these eat and be eaten systems, be they chains or webs, there are a species that pretty much only eat.  These are things like bears, wolves, and sharks that for all intents and purposes are not normally food for other species, but do eat a lot themselves.  This species is called the top predator.

As we have learned more about how food webs work, we have learned that the presence or absence of a top predator can have a big effect on the functioning of the food system and the related ecosystem as a whole.  Sever over-fishing of northwest Atlantic cod and related predators has left huge swaths of the northwest atlantic habitat without a top predator.  As a result the food web in those areas has shifted to a very different configuration and it is not clear that the system that supported the cod will be able to re-emerge simply with simply the reduction of the fishing pressure.

So presence, absence, or change in the top predator in a food web can tell us things about how that food web and its associate ecosystem are functioning or may be changing.  Following on this a strategy that monitors the health and resilience of top predators might serve as a proxy for the health and resilience of the larger systems that those beings are part of.

Life System Proxies: Forest cover

A few posts ago I noted that I would follow with some specific examples of Earth System proxies.  I got distracted, but here is a first one...

A clear indicator of the state of the Life subsystems of the Earth system is the amount of Earth's land surface that is covered by forests.  There are many reasons for this, not the least of which is that forested land is archetypal in western cultural images of "natural".  Forests house ecosystems that are more or less independent from humans; they provide homes to many of our cherished charismatic megafauna and they provide a whole host of ecosystem services ranging from materials to spiritual solace.  A couple of less obvious of these include gas exchange with the atmosphere that removes CO2 and releases O2 as through photosynthesis and moderating the hydrologic cycle - the rain forests of Brazil are sometimes referred to as the lungs of our planet.

So changes in the percentage and distribution of forest cover on Earth's land surface will change in very fundamental ways how the Earth system functions.  Prior to the Industrial Revolution (say 1776), the distribution of forest cover on Earth changed slowly in concert with other elements of the Earth system (e.g. during glacial cycles).  Following the industrial revolution and the attendant increased consumption of energy and expansion of human population that came with it, humans began to have a significant impact on where and how much forest there was on Earth.  For instance, much of what is now forest in New England, was cleared for farmland in the 18th century.  Those forests began to return as transportation corridors opened up to the west and allowed the much more fertile and easy to work lands of the midwest to take up some of the demand for food on along the East coast.

On a much larger scale (the economy is now global and removal rates are higher), similar economic pressures are driving the removal of rain forests in Brazil, Indonesia and parts of Africa in current times.  Rain forest soils and ecosystems are very different from the deciduous forests of New England and it is clear that re-growth of the rain forests will take much longer than those of New England.

If we monitor forests, where they are, how they are changing, we will be monitoring a part of Earth's Life system.  The challenge of course is to know what those variables tell us: Are those changes good or bad? and What futures do they signal or eliminate?

Earth System Proxies

For a large project that I am working on, I have been thinking about examples of things that hold a lot of information about the state of the Earth System.  And of course I have been doing that in the context of the the diagram presented here (and whose original files are no longer available to me due to the evolution of computer software and related technologies).  The bit of the diagram that is important is the middle bit with the 3 lobes.  I gave an introduction to this diagram many years ago, and some changes have occurred, not the least is that it now shows the natural / artificial system boundary that separates bits of the Earth system that are related to human intentionality from all of the other bits (and whose continued usefulness I now wonder about).

Examples of things that might represent the state of the Earth system include things like the CO2 concentration in the atmosphere, the state of the ENSO system.  ENSO is a great example, because it has teleconnections that influence climate variability across vast swaths of the entire planet AND we can predict it to a certain extent.  This means that in a rational / logical world we should be able to use our understanding of the physics of the ocean and atmosphere to make decisions that improve the quality of human life on Earth.  Unfortunately it is not that simple, as we discovered in the mid-1990s at Columbia.

Each member of a set of such proxies would have the following qualities:

1. It would be easy to measure.
2. It would contain a great deal of information about the current state of some portion of the Earth System; and perhaps tell us something about what is likely to happen in the near future.
3. It would be more or less independent of the other members of the set (in geek speak, the members of the set would be more or less orthogonal).
4. Changes in this measure would tell us something about whether life on Earth was getting better or worse.

In the next few posts I am going to play around with some ideas for proxies in the "Life" lobe.

On the demise of the Mean

Perhaps I should call this On the demise of the Normal.  More and more these days I encounter distributions where the median is a much better descriptor than the mean.  Of course if things are distributed normally then the median and the mean (and the mode) are all the same number.  But if things are abnormal then those definitions start to point to different parts of the distribution.

My first encounter with non-normal distributions came in graduate school as I was thinking about the distribution of elevations in topographic profiles.  Turns out that those things have a lot in common with power-law distributions.  So does the distribution of sizes of earthquakes.  And all sorts of other things in nature as well.  Then of course there were arguments about the differences between log-normal distributions and power-law distributions and how you might be able to tell in which was which by measuring things.  In the context here, it doesn't matter; neither one in normal.

I have been pondering this lately because I have been trying to write about proxies for the state of the human system part of the Earth system and central tendency indictors and variability around those have come up with considerable strength.  And now I am wondering if that most archetypal of all normal distributions - heights of humans - will stand up as normal over all of Earth.  Or does that example really only work in a suburban middle class classroom in the mid-1970s.

Which in turn makes one wonder whether in fact it is the normal distribution that is abnormal...

(ain't I clever!)