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.
Showing posts with label life system. Show all posts
Showing posts with label life system. Show all posts
February 28, 2010
February 27, 2010
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?
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?
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