Carrying Capacity

“Overshoot: (v.) to increase in numbers so much that the habitat’s carrying capacity is exceeded by the ecological load, which must in time decrease accordingly; (n.) the condition of having exceeded for the time being the permanent carrying capacity of the habitat.”
Overshoot, William Catton

This is a dense post. It gathers the core ecological concepts important to my position in a single source.

Energy flow through biological systems does not behave as a blind, dumb force. Last week we looked at how this energy supplies the herbivores and layers of carnivores, how it molds food webs with a roughly 10% efficiency between layers and we ended with a ratio of respiration to biomass which stood as a thermodynamic ordering function. The conclusion provides the jumping off point for today’s examination of carrying capacity:

‘We see there are finite quantities of material and a fixed flux of radiant energy on earth. Our planet is defined by these limitations. The thermodynamic energy laws give earth its characteristic dynamics, strictly delimiting what is and what is not possible.’

An ecosystem consists of a population of species and the changing environment they find themselves in. The environment is changed in large part by the very presence of the populations dwelling there. This progression through a series of stages is called succession. Each stage is termed a sere. Imagine a bare field and watch it evolve over a century or two. The bare field becomes grassland with weeds and other pioneering species, which in turn create the conditions for shrubs of all kinds to begin growing here and there. As the years go on the shrub density increases and the first trees of a pine forest find they have the conditions they need to survive. If the pine forest in turn gives way to an oak and hickory forest and the succession ends there then that last stage, last sere, is referred to as the climax community.

1280px-Forest_succession_depicted_over_timeIf the only major influences on the ecosystem remain those that come from the living populations, natures use of energy will keep the climax community running for centuries, even millennia. It is not a wholly static metric of energy flow to production but instead it pulses, which has been found to keep the populations fit. These climax communities are characterized by the strongest adaptability to shocks compared to any other possible configuration of living things and their environment. Life alters conditions such that they become more capable of hosting life; the Gaia hypothesis. This is due to the climax community containing the highest degree of species diversity of both plants and animals that this environment can indefinitely sustain. Energy has brought forth the maximization of use before being dissipated into entropy.

The climax community is a theoretical construct for an environment that has achieved a configuration that maximizes its carrying capacity indefinitely. It is 100% sustainable.

How the process works is educationally practical; our own species is caught in a number of circumstances related to these things. The energy path can be illustrated by comparing the ecosystem’s respiration to its overall production, P/R. Think of P as the rate of primary production (plants) or total photosynthesis. Respiration, R, as before is the ‘out-gassing’ of entropy. At first a rather scrappy set of plants and animals hit the scene, what we call the invasive species. Think weeds; aggressive and competitive. They have what it takes to survive in the harsher conditions of the early stages. The primary production greatly exceeds the respiration and the ratio P/R > 1. While P exceeds R organic matter will accumulate.

Too much accumulation of organic and inorganic matter can lead to a pollution problem. If the organic pollution overwhelms the ecosystem then respiration exceeds production and the ratio P/R < 1. The theory of succession states that an ecosystem tends towards a balance between the energy fixed in the biomass and the energy cost of maintenance in respiration, that is, tends towards P/R = 1. There is not an overall accumulation of organic material in the climax ecosystem, there is very little yield. What’s there instead is a flourishing of biodiversity where cooperation and symbiosis build complex systems with sophisticated feedback loops providing a resiliency the pioneering communities cannot achieve.

Odum_9.1_CIn the climax community the amount of standing biomass is maximized but interestingly this is not always what we humans want. Agriculture is a good example of deliberately holding back the process of succession to an earlier stage so that there continues to be larger yields of crops that we can use as food. Additionally, just as one characteristic of the climax community is that it has wide biodiversity, a characteristic of the pioneering, invasive community is that it is dominated by a monoculture. There is a tendency for a single plant to dominate just as we see on our farm fields with their acres of wheat and corn. It takes an enormous amount of energy to pause the process of succession on our farms. The petrochemical dependency of agribusiness, from tractor fuel to fertilizer, is well known. It is also well known that the right pest can wipe out an entire monoculture crop. Lacking the diversity of the climax community these critical ecosystems are vulnerable to shocks.

Still, even the climax community is not permanent. The larger change of sere ceases only until something from outside the system intervenes. In the real world everything changes; sooner or later a shock will come that is larger than what the environment can adapt to and it will regress or change completely. These shocks come from changes in either the inputs, the incoming energy, food and materials or the outputs such as we see in pollution where something produced in the system overwhelms the capacity of the larger environment to absorb it and break it down.

When considering the value of this theory that nature tends to balance P/R it is worth asking how the process behaves in extremus. One of the other characteristics of the pioneer, invasive species is that because they lack the feedback loops that would limit their population growth to sustainable levels their populations are prone to a phenomenon known as overshoot and die off. The (in)famous example is yeast introduced into a vat of wine. This simple ecosystem displays many of the most critical concepts necessary for understanding the current ecological predicament mankind finds itself in. In the diagram above it’s the ‘starting algal culture’ high in production and low in respiration.

The yeast consumes the nutrients from the sugary grapes producing a population explosion. The more yeast, the faster the sugars are consumed. It is party time in the wine vat, what ecologists refer to as the stage or age of exuberance. As we have learned, all ecosystems are defined by limits and this one is no different. There is a limited supply of the sugar nutrients and the expanding population is drawing down that resource; it is consuming it faster than it can be renewed. This ballooning population exceeds the carrying capacity of the vat with no way to replace what is being lost. We say the population of the yeast is in overshoot. Because this stage is unsustainable it will not be sustained; there will be a population crash until the resources can recover to a level adequate to sustain it. In the vat the pollution the yeast produce, the alcohol and carbon dioxide (our fermentation), fill the environment until the yeast is no longer able to survive. In that vat there is a die off to the point of extinction. There was a balance point in the vat between the number of yeast, their waste products and the ability of the mash to recycle them but this balance point was over shot. By exceeding the carrying capacity the yeast harmed the environment’s future carrying capacity, creating a downward spiral leading it, in this case, to zero. These words form the key take away: drawdown, overshoot, crash and die-off.

This ecological analysis highlights the difference between ecosystems that are sustainable and those that are not. To sustain the existing carrying capacity indefinitely the community populations can only be using renewable resources and those only at a rate that allows them to be renewed. This is an important point. Oil, for instance, is technically a renewable resource since new oil is being formed today, but the process takes millions of years. For all practical purposes oil is a non-renewable resource so with every barrel that we burn we draw down the total that remains in a usable form. Using any non-renewable resource is going to have the same characteristics. These are not methods of enlarging human carrying capacity, only exceeding it. Are there ways then that truly enlarge carrying capacity?

Another method is available. Humans are masters at this as well, the art of taking over other primary and secondary production for our own use. Every acre taken over for human settlement and raising our plant and animal foods increases the earth’s human carrying capacity at the expense of other species. This is simply the way it is, a necessary result of life unfolding on a finite planet. History is a tale full of examples of one kingdom usurping the lands and resources of another. These are other examples of leveraging the takeover method in human affairs. In these cases, all other things being equal, the addition to the carrying capacity can be a permanent one. For most of human history this has remained the case because the contextual environment in which human settlement occurred retained its integrity. The larger global environment was able to provide the inputs we required and process our outputs successfully. We were fairly successful at diverting a large percentage of the world’s life support capacity from supporting other life forms towards supporting ourselves.

Around 500 years ago something new came to be. It had taken all of pre-history and all of history up to the year 1500 for our species to multiply to 500 million; half a billion individuals scattered throughout the globe. At this time the European lands were full and population pressures kept the balance between the number of people and the carrying capacity of their environments more or less in balance. A famine or plague could eliminate large percentages of the population but in time the population would recover.

WorldPop_1970Then the Europeans discovered the new world, a whole hemisphere rich in natural resources. The largest takeover in human history commenced and an Age of Exuberance was begun which we are still living in today. An Age of Exuberance that is now coming to a close. Some nations seem to get away with supporting a population much greater than what could be provided for from their own lands. In these cases in order to form a complete analysis we need the idea of ghost acreage developed by George Borgstrom. Such nations were drawing upon invisible carrying capacity, which is capacity located elsewhere on the planet. “When Columbus set sail, there were roughly 24 acres of Europe per European. Life was a struggle to make the most of insufficient and unreliable resources. After Columbus… a total of 120 acres of land per person was available in the expanded European habitat – five times the pre-Columbian figure!” (Catton, 1980, pg. 24)

It took another three centuries for the human population to double. The globe sustained one billion of us around the year 1800. The operations of takeover had proven to be powerful, enough so that many ecologists who study these things think that perhaps about one billion people is the balance point of global, indefinite, carrying capacity for the human species in pre-industrial ecosystems.

The Age of Exuberance became the new normal; from now on, year after year, growth was expected. The renaissance and scientific revolutions, the war for independence and the drafting of the American Constitution all took place against this background. Fetters like the dead weight of superstitions which had haunted our ancestors were thrown off right and left. The new abundance supported widespread literacy for the first time as leisure hours spread among the peoples. Technological improvements became the definition of progress and all began to feel entitled to a “perpetually expansive life” as Catton had it. A belief in limitlessness began to become common currency in our cultures. With the western enlightenment came a humanism that dared to assert it would be possible by man’s own ingenuity to improve his fortunes, improve the ‘state of nature’ and improve his social relations. An Age of Exuberance indeed. It is not difficult to understand how, as again Catton had it, we have inherited the conviction that mankind is “largely exempt from nature’s constraints.”

The Age of Exuberance would have run its course as the benefits of takeover were again maximized but for another fortuitous discovery. James Young, a Scottish chemist, noticed petroleum seeping out of a coal mine in Alfreton, Derbyshire. In 1847 he managed to distil light thin oil that could be used in lamps along with thicker oil good for lubricating machinery. In 1848 he started a small business refining crude. Mankind began a draw down not from elsewhere but elsewhen. Now we were dealing with another kind of ghost acreage, call it phantom acreage. It was the combination of the New World and the fossil fuel based industrial age together that created the 500+ year Age of Exuberance and Abundance we have now learned to take as the normal state of affairs.

Next week will continue our look at how carrying capacity plays out in the real world where we will meet the strange denizen, Homo Colossus.

9 Replies to “Carrying Capacity”

  1. I posted the link to this in the Nature Bats Last Forum, stating that the article provided good basic education for the scientifically challenged such as myself.

    I’m wondering what are the policy implications of this writing. In that context, I’ve been thinking about Gail Tverberg’s blog article on Energy and the Economy, which clearly brings thorny policy questions to mind. I will paste some of what she says below. Can you help me understand how what you write does or does not relate to her article?


    Gail Tverberg says:

    August 18, 2014 at 7:05 am

    I wish the IPCC would rerun their model with reasonable assumptions. I don’t claim to have a “better” model than the IPCC.

    Also, if there have been huge changes by the time the climate changes, it may not make as much difference to the remaining much smaller population. It bothers me to have one group making forecasts as if the limits we are reaching in their area are the only limits we are reaching, not just one of a large number of limits we are reaching simultaneously. If we had ten or twenty different groups, each making forecasts of how the world would look if their limits were the only ones (for example, (1) soil erosion and soil quality; (2) continuing population growth; (3) inability to control infectious diseases as antibiotics lose their power and inability to produce enough GMOs to offset learning by insects as mutation offsets gains we have made; (4) decline in fish and ocean ecosystems for many reasons, including overfishing and pollution of many kinds; (5) resource depletion and effects of higher costs on people’s standards of livings; (6) inability to keep economic growth going, and because of this inability to repay debt with interest, and resulting collapse of the financial system: etc. ) then having one group screaming about how bad their result will be would at least be balanced out by some others. As it stands, the climate change folks have “cornered the market” in modeling money. Their model is right, only if there are no other limits.

  2. Thank you Artleads for sharing the link with the folks at Nature Bats Last. I have spent some time there myself.

    The work that Gail has been doing for years I see as very closely aligned to my own. The central message I think many of us are trying to get across is well highlighted in the article you reference; that the real world and the economy are inseparably linked. I made the same point today on the Archdruid’s forum. My contribution is simply approaching the central message from my own angle where the psychological aspects of our global problematique play a central role.

    The climate change models run for the IPCC reports do not generally include running out of the fuels that are causing the bulk of the changes to the atmosphere we refer to as climate change. Gail and Mr. Greer have both pointed out there are unreasonable assumptions of business as usual continuing long after its most probable pull date. This is due to the many other parts of the ecological crises such as those enumerated by Gail in the snippet you included. Peak Everything is the catchy phrase Richard Heinberg coined for this phenomenon. However I would caution against interpreting this as a willful blindness on the part of those climate scientists involved in the research the IPCC reports on. A wonderful resource for learning about the ins and outs of real climate modeling and the very impressive scientific cooperation and consensus that has accrued is A Vast Machine: Computer Models, Climate Data, and the Politics of Global Warming. Reading this I came to see the complexity of our climate models is at the very edge of what we are capable of understanding. There is a reason these simulations need supercomputers! There are a few model runs that do include Peak Oil but they are not included in the mainstream set the IPCC uses for its summary reports.

    I agree with Gail’s point that the climate crises is getting the bulk of the public’s attention at the expense of what may well be crises that will have more immediate impacts on our safety and social well being. It is interesting to ask why the climate change story is acceptable mass media material whereas the other items in Gail’s list of horrors are not (to which I would add the sixth extinction). For my part I have studied the science and been convinced that the weight of the evidence strongly supports the conclusion that the ecological crises is much larger than climate change alone. This is in part why my introductory posts set earth’s position in the larger context of deep time and deep space. I think it is with the larger view that we can find relief from the mistaken notion that we humans are somehow uniquely wicked and these hard times are our well deserved comeuppance. I propose instead that we humans are just like all other living things that stumble onto a new energy resource. There is a humility to my position that is a bit out of fashion just now but it works for me, and I am sticking to it.

  3. Thanks, ME. FWIW, I’ve long been laboring under the assumption that land use is the mother of the litany of crises. If you don’t build roads, cars can’t drive on them. If you don’t sprawl development on near-urban rural land, food security is enhanced. Sticking single tiny living units in the millions of unused urban spaces might support a saner alternative to nuclear family explosion. Nothing prevents fingers of wilderness (grazing land as Geoff Lawton terms it) from winding through cities. Not building on open land will protect biodiversity The list continues.

    Below is a brief response to Robbin Datta (in quotes) on NBL I include it since its short and somewhat sums up for me up the discussion that is missing.

    artleads Says:
    October 15th, 2014 at 5:44 am
    “Very small-scale wind-powered devices may help en route to oblivion. So might very small-scale passive solar. Could be enormously helpful once the phase of progressively decreasing energy flows is afoot. The windmills may offer a protein bonus in the form of bird carcasses at a time of progressively worsening food shortages. But neither jointly nor severally will they quell that methane monster.”

    My response (to which no one paid attention, btw):

    I gather that the “methane monster” has come to light for a relatively large public only in the past two years. How did that public feel about oblivion before then?

    Before the awareness of the methane monster, was there effective resistance to the oblivion trajectory? I doubt it, for no one up to this date can see the significance of land use and land development. Neither does anyone see the significance of watershed planning. No one (50 years or so after the phrase was first coined) thinks globally. (The MIC, perhaps.) No one criticizes individualism and separateness. So no one had a clue about resistance even before the monster’s known appearance.

  4. Artleads – Agree, to partner with the land instead of dominate and abuse it is the direction I would like to see things going. Leopold’s Land Ethic is a guiding light; “That land is a community is the basic concept of ecology, but that land is to be loved and respected is an extension of ethics.” As the threats to the ecosystems on which we rely grow ever more extreme I expect a counter-balancing protective reaction to greet them. We already see it.

    With the question of resistance to the ‘oblivion trajectory’ you hit on a puzzle. Protests against the malicious use of both peoples and lands fill the history books, they have always made great speeches, full of vigor and vinegar. What actually happens? What causes and conditions are brought to bear? Is there not a type of sleepwalking through history evident? More as these posts proceed.

  5. I might cross-post some of this conversation onto the NBL forum.

    You cite Jeffers:

    “We must uncenter our minds from ourselves;
    We must unhumanize our views a little, and become confident
    As the rock and ocean that we were made from.”

    This is exactly what I’m attempting to do. I keep saying (although no one seems to hear me) that it’s time to uncenter ourselves from human-first thinking and to put the land first..

    You say:

    “Protests against the malicious use of both peoples and lands fill the history books, they have always made great speeches, full of vigor and vinegar. What actually happens? What causes and conditions are brought to bear?”

    Protests against the malicious use of people, perhaps, but where was the like protest about land?

    Would you say that, prior to fossil fuel hegemony (that, as you say, fueled huge population increase) over-all GLOBAL conditions surrounding human interaction with the land were sustainable?

    But civilization is centered in cities. Protests against slavery (for instance) didn’t seem to center around the misuse of land, insofar as the liberating side merely sought to industrialize the land in their turn. (I’m supremely unread, so I will be happy to be corrected.) If so, wasn’t that less land friendly than what was there before?

    What appears to be going extinct are not just the species that disappear each day, but , more broadly, the land. The species that vanish are on and of the land. The topsoil, the forests, the wetlands, the grasslands (as well as the dispossessed people who lived off the land) are all subsumed under the heading LAND, and are all going under at roughly the same rate. Cities keep gobbling up the land and, along with that, urbanizing whatever was previously not urbanized.

    My point is that human needs can be met within the current boundaries of cities, and that they needn’t expand any further in SIZE.

    Resource Load Carrying Capacity and K­phase Technology
    by Peter Hartley (1993)

    I hope this will be of interest here. 🙂

    “KL = The resource load carrying capacity (resource use carrying capacity or impact carrying capacity) for a given resource R. KL is the load L that represents the maximum consumption or use (impact) of a given kind that R can withstand without irreversibly declining or losing suitability for that use, and without such use causing the irreversible decline of any other R.

    The supremely important feature of this concept, originated by William R. Catton, Jr., is its emphasis on the characteristics and requirements of R. [2] Emphasizing the well-being of R implies that engineering must regard the human relationship to nature as subject to usufructuary constraint. Usufruct is a legal term for the right of limited use and enjoyment of something without damaging that thing in anyway. An example is the old riparian principle of water rights, which gave dwellers along a river usufructuary access to its water—they could use the water in limited ways, as long as they did not diminish the river. [3]”

  7. Artleads – both comments are very pertinent, I am sure others will benefit from them as well.
    Cities dominate the flows from their surroundings. Whether symbiotic or parasitic depends on how you rank the productions unique to cities; universities, the arts, literacy and such.
    Chief Seattle’s timeless letter is one of the great protests against the abuse of land; “This we know: the earth does not belong to man, man belongs to the earth. All things are connected like the blood that unites us all. Man did not weave the web of life, he is merely a strand in it. Whatever he does to the web, he does to himself.”
    Ecological history does not show that the time just before the use of fossil fuels began mankind was globally in a sustainable relationship with the earth. There are places and times scattered here and there that point towards what is necessary but on the whole, no, what a sustainable culture might look like that uses only appropriate technology is not to be found in the past.

  8. “Would you say that, prior to fossil fuel hegemony (that, as you say, fueled huge population increase) over-all GLOBAL conditions surrounding human interaction with the land were sustainable? ”

    I was trying to suggest that the necessarily moderated population size (due to not having fossil fuels) made the planet as a whole viable, not that any previous culture exemplified sustainable practices.

  9. Ah, yes I can see that. The spike in population that created our existing condition of overshoot certainly starts around that time.

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