Population: Carrying Capacity and Limiting Factors in Natural systems
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This document discusses the concept of carrying capacity, which refers to the maximum population size of a species that an ecosystem can sustain indefinitely. It provides examples showing how ecosystems have finite resources and limits, and exceeding those limits can damage the ecosystem and lead to population crashes. The document warns that human population growth is on an unsustainable "J-curve" and that exceeding environmental limits risks collapse, as seen in other species. It emphasizes the importance of respecting natural limits to protect ecosystems for long-term human well-being.
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Population: Carrying Capacity and Limiting Factors in Natural systems
- 3. This presentation is a courtesy of The Wecskaop Project It is entirely free for use by scientists, students, and educators anywhere in the world. What Every Citizen Should Know About Our Planet Copyright 2012, The Wecskaop Project. All rights reserved.
- 5. How many individuals can a particular ecosystem [or planet] indefinitely support over a long period of time while continuing to function and without suffering severe or irreparable damage?
- 6. How many individuals can a particular ecosystem [or planet] indefinitely support over a long period of time while continuing to function and without suffering severe or irreparable damage? For scientists, the answer to such a question constitutes the system's carrying capacity
- 7. Since ecosystems are finite in So wisdom recommends protecting them and doing them no harm their size and resources, each has an upper limit to the population that it can support while continuing to provide food resources withstand impacts and damage tolerate or withstand wastes maintain, perpetuate, and repair itself and also provide the assorted Phytoplankton in the ecological services oceans, such as these diatoms, produce that allow a given population to exist more than half of the oxygen that we breathe
- 8. Since ecosystems are finite in their size and resources, each has an upper limit to the population that it can support while continuing to provide food resources withstand impacts and damage tolerate or withstand wastes maintain, perpetuate, and repair itself and also provide the assorted ecological services that allow a given population to exist
- 9. What happens if we destroy them or diminish their numbers or weaken their ability to function? Examples of crucial ecological services include each day’s production and replacement of most of the molecular O2 that we and most other animals con- sume every few seconds The fifty species of diatoms in the image above, for instance, are examples of phytoplankton in the earth’s oceans that produce more than half of the oxygen that we breathe
- 10. Other ecological services include, for instance, Pollination of vast percentages of flowering What happens if we destroy them or diminish their numbers ? plants everywhere, and dramatic contributions to the production of rainfall by the process of transpiration.
- 11. Environmental carrying capacities need not necessarily involve food and water, but can also reflect critical limits to the damages, wastes, eradications, and impacts that they can safely withstand – and to their capabilities for self-perpetuation, maintenance, and self-repair
- 13. Imagine an elevator, for example, that can safely accommodate 18 passengers and yet 83 or 247 or 1058 passengers begin to squeeze aboard
- 14. Notice that this is quite different than Malthus’s assessments involving food; So that the science and understandings today are far broader It is easy to understand that the stresses of excessive loading virtually ensure failures in one or more components, triggering the collapse of the entire system and the destruction of both the vehicle and its passengers
- 15. A similar unsettling scenario can be envisioned if one imagines an aircraft of finite size, only to notice that a line of more and more and more persons continue to endlessly board the aircraft
- 16. It is thus important to appreciate that carrying capacity in biological and biospheric systems is commonly far MORE than simply a matter of food, or water, or “resources”
- 17. Thus, more and more persons endlessly boarding an elevator or aircraft or vehicle or planet of finite capacity constitutes an egregiously-unwise behavior
- 18. A behavior that invites transgressions of at least one or more and/or
- 19. Thousands of examples of thresholds, limits, and tipping points (both known and unknown) exist in real-world natural and biospheric systems
- 20. Real-world thresholds As two quick examples of thresholds in real-world systems: One instance in a biological system can be seen in human blood which has buffers that maintain its pH at a mildly alkaline 7.4 level. Seemingly small transgressions, how- ever, beyond pH 7.3 (lower limit) or 7.5 (upper limit) result in acidosis or alkalosis, both of which are potentially fatal.
- 27. All three classical examples experienced 99%-plus die-offs and collapse at a time when the combined bodies or cells of each of the populations physically-occupied roughly 2/1000ths of 1% of their surrounding environment that appeared to remain theoretically-available to them
- 28. All three classical examples experienced 99%-plus die-offs and collapse at a time when the combined bodies or cells of each of the populations physically-occupied roughly 2/1000ths of 1% of their surrounding environment that appeared to remain theoretically-available to them
- 29. All three classical examples experienced 99%-plus die-offs and collapse at a time when the combined bodies or cells of each of the populations physically-occupied roughly 2/1000ths of 1% of their surrounding environment that appeared to remain theoretically-available to them
- 39. Not a very wise policy, was it?
- 68. Also notice that this graph of human population growth over the past 10,000 years is an extreme J-curve
- 69. How worrying should J-curves be? Unfortunately, humankind first learned with horror what J-curves can do from unspeakably deadly events at the close of World War II
- 70. Physicists know that exponential progressions and their resulting graphs which are known as J-curves exhibit a decided tendency to obliterate everything around themselves in every direction A graph of this shape on the display monitors of a nuclear power plant would send the plant’s engineers scrambling for the exits
Notas do Editor
- (1)Pollinators (such as bees and butterflies) not only pollinate plants in fields, mountains, and rainforests (that produce our oxygen), but also pollinate hundreds of crops that help us earn a living or keep us fed; (2) Each day earth’s atmosphere pulls water (by “transpiration”) that is in the soil in the morning upward through the bodies of plants, out their leaves, and into the atmosphere in time to fall as rain that same afternoon. During the summer in temperate latitudes, an average-sized maple tree releases 200 liters of water per hour into the atmosphere (Campbell, et al., 1999). Water moves up through the plant bodies at rates up to fifteen metersper hour (ibid). Thus, when we cut down the trees of a rainforest, transpiration of water into the atmosphere is diminished accordingly and the rainforest further deteriorates as the climate becomes ever drier. We thus see an ecological service in which undisturbed ecosystems help maintain both rainfall and climate.
- At the time of its peak population (just over 2000 individuals) the combined bodies of the entire herd physically-occupied roughly 2/1000ths of one percent of the total island area that appeared to remain theoretically-available to them. (In other words, their population peaked and began its catastrophic 99%-plus die-off in seemingly ‘vast open-space’ conditions and in a surrounding environment that visually-appeared to remain ALMOST ENTIRELY EMP-TY.) For more on this and other “too-late” / “they waited too-long” examples (including two other classical real-world examples on a similar scale) visit http://www.calameo.com/read/0006765193603424dcabe.
- These three classical examples and others like them strongly suggest that humankind’s seemingly-instinctive “vast open-space” suppositions and intuitions may be producing a widespread tendency to dangerously underestimate both the degree and the proximity of the humanitarian, civilizational, and biospheric dangers that our current trajectories portend.
- These three classical examples and others like them strongly suggest that humankind’s seemingly-instinctive “vast open-space” suppositions and intuitions may be producing a widespread tendency to dangerously underestimate both the degree and the proximity of the humanitarian, civilizational, and biospheric dangers that our current trajectories portend.
- “We… hereby warn all humanity of what lies ahead,” their written statement said. “A great change in our stewardship of the Earth and the life on it is required if vast human misery is to be avoided and our global home on this planet is not to be irretrievably mutilated.” The warning called for immediate action by world leaders to help curb “explosive population growth and harmful patterns of human activity and development,” and the article (by S. Bronstein, Cox News Service) points out that the four-page warning “marks the first time that so many of the world’s most distinguished scientists have issued a joint statement on the environment.” Biologist E. O. Wilson of Harvard, for example, said that the signed statement “represents the largest group of senior scientists from around the world to ever speak in unison on a single issue.
- “We… hereby warn all humanity of what lies ahead,” their written statement said. “A great change in our stewardship of the Earth and the life on it is required if vast human misery is to be avoided and our global home on this planet is not to be irretrievably mutilated.” The warning called for immediate action by world leaders to help curb “explosive population growth and harmful patterns of human activity and development,” and the article (by S. Bronstein, Cox News Service) points out that the four-page warning “marks the first time that so many of the world’s most distinguished scientists have issued a joint statement on the environment.” Biologist E. O. Wilson of Harvard, for example, said that the signed statement “represents the largest group of senior scientists from around the world to ever speak in unison on a single issue.
- The answer here is “no,” for even though more food feeds more people, it does not increase the self-perpetuation, self-maintenance, ecosystem service, and self-repair functioning of natural systems. In fact, the wastes, eradications, and damaging impacts inflicted by more and more people degrade, alter, and dismantle greater portions of these other critical systems and lessen their abilities for self-perpetuation, maintenance, and repair.
- Although “s-curves” have been widely seen in recent literature, the s-curve / demographic transition hypotheses that they represent warrant the following critiques: (1) Notice that a graph of worldwide human population numbers over the past 10,000 years is an extreme and quite-pronouncedJ-curve ( with a disquieting similarity to the same J-curve shapes seen in the exceedingly dangerous and deadly exponential progressions that characterized the nuclear fission reactions that ended World War II; and (2) Note that the imagined and fashionable “s-curves” that have been offered so often in recent years can only be achieved if the authors do not BEGIN their graph until, for example, the 1970s of 1980s, then bring it up to the present, and then extend it several decades into the future on the basis of their own assumptions, hopes, wishes, guesses, and suppositions (it seems appropriate, therefore, to note that conveniently omitting or excluding 9,800 years of data in order to force-fit the data set into an s-curve that does not otherwise exist is misleading at best). Thirdly, although the Demographic Transition hypothesis which is the basis of so many of today’s imagined and hoped-for futures is sometimes true and is sometimes descriptive, this is not always true. For one thing, much of today’s transition theory literature seems to often envision equilibrial “s-curve” outcomes as a more or less inevitable or automatic outcome of population growth, while at the same time omitting or at least ignoring the OTHER classical population outcome known as Climb-and-Collapse. Thus, even if demographic transition outcomes characterize some human populations in some societies and some cultures or at some periods in history, the fact that they sometimes occur in some cases does not mean that they always occur, nor that they automatically apply universally in all societies, cultures, and times in history, or even if they do occur, that they will occur quickly enough to avoid overshoot and collapse. Nor do they contemplate that each new medical advance and advance in life-extension and mortality reduction serve to re-initiate the imagined transition (with its period of explosive population growth) over and over and over again. Lastly it should be noted that even J-curve progressions do not rocket straight upward forever, so that even as J-curve progressions soar upward along the y-axis of their graph, they can routinely show late signs of slowing. In this latter case, however, the observed slowing does not denote the beginning of a happy transition to an equilibrial sustainability, but instead characterizes the moments immediately preceding the progression’s precipitous collapse to a value of zero.
- How large is a billion? Two thought-experiments in appendix two (see slides 87, 88, and 89) dramatically-underscore the immense size of each of our added billions. In both thought-experiments, the answer is 38,461 years.
- How large is a billion? Two thought-experiments in appendix two (see slides 87, 88, and 89) dramatically-underscore the immense size of each of our added billions. In both thought-experiments, the answer is 38,461 years.
- … Multiple independent lines of evidence ( “miles” of evidence …. )
- Recall that 100Nobel Laureates and 1400 other top scientists who were signatories to formal “warnings” to humanity were already expressing their warnings when world population had just passed five billion, and when only half of humankind were yet industrialized. Since then, we have now we reached and passed seven billion and according to recent U.N. medium and high-fertility world population projections we are headed toward 10, 11, 12, 13, 14, or 15.8 billion by the end of this century.
- Approximately 382,000 births per day minus approximately 155,000 deaths per day results in approximately 227,000 extra births each day, which result in approximately 83 million extra per year, 6 million extra per month, and 681,000 extra every three days (if today is Friday, by this same time on Monday, Earth will be home to 681,000 extra individuals – most of whom are arriving in regions where jobs, food, money, health care, and education are already in short supply). And if today is Monday, by this same time on Friday, Earth will be home to approximately 908,000 additional persons – whichnecessitates (assuming 25 students per classroom)completion of approximately 36,320 additional classrooms every four days.
- Speaking from a natural science / biology / biospherics-machinery perspective, multiple powerful independent lines of evidence argue quite powerfully that earth’s carrying capacity for a modern, industrialized humanity with, a prosperous standard of living for all is on the order of two billion or even somewhat less. Why? (1) On a worldwide basis, we were already inflicting damage, wastes, destruction, and eradication on atmospheric and biospheric systems in 1987 with a population of five billion and these impacts both continued and worsened with a 1999 population of six billion, followed by a seventh billion by 2011 (only half of whom were industrialized) – (and now we may be on-track toward 15.8 billion by century’s end?). If humankind’s worldwide population were to stop growing later today and did not grow at all thereafter, our current damaging and unsustainable impacts, wastes, and eradications might easily double as the least-developed half of humanity aspires to achieves an industrialized standard of living for all.