Carrying capacity

The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. In population biology, carrying capacity is defined as the environment's maximal load,[1] which is different from the concept of population equilibrium. Its effect on population dynamics may be approximated in a logistic model, although this simplification ignores the possibility of overshoot which real systems may exhibit.

Carrying capacity was originally used to determine the number of animals that could graze on a segment of land without destroying it. Later, the idea was expanded to more complex populations, like humans.[2] For the human population, more complex variables such as sanitation and medical care are sometimes considered as part of the necessary establishment. As population density increases, birth rate often increases and death rate typically decreases. The difference between the birth rate and the death rate is the "natural increase". The carrying capacity could support a positive natural increase or could require a negative natural increase. Thus, the carrying capacity is the number of individuals an environment can support without significant negative impacts to the given organism and its environment. Below carrying capacity, populations typically increase, while above, they typically decrease. A factor that keeps population size at equilibrium is known as a regulating factor. Population size decreases above carrying capacity due to a range of factors depending on the species concerned, but can include insufficient space, food supply, or sunlight. The carrying capacity of an environment may vary for different species and may change over time due to a variety of factors including: food availability, water supply, environmental conditions and living space. The origins of the term "carrying capacity" are uncertain, with researchers variously stating that it was used "in the context of international shipping"[3] or that it was first used during 19th-century laboratory experiments with micro-organisms.[4] A recent review finds the first use of the term in an 1845 report by the US Secretary of State to the US Senate.[3]


Several estimates of the carrying capacity have been made with a wide range of population numbers. A 2001 UN report said that two-thirds of the estimates fall in the range of 4 billion to 16 billion with unspecified standard errors, with a median of about 10 billion.[5] More recent estimates are much lower, particularly if non-renewable resource depletion and increased consumption are considered.[6][7] Changes in habitat quality or human behavior at any time might increase or reduce carrying capacity. Research conducted by the Australian National University and Stockholm Resilience Centre mentioned that there is a risk for the planet to cross the planetary thresholds and reach “Hothouse Earth” conditions.[8]. In this case, the Earth would see its carrying capacity severely reduced.[9]

In the view of Paul and Anne Ehrlich, "for earth as a whole (including those parts of it we call Australia and the United States), human beings are far above carrying capacity today."[10]

The application of the concept of carrying capacity for the human population has been criticized for not successfully capturing the multi-layered processes between humans and the environment, which have a nature of fluidity and non-equilibrium, and for sometimes being employed in a blame-the-victim framework.[11]

Supporters of the concept argue that the idea of a limited carrying capacity is just as valid applied to humans as when applied to any other species. Animal population size, living standards, and resource depletion vary, but the concept of carrying capacity still applies. The number of people is not the only factor in the carrying capacity of Earth. Waste and over-consumption, especially by wealthy and near-wealthy people and nations, are also putting significant strain on the environment together with human overpopulation. Population and consumption together appear to be at the core of many human problems.[12][10] Some of these issues have been studied by computer simulation models such as World3. When scientists talk of global change today, they are usually referring to human-caused changes in the environment of sufficient magnitude eventually to reduce the carrying capacity of much of Earth (as opposed to local or regional areas) to support organisms, especially Homo sapiens.[13]

Factors that govern carrying capacity

Some aspects of a system's carrying capacity may involve matters such as available supplies of food, water, raw materials, and/or other similar resources. In addition, there are other factors that govern carrying capacity which may be less instinctive or less intuitive in nature, such as ever-increasing and/or ever-accumulating levels of wastes, damage, and/or eradication of essential components of any complex functioning system. Eradication of, for example, large or critical portions of any complex system (envision a space vehicle, for instance, or an airplane, or an automobile, or computer code, or the body components of a living vertebrate) can interrupt essential processes and dynamics in ways that induce systems failures or unexpected collapse. (As an example of these latter factors, the "carrying capacity" of a complex system such an airplane is more than a matter of available food, or water, or available seating, but also reflects total weight carried and presumes that its passengers do not damage, destroy, or eradicate parts, doors, windows, wings, engine parts, fuel, and oil, and so forth.) Thus, on a global scale, food and similar resources may affect planetary carrying capacity to some extent so long as Earth's human passengers do not dismantle, eradicate, or otherwise destroy critical biospheric life-support capacities for essential processes of self-maintenance, self-perpetuation, and self-repair.

Thus, carrying capacity interpretations that focus solely on resource limitations alone (such as food) may neglect wider functional factors. If the humans neither gain nor lose weight in the long-term, the calculation is fairly accurate. If the quantity of food is invariably equal to the "Y" amount, carrying capacity has been reached. Humans, with the need to enhance their reproductive success (see Richard Dawkins' The Selfish Gene), understand that food supply can vary and also that other factors in the environment can alter humans' need for food. A house, for example, might mean that one does not need to eat as much to stay warm as one otherwise would. Over time, monetary transactions have replaced barter and local production, and consequently modified local human carrying capacity. However, purchases also impact regions thousands of miles away. For example, carbon dioxide from an automobile travels to the upper atmosphere. This led Paul R. Ehrlich to develop the I = PAT equation.[14]

I = P ∙ A ∙ T


I is the impact on the environment resulting from consumption
P is the population number
A is the consumption per capita (affluence)
T is the technology factor
Logistic curve examples
This is a graph of the population due to the logistic curve model. When the population is above the carrying capacity it decreases, and when it is below the carrying capacity it increases.

An important model related to carrying capacity (K), is the logistic, growth curve. The logistic growth curve depicts a more realistic version of how population growth rate, available resources, and the carrying capacity are inter-connected. As illustrated in the logistic growth curve model, when the population size is small and there are many resources available, population over-time increases and so does the growth rate. However, as population size nears the carrying capacity and resources become limited, the growth rate decreases and population starts to level out at K. This model is based on the assumption that carrying capacity does not change. One thing to keep in mind, however, is that carrying capacity of a population can increase or decrease and there are various factors that affect it. For instance, an increase in the population growth can lead to over-exploitation of necessary natural resources and therefore decrease the overall carrying capacity of that environment.[15]

Technology can play a role in the dynamics of carrying capacity and while this can sometimes be positive,[16] in other cases its influence can be problematic. For example, it has been suggested that in the past that the Neolithic revolution increased the carrying capacity of the world relative to humans through the invention of agriculture. In a similar way, viewed from the perspective of foods, the use of fossil fuels has been alleged to artificially increase the carrying capacity of the world by the use of stored sunlight, even though that food production does not guarantee the capacity of the Earth's climatic and biospheric life-support systems to withstand the damage and wastes arising from such fossil fuels. However, such interpretations presume the continued and uninterrupted functioning of all other critical components of the global system. It has also been suggested that other technological advances that have increased the carrying capacity of the world relative to humans are: polders, fertilizer, composting, greenhouses, land reclamation, and fish farming. In an adverse way, however, many technologies enable economic entities and individual humans to inflict far more damage and eradication, far more quickly and efficiently on a wider-scale than ever. Examples include machine guns, chainsaws, earth-movers, and the capacity of industrialized fishing fleets to capture and harvest targeted fish species faster than the fish themselves can reproduce are examples of such problematic outcomes of technology.

Agricultural capability on Earth expanded in the last quarter of the 20th century. But now there are many projections of a continuation of the decline in world agricultural capability (and hence carrying capacity) which began in the 1990s. Most conspicuously, China's food production is forecast to decline by 37% by the last half of the 21st century, placing a strain on the entire carrying capacity of the world, as China's population could expand to about 1.5 billion people by the year 2050.[17] This reduction in China's agricultural capability (as in other world regions) is largely due to the world water crisis and especially due to mining groundwater beyond sustainable yield, which has been happening in China since the mid-20th century.[18]

Lester Brown of the Earth Policy Institute, has said: "It would take 1.5 Earths to sustain our present level of consumption. Environmentally, the world is in an overshoot mode."[19]

Ecological footprint

One way to estimate human demand compared to ecosystem's carrying capacity is "ecological footprint" accounting. Rather than speculating about future possibilities and limitations imposed by carrying capacity constraints, Ecological Footprint accounting provides empirical, non-speculative assessments of the past. It compares historic regeneration rates, biocapacity, against historical human demand, ecological footprint, in the same year.[20][21] One result shows that humanity's demand footprint in 1999 exceeded the planet's bio-capacity by >20%.[20] However, this measurement does not take into account the depletion of the actual fossil fuels, "which would result in a carbon Footprint many hundreds of times higher than the current calculation."[22]

There is also concern of the ability of countries around to globe to decrease and maintain their ecological footprints. Holden and Linnerud, scholars working to provide a better framework that adequately judge sustainability development and maintenance in policy making, have generated a diagram that measures the global position of different countries around the world, which shows a linear relation between GDP PPP and ecological foot print in 2007. Possible answers to the question of where we are as individual countries attempting to reach sustainability and development methods to reduce ecological foot print. According to the Figure 1 diagram, the United States had the largest ecological foot print per capita along with Norway, Sweden, and Austria, in comparison to Cuba, Bangladesh, and Korea. [23]

See also


  1. ^ Hui, C (2006). "Carrying capacity, population equilibrium, and environment's maximal load". Ecological Modelling. 192 (1–2): 317–320. doi:10.1016/j.ecolmodel.2005.07.001.
  2. ^ "Carrying Capacity". The Sustainable Scale Project. Retrieved 16 February 2017.
  3. ^ a b Sayre, N. F. (2008). "The Genesis, History, and Limits of Carrying Capacity". Annals of the Association of American Geographers. 98: 120–134. doi:10.1080/00045600701734356.
  4. ^ Zimmerer, Karl S. (1994). "Human Geography and the "New Ecology": The Prospect and Promise of Integration" (PDF). Annals of the Association of American Geographers. 84: 108–125. doi:10.1111/j.1467-8306.1994.tb01731.x.
  5. ^ "UN World Population Report 2001" (PDF). p. 31. Retrieved 16 December 2008.
  6. ^ Ryerson, W. F. (2010), "Population, The Multiplier of Everything Else", in McKibben, D, The Post Carbon Reader: Managing the 21st Centery Sustainability Crisis, Watershed Media, ISBN 978-0-9709500-6-2
  7. ^ Brown, L. R. (2011). World on the Edge. Earth Policy Institute. Norton. ISBN 978-0-393-08029-2.
  8. ^ Trajectories of the Earth System in the Anthropocene
  9. ^ Planet at risk of heading towards irreversible “Hothouse Earth” state
  10. ^ a b Ehrlich, Paul R; Ehrlich, Anne H (2004), One with Nineveh: Politics, Consumption, and the Human Future, Island Press/Shearwater Books, pp. 137, 182, see also pages 76–236
  11. ^ Cliggett, Lisa (2001). "Carrying Capacity's New Guise: Folk Models for Public Debate and Longitudinal Study of Environmental Change". Africa Today. 48: 3–19. doi:10.1353/at.2001.0003.
  12. ^ Fred Pearce (2009-04-13). "Consumption Dwarfs Population as Main Environmental Threat". Yale University. Retrieved 2012-11-12.
  13. ^ Ehrlich, Paul R; Ehrlich, Anne H (2008), The Dominant Animal: Human Evolution and the Environment, Island Press/Shearwater Books, pp. 235, see also pages 234–309
  14. ^ Ehrlich, Paul R.; Holdren, John P. (1971). "Impact of Population Growth". Science. 171 (3977): 1212–1217. Bibcode:1971Sci...171.1212E. doi:10.1126/science.171.3977.1212. PMID 5545198.
  15. ^ Swafford, Angela Lynn. "Logistic Population Growth: Equation, Definition & Graph." N.p., 30 May 2015. Web. 21 May 2016. "Logistic Population Growth - Boundless Open Textbook." Boundless. N.p., n.d. Web. 21 May 2016.
  16. ^ Martire, Salvatore; Castellani, Valentina; Sala, Serenella (2015). "Carrying capacity assessment of forest resources: Enhancing environmental sustainability in energy production at local scale". Resources, Conservation and Recycling. 94: 11–20. doi:10.1016/j.resconrec.2014.11.002.
  17. ^ Economy, E., China vs. Earth, The Nation, May 7, 2007 issue
  18. ^ Nielsen, R., The Little Green Handbook, Picador, (2006) ISBN 978-0-312-42581-4
  19. ^ Brown, L. R. (2011). World on the Edge. Earth Policy Institute. Norton. p. 7. ISBN 978-0-393-08029-2.
  20. ^ a b Wackernagel, M.; Schulz, N.B.; et al. (2002). ""Tracking the ecological overshoot of the human economy". Proc. Natl. Acad. Sci. USA. 99 (14): 9266–9271. Bibcode:2002PNAS...99.9266W. doi:10.1073/pnas.142033699. PMC 123129. PMID 12089326.
  21. ^ Rees, W.E. and Wackernagel, M., Ecological Footprints and Appropriated Carrying Capacity: Measuring the Natural Capital Requirements of the Human Economy, Jansson, A., Folke, C., Hammer, M. and Costanza R. (ed.), Island Press, (1994)
  22. ^ "FAQ - Global Footprint Network". Retrieved 28 March 2018.
  23. ^ Holden, Erling; Linnerud, Kristin (May 2007). "The sustainable development area: satisfying basic needs and safeguarding ecological sustainability". Sustainable Development. 15 (3): 174–187. doi:10.1002/sd.313.


  • Gausset Q., M. Whyte and T. Birch-Thomsen (eds.) (2005) Beyond territory and scarcity: Exploring conflicts over natural resource management. Uppsala: Nordic Africa Institute
  • Tiffen, M, Mortimore, M, Gichuki, F. (1994) More people, less erosion: Environmental recovery in Kenya. London: Longman.
  • Shelby, Bo and Thomas A. Heberlein (1986) "Carrying capacity in recreation settings." Corvallis, OR: Oregon State University Press.
  • Karl S. Zimmerer (1994) Human geography and the "new ecology": the prospect and promise of integration. Annals of the Association of American Geographers 84, p. XXX;
  • Martire, S., Castellani, V., & Sala, S. (2015). Carrying capacity assessment of forest resources: Enhancing environmental sustainability in energy production at local scale. Resources, Conservation and Recycling, 94, 11-20.

External links


Ampacity is a portmanteau for ampere capacity defined by National Electrical Codes, in some North American countries. Ampacity is defined as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Also described as current-carrying capacity.

The ampacity of a conductor depends on its ability to dissipate heat without damage to the conductor or its insulation. This is a function of the

insulation temperature rating, the electrical resistance of the conductor material, the ambient temperature, and the ability of the insulated conductor to dissipate heat to the surrounds.

All common electrical conductors have some resistance to the flow of electricity. Electric current flowing through them causes voltage drop and power dissipation, which heats conductors. Copper or aluminum can conduct a large amount of current without damage, but long before conductor damage, insulation would, typically, be damaged by the resultant heat.

The ampacity for a conductor is based on physical and electrical properties of the material and construction of the conductor and of its insulation, ambient temperature, and environmental conditions adjacent to the conductor. Having a large overall surface area can dissipate heat well if the environment can absorb the heat.

In electrical cables different conditions govern, and installation regulations normally specify that the most severe condition along the run will govern each cable conductor's rating. Cables run in wet or oily locations may carry a lower temperature rating than in a dry installation. Derating is necessary for multiple cables in close proximity. When multiple cables are in close proximity, each contributes heat to the others and diminishes the amount of external cooling affecting the individual cable conductors. The overall ampacity of insulated cable conductors in a bundle of more than three cables must also be derated, whether in a raceway or cable. Usually the derating factor is tabulated in a nation's wiring regulations.

Depending on the type of insulating material, common maximum allowable temperatures at the surface of the conductor are 60, 75, and 90 °C, often with an ambient air temperature of 30 °C. In the United States, 105 °C is allowed with ambient of 40 °C, for larger power cables, especially those operating at more than 2 kV. Likewise, specific insulations are rated 150, 200, or 250 °C.

The allowed current in a conductor generally needs to be decreased (derated) when conductors are in a grouping or cable, enclosed in conduit, or an enclosure restricting heat dissipation. e.g. The United States National Electrical Code, Table 310.15(B)(16), specifies that up to three 8 AWG copper wires having a common insulating material (THWN) in a raceway, cable, or direct burial has an ampacity of 50 A when the ambient air is 30 °C, the conductor surface temperature allowed to be 75 °C. A single insulated conductor in free air has 70 A rating.

Ampacity rating is normally for continuous current, and short periods of overcurrent occur without harm in most cabling systems. Electrical code rules will give ratings for wiring where short-term loads are present, for example, in a hoisting motor. For systems such as underground power transmission cables, evaluation of the short-term over-load capacity of the cable system requires a detailed analysis of the cable's thermal environment and an evaluation of the commercial value of the lost service life due to excess temperature rise.

Design of an electrical system will normally include consideration of the current carrying capacity of all conductors of the system.

Some devices are limited by power rating, and when this power rating occurs below their current limit, it is not necessary to know the current limit to design a system. A common example of this is lightbulb holders.

Antihypotensive agent

An antihypotensive agent, also known as a vasopressor agent or pressor, is any medication that tends to raise low blood pressure. Some antihypotensive drugs act as vasoconstrictors to increase total peripheral resistance, others sensitize adrenoreceptors to catecholamines - glucocorticoids, and the third class increase cardiac output - dopamine, dobutamine.

If low blood pressure is due to blood loss, then preparations increasing volume of blood circulation—plasma-substituting solutions such as colloid and crystalloid solutions (salt solutions)—will raise the blood pressure without any direct vasopressor activity. Packed red blood cells, plasma or whole blood should not be used solely for volume expansion or to increase oncotic pressure of circulating blood. Blood products should only be used if reduced oxygen carrying capacity or coagulopathy is present. Other causes of either absolute (dehydration, loss of plasma via wound/burns) or relative (third space losses) vascular volume depletion also respond, although blood products are only indicated if significantly anemic.

Black-tailed deer

Two forms of black-tailed deer or blacktail deer that occupy coastal woodlands in the Pacific Northwest are subspecies of the mule deer (Odocoileus hemionus). They have sometimes been treated as a species, but virtually all recent authorities maintain they are subspecies.

The Columbian black-tailed deer (O. h. columbianus) is found in western North America, from Northern California into the Pacific Northwest and coastal British Columbia. The Sitka deer (O. h. sitkensis) is found coastally in British Columbia, southeast Alaska, and southcentral Alaska (as far as Kodiak Island).


Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.In vertebrates, it is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume), and contains proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and blood cells themselves. Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood. The blood cells are mainly red blood cells (also called RBCs or erythrocytes), white blood cells (also called WBCs or leukocytes) and platelets (also called thrombocytes). The most abundant cells in vertebrate blood are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. In contrast, carbon dioxide is mostly transported extracellularly as bicarbonate ion transported in plasma.

Vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated. Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin. Insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system. In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen.

Jawed vertebrates have an adaptive immune system, based largely on white blood cells. White blood cells help to resist infections and parasites. Platelets are important in the clotting of blood. Arthropods, using hemolymph, have hemocytes as part of their immune system.

Blood is circulated around the body through blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled.

Medical terms related to blood often begin with hemo- or hemato- (also spelled haemo- and haemato-) from the Greek word αἷμα (haima) for "blood". In terms of anatomy and histology, blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen.

Builder's Old Measurement

Builder's Old Measurement (BOM, bm, OM, and o.m.) is the method used in England from approximately 1650 to 1849 for calculating the cargo capacity of a ship. It is a volumetric measurement of cubic capacity. It estimated the tonnage of a ship based on length and maximum beam. It is expressed in "tons burden" (Early Modern English: burthen, Middle English: byrthen), and abbreviated "tons bm".

The formula is:

[clarification needed]


The Builder's Old Measurement formula remained in effect until the advent of steam propulsion. Steamships required a different method of estimating tonnage, because the ratio of length to beam was larger and a significant volume of internal space was used for boilers and machinery. In 1849, the Moorsom System was created in Great Britain. The Moorsom system calculates the cargo-carrying capacity in cubic feet, another method of volumetric measurement. The capacity in cubic feet is then divided by 100 cubic feet of capacity per gross ton, resulting in a tonnage expressed in tons.

Electrical busbar system

Electrical Busbar System sometimes simply referred to as Busbar system is a modular approach to Electrical wiring, where in instead of standard cable wiring to every single electrical device, the electrical devices are mounted on to a adapter which is directly fitted to current carrying busbar. This modular approach is being used in distribution boards, Automation Panels & other power kinds of installation in an electrical enclosure.Busbar system is subject to safety standards for design and installation along with electrical enclosure according to IEC 61439-1 and vary by locality, country or region. & the system depends on Allowable Busbar types and sizes are vary according to operating voltage and current carrying capacity,

Intraspecific competition

Intraspecific competition is an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals.

By contrast, interspecific competition occurs when members of different species compete for a shared resource. Members of the same species have very similar resources requirements whereas different species have a smaller contested resource overlap, resulting in intraspecific competition generally being a stronger force than interspecific competition.Individuals can compete for food, water, space, light, mates or any other resource which is required for survival or reproduction. The resource must be limited for competition to occur; if every member of the species can obtain a sufficient amount of every resource then individuals do not compete and the population grows exponentially. Exponential growth is very rare in nature because resources are finite and so not every individual in a population can survive, leading to intraspecific competition for the scarce resources.

When resources are limited, an increase in population size reduces the quantity of resources available for each individual, reducing the per capita fitness in the population. As a result, the growth rate of a population slows as intraspecific competition becomes more intense, making it a negatively density dependent process. The falling population growth rate as population increases can be modelled effectively with the logistic growth model. The rate of change of population density eventually falls to zero, the point ecologists have termed the carrying capacity (K). The carrying capacity of a population is the maximum number of individuals that can live in a population stably; numbers larger than this will suffer a negative population growth until eventually reaching the carrying capacity, whereas populations smaller than the carrying capacity will grow until they reach it.

Intraspecific competition doesn't just involve direct interactions between members of the same species (such as male deer locking horns when competing for mates) but can also include indirect interactions where an individual depletes a shared resource (such as a grizzly bear catching a salmon that can then no longer be eaten by bears at different points along a river).

The way in which resources are partitioned by organisms also varies and can be split into scramble and contest competition. Scramble competition involves a relatively even distribution of resources among a population as all individuals exploit a common resource pool. In contrast, contest competition is the uneven distribution of resources and occurs when hierarchies in a population influence the amount of resource each individual receives. Organisms in the most prized territories or at the top of the hierarchies obtain a sufficient quantity of the resources, whereas individuals without a territory don’t obtain any of the resource.

Irruptive growth

Irruptive growth, sometimes called Malthusian growth, is a growth pattern over time, defined by population explosions and subsequent sharp population crashes, or diebacks. It is an extension of the Malthusian growth model, specifically the growth pattern that causes a Malthusian catastrophe, and can occur when populations overshoot their carrying capacity, a phenomenon typically associated with r-strategists. Populations which exhibit irruptive growth do not stabilize around their carrying capacity, a feature of logistic growth. Irruptive growth occurs when a species reproduces more rapidly than the environment is capable of supporting with the available resources. Irruptive growth is studied in population ecology.

An irruption is any sudden change in the population density of an organism.

Length between perpendiculars

Length between perpendiculars (often abbreviated as p/p, p.p., pp, LPP, LBP or Length BPP) is the length of a ship along the waterline from the forward surface of the stem, or main bow perpendicular member, to the after surface of the sternpost, or main stern perpendicular member. When there is no sternpost, the centerline axis of the rudder stock is used as the aft end of the length between perpendiculars.Measuring to the stern post or rudder stock was believed to give a reasonable idea of the ship's carrying capacity, as it excluded the small, often unusable volume contained in her overhanging ends. On some types of vessels this is, for all practical purposes, a waterline measurement. In a ship with raked stems, naturally that length changes as the draught of the ship changes, therefore it is measured from a defined loaded condition.

Logistic function

A logistic function or logistic curve is a common "S" shape (sigmoid curve), with equation:


For values of x in the domain of real numbers from −∞ to +∞, the S-curve shown on the right is obtained, with the graph of f approaching L as x approaches +∞ and approaching zero as x approaches −∞.

The logistic function finds applications in a range of fields, including artificial neural networks, biology (especially ecology), biomathematics, chemistry, demography, economics, geoscience, mathematical psychology, probability, sociology, political science, linguistics, and statistics.

Maximum sustainable yield

In population ecology and economics, maximum sustainable yield or MSY is theoretically, the largest yield (or catch) that can be taken from a species' stock over an indefinite period. Fundamental to the notion of sustainable harvest, the concept of MSY aims to maintain the population size at the point of maximum growth rate by harvesting the individuals that would normally be added to the population, allowing the population to continue to be productive indefinitely. Under the assumption of logistic growth, resource limitation does not constrain individuals' reproductive rates when populations are small, but because there are few individuals, the overall yield is small. At intermediate population densities, also represented by half the carrying capacity, individuals are able to breed to their maximum rate. At this point, called the maximum sustainable yield, there is a surplus of individuals that can be harvested because growth of the population is at its maximum point due to the large number of reproducing individuals. Above this point, density dependent factors increasingly limit breeding until the population reaches carrying capacity. At this point, there are no surplus individuals to be harvested and yield drops to zero. The maximum sustainable yield is usually higher than the optimum sustainable yield and maximum economic yield.

MSY is extensively used for fisheries management. Unlike the logistic (Schaefer) model, MSY has been refined in most modern fisheries models and occurs at around 30% of the unexploited population size. This fraction differs among populations depending on the life history of the species and the age-specific selectivity of the fishing method.

However, the approach has been widely criticized as ignoring several key factors involved in fisheries management and has led to the devastating collapse of many fisheries. As a simple calculation, it ignores the size and age of the animal being taken, its reproductive status, and it focuses solely on the species in question, ignoring the damage to the ecosystem caused by the designated level of exploitation and the issue of bycatch. Among conservation biologists it is widely regarded as dangerous and misused.


Overpopulation occurs when a species' population exceeds the carrying capacity of its ecological niche. It can result from an increase in births (fertility rate), a decline in the mortality rate, an increase in immigration, or an unsustainable biome and depletion of resources. Moreover, it means that if there are too many people in the same habitat, people are limiting available resources to survive.

The change in number of individuals for unit area in a given locality is an Important variable that has a significant impact on the entire ecosystem.

The popular of a particular species varies along 2 dimensions :

1.Density (spatial variation)

2.Growth rate (over time)

Overshoot (population)

In population dynamics and population ecology, overshoot occurs when a population temporarily exceeds the long term carrying capacity of its environment. The environment usually has mechanisms in place to prevent overshoot. For example, plants are only able to regenerate and regrow a few times after being consumed before completely dying off. The consequence of overshoot is called a collapse, a crash or a die-off in which there is a decline in population density. The entire sequence or trajectory undergone by the population and its environment together is often termed 'overshoot-and-collapse'.

Overshoot can occur due to lag effects. Reproduction rates may remain high relative to the death rate. Entire ecosystems may be severely affected and sometimes reduced to less-complex states due to prolonged overshoot. The eradication of disease can trigger overshoot when a population suddenly exceeds the land's carrying capacity. An example of this occurred on the Horn of Africa when smallpox was eliminated. A region that had supported around 1 million pastoralists for centuries was suddenly expected to support 14 million people. The result was overgrazing, which led to soil erosion.

Pack animal

A pack animal, also known as a sumpter animal or beast of burden, is an individual or type of working animal used by humans as means of transporting materials by attaching them so their weight bears on the animal's back, in contrast to draft animals which pull loads but do not carry them.

Traditional pack animals are diverse including camels, goats, yaks, reindeer, water buffaloes, and llamas as well as the more familiar pack animals like horses, donkeys, and mules.

Paradox of enrichment

The paradox of enrichment is a term from population ecology coined by Michael Rosenzweig in 1971. He described an effect in six predator–prey models where increasing the food available to the prey caused the predator's population to destabilize. A common example is that if the food supply of a prey such as a rabbit is overabundant, its population will grow unbounded and cause the predator population (such as a lynx) to grow unsustainably large. That may result in a crash in the population of the predators and possibly lead to local eradication or even species extinction.

The term 'paradox' has been used since then to describe this effect in slightly conflicting ways. The original sense was one of irony; by attempting to increase the carrying capacity in an ecosystem, one could fatally imbalance it. Since then, some authors have used the word to describe the difference between modelled and real predator–prey interactions.

Rosenzweig used ordinary differential equation models to simulate the prey population that represented only prey populations. Enrichment was taken to be increasing the prey carrying capacity and showing that the prey population destabilized, usually into a limit cycle.

The cycling behavior after destabilization was more thoroughly explored in a subsequent paper (May 1972) and discussion (Gilpin and Rozenzweig 1972).


Payload is the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of the flight or mission, the payload of a vehicle may include cargo, passengers, flight crew, munitions, scientific instruments or experiments, or other equipment. Extra fuel, when optionally carried, is also considered part of the payload. In a commercial context (i.e., an airline or air freight carrier), payload may refer only to revenue-generating cargo or paying passengers.For a rocket, the payload can be a satellite, space probe, or spacecraft carrying humans, animals, or cargo. For a ballistic missile, the payload is one or more warheads and related systems; the total weight of these systems is referred to as the throw-weight.

The fraction of payload to the total liftoff weight of the air or spacecraft is known as the "payload fraction". When the weight of the payload and fuel are considered together, it is known as the "useful load fraction". In spacecraft, "mass fraction" is normally used, which is the ratio of payload to everything else, including the rocket structure.

Recreational kayak

A recreational kayak is a type of kayak that is designed for the casual paddler interested in recreational activities on a lake or flatwater stream; they presently make up the largest segment of kayak sales. Compared to other kayaks, recreational kayaks are characterized by having a larger cockpit opening for easy entry and exit and a wider beam (27–30 inches) for more stability on the water and are generally less than twelve feet in length, which makes them slower than a longer boat would be, but lighter, easier to handle in and out of the water, and less expensive. Due to the wider hull, recreational kayaks will not track (maintain a straight line) as well as longer, narrower models. They generally have limited cargo carrying capacity. Using less expensive materials like rotomolded polyethylene and including fewer options helps keep these boats inexpensive.

Root effect

The Root effect is a physiological phenomenon that occurs in fish hemoglobin, named after its discoverer R. W. Root. It is the phenomenon where an increased proton or carbon dioxide concentration (lower pH) lowers hemoglobin's affinity and carrying capacity for oxygen. The Root effect is to be distinguished from the Bohr effect where only the affinity to oxygen is reduced. Hemoglobins showing the Root effect show a loss of cooperativity at low pH. This results in the Hb-O2 dissociation curve being shifted downward and not just to the right. At low pH, hemoglobins showing the Root effect don't become fully oxygenated even at oxygen tensions up to 20kPa. This effect allows hemoglobin in fish with swim bladders to unload oxygen into the swim bladder against a high oxygen gradient. The effect is also noted in the choroid rete, the network of blood vessels which carries oxygen to the retina. In the absence of the Root effect, retia will result in the diffusion of some oxygen directly from the arterial blood to the venous blood, making such systems less effective for the concentration of oxygen. It has also been hypothesized that the loss of affinity is used to provide more oxygen to red muscle during acidotic stress.

Uday Express

UDAY Express or Utkrisht Double Decker Air Conditioned Yatri Express are completely Double-Decker AC chair car trains designed by Indian Railways. The coaches of the train have an anti-graffiti vinyl wrapped exterior and have been given a bright color scheme of yellow, orange and pink - somewhat similar to that of the Tejas Express. The train service has been envisioned as a 'luxury' train service for business travelers. According to Indian Railways, UDAY Express will cater to the "busiest routes" and increase carrying capacity by 40%. These trains have a seating capacity of 120 per coach (50 for upper deck, 48 for lower deck and 22 on the ends) as compared to Shatabdis which can seat up to 78.The first service was launched on June 10th, 2018 between Coimbatore Junction and Bangalore.

Major topics
Biological and
related topics
Human impact on
the environment
Events and
Related topics
Food webs
Example webs
Ecology: Modelling ecosystems: Other components

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