Food chain

A food chain is a linear network of links in a food web starting from producer organisms and ending at apex predator species, detritivores, or decomposer species. A food chain shows how the organisms are related with each other by the food they eat; each level of a food chain represents a different trophic level. A food chain differs from a food web, because the complex network of different animals' feeding relations are aggregated and the chain only follows a direct, linear pathway of one animal at a time. Natural interconnections between food chains make it a food web. A common metric used to the quantify food web trophic structure is food chain length. In its simplest form, the length of a chain is the number of links between a trophic consumer and the base of the web and the mean chain length of an entire web is the arithmetic average of the lengths of all chains in a food web; the food chain is a energy source diagram. Many food webs have a keystone species. A keystone species is a species that has a large impact on the surrounding environment and can directly affect the food chain.

If this keystone species dies off it can set the entire food chain off balance. Keystone species keep herbivores from depleting all of the foliage in their environment and preventing a mass extinction. Food chains were first introduced by the Arab scientist and philosopher Al-Jahiz in the 10th century and popularized in a book published in 1927 by Charles Elton, which introduced the food web concept; the length of a food chain is a continuous variable providing a measure of the passage of energy and an index of ecological structure that increases through the linkages from the lowest to the highest trophic levels. Food chains are used in ecological modeling, they are simplified abstractions of real food webs, but complex in their dynamics and mathematical implications. Ecologists have formulated and tested hypotheses regarding the nature of ecological patterns associated with food chain length, such as increasing length increasing with ecosystem size, reduction of energy at each successive level, or the proposition that long food chain lengths are unstable.

Food chain studies have an important role in ecotoxicology studies, which trace the pathways and biomagnification of environmental contaminants. Producers, such as plants, are organisms. All food chains must start with a producer. In the deep sea, food chains centered on hydrothermal vents and cold seeps exist in the absence of sunlight. Chemosynthetic bacteria and archaea use hydrogen sulfide and methane from hydrothermal vents and cold seeps as an energy source to produce carbohydrates. Consumers are organisms. All organisms in a food chain, except the first organism, are consumers. Food chain length is important because the amount of energy transferred decreases as trophic level increases. There are no more than five tropic levels in a food chain. Humans are able to receive more energy by going back a level in the chain and consuming the food before, for example getting more energy per pound from consuming a salad than an animal which ate lettuce; the efficiency of a food chain depends on the energy first consumed by the primary producers.

Heterotroph Lithotroph Trophic pyramid Predator-prey interaction


Namtso or Lake Nam is a mountain lake on the border between Damxung County of Lhasa prefecture-level city and Baingoin County of Nagqu Prefecture in the Tibet Autonomous Region of China 112 kilometres NNW of Lhasa. Namtso was born as a result of Himalayan tectonic plate movements; the lake lies at an elevation of 4,718 m, has a surface area of 1,920 km2. This salt lake is the largest lake in the Tibet Autonomous Region. However, it is not the largest lake on the Qinghai-Tibet Plateau; that title belongs to Qinghai Lake. Namtso has five uninhabited islands of reasonable size, in addition to two rocky outcrops; the islands have been used for spiritual retreat by pilgrims who walk over the lake's frozen surface at the end of winter, carrying their food with them. They spend the summer there, unable to return to shore again until the water freezes the following winter; this practice is no longer permitted by Chinese authorities. The largest of the islands is in the northwest corner of the lake, is about 2,100 m long and 800 m wide, rising to just over 100 m in the middle.

At its closest point it is about 3.1 km from the shore. The most remote island is, at its closest, 5.1 km from the shore. At summer time birds like Ruddy shelduck and cormorants migrate to the lake area, besides the fields of Astragalus, Roegneria nutans and Marram grass; the weather at Namtso is subject to abrupt, sudden change and snowstorms are common across the Nyainqêntanglha range. Namtso has an alpine tundra climate. Namtso is renowned as one of the most beautiful places in the Nyainqêntanglha mountain range, its cave hermitages have for centuries been the destination of Tibetan pilgrims. A surfaced road across Laken Pass at 5186 m was completed to the lake in 2005, enabling easy access from Lhasa and the development of tourism at the lake. Settlements in the area include Dobjoi and Cha'gyungoinba; the Tashi Dor monastery is located at the southeastern corner of the lake. Around the area's natural elements and anthropological background, a 2010 romantic drama 香格里拉 Shangri-La, starring China's popular actor Hu Ge, was broadcast at CCTV1 and received positive reviews.

Some scenes in the 2002 Hong Kong film The Touch were filmed at the lake. Namtso Lake was featured in the BBC TV series: Himalaya with Michael Palin. Asteroid 248388 Namtso, discovered by Italian astronomer Vincenzo Casulli in 2005, was named after the lake; the official naming citation was published by the Minor Planet Center on 5 October 2017. Laken Pass Kanas Lake


Errno.h is a header file in the standard library of the C programming language. It defines macros for reporting and retrieving error conditions using the symbol errno.errno acts like an integer variable. A value is stored in errno by certain library functions. At program startup, the value stored. Library functions store only values greater than zero. Any library function can alter the value stored before return. Most functions indicate that they detected an error by returning a special value NULL for functions that return pointers, −1 for functions that return integers. A few functions require the caller to preset errno to zero and test it afterwards to see if an error was detected; the errno macro expands to an lvalue with type int, sometimes with the extern and/or volatile type specifiers depending upon the platform. This was a static memory location, but macros are always used today to allow for multi-threading, so that each thread will see its own thread-local error number; the header file defines macros that expand to integer constants that represent the error codes.

The C standard library only requires three to be defined:EDOM Results from a parameter outside a function's domain, e.g. sqrtERANGE Results from a result outside a function's range, e.g. strtol on systems with a 32-bit wide longEILSEQ Results from an illegal byte sequence, e.g. mbstowcs on systems that use UTF-8. POSIX compliant operating systems like AIX, Linux or Solaris include many other error values, many of which are used much more than the above ones, such as EACCES for when a file cannot be opened for reading. C++11 additionally defines many of the same values found within the POSIX specification. Traditionally, the first page of Unix system manuals, named intro, lists all errno.h macros, but this is not the case with Linux, where these macros are instead listed in the errno. Stdio.h string.h W. Richard, Stevens. Advanced Programming in the UNIX Environment. Addison-Wesley Professional. ISBN 978-0321637734. Retrieved 27 February 2015. FreeBSD System: Error codes GNU C library manual: Error codes Lists of errno values on Linux, both numeric and symbolic