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Wednesday, September 23, 2020

Original face

From Wikipedia, the free encyclopedia

The original face is a term in Zen Buddhism, pointing to the nonduality of subject and object.

Origins

The phrase "original face" originates in Huangpo's Chuanhsin fayao (857) and the Hui-sin edition (967) of the Platform Sutra:

When you're not thinking of anything good and anything bad, at that moment, what is your original face?

This question appears in case 23 of the Mumonkan:

CASE 23. ENO'S GOOD AND EVIL

Eno, the sixth patriarch, was pursued by Monk Emyo up to Daiyurei. The patriarch, seeing Emyo coming, laid the robe and the bowl on a rock, and said to him, "This robe represents the faith. Is it to be fought for by force? You may take them now." Emyo went to move the bowl and the robe and yet they were as heavy as mountains. He could not move them. Hesitating and trembling, Emyo asked the patriarch, "I come for the teaching, not for the robe. Please enlighten me!" The patriarch said, "What is primordially Emyo (i.e., your true self), if you do not think this is good nor do you think this is evil?" At that moment Emyo was greatly awakened. His whole body was covered with sweat. Emyo cried, bowed, and said, "Is there or is there not any other (deep) significance (in Zen) than your secret words and teachings a minute ago?" The patriarch answered, "What I have told you is no secret at all. Once you have realized your own true self, the depth (in Zen) rather belongs to you!" Emyo said, "When I was at Obai with the other monks, I never realized what my true self was. Now you have dispersed the clouds of my ignorance to realize it, just like a man capable of discerning warm and cold by tasting water. From now on you are my teacher!" The patriarch said, "We both have Obai for our teacher. Guard your own self!"

Mumon's Comments: We should say that the sixth patriarch was in an emergency. This revelation of his, however, resembles the deed of an overly protective grandmother, who peeled a fresh lichi (a dessert fruit), removed its stone and put it to her grandchild's mouth ready for him to swallow.

You describe it in vain, you picture it to no avail,
Praising it is useless, cease to worry about it at all.
It is your true self, it has nowhere to hide,

Even if the universe is annihilated, it is not destroyed.

This koan is transformed in the question

What did your face look like before your parents were born?

Interpretation

The "original face" points to "the nonduality of subject and object":

[T]he phrase "father and mother" alludes to duality. This is obvious to someone versed in the Chinese tradition, where so much philosophical thought is presented in the imagery of paired opposites. The phrase "your original face" alludes to the original nonduality.

Comparable statements are: "Look at the flower and the flower also looks"; "Guest and host interchange".

It is not "pure consciousness", as it is often understood in western thinking, reached by "cleaning the doors of perception":

[A] pure consciousness without concepts, if there could be such a thing, would be a booming, buzzing confusion, a sensory field of flashes of light, unidentifiable sounds, ambiguous shapes, color patches without significance. This is not the consciousness of the enlightened Zen master.

Comments

Zen masters have commented on the original face:

"Sweep away thoughts!" means one must do zazen. Once thoughts are quieted, the Original Face appears. Thoughts can be compared to clouds. When clouds vanish, the moon appears. The moon of suchness is the Original Face. Thoughts are also like the fogging of a mirror. When you wipe away all condensation, a mirror reflects clearly. Quiet your thoughts and behold your Original Face before you were born!

— Daito

Cease practice based
On intellectual understanding,
Pursuing words and
Following after speech.
Learn the backward
Step that turns
Your light inward
To illuminate within.
Body and mind of themselves
Will drop away
And your original face will be manifest.

— Dogen

You cannot describe it or draw it,
You cannot praise it enough or perceive it.
No place can be found in which
To put the Original Face;
It will not disappear even
When the universe is destroyed.

— Mumon

Artistic impressions

Philip Whalen

The American poet Philip Whalen has written a poem, Metaphysical Insomnia Jazz Mumonkan xxix, inspired by the Original Face-koan:

Of

Course I could go to sleep right here
With all the lights on & the radio going

(April is behind the refrigerator)

Far from the wicked city
Far from the virtuous town
I met my fragile Kitty
In her greeny silken gown

fairly near the summit of Nanga Parbat & back again, the wind
flapping the prayer-flags

"IT IS THE WIND MOVING."
"IT IS THE FLAG MOVING."

Hypnotized by the windshield swipes, Mr. Harold Wood:
"Back & forth; back & forth."

We walked beside the moony lake
Eating dried apricots
Lemons bananas & bright wedding cake
& benefits forgot

"IT IS THE MIND MOVING."

& now I'm in my bed alone

Wide awake as any stone

Keith Kumasen has commented on this poem.

Stuart Davis

The American Buddhist musician Stuart Davis has recorded a song called "Original Face". The chorus goes:

There's a light bulb in everyone

Bright enough to swallow the sun,
Every mask will be erased,

There is just the original face.

Koan

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Koan

Kōan (公案) (/ˈkæn, -ɑːn/; Chinese: 公案; pinyin: gōng'àn, [kʊ́ŋ ân]; Korean: 공안 gong-an; Vietnamese: công án) is a story, dialogue, question, or statement which is used in Zen practice to provoke the "great doubt" and to practice or test a student's progress in Zen.

Etymology

The Japanese term kōan is the Sino-Japanese reading of the Chinese word gong'an (Chinese: 公案; pinyin: gōng'àn; Wade–Giles: kung-an; lit.: 'public case'). The term is a compound word, consisting of the characters "public; official; governmental; common; collective; fair; equitable" and "table; desk; (law) case; record; file; plan; proposal."

According to the Yuan dynasty Zen master Zhongfeng Mingben (中峰明本 1263–1323), gōng'àn originated as an abbreviation of gōngfǔ zhī àndú (公府之案牘, Japanese kōfu no antoku—literally the andu "official correspondence; documents; files" of a gongfu "government post"), which referred to a "public record" or the "case records of a public law court" in Tang dynasty China. Kōan/gong'an thus serves as a metaphor for principles of reality beyond the private opinion of one person, and a teacher may test the student's ability to recognize and understand that principle.

Commentaries in kōan collections bear some similarity to judicial decisions that cite and sometimes modify precedents. An article by T. Griffith Foulk claims

...Its literal meaning is the 'table' or 'bench' an of a 'magistrate' or 'judge' kung.

Gong'an was itself originally a metonym—an article of furniture involved in setting legal precedents came to stand for such precedents. For example, Di Gong'an (狄公案) is the original title of Celebrated Cases of Judge Dee, the famous Chinese detective novel based on a historical Tang dynasty judge. Similarly, Zen kōan collections are public records of the notable sayings and actions of Zen masters and disciples attempting to pass on their teachings.

Origins and development

China

Commenting on old cases

Gong'ans developed during the Tang dynasty (618–907) from the recorded sayings collections of Chán-masters, which quoted many stories of "a famous past Chán figure's encounter with disciples or other interlocutors and then offering his own comment on it". Those stories and the accompanying comments were used to educate students, and broaden their insight into the Buddhist teachings.

Those stories came to be known as gongan, "public cases". Such a story was only considered a gongan when it was commented upon by another Chán-master. This practice of commenting on the words and deeds of past masters confirmed the master's position as an awakened master in a lineage of awakened masters of the past.

Literary practice

Koan practice developed from a literary practice, styling snippets of encounter-dialogue into well-edited stories. It arose in interaction with "educated literati". There were dangers involved in such a literary approach, such as ascribing specific meanings to the cases. Dahui Zonggao is even said to have burned the woodblocks of the Blue Cliff Record, for the hindrance it had become to study of Chán by his students. Kōan literature was also influenced by the pre-Zen Chinese tradition of the "literary game"—a competition involving improvised poetry.

The style of writing of Zen texts has been influenced by "a variety of east Asian literary games":

  1. The extensive use of allusions, which create a feeling of disconnection with the main theme;
  2. Indirect references, such as titling a poem with one topic and composing a verse that seems on the surface to be totally unrelated;
  3. Inventive wordplay based on the fact that Hanzi (Chinese characters) are homophonic and convey multiple, often complementary or contradictory meanings;
  4. Linking the verses in a sustained string based on hidden points of connection or continuity, such as seasonal imagery or references to myths and legends.

Observing the phrase

During the Song dynasty (960–1297) the use of gongans took a decisive turn. Dahui Zonggao (1089–1163) introduced the use of kanhua, "observing the phrase". In this practice students were to observe (kan) or concentrate on a single word or phrase (huatou), such as the famous mu of the mu-koan.

In the eleventh century this practice had become common. A new literary genre developed from this tradition as well. Collections of such commented cases were compiled which consisted of the case itself, accompanied by verse or prose commentary.

Dahui's invention was aimed at balancing the insight developed by reflection on the teachings with developing samatha, calmness of mind. Ironically, this development became in effect silent illumination, a "[re-absorbing] of koan-study into the "silence" of meditation (ch'an)". It led to a rejection of Buddhist learning:

Some extent of Buddhist learning could easily have been recognized as a precondition for sudden awakening in Chan. Sung masters, however, tended to take the rejection literally and nondialectically. In effect, what they instituted was a form of Zen fundamentalism: the tradition came to be increasingly anti-intellectual in orientation and, in the process, reduced its complex heritage to simple formulae for which literal interpretations were thought adequate.

This development left Chinese Chan vulnerable to criticisms by neo-Confucianism, which developed after the Sung Dynasty. Its anti-intellectual rhetoric was no match for the intellectual discourse of the neo-Confucianists.

Interaction

The recorded encounter dialogues, and the koan collections which derived from this genre, mark a shift from solitary practice to interaction between master and student:

The essence of enlightenment came to be identified with the interaction between masters and students. Whatever insight dhyana might bring, its verification was always interpersonal. In effect, enlightenment came to be understood not so much as an insight, but as a way of acting in the world with other people

This mutual enquiry of the meaning of the encounters of masters and students of the past gave students a role model:

One looked at the enlightened activities of one's lineal forebears in order to understand one's own identity [...] taking the role of the participants and engaging in their dialogues instead

Kōan training requires a qualified teacher who has the ability to judge a disciple's depth of attainment. In the Rinzai Zen school, which uses kōans extensively, the teacher certification process includes an appraisal of proficiency in using that school's extensive kōan curriculum.

Contemporary koan-use

In China and Korea, "observing the phrase" is still the sole form of koan-practice, though Seung Sahn used the Rinzai-style of koan-practice in his Kwan Um School of Zen.

Japan

Japanese Zen, both Rinzai and Sōtō, took over the use of koan-study and commenting. In Sōtō-Zen, koan commentary was not linked to seated meditation.

Koan manuals

When the Chán-tradition was introduced in Japan, Japanese monks had to master the Chinese language and specific expressions used in the koan-training. The desired "spontaneity" expressed by enlightened masters required a thorough study of Chinese language and poetry. Japanese Zen imitated the Chinese "syntax and stereotyped norms".

In the officially recognized monasteries belonging to the Gozan (Five Mountain System) the Chinese system was fully continued. Senior monks were supposed to compose Chinese verse in a complex style of matched counterpoints known as bienli wen. It took a lot of literary and intellectual skills for a monk to succeed in this system.

The Rinka-monasteries, the provincial temples with less control of the state, laid less stress on the correct command of the Chinese cultural idiom. These monasteries developed "more accessible methods of koan instruction". It had three features:

  1. A standardized koan-curriculum;
  2. A standardized set of answers based on stereotypes Chinese sayings;
  3. A standardized method of secretly guiding students through the curriculum of koan and answers.

By standardizing the koan-curriculum every generation of students proceeded to the same series of koans. Students had to memorize a set number of stereotyped sayings, agyō, "appended words". The proper series of responses for each koan were taught by the master in private instruction-sessions to selected individual students who would inherit the dharma lineage.

Missanroku and missanchō, "Records of secret instruction" have been preserved for various Rinzai-lineages. They contain both the koan-curricula and the standardized answers. In Sōtō-Zen they are called monsan, an abbreviation of monto hissan, "secret instructions of the lineage". The monsan follow a standard question-and-answer format. A series of questions is given, to be asked by the master. The answers are also given by the master, to be memorized by the student.

Contemporary koan curricula

In the eighteenth century the Rinzai school became dominated by the legacy of Hakuin, who laid a strong emphasis on koan study as a means to gain kensho and develop insight. There are two curricula used in Rinzai, both derived from the principal heirs of Rinzai: the Takuju curriculum, and the Inzan curriculum. According to AMA Samy, "the koans and their standard answers are fixed."

Suppression in the Sōtō-school

During the late eighteenth and nineteenth century the tradition of koan-commentary became suppressed in the Sōtō-school, due to a reform movement that sought to standardise the procedures for dharma transmission. One reason for suppressing the koan-tradition in the Sōtō-school may have been to highlight the differences with the Rinzai-school, and create a clear identity. This movement also started to venerate Dogen as the founding teacher of the Sōtō-school. His teachings became the standard for the Sōtō-teachings, neglecting the fact that Dogen himself made extensive use of koan-commentary.

Doctrinal background

The popular western understanding sees kōan as referring to an unanswerable question or a meaningless statement. However, in Zen practice, a kōan is not meaningless, and not a riddle or a puzzle. Teachers do expect students to present an appropriate response when asked about a kōan.

Koans are also understood as pointers to an unmediated "Pure Consciousness", devoid of cognitive activity. Victor Hori criticizes this understanding:

[A] pure consciousness without concepts, if there could be such a thing, would be a booming, buzzing confusion, a sensory field of flashes of light, unidentifiable sounds, ambiguous shapes, color patches without significance. This is not the consciousness of the enlightened Zen master.

According to Hori, a central theme of many koans is the 'identity of opposites':

[K]oan after koan explores the theme of nonduality. Hakuin's well-known koan, "Two hands clap and there is a sound, what is the sound of one hand?" is clearly about two and one. The koan asks, you know what duality is, now what is nonduality? In "What is your original face before your mother and father were born?" the phrase "father and mother" alludes to duality. This is obvious to someone versed in the Chinese tradition, where so much philosophical thought is presented in the imagery of paired opposites. The phrase "your original face" alludes to the original nonduality.

Comparable statements are: "Look at the flower and the flower also looks"; "Guest and host interchange".

Koan-practice

Study of kōan literature is common to all schools of Zen, though with varying emphases and curricula. The Rinzai-school uses extensive koan-curricula, checking questions, and jakogo ("capping phrases", quotations from Chinese poetry) in its use of koans. The Sanbo Kyodan, and its western derivates of Taizan Maezumi and the White Plum Asanga, also use koan-curricula, but have omitted the use of capping phrases. In Chinese Chán and Korean Seon, the emphasis is on Hua Tou, the study of one koan throughout one's lifetime. In Japanese Sōtō Zen, the use of koans has been abandoned since the late eighteenth and nineteenth century.

Hua-tou or breakthrough-koan

In the Rinzai-school, the Sanbo Kyodan, and the White Plum Asanga, koan practice starts with the assignment of a hosshi or "break-through koan", usually the mu-koan or "the sound of one hand clapping". In Chinese Chán and Korean Seon, various koan can be used for the hua-tou practice.

Students are instructed to concentrate on the "word-head", like the phrase "mu". In the Wumenguan (Mumonkan), public case No. 1 ("Zhaozhou's Dog"), Wumen (Mumon) wrote:

... concentrate yourself into this 'Wú' ... making your whole body one great inquiry. Day and night work intently at it. Do not attempt nihilistic or dualistic interpretations."

Arousing this great inquiry or "Great Doubt" is an essential element of kōan practice. It builds up "strong internal pressure (gidan), never stopping knocking from within at the door of [the] mind, demanding to be resolved". To illustrate the enormous concentration required in kōan meditation, Zen Master Wumen commented,

It is like swallowing a red-hot iron ball. You try to vomit it out, but you can't.

Analysing the koan for its literal meaning won't lead to insight, though understanding the context from which koans emerged can make them more intelligible. For example, when a monk asked Zhaozhou (Joshu) "does a dog have Buddha-nature or not?", the monk was referring to the understanding of the teachings on Buddha-nature, which were understood in the Chinese context of absolute and relative reality.

Insight

The continuous pondering of the break-through koan (shokan) or Hua Tou, "word head", leads to kensho, an initial insight into "seeing the (Buddha-)nature.

The aim of the break-through koan is to see the "nonduality of subject and object":

The monk himself in his seeking is the koan. Realization of this is the insight; the response to the koan [...] Subject and object - this is two hands clapping. When the monk realizes that the koan is not merely an object of consciousness but is also he himself as the activity of seeking an answer to the koan, then subject and object are no longer separate and distinct [...] This is one hand clapping.

Various accounts can be found which describe this "becoming one" and the resulting breakthrough:

I was dead tired. That evening when I tried to settle down to sleep, the instant I laid my head on the pillow, I saw: "Ah, this outbreath is Mu!" Then: the in-breath too is Mu!" Next breath, too: Mu! Next breath: Mu, Mu! "Mu, a whole sequence of Mu! Croak, croak; meow, meow - these too are Mu! The bedding, the wall, the column, the sliding-door - these too are Mu! This, that and everything is Mu! Ha ha! Ha ha ha ha Ha! that roshi is a rascal! He's always tricking people with his 'Mu, Mu, Mu'!...

But the use of the mu-koan has also been criticised. According to AMA Samy, the main aim is merely to "'become one' with the koan". Showing to have 'become one' with the first koan is enough to pass the first koan. According to Samy, this is not equal to prajna:

The one-pointed, non-intellectual concentration on the hua-t’ou (or Mu) is a pressure-cooker tactics, a reduction to a technique which can produce some psychic experiences. These methods and techniques are forced efforts which can even run on auto-pilot. They can produce experiences but not prajana wisdom. Some speak of ‘investigating’ the hua-t’ou, but it is rather a matter of concentration, which sometimes can provide insights, yet no more than that.

Testing insight - or learning responses

Sassho – Checking questions

Teachers may probe students about their kōan practice using sassho, "checking questions" to validate their satori (understanding) or kensho (seeing the nature). For the mu-koan and the clapping hand-koan there are twenty to a hundred checking questions, depending on the teaching lineage. The checking questions serve to deepen the insight of the student, but also to test his or her understanding.

Those checking questions, and their answers, are part of a standardised set of questions and answers. Students are learning a "ritual performance", learning how to behave and respond in specific ways, learning "clever repartees, ritualized language and gestures and be submissive to the master’s diktat and arbitration."

Jakugo – Capping phrases

In the Rinzai-school, passing a koan and the checking questions has to be supplemented by jakugo, "capping phrases", citations of Chinese poetry to demonstrate the insight. Students can use collections of those citations, instead of composing poetry themselves.

Post-satori practice

After the initial insight further practice is necessary, to deepen the insight and learn to express it in daily life. In Chinese Chán and Korean Seon, this further practice consists of further pondering of the same Hua Tou. In Rinzai-Zen, this further practice is undertaken by further koan-study, for which elaborate curricula exist. In Sōtō-Zen, Shikantaza is the main practice for deepening insight.

Varieties in koan-practice

Chinese Chán and Korean Seon

In Chinese Chán and Korean Seon, the primary form of Koan-study is kanhua, "reflection on the koan", also called Hua Tou, "word head". In this practice, a fragment of the koan, such as "mu", or a "what is"-question is used by focusing on this fragment and repeating it over and over again:

Who is it who now repeats the Buddha's name?

Who is dragging this corpse about?
What is this?
What is it?
What was the original face before my father and mother were born?

Who am I?

The student is assigned only one hua-tou for a lifetime. In contrast to the similar-sounding "who am I?" question of Ramana Maharshi, hua-tou involves raising "great doubt":

This koan becomes a touchstone of our practice: it is a place to put our doubt, to cultivate great doubt, to allow the revelation of great faith, and to focus our great energy.

Japanese Rinzai

Kōan practice is particularly important among Japanese practitioners of the Rinzai sect.

Importance of koan-study

This importance is reflected in writings in the Rinzai-school on the koan-genre. Zhongfeng Mingben (1263–1323), a Chinese Chán-master who lived at the beginning of the Yuan Dynasty, revitalized the Rinzai-tradition, and put a strong emphasis on the use of koans. He saw the kung-ans as "work of literature [that] should be used as objective, universal standards to test the insight of monks who aspired to be recognized as Ch'an masters":

The koans do not represent the private opinion of a single man, but rather the hundreds and thousands of bodhisattvas of the three realms and ten directions. This principle accords with the spiritual source, tallies with the mysterious meaning, destroys birth-and-death, and transcends the passions. It cannot be understood by logic; it cannot be transmitted in words; it cannot be explained in writing; it cannot be measured by reason. It is like the poisoned drum that kills all who hear it, or like a great fire that consumes all who come near it. What is called "the special transmission of the Vulture Peak" was the transmission of this; what is called the "direct pointing of Bodhidharma at Shao-lin-ssu" is this.

Musō Soseki (1275–1351), a Japanese contemporary of Zhongfeng Mingben, relativized the use of koans. The study of koans had become popular in Japan, due to the influence of Chinese masters such as Zhongfeng Mingben. Despite belonging to the Rinzai-school, Musō Soseki also made extensive use of richi (teaching), explaining the sutras, instead of kikan (koan). According to Musō Soseki, both are upaya, "skillful means" meant to educate students. Musō Soseki called both shōkogyu, "little jewels", tools to help the student to attain satori.

Koan curricula

In Rinzai a gradual succession of koans is studied. There are two general branches of curricula used within Rinzai, derived from the principal heirs of Rinzai: the Takuju curriculum, and the Inzan curriculum. However, there are a number of sub-branches of these, and additional variations of curriculum often exist between individual teaching lines which can reflect the recorded experiences of a particular lineage's members. Koan curricula are, in fact, subject to continued accretion and evolution over time, and thus are best considered living traditions of practice rather than set programs of study.

Koan practice starts with the shokan, or "first barrier", usually the mu-koan or the koan "What is the sound of one hand clapping?" After having attained kensho, students continue their practice investigating subsequent koans. In the Takuju-school, after breakthrough students work through the Gateless Gate (Mumonkan), the Blue Cliff Record (Hekigan-roku), the Entangling Vines (Shumon Kattoshu), and the Collection of Wings of the Blackbird (鴆羽集, Chin'u shū). The Inzan-school uses its own internally generated list of koans.

Hakuin's descendants developed a fivefold classification system:

  1. Hosshin, dharma-body koans, are used to awaken the first insight into sunyata. They reveal the dharmakaya, or Fundamental. They introduce "the undifferentitated and the unconditional".
  2. Kikan, dynamic action koans, help to understand the phenomenal world as seen from the awakened point of view; Where hosshin koans represent tai, substance, kikan koans represent yu, function.
  3. Gonsen, explication of word koans, aid to the understanding of the recorded sayings of the old masters. They show how the Fundamental, though not depending on words, is nevertheless expressed in words, without getting stuck to words.
  4. Hachi Nanto, eight "difficult to pass" koans. There are various explanations for this category, one being that these koans cut off clinging to the previous attainment. They create another Great Doubt, which shatters the self attained through satori. It is uncertain which are exactly those eight koans. Hori gives various sources, which altogether give ten hachi nanto koans:
    • Miura and Sasaki:
      • Nansen's Flower (Hekigan-roku Case 40)
      • A Buffalo Passes the Window (Mumonkan Case 38)
      • Sōzan's Memorial Tower (Kattō-shō Case 140)
      • Suigan's Eyebrows (Hekigan-roku Case 8)
      • Enkan's Rhinoceros Fan (Hekigan-roku Case 91)
    • Shimano:
      • The Old Woman Burns the Hut (Kattō-shō Case 162)
    • Asahina Sōgen:
      • Goso Hōen's "Hakuun Said 'Not Yet'" (Kattō-shō Case 269)
      • Shuzan's Main Cable (Kattō-shō Case 280).
    • Akizuki:
      • Nansen Has Died (Kattō-shō Case 282)
      • Kenpō’s Three Illnesses (Kattō-shō Case 17).
  5. Goi jujukin koans, the Five Ranks of Tozan and the Ten Grave Precepts.

According to Akizuki there was an older classification-system, in which the fifth category was Kojo, "Directed upwards". This category too was meant to rid the monk of any "stink of Zen". The very advanced practitioner may also receive the Matsugo no rokan, "The last barrier, and Saigo no ikketsu, "The final confirmation". "The last barrier" when one left the training hall, for example "Sum up all of the records of Rinzai in one word!" It is not meant to be solved immediately, but to be carried around in order to keep practising. "the final confirmation" may be another word for the same kind of koan.

Post-satori practice

Completing the koan-curriculum in the Rinzai-schools traditionally also led to a mastery of Chinese poetry and literary skills:

[D]isciples today are expected to spend a dozen or more years with a master to complete a full course of training in koan commentary. Only when a master is satisfied that a disciple can comment appropriately on a wide range of old cases will he recognize the latter as a dharma heir and give him formal "proof of transmission" (J. inka shomei). Thus, in reality, a lot more than satori is required for one to be recognized as a master (J. shike, roshi) in the Rinzai school of Zen at present. The accepted proof of satori is a set of literary and rhetorical skills that takes many years to acquire.

After completing the koan-training, Gogo no shugyo, post-satori training is necessary:

[I]t would take 10 years to solve all the kōans [...] in the sōdō. After the student has solved all koans, he can leave the sōdō and live on his own, but he is still not considered a roshi. For this he has to complete another ten years of training, called "go-go-no-shugyō" in Japanese. Literally, this means "practice after satori/enlightenment", but Fukushima preferred the translation "special practice". Fukushima would explain that the student builds up a "religious personality" during this decade. It is a kind of period that functions to test if the student is actually able to live in regular society and apply his koan understanding to daily life, after he has lived in an environment that can be quite surreal and detached from the lives of the rest of humanity. Usually, the student lives in small parish temple during this decade, not in a formal training monastery.

Breathing practices

Hakuin Ekaku, the 17th century revitalizer of the Rinzai school, taught several practices which serve to correct physical and mental imbalances arising from, among other things, incorrect or excessive koan practice. The "soft-butter" method (nanso no ho) and "introspection method" (naikan no ho) involve cultivation of ki centered on the tanden (Chinese:dantian). These practices are described in Hakuin's works Orategama and Yasen Kanna, and are still taught in some Rinzai lineages today.

Japanese Sōtō

Though few Sōtō practitioners concentrate on kōans during meditation, the Sōtō sect has a strong historical connection with kōans, since many kōan collections were compiled by Sōtō priests.

During the 13th century, Dōgen, founder of the Sōtō sect in Japan, quoted 580 kōans in his teachings. He compiled some 300 kōans in the volumes known as the Greater Shōbōgenzō. Dōgen wrote of Genjokōan, which points out that everyday life experience is the fundamental kōan.

However, according to Michel Mohr,

...kōan practice was largely expunged from the Sōtō school through the efforts of Gentō Sokuchū (1729–1807), the eleventh abbot of Entsuji, who in 1795 was nominated abbot of Eiheiji".

Sanbo Kyodan and White Plum Asanga

The Sanbo Kyodan school and the White Plum Asanga, which originated with the Sōtō-priest Hakuun Yasutani, incorporates koan-study. The Sanbo kyodan places great emphasis on kensho, initial insight into one's true nature, as a start of real practice. It follows the so-called Harada-Yasutani koan-curriculum, which is derived from Hakuin's student Takuju. It is a shortened koan-curriculum, in which the so-called "capping phrases" are removed. The curriculum takes considerably less time to study than the Takuju-curriculum of Rinzai.

To attain kensho, most students are assigned the mu-koan. After breaking through, the student first studies twenty-two "in-house" koans, which are "unpublished and not for the general public", but are nevertheless published and commented upon. There-after, the students goes through the Gateless Gate (Mumonkan), the Blue Cliff Record, the Book of Equanimity, and the Record of Transmitting the Light.[76] The koan-curriculum is completed by the Five ranks of Tozan and the precepts.

Classical kōan collections

Kōans collectively form a substantial body of literature studied by Zen practitioners and scholars worldwide. Kōan collections commonly referenced in English include:

  • The Blue Cliff Record (Chinese: Bìyán Lù; Japanese: Hekiganroku), 12th century;
  • The Book of Equanimity (also known as the Book of Serenity; Chinese: Cóngróng Lù; Japanese: Shoyoroku), 12th century;
  • The Gateless Gate (also known as The Gateless Barrier; Chinese: Wúménguān; Japanese: Mumonkan) collected during the 13th century).

In these and subsequent collections, a terse "main case" of a kōan often accompanies prefatory remarks, poems, proverbs and other phrases, and further commentary about prior emendations.

The Blue Cliff Record

The Blue Cliff Record (Chinese: 碧巖錄 Bìyán Lù; Japanese: Hekiganroku) is a collection of 100 kōans compiled in 1125 by Yuanwu Keqin (圜悟克勤 1063–1135).

The Book of Equanimity

The Book of Equanimity or Book of Serenity (Chinese: 從容録 Cóngróng lù; Japanese: 従容録 Shōyōroku) is a collection of 100 Kōans by Hongzhi Zhengjue (Chinese: 宏智正覺; Japanese: Wanshi Shōgaku) (1091–1157), compiled with commentaries by Wansong Xingxiu (1166–1246). The full title is The Record of the Temple of Equanimity With the Classic Odes of Venerable Tiantong Jue and the Responsive Commentary of Old Man Wansong 萬松老評唱天童覺和尚 頌古從容庵錄 (Wansong Laoren Pingchang Tiantong Jue Heshang Songgu Congrong An Lu) (Taisho Tripitaka Vol. 48, No. 2004)

The Gateless Gate

The Gateless Gate (Chinese: 無門關 Wumenguan; Japanese: Mumonkan) is a collection of 48 kōans and commentaries published in 1228 by Chinese monk Wumen (無門) (1183–1260). The title may be more accurately rendered as Gateless Barrier or Gateless Checkpoint).

Five kōans in the collection derive from the sayings and doings of Zhaozhou Congshen, (transliterated as Chao-chou in Wade-Giles and pronounced Jōshū in Japanese).

Treasury of the True Dharma Eye

Dahui Zonggao (大慧宗杲) (1089–1163) the Zhengfayan zang (正法眼藏), "Treasury of the true dharma eye" (W-G.: Cheng-fa yen-tsang, (J.: Shōbōgenzō) a collection of koans and dialogues compiled between 1147 and 1150 by Dahui Zonggao . Dahui's 'Treasury' is composed of three scrolls prefaced by three short introductory pieces. The Zongmen liandeng huiyao 宗門聯燈會要 was compiled in 1183 by Huiweng Wuming 晦翁悟明 (n.d.), three generations after Dahui in the same line; the sermon is found in zh 20 (x 79: 173a).

Other kōan collections compiled and annotated by Sōtō priests include:

  • Treasury of the true dharma eye (Jap. Shobogenzo (正法眼蔵), compiled by Eihei Dogen (永平道元), 13th Century.
  • The Iron Flute (Japanese: Tetteki Tōsui 鐵笛倒吹, compiled by Genrō Ōryū 玄楼奥龍 in 1783)
  • Verses and Commentaries on One Hundred Old Cases of Tenchian (Japanese: Tenchian hyakusoku hyoju, compiled by Tetsumon in 1771.)

Examples of traditional kōans

Does a dog have Buddha-nature

A monk asked Zhàozhōu, "Does a dog have Buddha nature or not?" Zhaozhou said, "".

("Zhaozhou" is rendered as "Chao-chou" in Wade-Giles, and pronounced "Joshu" in Japanese. "Wu" appears as "mu" in Japanese, meaning "no", "not", "nonbeing", or "without" in English. This is a fragment of Case No. 1 of the Wúménguān. However, another koan presents a longer version, in which Zhaozhou answered "yes" in response to the same question asked by a different monk: see Case No. 18 of the Book of Serenity.)

The sound of one hand

Two hands clap and there is a sound. What is the sound of one hand? (隻手声あり、その声を聞け)

Victor Hori comments:

...in the beginning a monk first thinks a kōan is an inert object upon which to focus attention; after a long period of consecutive repetition, one realizes that the kōan is also a dynamic activity, the very activity of seeking an answer to the kōan. The kōan is both the object being sought and the relentless seeking itself. In a kōan, the self sees the self not directly but under the guise of the kōan ... When one realizes ("makes real") this identity, then two hands have become one. The practitioner becomes the kōan that he or she is trying to understand. That is the sound of one hand.

Original Face

Huìnéng asked Hui Ming, "Without thinking of good or evil, show me your original face before your mother and father were born." (This is a fragment of case No. 23 of the Wumenguan.)

Killing the Buddha

If you meet the Buddha, kill him. (逢佛殺佛)

— Linji

Other koans

  • A student asked Master Yun-Men (A.D. 949) "Not even a thought has arisen; is there still a sin or not?" Master replied, "Mount Sumeru!"
  • A monk asked Dongshan Shouchu, "What is Buddha?" Dongshan said, "Three pounds of flax." (This is a fragment of case No. 18 of the Wumenguan as well as case No. 12 of the Blue Cliff Record.)
  • A monk asked Zhaozhou, "What is the meaning of the ancestral teacher's (i.e., Bodhidharma's) coming from the west?" Zhaozhou said, "The cypress tree in front of the hall." (This is a fragment of case No. 37 of the Wumenguan as well as case No. 47 of the Book of Serenity.)

Food web

From Wikipedia, the free encyclopedia
 

A food web (or food cycle) is the natural interconnection of food chains and a graphical representation (usually an image) of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs. To maintain their bodies, grow, develop, and to reproduce, autotrophs produce organic matter from inorganic substances, including both minerals and gases such as carbon dioxide. These chemical reactions require energy, which mainly comes from the Sun and largely by photosynthesis, although a very small amount comes from bioelectrogenesis in wetlands, and mineral electron donors in hydrothermal vents and hot springs. A gradient exists between trophic levels running from complete autotrophs that obtain their sole source of carbon from the atmosphere, to mixotrophs (such as carnivorous plants) that are autotrophic organisms that partially obtain organic matter from sources other than the atmosphere, and complete heterotrophs that must feed to obtain organic matter. The linkages in a food web illustrate the feeding pathways, such as where heterotrophs obtain organic matter by feeding on autotrophs and other heterotrophs. The food web is a simplified illustration of the various methods of feeding that links an ecosystem into a unified system of exchange. There are different kinds of feeding relations that can be roughly divided into herbivory, carnivory, scavenging and parasitism. Some of the organic matter eaten by heterotrophs, such as sugars, provides energy. Autotrophs and heterotrophs come in all sizes, from microscopic to many tonnes - from cyanobacteria to giant redwoods, and from viruses and bdellovibrio to blue whales.

Charles Elton pioneered the concept of food cycles, food chains, and food size in his classical 1927 book "Animal Ecology"; Elton's 'food cycle' was replaced by 'food web' in a subsequent ecological text. Elton organized species into functional groups, which was the basis for Raymond Lindeman's classic and landmark paper in 1942 on trophic dynamics. Lindeman emphasized the important role of decomposer organisms in a trophic system of classification. The notion of a food web has a historical foothold in the writings of Charles Darwin and his terminology, including an "entangled bank", "web of life", "web of complex relations", and in reference to the decomposition actions of earthworms he talked about "the continued movement of the particles of earth". Even earlier, in 1768 John Bruckner described nature as "one continued web of life".

Food webs are limited representations of real ecosystems as they necessarily aggregate many species into trophic species, which are functional groups of species that have the same predators and prey in a food web. Ecologists use these simplifications in quantitative (or mathematical representation) models of trophic or consumer-resource systems dynamics. Using these models they can measure and test for generalized patterns in the structure of real food web networks. Ecologists have identified non-random properties in the topographic structure of food webs. Published examples that are used in meta analysis are of variable quality with omissions. However, the number of empirical studies on community webs is on the rise and the mathematical treatment of food webs using network theory had identified patterns that are common to all. Scaling laws, for example, predict a relationship between the topology of food web predator-prey linkages and levels of species richness.

Taxonomy of a food web

A simplified food web illustrating a three trophic food chain (producers-herbivores-carnivores) linked to decomposers. The movement of mineral nutrients is cyclic, whereas the movement of energy is unidirectional and noncyclic. Trophic species are encircled as nodes and arrows depict the links.
 
Food webs are the road-maps through Darwin's famous 'entangled bank' and have a long history in ecology. Like maps of unfamiliar ground, food webs appear bewilderingly complex. They were often published to make just that point. Yet recent studies have shown that food webs from a wide range of terrestrial, freshwater, and marine communities share a remarkable list of patterns.

Links in food webs map the feeding connections (who eats whom) in an ecological community. Food cycle is an obsolete term that is synonymous with food web. Ecologists can broadly group all life forms into one of two trophic layers, the autotrophs and the heterotrophs. Autotrophs produce more biomass energy, either chemically without the sun's energy or by capturing the sun's energy in photosynthesis, than they use during metabolic respiration. Heterotrophs consume rather than produce biomass energy as they metabolize, grow, and add to levels of secondary production. A food web depicts a collection of polyphagous heterotrophic consumers that network and cycle the flow of energy and nutrients from a productive base of self-feeding autotrophs.

The base or basal species in a food web are those species without prey and can include autotrophs or saprophytic detritivores (i.e., the community of decomposers in soil, biofilms, and periphyton). Feeding connections in the web are called trophic links. The number of trophic links per consumer is a measure of food web connectance. Food chains are nested within the trophic links of food webs. Food chains are linear (noncyclic) feeding pathways that trace monophagous consumers from a base species up to the top consumer, which is usually a larger predatory carnivore.

Linkages connect to nodes in a food web, which are aggregates of biological taxa called trophic species. Trophic species are functional groups that have the same predators and prey in a food web. Common examples of an aggregated node in a food web might include parasites, microbes, decomposers, saprotrophs, consumers, or predators, each containing many species in a web that can otherwise be connected to other trophic species.

Trophic levels

A trophic pyramid (a) and a simplified community food web (b) illustrating ecological relations among creatures that are typical of a northern Boreal terrestrial ecosystem. The trophic pyramid roughly represents the biomass (usually measured as total dry-weight) at each level. Plants generally have the greatest biomass. Names of trophic categories are shown to the right of the pyramid. Some ecosystems, such as many wetlands, do not organize as a strict pyramid, because aquatic plants are not as productive as long-lived terrestrial plants such as trees. Ecological trophic pyramids are typically one of three kinds: 1) pyramid of numbers, 2) pyramid of biomass, or 3) pyramid of energy.

Food webs have trophic levels and positions. Basal species, such as plants, form the first level and are the resource limited species that feed on no other living creature in the web. Basal species can be autotrophs or detritivores, including "decomposing organic material and its associated microorganisms which we defined as detritus, micro-inorganic material and associated microorganisms (MIP), and vascular plant material." Most autotrophs capture the sun's energy in chlorophyll, but some autotrophs (the chemolithotrophs) obtain energy by the chemical oxidation of inorganic compounds and can grow in dark environments, such as the sulfur bacterium Thiobacillus, which lives in hot sulfur springs. The top level has top (or apex) predators which no other species kills directly for its food resource needs. The intermediate levels are filled with omnivores that feed on more than one trophic level and cause energy to flow through a number of food pathways starting from a basal species.

In the simplest scheme, the first trophic level (level 1) is plants, then herbivores (level 2), and then carnivores (level 3). The trophic level is equal to one more than the chain length, which is the number of links connecting to the base. The base of the food chain (primary producers or detritivores) is set at zero. Ecologists identify feeding relations and organize species into trophic species through extensive gut content analysis of different species. The technique has been improved through the use of stable isotopes to better trace energy flow through the web. It was once thought that omnivory was rare, but recent evidence suggests otherwise. This realization has made trophic classifications more complex.

Trophic dynamics

The trophic level concept was introduced in a historical landmark paper on trophic dynamics in 1942 by Raymond L. Lindeman. The basis of trophic dynamics is the transfer of energy from one part of the ecosystem to another. The trophic dynamic concept has served as a useful quantitative heuristic, but it has several major limitations including the precision by which an organism can be allocated to a specific trophic level. Omnivores, for example, are not restricted to any single level. Nonetheless, recent research has found that discrete trophic levels do exist, but "above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores."

A central question in the trophic dynamic literature is the nature of control and regulation over resources and production. Ecologists use simplified one trophic position food chain models (producer, carnivore, decomposer). Using these models, ecologists have tested various types of ecological control mechanisms. For example, herbivores generally have an abundance of vegetative resources, which meant that their populations were largely controlled or regulated by predators. This is known as the top-down hypothesis or 'green-world' hypothesis. Alternatively to the top-down hypothesis, not all plant material is edible and the nutritional quality or antiherbivore defenses of plants (structural and chemical) suggests a bottom-up form of regulation or control. Recent studies have concluded that both "top-down" and "bottom-up" forces can influence community structure and the strength of the influence is environmentally context dependent. These complex multitrophic interactions involve more than two trophic levels in a food web.

Another example of a multi-trophic interaction is a trophic cascade, in which predators help to increase plant growth and prevent overgrazing by suppressing herbivores. Links in a food-web illustrate direct trophic relations among species, but there are also indirect effects that can alter the abundance, distribution, or biomass in the trophic levels. For example, predators eating herbivores indirectly influence the control and regulation of primary production in plants. Although the predators do not eat the plants directly, they regulate the population of herbivores that are directly linked to plant trophism. The net effect of direct and indirect relations is called trophic cascades. Trophic cascades are separated into species-level cascades, where only a subset of the food-web dynamic is impacted by a change in population numbers, and community-level cascades, where a change in population numbers has a dramatic effect on the entire food-web, such as the distribution of plant biomass.

Energy flow and biomass

Energy flow diagram of a frog. The frog represents a node in an extended food web. The energy ingested is utilized for metabolic processes and transformed into biomass. The energy flow continues on its path if the frog is ingested by predators, parasites, or as a decaying carcass in soil. This energy flow diagram illustrates how energy is lost as it fuels the metabolic process that transform the energy and nutrients into biomass.

The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.
An expanded three link energy food chain (1. plants, 2. herbivores, 3. carnivores) illustrating the relationship between food flow diagrams and energy transformity. The transformity of energy becomes degraded, dispersed, and diminished from higher quality to lesser quantity as the energy within a food chain flows from one trophic species into another. Abbreviations: I=input, A=assimilation, R=respiration, NU=not utilized, P=production, B=biomass.

Food webs depict energy flow via trophic linkages. Energy flow is directional, which contrasts against the cyclic flows of material through the food web systems. Energy flow "typically includes production, consumption, assimilation, non-assimilation losses (feces), and respiration (maintenance costs)." In a very general sense, energy flow (E) can be defined as the sum of metabolic production (P) and respiration (R), such that E=P+R.

Biomass represents stored energy. However, concentration and quality of nutrients and energy is variable. Many plant fibers, for example, are indigestible to many herbivores leaving grazer community food webs more nutrient limited than detrital food webs where bacteria are able to access and release the nutrient and energy stores. "Organisms usually extract energy in the form of carbohydrates, lipids, and proteins. These polymers have a dual role as supplies of energy as well as building blocks; the part that functions as energy supply results in the production of nutrients (and carbon dioxide, water, and heat). Excretion of nutrients is, therefore, basic to metabolism." The units in energy flow webs are typically a measure mass or energy per m2 per unit time. Different consumers are going to have different metabolic assimilation efficiencies in their diets. Each trophic level transforms energy into biomass. Energy flow diagrams illustrate the rates and efficiency of transfer from one trophic level into another and up through the hierarchy.

It is the case that the biomass of each trophic level decreases from the base of the chain to the top. This is because energy is lost to the environment with each transfer as entropy increases. About eighty to ninety percent of the energy is expended for the organism's life processes or is lost as heat or waste. Only about ten to twenty percent of the organism's energy is generally passed to the next organism. The amount can be less than one percent in animals consuming less digestible plants, and it can be as high as forty percent in zooplankton consuming phytoplankton. Graphic representations of the biomass or productivity at each tropic level are called ecological pyramids or trophic pyramids. The transfer of energy from primary producers to top consumers can also be characterized by energy flow diagrams.

Food chain

A common metric used to quantify food web trophic structure is food chain length. Food chain length is another way of describing food webs as a measure of the number of species encountered as energy or nutrients move from the plants to top predators. There are different ways of calculating food chain length depending on what parameters of the food web dynamic are being considered: connectance, energy, or interaction. In its simplest form, the length of a chain is the number of links between a trophic consumer and the base of the web. The mean chain length of an entire web is the arithmetic average of the lengths of all chains in a food web.

In a simple predator-prey example, a deer is one step removed from the plants it eats (chain length = 1) and a wolf that eats the deer is two steps removed from the plants (chain length = 2). The relative amount or strength of influence that these parameters have on the food web address questions about:

  • the identity or existence of a few dominant species (called strong interactors or keystone species)
  • the total number of species and food-chain length (including many weak interactors) and
  • how community structure, function and stability is determined.

Ecological pyramids

Illustration of a range of ecological pyramids, including top pyramid of numbers, middle pyramid of biomass, and bottom pyramid of energy. The terrestrial forest (summer) and the English Channel ecosystems exhibit inverted pyramids.Note: trophic levels are not drawn to scale and the pyramid of numbers excludes microorganisms and soil animals. Abbreviations: P=Producers, C1=Primary consumers, C2=Secondary consumers, C3=Tertiary consumers, S=Saprotrophs.
 
A four level trophic pyramid sitting on a layer of soil and its community of decomposers.
 
A three layer trophic pyramid linked to the biomass and energy flow concepts.

In a pyramid of numbers, the number of consumers at each level decreases significantly, so that a single top consumer, (e.g., a polar bear or a human), will be supported by a much larger number of separate producers. There is usually a maximum of four or five links in a food chain, although food chains in aquatic ecosystems are more often longer than those on land. Eventually, all the energy in a food chain is dispersed as heat.

Ecological pyramids place the primary producers at the base. They can depict different numerical properties of ecosystems, including numbers of individuals per unit of area, biomass (g/m2), and energy (k cal m−2 yr−1). The emergent pyramidal arrangement of trophic levels with amounts of energy transfer decreasing as species become further removed from the source of production is one of several patterns that is repeated amongst the planets ecosystems. The size of each level in the pyramid generally represents biomass, which can be measured as the dry weight of an organism. Autotrophs may have the highest global proportion of biomass, but they are closely rivaled or surpassed by microbes.

Pyramid structure can vary across ecosystems and across time. In some instances biomass pyramids can be inverted. This pattern is often identified in aquatic and coral reef ecosystems. The pattern of biomass inversion is attributed to different sizes of producers. Aquatic communities are often dominated by producers that are smaller than the consumers that have high growth rates. Aquatic producers, such as planktonic algae or aquatic plants, lack the large accumulation of secondary growth as exists in the woody trees of terrestrial ecosystems. However, they are able to reproduce quickly enough to support a larger biomass of grazers. This inverts the pyramid. Primary consumers have longer lifespans and slower growth rates that accumulates more biomass than the producers they consume. Phytoplankton live just a few days, whereas the zooplankton eating the phytoplankton live for several weeks and the fish eating the zooplankton live for several consecutive years. Aquatic predators also tend to have a lower death rate than the smaller consumers, which contributes to the inverted pyramidal pattern. Population structure, migration rates, and environmental refuge for prey are other possible causes for pyramids with biomass inverted. Energy pyramids, however, will always have an upright pyramid shape if all sources of food energy are included and this is dictated by the second law of thermodynamics.

Material flux and recycling

Many of the Earth's elements and minerals (or mineral nutrients) are contained within the tissues and diets of organisms. Hence, mineral and nutrient cycles trace food web energy pathways. Ecologists employ stoichiometry to analyze the ratios of the main elements found in all organisms: carbon (C), nitrogen (N), phosphorus (P). There is a large transitional difference between many terrestrial and aquatic systems as C:P and C:N ratios are much higher in terrestrial systems while N:P ratios are equal between the two systems. Mineral nutrients are the material resources that organisms need for growth, development, and vitality. Food webs depict the pathways of mineral nutrient cycling as they flow through organisms. Most of the primary production in an ecosystem is not consumed, but is recycled by detritus back into useful nutrients. Many of the Earth's microorganisms are involved in the formation of minerals in a process called biomineralization. Bacteria that live in detrital sediments create and cycle nutrients and biominerals. Food web models and nutrient cycles have traditionally been treated separately, but there is a strong functional connection between the two in terms of stability, flux, sources, sinks, and recycling of mineral nutrients.

Kinds of food webs

Food webs are necessarily aggregated and only illustrate a tiny portion of the complexity of real ecosystems. For example, the number of species on the planet are likely in the general order of 107, over 95% of these species consist of microbes and invertebrates, and relatively few have been named or classified by taxonomists. It is explicitly understood that natural systems are 'sloppy' and that food web trophic positions simplify the complexity of real systems that sometimes overemphasize many rare interactions. Most studies focus on the larger influences where the bulk of energy transfer occurs. "These omissions and problems are causes for concern, but on present evidence do not present insurmountable difficulties."

Paleoecological studies can reconstruct fossil food-webs and trophic levels. Primary producers form the base (red spheres), predators at top (yellow spheres), the lines represent feeding links. Original food-webs (left) are simplified (right) by aggregating groups feeding on common prey into coarser grained trophic species.

There are different kinds or categories of food webs:

  • Source web - one or more node(s), all of their predators, all the food these predators eat, and so on.
  • Sink web - one or more node(s), all of their prey, all the food that these prey eat, and so on.
  • Community (or connectedness) web - a group of nodes and all the connections of who eats whom.
  • Energy flow web - quantified fluxes of energy between nodes along links between a resource and a consumer.
  • Paleoecological web - a web that reconstructs ecosystems from the fossil record.
  • Functional web - emphasizes the functional significance of certain connections having strong interaction strength and greater bearing on community organization, more so than energy flow pathways. Functional webs have compartments, which are sub-groups in the larger network where there are different densities and strengths of interaction. Functional webs emphasize that "the importance of each population in maintaining the integrity of a community is reflected in its influence on the growth rates of other populations."

Within these categories, food webs can be further organized according to the different kinds of ecosystems being investigated. For example, human food webs, agricultural food webs, detrital food webs, marine food webs, aquatic food webs, soil food webs, Arctic (or polar) food webs, terrestrial food webs, and microbial food webs. These characterizations stem from the ecosystem concept, which assumes that the phenomena under investigation (interactions and feedback loops) are sufficient to explain patterns within boundaries, such as the edge of a forest, an island, a shoreline, or some other pronounced physical characteristic.

An illustration of a soil food web.

Detrital web

In a detrital web, plant and animal matter is broken down by decomposers, e.g., bacteria and fungi, and moves to detritivores and then carnivores. There are often relationships between the detrital web and the grazing web. Mushrooms produced by decomposers in the detrital web become a food source for deer, squirrels, and mice in the grazing web. Earthworms eaten by robins are detritivores consuming decaying leaves.

"Detritus can be broadly defined as any form of non-living organic matter, including different types of plant tissue (e.g. leaf litter, dead wood, aquatic macrophytes, algae), animal tissue (carrion), dead microbes, faeces (manure, dung, faecal pellets, guano, frass), as well as products secreted, excreted or exuded from organisms (e.g. extra-cellular polymers, nectar, root exudates and leachates, dissolved organic matter, extra-cellular matrix, mucilage). The relative importance of these forms of detritus, in terms of origin, size and chemical composition, varies across ecosystems."

Quantitative food webs

Ecologists collect data on trophic levels and food webs to statistically model and mathematically calculate parameters, such as those used in other kinds of network analysis (e.g., graph theory), to study emergent patterns and properties shared among ecosystems. There are different ecological dimensions that can be mapped to create more complicated food webs, including: species composition (type of species), richness (number of species), biomass (the dry weight of plants and animals), productivity (rates of conversion of energy and nutrients into growth), and stability (food webs over time). A food web diagram illustrating species composition shows how change in a single species can directly and indirectly influence many others. Microcosm studies are used to simplify food web research into semi-isolated units such as small springs, decaying logs, and laboratory experiments using organisms that reproduce quickly, such as daphnia feeding on algae grown under controlled environments in jars of water.

While the complexity of real food webs connections are difficult to decipher, ecologists have found mathematical models on networks an invaluable tool for gaining insight into the structure, stability, and laws of food web behaviours relative to observable outcomes. "Food web theory centers around the idea of connectance." Quantitative formulas simplify the complexity of food web structure. The number of trophic links (tL), for example, is converted into a connectance value:

,

where, S(S-1)/2 is the maximum number of binary connections among S species. "Connectance (C) is the fraction of all possible links that are realized (L/S2) and represents a standard measure of food web complexity..." The distance (d) between every species pair in a web is averaged to compute the mean distance between all nodes in a web (D) and multiplied by the total number of links (L) to obtain link-density (LD), which is influenced by scale dependent variables such as species richness. These formulas are the basis for comparing and investigating the nature of non-random patterns in the structure of food web networks among many different types of ecosystems.

Scaling laws, complexity, chaos, and pattern correlates are common features attributed to food web structure.

Complexity and stability

Food webs are extremely complex. Complexity is a measure of an increasing number of permutations and it is also a metaphorical term that conveys the mental intractability or limits concerning unlimited algorithmic possibilities. In food web terminology, complexity is a product of the number of species and connectance. Connectance is "the fraction of all possible links that are realized in a network". These concepts were derived and stimulated through the suggestion that complexity leads to stability in food webs, such as increasing the number of trophic levels in more species rich ecosystems. This hypothesis was challenged through mathematical models suggesting otherwise, but subsequent studies have shown that the premise holds in real systems.

At different levels in the hierarchy of life, such as the stability of a food web, "the same overall structure is maintained in spite of an ongoing flow and change of components." The farther a living system (e.g., ecosystem) sways from equilibrium, the greater its complexity. Complexity has multiple meanings in the life sciences and in the public sphere that confuse its application as a precise term for analytical purposes in science. Complexity in the life sciences (or biocomplexity) is defined by the "properties emerging from the interplay of behavioral, biological, physical, and social interactions that affect, sustain, or are modified by living organisms, including humans".

Several concepts have emerged from the study of complexity in food webs. Complexity explains many principals pertaining to self-organization, non-linearity, interaction, cybernetic feedback, discontinuity, emergence, and stability in food webs. Nestedness, for example, is defined as "a pattern of interaction in which specialists interact with species that form perfect subsets of the species with which generalists interact", "—that is, the diet of the most specialized species is a subset of the diet of the next more generalized species, and its diet a subset of the next more generalized, and so on." Until recently, it was thought that food webs had little nested structure, but empirical evidence shows that many published webs have nested subwebs in their assembly.

Food webs are complex networks. As networks, they exhibit similar structural properties and mathematical laws that have been used to describe other complex systems, such as small world and scale free properties. The small world attribute refers to the many loosely connected nodes, non-random dense clustering of a few nodes (i.e., trophic or keystone species in ecology), and small path length compared to a regular lattice. "Ecological networks, especially mutualistic networks, are generally very heterogeneous, consisting of areas with sparse links among species and distinct areas of tightly linked species. These regions of high link density are often referred to as cliques, hubs, compartments, cohesive sub-groups, or modules...Within food webs, especially in aquatic systems, nestedness appears to be related to body size because the diets of smaller predators tend to be nested subsets of those of larger predators (Woodward & Warren 2007; YvonDurocher et al. 2008), and phylogenetic constraints, whereby related taxa are nested based on their common evolutionary history, are also evident (Cattin et al. 2004)." "Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs."

Food webs are also complex in the way that they change in scale, seasonally, and geographically. The components of food webs, including organisms and mineral nutrients, cross the thresholds of ecosystem boundaries. This has led to the concept or area of study known as cross-boundary subsidy. "This leads to anomalies, such as food web calculations determining that an ecosystem can support one half of a top carnivore, without specifying which end." Nonetheless, real differences in structure and function have been identified when comparing different kinds of ecological food webs, such as terrestrial vs. aquatic food webs.

History of food webs

Victor Summerhayes and Charles Elton's 1923 food web of Bear Island (Arrows point to an organism being consumed by another organism).

Food webs serve as a framework to help ecologists organize the complex network of interactions among species observed in nature and around the world. One of the earliest descriptions of a food chain was described by a medieval Afro-Arab scholar named Al-Jahiz: "All animals, in short, cannot exist without food, neither can the hunting animal escape being hunted in his turn." The earliest graphical depiction of a food web was by Lorenzo Camerano in 1880, followed independently by those of Pierce and colleagues in 1912 and Victor Shelford in 1913. Two food webs about herring were produced by Victor Summerhayes and Charles Elton and Alister Hardy in 1923 and 1924. Charles Elton subsequently pioneered the concept of food cycles, food chains, and food size in his classical 1927 book "Animal Ecology"; Elton's 'food cycle' was replaced by 'food web' in a subsequent ecological text. After Charles Elton's use of food webs in his 1927 synthesis, they became a central concept in the field of ecology. Elton organized species into functional groups, which formed the basis for the trophic system of classification in Raymond Lindeman's classic and landmark paper in 1942 on trophic dynamics. The notion of a food web has a historical foothold in the writings of Charles Darwin and his terminology, including an "entangled bank", "web of life", "web of complex relations", and in reference to the decomposition actions of earthworms he talked about "the continued movement of the particles of earth". Even earlier, in 1768 John Bruckner described nature as "one continued web of life".

Interest in food webs increased after Robert Paine's experimental and descriptive study of intertidal shores suggesting that food web complexity was key to maintaining species diversity and ecological stability. Many theoretical ecologists, including Sir Robert May and Stuart Pimm, were prompted by this discovery and others to examine the mathematical properties of food webs.

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