Editing Food web (section)

==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 10<sup>7</sup>, over 95% of these species consist of [[microbes]] and [[invertebrates]], and relatively few have been named or classified by [[taxonomists]].<ref name="May88">{{cite journal | last1=May | first1=R. M. | title=How many species are there on Earth? | journal=Science | year=1988 | volume=241 | pages=1441–1449 | doi=10.1126/science.241.4872.1441 | url=http://www.cerium.ca/IMG/pdf/May_2520_281988_29_1_.pdf | issue=4872 | pmid=17790039 | bibcode=1988Sci...241.1441M | s2cid=34992724 | access-date=2011-06-13 | archive-url=https://web.archive.org/web/20130511191031/http://www.cerium.ca/IMG/pdf/May_2520_281988_29_1_.pdf | archive-date=2013-05-11 | url-status=dead }}</ref><ref name="Beattie10">{{cite journal | last1=Beattie  | first1=A. | last2=Ehrlich | first2=P. | title=The missing link in biodiversity conservation. | journal=Science | year=2010 | volume=328 | issue=5976 | pages=307–308 | doi=10.1126/science.328.5976.307-c | pmid=20395493 | bibcode=2010Sci...328..307B }}</ref><ref name="Ehrlich08">{{cite journal | last1=Ehrlich | first1=P. R. | last2=Pringle | first2=R. M. | title=Colloquium Paper: Where does biodiversity go from here? A grim business-as-usual forecast and a hopeful portfolio of partial solutions | journal=Proceedings of the National Academy of Sciences | volume=105 | issue=S1 | pages=11579–11586 | doi=10.1073/pnas.0801911105 | pmid=18695214 | pmc=2556413| bibcode=2008PNAS..10511579E | year=2008 | doi-access=free }}</ref> 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.<ref name="Hariston93">{{cite journal
 |last1=Hairston
 |first1=N. G.
 |title=Cause-effect relationships in energy flow, trophic structure, and interspecific interactions.
 |journal=The American Naturalist
 |volume=142
 |issue=3
 |pages=379–411
 |year=1993
 |url=http://limnology.wisc.edu/courses/zoo955/Spring2005/food%20web%20seminar%20papers/hairston93AmNat.pdf
 |doi=10.1086/285546
 |url-status=dead
 |archive-url=https://web.archive.org/web/20110720120313/http://limnology.wisc.edu/courses/zoo955/Spring2005/food%20web%20seminar%20papers/hairston93AmNat.pdf
 |archive-date=2011-07-20
 |hdl=1813/57238
 |s2cid=55279332
 |hdl-access=free
 |accessdate=2011-06-14
 }}</ref> "These omissions and problems are causes for concern, but on present evidence do not present insurmountable difficulties."<ref name="Pimm91" />{{rp|669}}

[[File:Food web and trophic level of the Chengjiang and Burgess Shale - journal.pbio.0060102.g001.jpg|thumb|upright=1.85|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.<ref name="Dunne08"/>]]

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.<ref name="Pimm91" /><ref name="Ricklefs96">{{cite book |title=The Economy of Nature |last= Rickleffs |first= Robert E. |year=1996 |publisher=[[University of Chicago Press]] |isbn=978-0-7167-3847-3 |page=678}}</ref>
* '''[[Paleoecology|Paleoecological]] web''' - a web that reconstructs ecosystems from the fossil record.<ref name="Dunne08">{{cite journal |  last1=Dunne | first1 = J. A. | last2 = Williams | first2 = R. J. | last3 = Martinez | first3 = N. D. | last4 = Wood | first4 = R. A. | last5 = Erwin | first5 = D. H. | last6 = Dobson | first6 = Andrew P. | title = Compilation and Network Analyses of Cambrian Food Webs. | year = 2008 | journal = PLOS Biology | volume =  6 | issue=4 | doi = 10.1371/journal.pbio.0060102 | pmid = 18447582 | pmc = 2689700 | pages = e102 | doi-access = free }}</ref>
* '''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.<ref name="Paine80" /><ref name="Krause03">{{cite journal | last1=Krause | first1=A. E. | last2=Frank | first2=K. A. | last3=Mason | first3=D. M. | last4=Ulanowicz | first4=R. E. | last5=Taylor | first5=W. W. | year=2003 | title=Compartments revealed in food-web structure |doi=10.1038/nature02115| journal=Nature | volume=426 | issue=6964 | pages=282–285 | url=http://www.glerl.noaa.gov/pubs/fulltext/2003/20030014.pdf | pmid=14628050| bibcode=2003Natur.426..282K | hdl=2027.42/62960 | s2cid=1752696 | hdl-access=free }}</ref> 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."<ref name="Ricklefs96" />{{rp|511}}

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 web]]s, aquatic food webs, [[soil food web]]s, Arctic (or polar) food webs, terrestrial food webs, and [[microbial food web]]s. 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.<ref name="Bormann67" /><ref name="Polis97" /><ref name="O'Neil01" />

[[File:Soil food webUSDA.jpg|thumb|upright=1.75|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.<ref>{{cite book | last1= Gönenç| first1= I. Ethem| last2= Koutitonsky| first2= Vladimir G.| last3= Rashleigh| first3= Brenda| title= Assessment of the Fate and Effects of Toxic Agents on Water Resources| year= 2007| publisher= Springer| page= 279| url= https://books.google.com/books?id=nBQYnbsUrBQC&q=Water+Resources+grazing+detrital+web&pg=PA278| isbn= 978-1-4020-5527-0}}</ref> 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. [[Earthworm]]s eaten by robins are detritivores consuming decaying leaves.<ref>{{cite book | author= Gil Nonato C. Santos|author2=Alfonso C. Danac |author3=Jorge P. Ocampo  | title= E-Biology II| year= 2003| publisher= Rex Book Store| page= 58| url= https://books.google.com/books?id=L9TwLvnIvnkC&q=grazing+web+detrital+web&pg=PA58| isbn= 978-971-23-3563-1}}</ref>

"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 [[leachate]]s, 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."<ref name="Moore04" />{{rp|585}}