(constant connectance hypothesis ).

The constant connectance hypothesis states that among community food webs, trophic links increase approximately as the square of the number of functionally distinct or "trophic' species. This hypothesis is corroborated by analysis of 175 community food webs (2-93 trophic species), which shows that the exponent of the link-species relationship is approximately two. This scaling contradicts the widely accepted link-species scaling law, which asserts that links increase linearly with the number of species and that the link- species exponent is one. Large food webs have many more links and much longer food chains than previously suggested. -from Author

constant connectance hypothesis ..

but the log-log regression approach appears to reject the constant connectance hypothesis more …

Constant connectance hypothesis

N2 - Ecologists have found many patterns in food-web structure. Some, like the constant connectance hypothesis, lack definitive explanatory mechanisms. In response, we investigated whether community assembly mechanisms could explain why trophic complexity consistently scales with species richness among ecosystems. We analyzed how food-web structure developed during the community assembly recorded in Simberloff and Wilson's classic biogeography experiment. Using their arthropod surveys, we constructed six time series of food-webs from pre- and post-defaunation censuses of six experimental islands, and synthesized trophic information for 250 species from the literature and expert sources. We found that the fraction of specialist species increased and the fraction of generalists decreased during food-web assembly. Directed connectance initially declined over time, despite an increase in species richness, but eventually leveled off as predicted by the constant connectance hypothesis of diversity-complexity scaling. The initial decline was explained by later colonization by trophic specialists, probably due to limited resource availability during early colonization. Late-colonizing super-generalists maintained constant connectance at later dates. This relationship between colonization success and trophic breadth helps explain food-web patterns and corroborates assertions that community assembly is systematically influenced by species' trophic breadths.

Constant connectance in community food webs — …

Ecologists have found many patterns in food-web structure. Some, like the constant connectance hypothesis, lack definitive explanatory mechanisms. In response, we investigated whether community assembly mechanisms could explain why trophic complexity consistently scales with species richness among ecosystems. We analyzed how food-web structure developed during the community assembly recorded in Simberloff and Wilson's classic biogeography experiment. Using their arthropod surveys, we constructed six time series of food-webs from pre- and post-defaunation censuses of six experimental islands, and synthesized trophic information for 250 species from the literature and expert sources. We found that the fraction of specialist species increased and the fraction of generalists decreased during food-web assembly. Directed connectance initially declined over time, despite an increase in species richness, but eventually leveled off as predicted by the constant connectance hypothesis of diversity-complexity scaling. The initial decline was explained by later colonization by trophic specialists, probably due to limited resource availability during early colonization. Late-colonizing super-generalists maintained constant connectance at later dates. This relationship between colonization success and trophic breadth helps explain food-web patterns and corroborates assertions that community assembly is systematically influenced by species' trophic breadths.

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and the relationship is best described by the constant connectance hypothesis ..

Name Stars Updated; Constant Connectance in Community Food Webs

The occurrence of neutral forbidden links also explains why the slope of the complexity-diversity relationship varies with immigration. At low immigration rates, turnover is low, most species are abundant and any species is likely to realize a high number of links. The slope of the complexity-diversity relationship is elevated because there are only few neutral forbidden links. At high immigration rates however, there is a large number of rare and short-lived species realizing few links because of high species turnover , (see ). The slope of the complexity-diversity relationship is then much shallower, and species tend to have a constant (and maximum) number of links (as proposed by the link species scaling law). These results show how immigration and neutral drift, by shaping the abundance distribution of species, can produce either a single large-scale or different small-scale complexity-diversity relationships. This corresponds to what is observed in empirical networks which alternatively support the link scaling law, the constant connectance hypothesis or fall in between , .

The constant connectance hypothesis did not hold for our networks. It was found that network structure changed with season and location.

Complexity in quantitative food webs (2009 ..

Among these patterns the density of links in networks has been of central interest as it is associated with the complexity-stability relationship , . Two major complexity-diversity scaling laws have been proposed: in the first case, consumers are constrained to a constant number of interactions (“link species scaling law” ), while in the second they are constrained to feed on a constant proportion of the species pool (“constant connectance” ). These scaling laws have been extensively tested, and the current consensus is that observed patterns take an intermediate form , . Beyond complexity-diversity relationships, two other patterns, related to the structure of links among species, have particularly been investigated during the past decade. Nestedness measures to what extent interactions by specialists are nested within those realized by generalists , and modularity measures the compartmentalization of the network into relatively independent community modules (e.g. , ). A nested interaction structure is hypothesized, at least, to buffer communities against extinctions or temporal fluctuations in the abundance of specialist species , and to promote species coexistence . Modularity is hypothesized to increase the stability of interaction networks since disturbances are less likely to spread across different modules that are weakly connected (; see however ).

Ecologists have found many patterns in food-web structure. Some, like the constant connectance hypothesis, lack definitive explanatory mechanisms.

Food Webs & Ecological Networks Flashcards | Quizlet

N2 - The constant connectance hypothesis states that among community food webs, trophic links increase approximately as the square of the number of functionally distinct or "trophic' species. This hypothesis is corroborated by analysis of 175 community food webs (2-93 trophic species), which shows that the exponent of the link-species relationship is approximately two. This scaling contradicts the widely accepted link-species scaling law, which asserts that links increase linearly with the number of species and that the link- species exponent is one. Large food webs have many more links and much longer food chains than previously suggested. -from Author