title: Early Cambrian food webs on a trophic knife-edge? A hypothesis and preliminary data from a modern stromatolite-based ecosystem.
abstract: Here we use the theory of ecological stoichiometry to propose and provide a preliminary test of a novel hypothesis that the Cambrian 'explosion' may have been triggered by changes in circulating P availability in the biosphere. We exposed living stromatolites from a spring-fed stream in Mexico to a gradient of P enrichment to examine subsequent effects on stromatolite C : P ratio and on the primary grazer, an endemic snail. Consistent with a previously hypothesized stoichiometric 'knife-edge', snail performance was maximal at intermediate P-enrichment, indicating in situ stoichiometric constraints because of high stromatolite C : P ratio along with high sensitivity to excessive P intake. These results are consistent with the idea that stoichiometric constraints may have delayed the evolutionary proliferation of animals in ancient stromatolite-dominated ecosystems and also suggest that high food P content can significantly impair consumers. We propose that ecosystem P availability may have impacted both the expansion and decline of animal taxa in the history of life.
authors.forename: James J
authors.initials: JJ
authors.lastname: Elser
authors.forename: James
authors.initials: J
authors.lastname: Watts
authors.forename: John H
authors.initials: JH
authors.lastname: Schampel
authors.forename: Jack
authors.initials: J
authors.lastname: Farmer
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002244:Carbon; D000458:Cyanobacteria / Q000378:metabolism; D017377:Diatoms / Q000378:metabolism; D005308:Fertilizers; D020387:Food Chain; D010758:Phosphorus; D012908:Snails / Q000502:physiology
chemical_list: D005308:Fertilizers; D010758:Phosphorus; D002244:Carbon