DOI: 10.5061/dryad.ps1h0
title: Data from: Longer food chains in pelagic ecosystems: trophic energetics of animal body size and metabolic efficiency

description: Factors constraining the structure of food webs can be investigated by
 comparing classes of ecosystems. We find that pelagic ecosystems, those
 based on one-celled primary producers, have longer food chains than
 terrestrial ecosystems. Yet pelagic ecosystems have lower primary
 productivity, contrary to the hypothesis that greater energy flows permit
 higher trophic levels. We hypothesize that longer food chain length in
 pelagic ecosystems, compared with terrestrial ecosystems, is associated
 with smaller pelagic animal body size permitting more rapid trophic energy
 transfer. Assuming negative allometric dependence of biomass production
 rate on body mass at each trophic level, the lowest three pelagic animal
 trophic levels are estimated to add biomass more rapidly than their
 terrestrial counterparts by factors of 12, 4.8, and 2.6. Pelagic animals
 consequently transport primary production to a fifth trophic level 50–190
 times more rapidly than animals in terrestrial webs. This difference
 overcomes the approximately fivefold slower pelagic basal productivity,
 energetically explaining longer pelagic food chains. In addition,
 ectotherms, dominant at lower pelagic animal trophic levels, have high
 metabolic efficiency, also favoring higher rates of trophic energy
 transfer in pelagic ecosystems. These two animal trophic flow mechanisms
 imply longer pelagic food chains, reestablishing an important role for
 energetics in food web structure.
description: SupplementaryTables:
 Data on trophic levels and body lengths of trophic species in 9 pelagic
 and 9 terrestrial food websAdult body lengths of
 all trophic species in these 18 webs were taken from reported values in
 the literature and on the Internet. The trophic level of each trophic
 species was determined from food web graphs, designating primary producers
 as trophic level 1, herbivores as trophic level 2, and so on. Six of 9
 pelagic and 2 of 9 terrestrial webs explicitly indicated principal energy
 flow pathways in the food web graphs. Where food web diagrams indicated
 the relative strength of multiple trophic pathways (such as a predator
 consuming a range of prey species from various trophic levels, e.g. by the
 width of arrows), the strongest pathways were used to determine food chain
 length and trophic levels. Otherwise, directed trophic links were used as
 given. The 18 webs are selected from the 113 food webs analyzed by Briand
 and Cohen (1987, Science 238:956-960). These data were used to estimate
 geometric mean body length by trophic level for animals in pelagic and
 terrestrial food webs. Table S1 gives summary information and a
 description for all 18 webs. Table S2 gives the lengths and trophic levels
 for all trophic species in the 9 pelagic webs. Table S3 gives the lengths
 and trophic levels for all trophic species in the 9 terrestrial webs. The
 9 pelagic webs chosen were the 9 of 113 Briand and Cohen webs with longest
 maximum food chain length that also had only one-celled primary producers.
 The 9 terrestrial webs were individually chosen as those having similar
 numbers of trophic species as the 9 pelagic webs (to minimize differences
 between pelagic and terrestrial food webs arising from more detail having
 been included in the published food web graphs).SupplementaryTables.docx