Data from: Longer food chains in pelagic ecosystems: trophic energetics of animal body size and metabolic efficiency

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.