![]() Most prey are shared by many predators and many taxa are omnivorous (feeding at more than one trophic level) 14. Natural communities are, however, rarely neatly conceptualized by food chains formed by groups of organisms assigned to discrete trophic levels such as carnivores or herbivores 13, 14. 8 found that mean prey body mass varied little over the prey biomass gradient, and thus their results are consistent with the role of density-dependent processes driving sub-linear predator-prey biomass scaling. Two possible reasons explain the sub-linear scaling of prey productivity with prey biomass: (1) constraints on individual rates which scale allometrically with body mass 11 that could lead to sub-linear community scaling with a systematic relation of body size to biomass 12, and/or (2) density-dependent effects - i.e. 1a), then prey productivity should also be sub-linearly related to prey biomass. These empirical patterns could be underpinned by systematic changes in total prey production available to predators 8, 9 – that is, because predator biomass and prey productivity are linearly related 8, 10 if predator biomass is sub-linearly related to prey biomass (Fig. The power-law exponent, k, has been found to be <1 and consistently close to ¾ across ecosystem types, implying biomass pyramids become systematically more bottom-heavy with increasing prey biomass (Fig. This ‘predator-prey power law’ 8, therefore, takes the form: y = cx k, where c is the normalisation coefficient and k is the dimensionless scaling exponent. dik-dik, buffalo and other herbivores) in a sub-linear fashion on double logarithmic scales 8. ![]() total biomass of lions, hyenas, and other large carnivores) was found to scale with the biomass of their prey, x, (e.g. However, the principal mechanisms responsible for driving these patterns in natural systems remains uncertain because of a lack of empirical data, and investigations of how these patterns may change along environmental gradients are still in their infancy.Ī previous finding highlights remarkable regularity in how the ratio of predator-to-prey biomass changes across a gradient of prey biomass in both aquatic and terrestrial systems 8. Theoretical syntheses have highlighted a plethora of possible mechanisms that can drive energy flow through food webs and thus differences in the shape of biomass pyramids and the ratio of predator-to-prey biomass 6, 7. That is, biomass pyramids tend to be ‘bottom heavy’ in size-structured assemblages, where trophic level increases with body size 3, although this pattern is by no means universal 6. When partitioning individuals or species into trophic levels, the distribution of biomass along food chains tends to form a characteristic ‘pyramid’ pattern with greater standing stocks of biomass at lower trophic levels 1. The ratio of predator-to-prey biomass provides a key measure of trophic structure and community dynamics 1, 2, 3 and is linked to many ecosystem functions and services 4, 5. Understanding the processes that drive the structure and functioning of ecosystems is a fundamental goal in ecology. These general patterns in trophic structure are compatible with a systematic form of density dependence that holds among complex feeding interactions across levels of organization, irrespective of ecosystem type. Across food webs, a similar sub-linear scaling pattern emerges between total predator biomass and the combined biomass of all prey within a food web. more prey biomass supports proportionally less predator biomass. We find a consistent, sub-linear scaling pattern whereby predator biomass scales with the total biomass of their prey with a near ¾-power exponent within food webs - i.e. ![]() We test whether sub-linear scaling between predator and prey biomass (a potential signal of density-dependent processes) emerges within ecosystem types and across levels of biological organisation. Here, we address this shortcoming by characterising the biomass structure of 141 freshwater, marine and terrestrial food webs, spanning a broad gradient in community biomass. ![]() omnivory) that may govern community structure. The ratio of predator-to-prey biomass is a key element of trophic structure that is typically investigated from a food chain perspective, ignoring channels of energy transfer (e.g.
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