Premium
Synthesis: comparing effects of resource and consumer fluxes into recipient food webs using meta‐analysis
Author(s) -
Allen Daniel C.,
Wesner Jeff S.
Publication year - 2016
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/15-1109.1
Subject(s) - food web , trophic level , ecosystem , resource (disambiguation) , ecology , environmental science , predation , trophic cascade , biology , computer network , computer science
Here we synthesize empirical research using meta‐analysis to compare how consumer and resource fluxes affect recipient food webs. We tested the following hypotheses: (H 1 ) The direct effects of resource fluxes (bottom‐up) should be stronger than the direct effects of consumer fluxes (top‐down), because resource fluxes are permanent (do not return to the food web in which they were produced) but consumer fluxes may not be (consumers can leave). (H 2 ) Following H 1 , the indirect effects should attenuate (weaken) more quickly for consumer fluxes than for resource fluxes due to their direct effects being weaker. (H 3 ) The effects of resource fluxes should be stronger when recipient food webs are in different ecosystems than donor food webs due to differences in elevation that accompany cross‐ecosystem food web interfaces, often increasing flux quantity due to gravity, while the effects of consumer fluxes should be stronger when donor and recipient food webs are in the same ecosystem as they should more easily assimilate into the recipient food web. We found no differences in the magnitude of bottom‐up and top‐down direct effects for resource and consumer fluxes, but top‐down direct effects were 122% stronger than top‐down indirect effects. Indirect effects of prey and predator fluxes quickly attenuated while indirect effects of non‐prey resource and herbivore fluxes did not, as the overall direct effects of prey and predator fluxes were 123% and 163% stronger than their indirect effects, respectively. This result suggests that the magnitude of indirect effects decrease as the trophic level of resource and consumer fluxes increases, and also contrasts with results from studies showing in situ top‐down indirect effects are stronger than in situ bottom‐up indirect effects. We found that resource and consumer flux effect sizes were similar when they occurred between ecosystems, but when they occurred within ecosystems predator flux effects were 107% stronger than nutrient flux effects. Finally, we found that observational studies had higher effect sizes than manipulative studies. Future research should focus on how resource and consumer fluxes might interact and generate feedbacks in empirical studies of natural food webs, and what ecological factors might affect their relative strength.