Environmental determinants of food-chain length: A meta-analysis

Background/Question/Methods

Food-chain length is an important character of ecological communities that affects many of their functional aspects.  Recently, an increasing number of studies have tested the effects of productivity, disturbance, or ecosystem size on food-chain length in a variety of natural systems.  To summarize findings from these works, a formal meta-analysis was conducted.  

Results/Conclusions

The mean effect of productivity was significantly positive, and that of ecosystem size was significantly positive, while the mean effect of disturbance was negative, but not significant.  The magnitude of the mean effect was the largest for ecosystem size, the second largest for productivity, and the smallest for disturbance.  These results lend general support to previous theories predicting the effect of productivity and ecosystem size, but fail to provide strong support to the prediction regarding disturbance.  These patterns oppose the notion that there exists a single universal determinant of food-chain length.  Moreover, the meta-analysis found that the effect sizes of primary studies were significantly heterogeneous for the ecosystem-size effect and for the disturbance effect, and no indication of heterogeneity was found for the productivity effect.  These differences might reflect different mechanisms by which each of potential determinants influences food-chain length.