Ecosystem functions and their stability depend on food web structure. However, the influence of upper portions of food webs – such as predator diversity and intraguild predation strength – on ecosystem stability has scarcely been explored. So far, it has been shown that increased predator diversity can enhance plant biomass via stronger top-down control, which theoretically should stabilize plant biomass. Yet, predator diversity often leads to intraguild predation, which counteracts this positive effect of predator diversity on top-down control. Thus, we predicted that predator diversity and intraguild predation would have countervailing effects on biomass and stability of primary producers. We simulated temporal dynamics of simple food webs consisting of primary producers, herbivores, and one or two predator species exhibiting varying degrees of intraguild predation. The species varied in demographic rates (in all trophic levels), defense against predation (for producers and herbivores), and feeding preferences (for herbivores and predators), based on simple allometric scaling assumptions. The food webs are based on generalized (Holling “type 2.5”) functional responses and were parameterized using data from pelagic food webs.
Results/Conclusions
Predator diversity and intraguild predation generally had opposite effects on the biomass and stability of lower trophic levels in the model. Increasing predator diversity strengthened top-down control of community herbivore biomass, generally leading to enhanced and more temporally stable primary producer biomass. In contrast, increasing intraguild predation reduced top-down control of herbivores, resulting in lower mean primary producer biomass exhibiting large fluctuations under most conditions. In an interesting exception, very strong intraguild predation rescued the stability of producer biomass, but mean producer biomass remained low. These results suggest that the structure of upper portions of food webs (predator diversity and intraguild predation) may be important in determining the performance and stability of ecosystem functions related to primary producers. Furthermore, managing to sustain multiple predators exhibiting low intraguild predation could represent a strategy for improving crop yields and their stability via biological control.