Abstract
- 1. Using a subtidal marine food web as a model system, we examined how food chain length (predators present or absent) and the prevalence of omnivory influenced temporal stability (and its components) of herbivores and plants. 2. We measured temporal stability as the inverse of the coefficient of variation of abundance over time). Predators and omnivory could influence temporal stability through effects on abundance (the “abundance” effect), summed variance across taxa (the “portfolio effect”), or summed covariances among taxa (the “covariance effect). 3. We found that increasing food chain length by predator addition destabilized aggregate herbivore abundance and (marginally) stabilized plants through their cascading effects on abundances in each trophic level. Thus, predators generally stabilized plants and destabilized herbivores through the overyielding effect. We also found that the stability of herbivore abundance declined with increasing prevalence of omnivory among top predators, while plants were not affected. 4. Our results suggest that herbivores are more sensitive than plants to changes in food web structure due to predator additions by invasion or deletions such as might occur via harvesting and habitat loss.