Top-down control of herbivores varies with ecosystem types

1. Bjorkman et al. comment on Adams and Zhang's finding of more leaf herbivory with increasing latitude, pointing out that top-down control by predators on insect herbivores might cause less herbivory in warmer regions. 2. Stronger top-down control with more plant diversity has been found mostly in systems that are less diverse overall, such as agricultural fields and grassland. Studies have also concentrated on small spatial scales. Whether top-down control is relatively more important at large spatial scales in the most highly diverse tropical or warm temperate forests is still in doubt. 3. Synthesis. The importance of top-down predator control of herbivores may vary with the system studied. Future work to understand the controls of herbivores needs to precisely monitor and compare the dynamics of individual herbivore species and their predators at a large spatial scale.