Proposes several factors that keep herbivores from eating all plants:
1. Plants have defences against herbivores.
2. Nutrients, not energy, limits herbivores.
3. Abiotic factors limit herbivores, such as temperature changes etc.
4. Intraspecific competition limit herbivores. IE Territorial disputes etc.
5. Interspecific interactions limit herbivores. IE Predators, disease and parasites.