One way that plants could differ in their susceptibility to herbivores is through defense trade-off. Defense trade-off theory is commonly used to be seen as a fundamental theory to maintain ecological evenness. Plants can make a trade-off response to resource allocation, such as between defense and growth. Defenses against herbivory on plant diversity can vary in different situations. It can be neutral, detrimental or beneficial for plant fitness. Even in the absence of defensive trade-offs, herbivores may still be able to increase plant diversity, such as herbivores prefer subordinate species rather than dominant species. 