The influence of grazing on the evolution, morphology and physiology of plants as modular organisms

Plants are modular organisms, i.e. they consist of repetitive multicellular units. The integrity of the plant is arranged by active meristems that hormonally suppress activity of other meristems. This basic design makes it possible for plants to have semi-independent, or totally independent, parts even within one structural individual. Accordingly, plant parts like ramets or branches may be qualitatively different because of developmental, environmental or genetical influences. They may respond to herbivory separately from other parts in the same structural individual. The modular structure allows easy recovery after damage by herbivores. Simultaneously it may constrain possible functions and lead to seemingly non-optimal responses. Effects of herbivory on the very basic modular design must be limited. Instead, herbivory may function as an evolutionary force modifying regulation of plant structure and function, like location of meristems, and rules determining outcomes of interactions among meristems. Indirectly, herbivory may prevent evolution of more unitary plant individuals.