Final answer:
The few plant species that persist in unfenced areas exposed to herbivores are either tolerant to herbivory, not preferred by herbivores due to deterrents, or have adaptations like rapid growth rates to quickly recover from being eaten.
Step-by-step explanation:
Observing the differences in plant biomass between fenced areas that protect against herbivory and unfenced areas provides insights into the impacts of grazing on plant communities. Plants that persist in unfenced areas exhibit certain characteristics that allow them to survive despite the presence of herbivores. These include being tolerant of being eaten, not being preferred by herbivores, having mechanisms to deter herbivores, or growing rapidly to compensate for the damage caused by grazing.
Some plants can survive in unfenced areas due to producing chemical deterrents or physical structures that make them less palatable or even toxic to herbivores. Others might simply be less visible or attractive, reducing the likelihood of being located and consumed. Additionally, rapid growth rates can help some species to bounce back after being grazed, maintaining their populations despite ongoing herbivory.
The final answer to the question of what characteristics allow the few plant species to remain in unfenced areas is that these species are either 1) tolerant to herbivory, 2) not preferred by herbivores, 3) not easily located by herbivores, or 4) they have high growth rates to compensate for grazing losses. The most relevant characteristics in this context are that the plants are either tolerant to herbivory or not preferred by herbivores due to certain adaptations, such as the production of deterrent chemicals.