<P> The back and forth relationship of plant defense and herbivore offense can be seen as a sort of "adaptation dance" in which one partner makes a move and the other counters it . This reciprocal change drives coevolution between many plants and herbivores, resulting in what has been referred to as a "coevolutionary arms race". The escape and radiation mechanisms for coevolution, presents the idea that adaptations in herbivores and their host plants, has been the driving force behind speciation . </P> <P> While much of the interaction of herbivory and plant defense is negative, with one individual reducing the fitness of the other, some is actually beneficial . This beneficial herbivory takes the form of mutualisms in which both partners benefit in some way from the interaction . Seed dispersal by herbivores and pollination are two forms of mutualistic herbivory in which the herbivore receives a food resource and the plant is aided in reproduction . </P> <P> Herbivorous fish and marine animals are an indispensable part of the coral reef ecosystem . Since algae and seaweeds grow much faster than corals they can occupy spaces where corals could have settled . They can outgrow and thus outcompete corals on bare surfaces . In the absence of plant - eating fish, seaweeds deprive corals of sunlight . They can also physically damage corals with scrapes . </P> <P> The impact of herbivory can be seen in areas ranging from economics to ecological, and both . For example, environmental degradation from white - tailed deer (Odocoileus virginianus) in the US alone has the potential to both change vegetative communities through over-browsing and cost forest restoration projects upwards of $750 million annually . Agricultural crop damage by the same species totals approximately $100 million every year . Insect crop damages also contribute largely to annual crop losses in the U.S. Herbivores affect economics through the revenue generated by hunting and ecotourism . For example, the hunting of herbivorous game species such as white - tailed deer, cottontail rabbits, antelope, and elk in the U.S. contributes greatly to the billion - dollar annually hunting industry . Ecotourism is a major source of revenue, particularly in Africa, where many large mammalian herbivores such as elephants, zebras, and giraffes help to bring in the equivalent of millions of US dollars to various nations annually . </P>

What is the main source of energy for the herbivore