Eating or being eaten?
In the savannah, we can often find physiological adaptations in both the herbivores and the plants they feed on. To defend themselves, many graminaceous plants have made their tissues leathery by concentrating silica and lignin within them; others have produced poisonous, irritating or nauseating substances; other plants have turned their leaves into pointy or hooked thorns; some plants grow amidst poisonous plants for protection or to attract painful-bite ants. On the other hand, herbivores have developed a very effective grinding set of teeth, prehensile lips and tongue to tear off leaves and herbs easily, long necks to reach different layers of vegetation and such digestive systems as rumination which are useful for the most indigestible vegetal parts. Other herbivores are insensitive to poisons and chemical weapons, such as the black rhinoceros which in some areas mainly eats euphorbias, a plant producing a milk which irritates man as well; others can chew thorns and prickles because the mucous membranes of their mouths have a special protective coating.