ESTIVATION: A prolonged dormant or sleeplike state that enables an animal to survive the summer in a hot climate. As in hibernation, breathing and heartbeat slow down, and the animal neither eats nor drinks. ESTUARY: The portion of a river or coastal wetland affected by the rise and fall of the tide, containing a graded mixture of fresh and salt water. EVERGLADE: A tract of marshy land covered in places with tall grasses. (In this book, “the everglades” refers to the river of grass; “Everglades” refers to the park, which contains other habitats besides everglades.) EXOTIC: A foreign plant or animal that has been introduced, intentionally or unintentionally, into a new area. FOOD CHAIN: A series of plants and animals linked by their food relationships, beginning with a green plant and ending with a predator. HABITAT: The place where an organism lives; the immediate surroundings, living and unliving, of an organism. The habitat of the pine warbler is the pinelands; the habitat of an internal parasite of this bird is the body of the warbler. HAMMOCK: A dense growth of broad-leaved trees on a slightly elevated area, not wet enough to be a swamp. In the park, hammocks are surrounded either by pineland or by marshland (glades). HARDWOOD TREES: Trees with broad leaves (as opposed to conebearing trees, which have needles or scales). Most hardwood trees are deciduous, though many in south Florida retain their leaves throughout the year. KEY: A reef or low-lying island. In south Florida, the term “key” is often also applied to hammocks or pinelands, which occupy areas where the limestone is raised above the surrounding wetlands. LIMESTONE: A sedimentary rock derived from the shells and skeletons of animals deposited in seas, and consisting mostly of calcium carbonate. Soluble in water having a slight degree of acidity, it is often characterized by caverns and, in the everglades, by a very pitted surface. The rock underlying most of the park is the Miami Oölite (pronounced OH-uh-lite), formed during a recent glacial period. Oölitic limestone is composed of tiny round concretions, only indirectly derived from marine shells. MANGROVE: Any of a group of tropical or subtropical trees, growing in estuaries and other low-lying coastal areas, usually producing aerial roots or prop roots and often forming dense growths over a large area. In south Florida there are four species, belonging to three different families. MARSH: A wetland, salt or fresh, where few if any trees and shrubs grow, characterized by grasses and sedges; in fresh-water marshes, cattails are common. MARL: In this book, used in the sense of a deposit of mixed limestone and smaller amounts of clay; south Florida marls are sometimes called lime muds. PEAT: Partly decayed, moisture-absorbing plant matter accumulated in bogs, swamps, etc. PREDATOR: An animal that lives by capturing other animals for food.