The document compares different ecosystems by describing their climates and key characteristics. Tropical rainforests have hot, wet climates all year and contain the greatest diversity of plants and animals. Temperate forests' climates change with warm summers and cold winters, and they receive less rain than rainforests. Wetlands are covered in water most of the year, found along rivers and coasts, and help absorb flood waters and cleanse dirty water. Oceans are the largest ecosystem and most living things inhabit the sunlit, shallow areas near the surface.