For each 1,000 foot rise in altitude there is a 4° F drop in temperature. For example, if at sea level the average temperature is 75° F, at 10,000 feet the average temperature would be only 35° F. This has a dramatic effect on plant and animal distribution.
In tropical mountainous areas several types of forests occur. At sea level there are lowland rain forests and mangroves. Montane forests are cooler and may contain deciduous trees. At cloud level moist, dripping cloud forests may occur. They are cooler than lowland forests. High mountains may also have alpine, tundra and snow covered peaks.
The special characteristics that enable plants and animals to be successful in a particular environment are called adaptations. Camouflage, as in a toad's ability to blend in with its surroundings, is a common example of an adaptation. The bright orange color of a monarch butterfly is an adaptation to warn potential predators that the butterfly is poisonous and prevent it from being eaten. These special features have evolved over long periods of time, through the process of natural selection. They afford the organism a better chance to survive in its surroundings.
Deserts, where the environment is generally hot and extremely dry, provide many striking examples of how plants and animals are adapted to their surroundings. Plants have evolved many adaptations to cope with the lack of water. Some desert plants such as the barrel cactus have expandable stems for storing water. Other plants have adaptations that reduce water loss from their leaves, the part of a plant through which most of the water is lost. Others have a waxy coating on the leaves, or have small leaves, that reduce the surface area exposed to the drying elements. In many cases, desert plants have no leaves at all. Photosynthesis, which normally occurs in green leaves, is carried out in the stems which are themselves green with the pigment chlorophyll.
Desert animals also have many adaptations as well to help them survive in the desert climate. Many are nocturnal, being active during the cool night rather than the hot daylight hours. The kangaroo rat conserves water by excreting a solid urine rather than liquid.
In sharp contrast, the climate of the tropical rain forest is hot and wet. With over 80 inches of rain per year as opposed to the desert's 10 inches or less, plants have adaptations which enable them to shed water efficiently rather than to hold it. The leaves of many rain forest plants have drip tips for this purpose. Buttress and stilt roots are thought to provide extra support for trees growing in spongy, wet soils.
Tropical rain forest plants also have adaptations to take in what little light is available on the dark forest floor. Large leaves are common; they increase the amount of sunlight a plant can capture. Other plants, like orchids, bromeliads and ferns, grow as epiphytes high up in the canopy where there is more sunlight.
The adaptations discussed above are all adaptations to specific climatic conditions, but organisms have also developed adaptations to other aspects of their environment. Some animals have adapted to eat a certain type of food; others have adapted to avoid being eaten themselves. Most animals have behavioral adaptations which help them attract a mate. In the plant world many flowers have evolved specific structures that help insure pollination by the insects they attract.
Descriptions of some of the main adaptations of tropical rain forest plants follow.
Through thousands of years of natural selection forest people have evolved to be smaller than people who do not live in the rain forest. They also sweat less because the forest's high humidity means that sweat cannot evaporate, making sweating a poor way to cool off. Forest people also drink less water because their food contains a lot of water.
Forest people have accumulated a great wealth of knowledge about the forest and have learned how to live in the forest without damaging it. They know how to use thousands of edible, medicinal and poisonous plants and how to grow crops in the forest's poor soil. They also know how to hunt and fish without driving the animals to extinction.
