Because the rain forest is a very diverse habitat, it contains many different species of plants and animals in close proximity to each other. These species often have complex relationships, many of which are beneficial to the participants. Such relationships are called symbiotic or mutualistic. In mutualism examples, mammals, birds, reptiles and insects may interact with plants and with each other to help with food, reproduction or to protect against predators. To survive in the rain forest, it is often useful to have some help from a species with which you are not competing.
TL;DR (Too Long; Didn't Read)
Symbiotic relationships in the rainforest are interactions between species in which the partners benefit. Symbiotic relationships are often broad, such as pollination of plants by insects in return for nectar. They may also involve just two species with specific benefits, or one species with several relationships in a complex series of interactions.
Types of Symbiotic Relationships
Many symbiotic relationships in the rainforest are broad, across several species, such as when insects pollinate plants and get pollen or nectar as food in return. Other symbiotic relationships only involve two species and are unique. For example certain rain forest caterpillars secrete a sweet chemical on their backs that a specific species of ant will eat. In return, the ants will protect the caterpillars.
Some organisms rely on several different relationships with different species, receiving and producing benefits in each one. For example, a Brazil nut tree relies on the orchid bees for pollination and attracts them with nectar. The tough seed pods can only be opened by a ground-dwelling rodent called an agouti that eats some of the nuts and buries others, some of which eventually become new Brazil nut trees.
Examples of Mutualism in Tropical Rainforest Ecosystems
The complex web of interactions among the species of the rain forest often involves insects, plants and primitive organisms such as fungi. Ants are especially likely to form various symbiotic relationships. For example, the leaf cutter ant has symbiotic relationships with fungi that they grow as food.
The leaf cutter ants cut small pieces off leaves in the jungle and take them underground into their tunnels. They create small chambers where they store the leaf cuttings. Fungus grows on the leaves and the ants use bits of the fungus to feed their young. Through the symbiotic relationship, both the fungus and the young ants get fed.
A chocolate tree has a much more complicated series of symbiotic relationships with a variety of other species, providing a complex example of mutualism in the tropical rainforest. To ensure pollination, the chocolate tree produces tiny buds that die and rot. These are ideal homes for the midges that it needs to pollinate its flowers. Once the flowers are pollinated, they grow into large, brightly-colored seed pods. The seed pods are filled with a delicious, fleshy pulp and bitter seeds. With these pods, the chocolate tree attracts monkeys and squirrels that eat the pods but spit out the bitter seeds, in another symbiotic relationship. The chocolate tree relies on this relationship to scatter its seeds so more chocolate trees can grow.
A more complex three-way arrangement is the infestation of chocolate trees with mealy bugs. The bugs don't harm the chocolate tree but the tree doesn't receive any direct benefit either. The mealy bugs are raised and taken care of by black ants that eat the waste honeydew the mealy bugs produce. In their own symbiotic relationship, the black ants keep other insects away from the mealy bugs, and as a side benefit, keep away other insects that could harm the chocolate tree.
The chocolate tree has one more symbiotic relationship down by its roots. A fungus grows on the roots and receives its nourishment from the tree. The chocolate tree in turn is able to absorb nutrients from the soil more effectively due to the presence of the fungus. Symbiotic relationships are not limited to rain forests and even humans have symbiotic relationships with domesticated animals and plants. In the rain forest, there are more such interactions and very complex ones because there are so many different species in a small space.