Plant and Animal Interactions

Tropical rain forests are the stage for many of the world's most complex and interesting plant and animal interactions. These interactions play important roles in plant defenses, pollination and seed dispersal. Following are just a few examples.


ANTS

Ants can occur anywhere in tropical rain forests from the tops of trees to the forest floor. They are so prevalent that in a one square yard area of typical forest, 800 individuals from 12 different species of ants can be found. In addition to playing an important role in recycling nutrients many have mutually beneficial relationships with plants.

Aztec Ants

Aztec ant on Cecropia tree

Aztec ants establish colonies inside the hollow stems of Cecropia trees. The ants feed on the sugary solution excreted by small plant-sucking insects which the ants introduce and maintain. The fierce ants protect the tree from other foragers and climbing vines which could cover the plant. They collect small nutritious outgrowths from the base of the Cecropia leaves which they use as food for themselves and their young. Many other species of plants, including certain Acacia species, have a similar relationship with their resident species of ant.

Leaf Cutter Ants

Leaf cutter ant with leaf section

Leaf cutter ants (Atta spp.) cut sections of leaves and transport them to their underground nests. The ants chew the leaves into a pulp, mix it with a special fungus and fertilize it with their fecal material. The ants then feed upon the fungus, not the leaves.


PLANT TOXINS

Many tropical rain forest plants contain alkaloids and other chemicals that make them distasteful or poisonous to foraging insects. These chemicals play an important role in plant defense and many have important uses in medicines as well. Some insects, such as the heliconiine butterflies, have developed mechanisms to exploit these chemicals to their advantage.

Heliconiine butterfly on passion flower, Tetrastylis

Heliconiine Butterflies

Adult heliconiine butterflies lay their eggs on passion flower vines. The young emerge and feed upon the leaves. The adult butterflies produce and store chemicals in their bodies which make them poisonous to birds that would prey upon them. Birds have learned to recognize the color pattern of the heliconiine butterflies and avoid them. Other non-toxic butterflies have evolved to mimic the pattern of the toxic heliconiine, hence they share in the protection.


POLLINATION

Unlike temperate forests where many plants are wind-pollinated, most tropical rain forest plants rely upon animals for pollination. Insects, birds and mammals pollinate the plants inadvertently by transferring pollen from flower to flower in their quest for food (nectar and/or pollen). The lack of wind in tropical rain forests and the greater distance between individuals of a plant species are two factors that may have contributed to the selection of these methods over wind pollination.

Hummingbird with Hibiscus

Birds

Bird pollination is found throughout the world with the exception of Europe and Asia north of the Himalayas. It occurs most commonly in the tropics. Hummingbirds and sunbirds are two important groups of bird pollinators, with hummingbirds found only in the Americas. Flowers pollinated by birds are usually brightly colored in reds, oranges or yellows. The flowers are borne away from the foliage, produce copious, watery nectar and may be strongly constructed to support the weight of the bird. Most bird-pollinated flowers are odorless as birds lack a good sense of smell.

Bats

Bat with durian, Durio, flowers

Most bats feed on nectar and pollen, insects, or fruit, with the exception of a few species that feed on fish, animal blood or other bats. They are extremely important pollinators and seed dispersers in the tropics.

Bats are nocturnal, have a keen sense of smell and most have poor eyesight. They are attracted to flowers which give off a musty or sour scent. The flowers generally open only at night and are pale in color. The flowers are strongly constructed to support the claws and weight of the bat. They are bell-, brush- or ball-shaped and hang clear of foliage or are located on exposed trunks or branches where bats can reach them.

Butterflies and Moths

Heliconiine butterfly on Lantana

Flowers adapted to pollination by butterflies and moths tend to produce nectar at the base of a slender, tubular flower. Butterflies are active mainly during the day while moths are predominately nocturnal. Flowers frequented by butterflies display a greater color range than do flowers pollinated by moths; reds, yellows, pinks, purple are common. Moth-pollinated flowers are generally pale or white in color and give off a sweet scent at night.

Hawk moth with Brunfelsia


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