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The Tropical Rainforest
Key Feature of Tropical Rainforests
Tropical Rainforests have more biodiversity (different kinds of species) than
any biome on earth. About 75% of all animals species live in Tropical
Rainforests. In one hectare (1 hm2), there might be 807 trees which would
represent 313 different tree species. In other words, if you walked over an
area of a hectare, you would find only an average of 2.6 trees of the same
kind. All the other 804 trees would be different.
Tropical Rainforest Food Webs
Tropical rainforests have extensive food webs which help to maintain
stability as long as they are not disturbed.
Largest Reservoir of Unclassified Species
Tropical Rainforests have the largest number of unclassified species of
any environment on earth. It is estimated that at least 1 million new
species will be found in Tropical Rainforests if they survive and are
An Endangered Environment
Tropical Rainforests are rapidly being exploited and deforested to raise crops
and provide pastures for grazing animals. They are the most endangered
environments as they are being rapidly destroyed for short term profits.
Brazil lost a rainforest area larger than Greece from 2000-2006. By 2030, it is
estimated that Brazils rainforest area will be further reduced by 40%.
Location of Tropical Rainforests
Tropical Rainforests are located within 28 of latitude from the equator.
Climate Favouring Tropical Rainforests
Tropical Rainforests form in climates with high average, even
temperatures (18 C or more annual average) and high average, even
rainfall (1750-2000 mm is typical but they can form with as little as
1680 mm or as much as 10 000 mm)
Decomposition Rates in Tropical Rainforests
Tropical Rainforests have rapid decomposition rates with wastes or
dead organisms usually totally disappearing within a few days or
weeks as scavengers and decomposers rapidly break down organic
Tropical Rainforest Soils
Tropical Rainforest soils are called latosols. They are typically reddish
or yellowish in colour due to the high degree of oxidation of iron
compounds in the soil. Tropical rainforest soils are very nutrient poor
(rapid decomposition of organic matter prevents humus formation),
typically do not develop horizon structure, and can be very deep.
Highly Competitive Organisms
Because there are so many different kinds of organisms in a Tropical
rainforests, there is much competition for food.
Very Specialized Organisms
In order to reduce their competition over against other species, Tropical
rainforest species tend to be highly specialized to obtain a very particular
food item, not of value to other species. Biologists use the term, niche, to
refer to what an organism does to stay alive – its profession. Tropical
rainforest organisms have very specialized niches, very unique ways of
feeding, reproducing and staying alive. The orchid mantis mimicks orchid
flowers and catches insects lured to it. The koala eats mostly eucalyptus
leaves, poisonous to most other organisms.
Examples of Specialized Rainforest Organisms
Pygmy gliders are small, nocturnal opossums which feed on insects,
sap, buds, pollen and nectar. They use flaps of skin to glide up to 25
Examples of Specialized Rainforest Organisms
Swan-sized Rhinoceros hornbill birds feed on fruits, insects and rodents.
After mating, the female finds a hollow tree and the male seals up the hole
with mud and dung. The female incubates the eggs inside the tree while
being fed by the male through a small hole or slit which the female also uses
to defecate through. The young and mother are fed by the male until they
are old enough to make it on their own.
Examples of Specialized Rainforest Organisms
Glow worms are not worms but larvae of a mosquito-like fly. They
build silken thread covered with mucous that can trap insects which
they feed on. To lure insects, they produce a bluish light using a
chemical called luciferin, an enzyme and an energy compound.
Examples of Specialized Rainforest Organisms
Epiphytes or air plants are common in tropical rainforests. These
plants grow on other plants and have aerial roots which absorb water
and a few nutrients from the air or the plant they are on. They are not
parasitic, not harming the plants they grow on. Orchids and Spanish
moss are epiphytes.
Biomass Location in Tropical Rainforests
Unlike most environments, a Tropical rainforests biomass (total mass of
organic matter in living organisms, their wastes and dead remains) is 99.9 %
in the living organisms with virtually none in wastes or dead remains.
Contrast this to a temperate rainforest which may have as much as 40% of its
biomass is in decomposing materials on the forest floor.
Forest Structure of a Tropical Rainforest
Tropical rainforests are highly stratified into four distinct layers. There
is an upper canopy, an understory, an emergent layer above the
canopy, a shrub layer and perhaps a herb or ground cover layer.
The Emergent Layer
The emergent layer is made up of very tall trees about 70-80 m tall. To
maintain their stability, these tall trees often have cone-like buttress
roots which help to prop the trees and keep them upright.
The Canopy Layer
The Canopy layer (from height of 3 m (10 ft) to 30 –r 45 m tall) of a tropical
rainforests contains most of the organisms living in a rainforest. Many of the
epiphytes with aerial roots living on trees but not harming them are found in
this layer.
The Understory Layer
This layer of the tropical rainforest includes small trees and bushes
from 1m-3m tall. This layer is in shade (gets 5% of sunlight) so many
plants in this layer have large flat leaves to absorb as much sunlight as
possible. Predators in this layer include boa constrictors and cats like
the jaguar, panther, mountain lion and tiger.
The Rainforest Floor
This layer often has few plants since the light is so dim (about 2% of
sunlight at the top of the rainforest) at the floor level of a tropical
rainforest. Organisms may be spotted for camoflage. Large leaves are
a plant adaptation to capture the little sunlight falling on this area.
Pharmaceutical Value of Rainforests
More than a quarter of all natural medicines come from Tropical
rainforests. Scientists are concerned that the present rainforest
destruction will rob future generations of many medicines that remain
to be discovered in the plants and animals of tropical rainforests.
Pharmaceuticals from Rainforests
Two-thirds of all cancer fighting medicines have come plants in tropical
rainforests. One-half of all known plant species are found in tropical
rainforests. 1 mi2 in a tropical rainforest would have 1,500 flowering
plant species and 750 tree species. 120 prescription drugs are
compounds that have come from tropical rainforest plants.
Pharmaceuticals from Rainforests
A unique periwinkle species from Madagascar rainforests has a compound
that has increased leukemia survival from 20% to 80%. Unfortunately this
periwinkle species has gone extinct due to deforestation. Compounds from
rainforest plants today are used to treat malaria, heart disease, bronchitis,
hypertension, rheumatism, diabetes, arthritis, glaucoma, dysentery and
Just the Tip of the Iceberg
What pharmaceuticals scientists have discovered in tropical rainforest
plants is just the tip of the iceberg of useful medicinal compounds that
may be discovered if tropical rainforests survive their present
destruction by human “developers”.
Tropical Rainforest Animals
Tropical Rainforest parrots have tough beaks for cracking and eating
seeds and fruits.
Tropical Rainforest Animals
Slow moving sloths feed mostly on leaves and buds of the cecropia
tree. They spend most of their lives in the rainforest canopy.
Tropical Rainforest Animals
The jaguar is a predator of the forest floor and understory layer. The
patterened coat of the jaguar helps to camouflage it in the shady
layers it roams.
Tropical Rainforest Animals
Tapirs are pig-sized herbivores. They have long prehensile snouts that
they use to grasp bushes out of reach.
Tropical Rainforest Animals
The okapi is a congo rainforest animal that is related to giraffes and
has a coat with markings similar to a zebra. It has a long tongue used
to strip buds and leaves from understory bushes and trees.
Tropical Rainforest Animals
African rainforest gorillas are herbivores and live together in groups
called troops.
Tourist being
groomed 
Tropical Rainforest Animals
Anacondas are the world’s largest
snakes which can reach lengths of
over 22 ft and whose mouths and
bodies expand to eat prey much
larger than themselves.
Tropical Rainforest Plants
Mohagany trees are cut for their lumber used for paneling or furniture.
Tropical Rainforest Plants
Teak trees are valued for their lumber which is weather resistant and
has been used for outdoor furniture as well as indoor furniture.
Tropical Rainforest Plants
Brazil nut trees are South American rainforest trees that are in the
emergent layer. They produce pods with shelled seeds from which the
nuts are taken.
Tropical Rainforest Plants
Banana plants are the largest flowering herbaceous plants. They are
not woody trees. The fruit of a banana plant is technically a berry. In
the rainforest they would be in the understory layer.
Tropical Rainforest Plants
Orchids are epiphytes found in tropical rain forests. Their unusual and
colourful shapes sometimes mimic their pollinators.
Tropical Rainforest Plants
Rafflesia is a parasitic plant whose only visible part is large flowers
over 1 m across. They look and smell like decaying flesh so they
attract flies as pollinators. The stench of the flower has been said to
be almost strong enough to make a person pass out.
Tropical Rainforest Plants
The amazon rainforest has giant lily pads that can support the weight
of a small person. Victoria water lilies can be up to 3 m across with
stalks going 8 m deep to the river bed.
End of Presentation