8.11B: Interdependence
Organisms and Environments
A Fight for Life in the Tropical Rainforest
Lexile 1060L
1
It is morning in the tropical rainforest. Rain falls from
high in the sky, trickling down through the many and
diverse layers of the rainforest. The emergent layer is
the first to feel the rain. Drops splash off the leaves
of the Kapok and Brazil Nut Tree. Harpy Eagles and
butterflies are some of the first animals to feel the
rain. The plants and animals that live in this highest
layer of the rainforest are specially adapted to survive
in the difficult environment. They must be able to
tolerate high temperatures, plentiful sunlight, and
high winds. The trees that grow to this highest level have large leaves
covered with a waxy substance that helps them retain enough water to
survive.
2
The next level down is the canopy level. This level contains most of the
rainforest’s living organisms. Toucans, sloths, monkeys, and tree frogs are
animals commonly found in the canopy level. Since so many organisms live
in this level, competition for resources is fierce here. Plants and animals are
usually in constant competition for abiotic resources, like sunlight, water and
even good soil. Also at this level, there is a dense canopy of plants, creating
an umbrella of branches and leaves. Each plant strives to get enough sunlight
to live. Since water is plentiful in the tropical rainforest most of the
competition is for sunlight and nutrients. The canopy level plants form such a
thick covering of branches and leaves that very little sunlight filters down to
the understory layer.
3
The understory gets far less light than the canopy stratum of the rainforest.
This layer of the rainforest is home to most of the biome’s insects. Large cats
also roam the rainforest, including the jaguar and the ocelot which feed on
1 8.11B: Interdependence
Organisms and Environments
birds and other animals that live there. This level is also home to many
species of monkeys, birds, and sloths, as well as plants such as orchids, ginger,
and passionflower.
4
The Swollen Thorn Acacia tree uses ingenious tactics to help get the sunlight
it needs to survive and stay free of epiphytes. It hosts colonies of Bullhorn
Acacia ants. These ants cut down any root or vine that tries to grow on the
Swollen Thorn tree. This protective action lets the Acacia grow quickly and
stay healthy. In return for their protection, the Acacia tree gives the Bullhorn
ants shelter and food in the form of hollows inside the tree and a sugary food
source at the base of the leaves.
5
While the plants strive to survive, the animals of the rainforest are busy
competing to eat plants as well as each other. Many animals of the rainforest
eat fruit, which is plentiful here. In order to survive in this highly populated
ecosystem, most animals have carved out a highly specialized niche for
themselves. Sloths, for example, do not have to compete with many animals
for food because they eat a food that most animals cannot live on: leaves.
They have a large digestive system that allows them to get nutrients from
leaves.
6
The lowest level of the rainforest is the forest floor. This level of the rainforest
gets very little light. It is usually sparse enough to easily walk through and is
covered by the roots of trees and plants. The soil in the rainforest does not
have many nutrients, and the nutrients that it does have are quickly washed
away by the rain. Trees use a shallow root system to effectively grab nutrients
that are found of the surface of the ground. Sloths spend most of their lives
in one tree. They climb down from that tree each week to defecate at the
base of their tree. Scientist speculate that sloths do this to fertilize their tree
and give it precious nutrients that are hard to come by on the rainforest floor.
It is another example of rainforest symbiosis.
7
The rainforest holds a large amount of the words biotic, or living species, and
these organisms are constantly engaging in a fight for life. They must
compete for sun, shelter and food, just like all life on planet Earth.
2 8.11B: Interdependence
Organisms and Environments
1
2
3
The highest level in the rainforest is
called the —
A
canopy level.
B
understory level.
C
emergent level.
D
floor level.
4
An example of an abiotic factor
would be —
A
plants.
B
sunlight.
C
food.
D
animals.
3 Based on the information in this
passage, the reader can reasonably
conclude that —
A
animals in the rainforest are
strictly independent of each
other.
B
animals in the rainforest have
found ways to thwart their
competition and survive.
C
all animals in the rainforest have
the same adaptations.
D
animals in the rainforest all
need the same amount of sun.
Which words help the reader
understand the meaning of stratum
in paragraph 3?
A
“far less light”
B
“insects”
C
“home to “
D
“This layer”
8.11B: Interdependence
Organisms and Environments
5
Which of the following is the best
summary of the story?
A
B
6
Rainforest organisms do not usually
have to compete for —
Many different animals live in
the rainforest. They all find it
difficult to live there.
A
food.
B
sunlight.
Many animals live in the
rainforest. The sloth has found
an interesting way to keep his
tree fertilized.
C
nutrients.
D
water.
C
Different plants and animals live
in the rainforest. They must
compete for sunshine.
Epiphytes live on other trees
until they kill them.
D
Different plants and animals live
in the rainforest. Although
there is fierce competition for
sunshine, many animals and
plants have adapted to the
environment and found a way
to thrive.
4