Food Webs
Most food chains have no more than four or five
links.
There cannot be too many links in a single food
chain because the animals at the end of the chain
would not get enough food (and hence energy) to
stay alive.
Most animals are part of more than one food
chain and eat more than one kind of food in order
to meet their food and energy requirements.
These interconnected food chains form a food
web.
•
Do you know why there are more
herbivores than carnivores?
In a food chain, energy is passed from one link to another.
When a herbivore eats, only a fraction of the energy (that it
gets from the plant food) becomes new body mass; the rest
of the energy is lost as waste or used up by the herbivore to
carry out its life processes (e.g., movement, digestion,
reproduction). Therefore, when the herbivore is eaten by a
carnivore, it passes only a small amount of total energy (that
it has received) to the carnivore. Of the energy transferred
from the herbivore to the carnivore, some energy will be
"wasted" or "used up" by the carnivore. The carnivore then
has to eat many herbivores to get enough energy to grow.
Because of the large amount of energy that is lost at each
link, the amount of energy that is transferred gets lesser and
lesser ...
The following is a possible food web:
A change in the size of one population in a food
chain will affect other populations.
This interdependence of the populations within a
food chain helps to maintain the balance of plant
and animal populations within a community. For
example, when there are too many giraffes; there
will be insufficient trees and shrubs for all of them
to eat. Many giraffes will starve and die. Fewer
giraffes means more time for the trees and shrubs
to grow to maturity and multiply. Fewer giraffes
also means less food is available for the lions to
eat and some lions will starve to death. When there
are fewer lions, the giraffe population will increase.
Desert Biomes
• The picture shows a desert food web.
Desert biomes receive less than 10 inches of rain per year.
Plant adaptations: Desert plants differ in the ways they adapt
themselves to the hot and dry environment.
Some desert plants have a short life cycle. When the rains come,
these plants sprout quickly, flower and die. Their seeds lie dormant
in the soil, until the next rain enables them to germinate and bloom.
Most desert plants grow far apart and their roots extend out so that
each plant can get water and minerals from a large area. Other
desert plants have roots that extend deep into the ground to obtain
water from deep beneath the ground.
When it rains, cactuses and other succulent (juicy) plants take up as
much water as possible and store it in their leaves and stems which
will provide the water they need during the dry months. Their waxy
leaves and stems also slow down water loss through transpiration.
Other plants survive by shedding their leaves in dry periods to
reduce water loss.
• Animal adaptations: Desert animals include many kinds of insects,
spiders, reptiles, birds and mammals. They are adapted to the heat
as well as scarcity of water.
Deer, foxes, wolves and other animals may visit a desert after a
rainfall in search of food. Butterflies and bees emerge from their
pupa state to feed on the flowers that bloom. The insects breed
quickly so that the next generation reaches the pupa stage before
the desert dries up.
The jackrabbit's light-coloured fur helps it blend into its surroundings
and its large ears help it to keep cool by giving off heat. Many small
animals hide under rocks or dig burrows underground and stay there
during the day to escape the heat and the sun. Most desert animals
are nocturnal - they avoid the extreme midday heat by feeding at
night, when the temperature has dropped and the air is much cooler.
Some of them are dormant (inactive) in the summer.
Larger desert animals try to stay in shady areas during the day. They
obtain water from the food they eat and from the few water holes
that exist in a desert. The camel stores its food as fat in large humps
on its back. The stored fats are broken down to help the camel
survives long periods without food and water.
Taiga: Boreal Forests
• The picture shows a food web in a temperate
coniferous forest.
Coniferous forests are divided into two types temperate forests (in mild climates usually along
the coastlines) and boreal forests also called taiga
(in sub-arctic climates that lie immediately south of
the tundra).
Boreal forests are found in the northernmost parts
of North America, Europe and Asia where
summers are short and moist while winters are
long and cold. Trees found in boreal forests include
such evergreen conifers as balsam firs, black
spruces, jack pines and white spruces. Nearly all
conifers are evergreen.
• They usually have needle-shaped or scale-like leaves
with thick cuticles to reduce loss of water through
transpiration. They typically have straight trunks with
horizontal branches varying more or less regularly in
length from bottom to top, so that the trees are conical in
shape. Their pointy, triangular shape helps the trees to
shed heavy snow which would otherwise break or
damage the branches. Conifers have shallow root
system that allows the trees to take in the water as soon
as the surface ice/snow melts.
Few plants grow on the floor of boreal forests. Thick
layers of old needles build up beneath the trees. These
needles contain acids that are slowly released as the
needles decay. Water carries the acids and dissolved
minerals deep into the soil. As a result, the topsoil is
often not nutrient rich thus unable to support many types
of small plants. The plants at the base of these trees are
usually ferns, lichens and mosses.
Adaptations to A Temperate Deciduous Forest
Biome
•
The picture shows a food web in a temperate deciduous forest.
The Temperate Deciduous Forest biome has four seasons of winter, spring, summer and
fall. Animals and plants have special adaptations to cope with these yearly changes.
Plant adaptations
Deciduous trees are trees that shed their leaves once a year at the approach of a cold or
dry season and later grow new leaves. (Plants that keep their foliage throughout the year
are called evergreens.) Deciduous trees usually have broad leaves e.g., ash, beech, birch,
maple and oak.
In SUMMER, their broad green leaves help capture sunlight needed to make food through
photosynthesis.
As temperatures drop, the tree cuts off the supply of water to the leaves and seals off the
area between the leaf stem and the tree trunk. With limited sunlight and water, the leaves
are unable to continue producing chlorophyll (green pigment in leaves) causing them to
change into the beautiful red, yellow and orange leaf colours of FALL.
In WINTER, it is too cold for the trees to protect their leaves from freezing, so they simply
loose them and seal up the places where the leaves attach to the branch. Losing their
leaves helps trees to conserve water loss through transpiration. (Dried leaves continue to
hang on the branches of some deciduous trees until the new leaves come out.)
Before the leaves die, some of the food material they contain is drawn back into the twigs
and branches where it is stored and used the following spring.
The warmer temperatures of SPRING signal to the trees that they can grow new leaves
again, and restart the cycle.
• Animal adaptations
Animals in temperate deciduous forests also have to adapt to the
changing seasons. They must be able to cope with cold winters when
food is in short supply. Migration and hibernation are two adaptations
used by the animals in this biome.
A great variety of birds migrate to warmer places where they can find
food more easily.
Some mammals (e.g., bears) hibernate during the cold winter months.
Hibernation is an inactive, sleeplike state that some animals enter during
the winter. Animals that hibernate protect themselves against the cold
and reduce their need for food. A hibernating animal's body temperature
is lower than normal, and its heartbeat and breathing slow down greatly.
An animal in this state needs little energy to stay alive and can live off fat
stored in its body. Thus, hibernating animals can more easily survive the
cold winter months.
• Squirrels, chipmunks, and some jays often store large supplies of food
(such as nuts and seeds) in the ground, under fallen leaves, or in tree
hollows for use during the cold winters when food is scarce. Cold
temperatures help prevent the decomposition of the nuts and seeds.
Temperate Rainforest