Lesson Notes: Ecology Part 2
Name: _________________________________ (
) Class: 2 ___ Date: _________
Ecology is the study of the relationships between plants and animals and their
environments. The most complex ecological features to study are the subtle
interactions between living things. For example, did you know that strawberry plants
thrive under a pine needle mulch? We really don't know why. Foreign pine trees did
poorly in Australia until a particular root fungus was brought into the country. It now
appears that many fungi infecting plant roots actually assist the plant to obtain
nutrients! Red-back spiders and daddy-long-legs do not occur together. Again the
reason is unknown. There is even evidence to suggest that some of our major iron-ore
deposits were created by bacteria!
The most easily understood relationship in nature is the predator-prey interaction.
These interactions are illustrated as food chains, food webs and food pyramids.
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Food chains indicate the flow of energy along a sequence of organisms. The energy
originates in the sun and is first utilised by plants. Almost all food chains start with a
plant (there are rare instances where the food chain starts with chemosynthetic
bacteria, as in the mid-ocean ridges). Less than 10 per cent of energy actually passes
down each step of a food chain since most energy is used up in simply living. Plants
are known as the producer organisms since they produce their own food. Herbivores plant-eating animals, such as rabbits - are often called 'first-order consumers', and
predators are termed `second' or 'third-order consumers' according to how far along
the food chain they occur. Predators which feed only on other animals are called
carnivores while those, like humans, which can eat plants and animals, are referred to
as omnivores.
Producer  First-order  Second-order  Third-order
consumer
consumer
consumer
But does a food chain ever end? After all, even a lion eventually gets sick and dies
and is devoured by bacteria. Bacteria and fungi are called decomposers. Bacteria and
fungi recycle carbon and nitrogen. Without decomposers, life on earth would soon
stop because all available carbon - the basis of all life forms on earth - would be used
up.
A habitat contains a community of living things
The habitat of a living organism is the place where it lives. Some examples of habitats
are a pond, a hedgerow around the school grounds, a rocky seashore. A wide variety
of living things are found in a habitat. All the living things in a habitat are called a
community. A community is made up of many different species of animals, plants,
fungi, bacteria and protoctista.
This rock pool community is made up of
various seaweeds, a sea slug, mussels,
snakelocks anemones, winkles, a shore crab
and limpets.
The figure below shows an example of a habitat. All the different living
organisms in the pond make up its community. All the organisms of one
species in the pond make up a population. All the duckweed, for example,
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makes up the duckweed population. A population is all the organisms of a
particular species; in a particular habitat.
Each kind of organism in the pond has its role to ply in the community. The water
weeds, for example, take carbon dioxide from the water in daylight, releasing oxygen
which the animals use in respiration. At night, the weeds take in more oxygen than
they give out. The weeds provide food for the herbivorous animals. They act as
surfaces to which tiny organisms can attach themselves.
All of these things are part of the niche of the water weeds. An organism's niche can
be thought of as its `profession' in the community in which it lives. Each kind of
organism in a community has a different niche. Niches of different species can
overlap, but are never identical. If you make a detailed study of a habitat, you may be
able to find out quite a lot about some of the species you discover. You will find that
different kinds of plants, for example, live in slightly different places, reproduce in
slightly different ways, and provide food for different kinds of animals. Each species
has its own particular niche.
An ecosystem is made up of interacting living and non-living things
The pond shown previously does not contain living things on1y. It also contains
mud, stones, water, and gases dissolved in the water. These non-living parts of the
pond affect the Living organisms in it. They are part of the pond ecosystem.
An ecosystem consists of a community and its environment. The living organisms
affect each other. They affect their environment, and are affected by their
environment. An ecosystem consists of both living and non-living things.
Although a pond is an example of an ecosystem, you can also think of ecosystems
on a much larger scale. The whole of the Earth is one big ecosystem!
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Organisms are adapted to live in their environment
Each species of organism has a particular type of habitat in which it is adapted to live.
Limpets, for example, are adapted to live on rocky shores where they are covered by
the tide for part of the day. Their shell protects them from predators and stops them
from drying out when the tide is out. Their strong muscular foot clamps them tightly
to the rock so that they are not dislodged by waves. They have a rasping tongue which
scrapes algae off the rocks when the tide covers them.
The factors which affect a living organism can be divided into physical factors and
biotic factors. Physical factors are non-living ones. In the case of the limpet, some of
the most important physical factors are the tide which repeatedly covers and uncovers
it, the waves which splash against it, the rock on which it lives, and the temperature of
the air and water around it. The biotic factors are the other limpets around it (which
might take up space or eat food it might have used), the algae which it eats, and
predators which try to eat it.
The adaptations of the limpet
enable it to live successfully in its
environment and to cope with the
environmental factors which affect
it. The factors are different in
different places, so organisms
need different adaptations to be
able to live there. A limpet would
not survive long in an oak wood,
or even on a sandy sea shore.
Rain forests are some of the most complex ecosystems in the world. This one is in
the Monteverde Cloud Forest Reserve in Costa Rica.
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Discussion
1. Study the food web below, drawn for a small island in the South Pacific, then
answer the questions related to it.
If the island were heavily sprayed with insecticide, killing most of
the insects:
a. How would the ridon population be affected?
b. What would be the effect on the org population?
c. What would happen to the molak population?
2. Study this food web for a small island. These were the only living things on
the island.
a. Name the only producer.
b. Name a herbivore.
c. Name two competitors.
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d. A disease killed all lards. How does this affect the
number of
(i) nairps (ii) foys (iii) geeks?
e. Which are likely to be most numerous, lards or foys? Why?
f. A new organism is introduced to the island, which drives the funks and
foys almost to the point of extinction. How does this affect the funp?
3. This graph profiles four species of grass along a transect. Describe the
relationship of kikuyu to winter grass. How does the population of clover
relate to either?
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