Lesson Notes: Introduction to Ecology 1
Name: _________________________________ (
) Class: 2 ___ Date: _________
The environment of an organism (plant or animal) is made up of all the factors around
that organism which affect its survival and, of course, the survival of its species. On
the one hand, an organism, such as a rabbit, may die because of low temperatures,
being eaten, a disease such as myxomatosis, lack of food, a fight with another rabbit,
an accident (for example, a burrow cave-in), a cyclone. On the other hand, its wellbeing is improved by plenty of food and water, good nesting sites and favourable
weather conditions. These and other factors are classified by biologists as biotic and
abiotic factors.
Biotic factors are those involving other living things. Abiotic (a = without) factors
are non-living facets of the environment, such as humidity, temperature, rainfall, soil
nutrients, exposure to wind or the hot sun, air and water pressure, and light intensity.
Biotic factors may be described in terms of members of the same species (for example,
competition, social groupings) or members of other species (predators, prey,
competitors or collaborators of various kinds).
The requirements of an organism may vary during the life of that organism or from
season to season. An extreme example is seen in the caterpillar and butterfly which
have needs that change dramatically. Another is the seasonal requirements of birds
during breeding periods; many birds migrate to meet their changing needs.
Humans understand only the smallest fraction of the needs of the organisms of this
earth. Most we know only in the broadest sense.
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Case Study: Rabbits in Australia
The history of the rabbit's rise and fall in Australia is most instructive in terms of the
factors which affect the livelihood of an organism. It is also an excellent example of
how things can go wrong!
Read the following account and answer the questions which follow.
An animal in its natural environment is in balance with it, and its
population remains fairly constant or fluctuates in a predictable
cycle. Though some animals seem to compete for resources, their
needs are subtly different so that, while living in the same
environment, they do not compete. Competition could result in a
winner and the extinction of one species or it could result in the
evolution of two species that no longer compete.
Domestic rabbits were brought to Australia with the First Fleet in
1788. By the early 1800s they were established in the wild around
Sydney, the descendants of escapees and those set free.
However, the great rabbit plague began with 12 wild rabbits
introduced for hunting purposes to a property near Geelong in
Victoria in 1859. By 1907 they had reached Geraldton in Western
Australia, and Queensland by 1886. They stripped the country bare
and turned many properties to desert. They came to occupy the
whole southern continent to approximately the Tropic of
Capricorn.
What caused this amazing spread of rabbits? Clearly the climate
was ideal, much like that of their native Spain. Populations, of
course, varied in density according to availability of water and
food, but native predators (mostly wedge-tailed eagles, dingoes
and snakes) had no effect on their spread. Rabbits rapidly outreproduced native marsupials. Foxes and ferrets were introduced
but are now themselves a problem. Despite much research over a
long period of time, the key to stable (low) rabbit numbers in
Australia has proved elusive. There must be myriad factors that
have kept rabbits in check in other countries.
Finally, the disease myxomatosis was brought into the country in
1950. Within three years the entire Australian rabbit population
was reduced to a small fraction of what it was. The disease was
spread by mosquito bites, so was most effective in moist regions.
In 1969 the rabbit flea was introduced to help the spread of the
disease in arid regions. Today, as you may know, rabbits are again
presenting an increasing threat. Not only are they growing in
resistance (survival of the fittest) but the disease keeps weakening
(it is hardly in the interest of the disease to kill its host so the
weaker strains survive).
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Discussion Questions:
1. What abiotic factors have been mentioned that affect the survival of rabbits?
Can you add any?
2. What biotic factors were mentioned? What others can you add?
3. How did abiotic factors affect the spread of myxomatosis? Why was the rabbit
flea considered useful?
4. Explain, in your own words, why rabbits became a problem in Australia.
5. In recent years, the rabbit population has been devastated by the calcivirus.
Research this disease and write a short summary about it.
Science in Focus
 Myxomatosis has been reasonably successful in Australia, but in Europe the
disease has been so effective that the rabbit is now almost extinct and so is
protected.
 Very few herbivores can digest cellulose, the primary component of plant cell
walls. Most depend on micro-organisms to digest the cellulose for them. Cows
have huge stomachs in which this occurs. Rabbits and horses have a giant
appendix where this goes on. Without the microbes most herbivores would die.
 A population refers to the number of organisms of one species living in one area,
for example, a population of koalas.
 A community refers to all the organisms (both plants and animals) living in the
one area, for example, a rainforest community.
 The habitat is the type of area where an organism lives, for example, the habitat
of the dugong is seagrass beds.
 The niche of an organism is its exact role and physical living place of a species. It
is unique to each species (such that the only competitors in a balanced ecosystem
are members of the same species).
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Some Common Terms Used in Ecology
ecology The study of how organisms interact with each other and their
physical environment.
ecosystem The community living in an area and its physical environment.
community All species or populations living in the same area.
species One or more populations of interbreeding or potentially interbreeding
organisms that are reproductively isolated in nature from all other organisms.
Populations of individuals capable of interbreeding and producing viable,
fertile offspring.
population A group of individuals of the same species living in the same
area at the same time and sharing a common gene pool. A group of
potentially interbreeding organisms in a geographic area.
producers The first level in a food pyramid; consist of organisms that
generate the food used by all other organisms in the ecosystem; usually
consist of plants making food by photosynthesis.
consumers The higher levels in a food pyramid; consist of primary
consumers, which feed on the producers, and secondary consumers, which
feed on the primary consumers.
Decomposers organisms that break down dead organisms
Habitat the place an organism stays in
niche The biological role played by a species.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookpopecol.html
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