2. What is Ecology?
• Ecology is the study of how organisms
(such as plants and animals) interact with
each other and with their physical environment.
• Organisms do not live in isolation.
• They interact with one another in a number of
ways, but especially because they eat each other.
• They also compete with each other for necessities
such as food, water, shelter, space and mates.
• Organisms interact with and alter their
surroundings when they carry out functions such
as feeding, breeding and activities such as
photosynthesis.
3. Populations
• Organisms of a species usually live together in
what is called a population.
• A population is a group of organisms of the same
species which live in a defined geographic area
(space) at the same time.
4. Living in Communities
• Different kinds of populations (for example koalas,
eucalypts and insects) live together and interact
with each other in what is called a community.
• A community is made up of the living component
of the environment. (ie. the different groups of
living organisms living together in the same place –
their habitat).
5. Ecosystems
• A community of living organisms interacting with
one another in a particular place, at a particular
time, together with their physical surroundings is
called an ecosystem.
• Ecosystems therefore consist of a community and
its physical surroundings.
• A tropical rainforest is an
example of an ecosystem, as is
a desert or a marine rock
pool or even a man-made city.
• Ecosystems can be small or
large but all are largely
self-sustaining.
6.
7. Biosphere
• The biosphere is the total of all areas where living
things are found including the hydrosphere (seas,
lakes & rivers), lithosphere (soil) and the
atmosphere.
• Energy enters the biosphere
and each of its ecosystems
most often in the form of
sunlight.
• Even ecosystems that are
physically far apart are
interconnected & interrelated
eg. global warming.
8. Habitats
• The type of place where an
organism lives is its habitat.
• It is the place or “address” that you would go to find
the organism in a particular geographic locality.
• Some organisms live only in one type of habitat,
other organisms live in a greater range of habitats.
• Some organisms move to different places
according to seasonal changes.
• Within a habitat there are local areas called
microhabitats – a small living space within a
larger habitat.
9. Population Size
• Determined by changes in:
1. Natality – birth rate of young
2. Mortality – death rate
3. Immigration – new organisms entering area
4. Emigration – organisms leaving area
• Populations are often affected by all of these things.
• The overall change in population size can be
calculated using the following equation:
• Natality and Immigration – addition of organisms
• Mortality and Emigration – subtraction of organisms
Population change = (natality + immigration) – (mortality +
emigration)
10. Population Growth
When a species enters a new environment:
• Initially there is a slow increase in numbers (due to
low reproduction rate & lack of mates)
• Then a very rapid increase in numbers due to
increased natality & little competition for resources.
• And then, population numbers remain constant and
competition for resources
increases.
• The population has now
reached the carrying
capacity of the environment.
11. • This growth can be represented by the following
curve (called a sigmoid growth curve):
plateau
phase
- constant
numbers
- carrying
capacity
exponential
growth
- rapid
increase in
numbers
initial
phase
- slow
increase in
numbers
12. Carrying Capacity
• The maximum number of individuals of a species
that can be sustainably supported by the
environment is the carrying capacity of that
ecosystem.
• The changes in population over
time eventually balance one
another (eg. birth and death
rates) and the population size
reaches a more or less constant
level (plateau phase).
13. Biotic and Abiotic Factors
• Ecosystems are influenced by a number of factors.
• Biotic factors are the living component of the
environment.
• Abiotic factors are the non-living or physical
factors in the environment.
• All populations have the potential for exponential
growth – the rapid increase in population numbers.
• However, certain factors limit this growth.
• The presence of these factors (whether biotic or
abiotic) means that the environment’s carrying
capacity is not always reached.
14. Factors Limiting Population Increase
• Population increase is limited by a number of factors
which usually relate to the habitat.
symbiosis
BIOTIC
(living)
1. Competitors
2. Predator, prey
presence
3. Parasites
4. Commensalism
5. Mutualism
6. Mates
ABIOTIC
(non-living)
1. Availability of water
2. Availability of shelter
3. Climate
4. Seasons
15. Competition
• There are two different types of competition:
• Intra-specific: competition between individuals of
the same species.
• Inter-specific: competition between individuals of
different species.
• Competition may result due to a struggle for the
same supply of food, water, space, nest sites,
mates or other environmental resources in limited
supply.
• Inter-specific competition can
lead to a species being forced from
a habitat by its competitor.
16. Symbiosis
• Symbiosis occurs when different
species live together in a close
partnership.
• There are three different types: mutualism,
commensalism and parasitism.
• Mutualism: A partnership between two different
kinds of organism where both of them benefit.
• Commensalism: A relationship where one
organism benefits and the other is neither harmed
nor benefits.
• Parasitism: One organism (the parasite) benefits
and the other (the host) is harmed.
18. Studying Ecosystems
• Important to use a random sample
to ensure that every individual in a
population has an equal chance of being selected
(like picking names from a hat).
• A number of methods used including quadrats and
transects.
• A quadrat is a square, rectangular or circular
patch of vegetation used to sample an area of an
ecosystem.
• An area of known size is randomly selected from
the total area.
• The number of organisms from a population is
counted in this area.
19. • This number is used to
estimate the total
population size.
• Quadrats can be located
at
random in an area or
they
can be placed at
regular
intervals along a
line or
transect.
20. Other Methods
• While quadrats are ideal for sampling plants, fungi
or small animals such as insects, they are not used
for studying larger animals.
• Instead a method called the capture-mark-release-
recapture method is used:
– Organisms collected from area and marked.
– Organisms released into same area and mix with
unmarked individuals.
– After time, organisms collected
from the same area.
– Count how many of the total
organisms captured are in fact
recaptured (marked).
– Formula applied to estimate
total population size.
21. Statistics
• Statistics are an important tool for
ecologists to use when studying
ecosystems.
• Statistical methods are used to calculate population
sizes after collection of results via random samples
collected from quadrats or the capture-mark-
release-recapture of animals.
• It is important that you are able to calculate means
of data using the formula as follows:
Mean = Sum of the values
Number of values
