1. Unit 2: Dynamic Ecosytems

2.  The environment refers to all the factors
present that impact on an organism. We
categorise an environment into the abiotic
and biotic factors.

3.  Abiotic factors are the physical and chemical
factors present in an environment. Some
examples are temperature, light intensity, pH
of the soil, concentration of oxygen in water,
etc.

4.  Biotic factors refer to the living things within
the environment. Some examples include the
presence of organisms of the same species,
competitors (compete for food, water, etc),
collaborators (work with the species to an
advantage), predators, parasites, etc.

5.  Differences in physical conditions vertically
across a habitat give rise to stratification.

6.  Differences in abiotic conditions give rise to
stratification. These differences include the
amount of light present, the strength of the
wind and the humidity.
 These different conditions support different
communities of organisms.

7.  Just are varying abiotic factors in a rainforest
lead to stratification, the changing water
level associated
with tides creates
intertidal zonation.

9.  It is important to measure factors within environments to
better understand how they function. This knowledge is vital
to conservation and restoration of the natural environment.
 Qualitative data refers to descriptions not involving
numbers. E.g. the environment on the side of the cliff is
rocky and very exposed to the elements.
 Quantitative data involves measurements e.g. the average
temperature during the day was 32 degrees.

10.  Geographic range refers
to the area over which
can organism is found.
 Geographic distribution
refers to the spread of an
organism within an
ecosystem.
 Abundance refers to the
number of organisms
Geographic Range of the
present in an ecosystem
Platypus.

11.  What limits range and distribution? The resources
available in an environment and the ability of the
organism to obtain these resources (dependent on
adaptations) limit the organisms range and
distribution. Generally the greater the tolerance
range of an organism the greater its range and
distribution. Biotic factors can be responsible for
limiting distribution within an ecosystem. Such
factors include food sources and predators.

13.  It is important to know not only which species
of organisms are present in an ecosystem and
the relationships that exist between then but
also where exactly these species are located
within the ecosystem and how many of them
are alive.
 Species are rarely spread evenly through an
ecosystem rather they occur in patterns of
distribution. Some common patterns are:

14.  Random distribution-
organisms are irregularly
spaced and the location
of one species does not
appear to affect the
location of another;
more common in plant
populations.

15.  Uniform or continuous
distribution- organisms
are evenly spaced the
presence of one
organism determines
how close or distant
another organism will
be; common in animal
populations that are
territorial.

16.  Clumped or grouped
distribution- a number
of individuals are
grouped together and
the groups make up
the population as a
whole; this may be to
do with social
behaviours such as
schools of fish

17.  It is not always possible to directly measure a
population. How can you count all of the
birds within an ecosystem or all of the blades
of grass?
 Instead ecologists use sampling techniques
to provide estimates of populations.
 Such techniques include transects, quadrats,
and capture-mark-recapture.

18. For organisms that do not move a quadrat can be a good
method of estimating distribution and abundance.
Quadrats can also be used to measure density. The
position of quadrats within an ecosystem is selected at
random. The number of particular species within the
quadrat are counted and recorded. The total of all of the
quadrats are averaged.

19.  A line transect can be used to
measure the distribution of species
in an ecosystem. They are especially
helpful where we see environmental
gradients- gradual changes in an
ecosystem.
 We can also use vertical transect to
investigate stratification in forests
for example where different
amounts of light, humidity and wind
levels impact different species.

20.  Capture-mark-recapture is a method used to
estimate the population of mobile species.
 Step 1 is to capture organisms randomly in a
way that they are not harmed.
 Step 2 is to mark these organisms ensuring that
the marking does not attract predators or cause
harm. Tagging is a common form of marking
animals. Insects are usually marked with a dot of
ink. The animals are then returned to the
environment.

21.  Step 3 occurs some time after
release. Organisms are
captured again and the number
of marked organisms is
counted. From this information
the population is estimated
using the formula below:

22.  Dr. T., an ecologist, wanted to
find out how many frogs live in
a small pond.
 On the first trip to the pond, 55
frogs were caught, banded, and
released.
 The second trip to the pond, 72
frogs were caught, of those 72
frogs, 12 were banded.
Assuming the banded frogs had thoroughly mixed with the
unbanded frogs, how many frogs live in the pond?

23. Remember:
Information
55 frogs were caught, banded
The second trip to the
pond, 72 frogs were = 330frogs
caught, 12 were banded

24.  Density refers to the number of individuals in
a given area. Knowing the density of a
population can help assess whether or not an
ecosystem is able to provide sufficient
resources to support populations. This is
known as the carrying capacity of the
ecosystem.