Topic 4: Distribution and Abundance - PrelimBio

Populations and communities
Topic 4: Distribution and Abundance
Part of the Local Ecosystems Module
Spotlight Biology Preliminary Text Chapter 3
Authors: D. Heffernan, J. Bastina, B. Grieve, K.
Humphreys, A. Sartor
Science Press 2002
Distribution and Abundance
Distribution of a species
is where a species lives,
how it’s ‘distributed’ on a
continent. Abundance
is the number of species
living in an area.
-For example, a red river
gum tree is distributed all
over Australia. However it
is more abundant along
river courses.
Distribution and Abundance
There are many factors that affect the
distribution and abundance in terrestrial and
aquatic environments including:
 Availability of food
 Abundance and range of predators
 Competition for food and resources
 Climate conditions (temp/rainfall)
 Chemical conditions (pH/availability of gases)
 Parasites and disease
Distribution and Abundance
Both distribution and
abundance can change
from year to year. When
the Menindee Lake System
floods, there are flocks of
pelicans nesting in the
remote desert
environment of Western
NSW. When the system
dries out, they move to
other areas where there is
Distribution and Abundance
The abundance can also
change even if the
distribution doesn’t. When
mouse populations reach
plague proportion the
abundance of mouse
eating organisms like
snakes increase. When
food for the mice runs
out, their numbers decline
and so does that of the
The Forests ‘Terrestrial Ecosystems’
Land areas that include mountains, valleys, plains,
deserts, grasslands and forests are referred to as
‘terrestrial ecosystems’. Places on land where
organisms live.
The Forests
Forests are areas high in rainfall and have many plants
and animals with interesting adaptions. The leaf litter
alone supports a range of organisms that are important
to the balance of the entire ecosystem. There are
many factors that influence distribution and abundance
in these terrestrial environments. (We’ll discuss these in
more detail next module)
Plants of the Forest
The forests in Australia can be divided into 4 main
1. Open forests
2. Tall, Closed forests
3. Temperate rainforests
4. Tropical rainforests
**Hand out ‘Vegetation types across NSW Table’
(pg 78 Spotlight Text)
Plants of the Forest
Open Forests
 Contain relatively short,
somewhat knotted
eucalypts and an
understory of droughtresistant shrubs. They
grow in drier regions
with poor soil. Around
Sydney they are found on
porous sandstone ridges.
Plants of the Forest
Tall, closed forests
 Contain taller and
straighter eucalypts.
Because of the fairly
closed canopy above, less
light reaches the softer
leaved shrubs beneath.
Wet sclerophyll forests
generally grow on better
soils with moderate
Plants of the Forest
Temperate Rainforests
 Exist in cooler, higher
rainfall areas where the
soil is good. The
eucalypts are often very
tall and straight, and a
number of other larger
tree types may be
present. There may also
be a well-developed
understory of ferns.
Plants of the Forest
Tropical Rainforests
 Exist in the warmer areas
of extreme rainfall. They
contain few if any
eucalypts. There is no
understory because the
light intensity beneath the
dense tree canopy is very
poor. The diversity of trees
can be huge. 1 hectare can
contain more than 200
different species.
Animals of the Forest
Many animals that live in forests have adaptations for
living in trees. Here are a few examples:
 Lizards: Special pads on their toes and feet, and
some have large claws
 Frogs: Have suction cups on their toes
 Possums have sharp claws and large folds between
their les that allow them to glide from tree to tree.
 Kaolas have large claws and large back legs.
Animals of the Forest
Animals of the forest floor
are also very interesting. This
 Wombats
 Bandicoots
 Wallabies
A few that survive on
termites and ants include:
 Anteater
 Numbat
 Echidna
Freshwater Streams
Freshwater streams are also a
part of our forests. Aquatic
ecosystems include the
oceans, estuaries, coral reefs,
lakes and freshwater streams.
Many factors affect the
distribution and abundance of
organisms in these
Freshwater Streams
Several important factors
that affect the distribution
and abundance of organisms
in freshwater streams
 Rate of flow
 Nature of the rock along
the bottom
 Amount of sediment
 Levels of dissolved
 Levels of dissolved oxygen
Plants of Freshwater Streams
Many of the plants in our
fresh water streams are
microscopic phytoplankton
(algae). Algae are the start
of nearly all food chains.
Algae attached to rocks and
logs are more important in
flowing streams and free
floating algae is more
important in lakes and
Plants of Freshwater Streams
Another source of plant
matter in freshwater streams
are the plants growing along
the banks. They contribute
potential food when their
leaves and branches fall into
the water. Rushes and sedges
including cumbungi and
fallen trees provide habitat
for fish and other organisms.
Animals of Freshwater Streams
Freshwater streams are home to
many species of fish which
 Perch
 Cod
 bony bream.
These streams are also home to
many invertebrates which
 Waterboatman
 Whirligig beetle
 Backswimmer
 Waterstrider
Animals of Freshwater Streams
Waterstriders have fine hairs
on the ends of their legs to
prevent them from breaking
the surface tension of water.
This allows them to ‘stride’
across the top.
Backswimmers lie on their
backs and use their legs like
paddles to get around in the
water. They have eyes
adapted to viewing above and
below the water.
Answer the following questions your notebooks. Come to class
prepared to discuss next lesson. Remember you will also be
marked as attempting/not attempting these.
1. Contrast distribution with abundance
2. Identify the factors which determine the distribution and
abundance of a species in either a terrestrial of aquatic
3. Construct a table to compare the following abiotic factors
of aquatic and terrestrial environments: Availability of
oxygen, temperature variation, pressure variation,
viscosity, light penetration, buoyancy and availability of
ions (hint: See the handout I gave you. Reconstruct in your own
words though!)

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