A Local Ecosystem
Abiotic features of the environment
Abiotic features are the non-living
components of the environment. They
include,
 Physical features: temperature, rainfall,
wind, light intensity, humidity, soil type,
water, landform
 Chemical features: pH of soil or water,
salinity, availability of gases
Biotic features of the environment
Biotic features are the living components of
the environment. This includes:
 Plants
 Animals
 Micro-organisms
Aquatic environments
Environments can be
classified as aquatic (water)
or terrestrial (land). Aquatic
environments can be either
freshwater or marine
(saltwater).
Terrestrial environments
Terrestrial environments are found in
different climates and range from deserts,
grasslands
and rainforests to
mountain regions.
Aquatic v’s terrestrial
Organisms living in aquatic and terrestrial
environments have to survive different abiotic
conditions. When comparing the difference
between the two it is necessary to look at
features such as: buoyancy, pressure,
temperature, availability of gases, light
penetration and viscosity.
Community and population
A community can be defined as the set of
interacting organisms within an ecosystem. A
population is a group
of individuals of the
same species
living in the
same area.
Distribution
Distribution refers to the region where an
organism is found.
Distribution of rabbits in Australia
Adapted from: Clarke GM et al (2000).
Environmental Pest Species in Australia.
Internal report, Department of the
Environment and Heritage, Canberra.
Transects
The distribution of plants can be determined
by marking out a straight line across an area,
noting the types of plants present, and plotting
their position along this line on a diagram. This
indicates the distribution of plants along a crosssection of the ecosystem. This cross-section is
called a transect.
Transects
Georges River Environmental Education Centre http://www.georgesrive.schools.nsw.edu.au/Vegetation_study.htm
Abundance
Abundance is the number of individuals of the
same species within an area. Abundance is
usually found by taking
small samples of a
community and using
the data to estimate the
population in the
ecosystem as a whole.
Quadrats
The abundance of a plant species is often found
by marking out quadrats. Individuals within the
quadrats are counted and the average number
per area (density) is calculated. This information
can then be used to estimate the abundance in
the whole ecosystem. The more quadrats used,
the more accurate the estimate.
Quadrats
Capture – mark - recapture
This method of sampling involves:
 catching a number of individuals of a species
 marking or tagging them
 releasing them again
 at a later time catching another group and
counting the number of tagged individuals
among them
This method is useful for mobile populations.
Trends in population estimates
Variable that can influence population size over
time include,
 Birth rate
 Death rate
 Migration rate
 Environmental factors such as availability of
food, shelter and water, presence of predators
Photosynthesis
The initial source of energy in an ecosystem is
light from the sun. Some of the light absorbed by
plants is converted through photosynthesis into
chemical energy in the form of carbohydrates
such as glucose. Photosynthesis is summarised
as:
light
carbon dioxide + water
REACTANTS
glucose + oxygen
ENERGY
SOURCE
PRODUCTS
Respiration
Some of the glucose produced by
photosynthesis is broken down during the
process of respiration. Respiration can be
summarised as follows:
Glucose + oxygen
water + carbon + energy
dioxide
The energy produced during respiration is then
used for cellular processes.
Energy transfer in an ecosystem
Light energy
Converted into
carbohydrates
Chlorophyll
Photosynthesis
Glucose
Transported through the plant
Respiration
Energy for cell processes
Uses of energy by organisms
Living organisms need a constant supply of
energy to maintain cellular activities and stay
alive. In ecosystems the initial source of energy
is light from the sun. This is used by plants
during photosynthesis to produce carbohydrates.
Organisms (i.e. plants) that can manufacture their
own food from inorganic materials are called
autotrophs.
Producers and consumers
Green plants provide the entire input of energy
to an ecosystem and are called producers. When
animals (herbivores) eat plants, the
carbohydrates stored in plants are converted
back into glucose. The glucose is broken down
during respiration to provide the animal’s
energy requirements. Similarly, when carnivores
eat other animals, this chemical energy is
passed on.
Energy transfer in ecosystems
Eaten by
Plant
Converted
into other
substances
animal
Carbohydrates
digested to
glucose
Respiration
Energy for
animal cellular
process
Food chains and webs
Food chains show the flow of energy through
ecosystems.
PRODUCER
grass
FIRST ORDER
CONSUMER
wallaby
SECOND ORDER
CONSUMER
dingo
Trophic levels
Animals are consumers. An organism that feeds
on plants is a first-order consumer. An organism
that feeds on a first-order consumer is called a
second-order consumer, and so on. The level
occupied by a consumer in a food chain is
referred to as a feeding or TROPHIC level. Firstorder consumers occupy the first trophic level;
second-order consumers occupy the second
trophic level, and so on.
Food webs
The interrelationship between many food chains
is called a
food web.
Biomass
Biomass is an estimate of the amount of matter
in a given population of organisms. Biomass
for different trophic levels is compared in a
biomass pyramid. A biomass pyramid shows
how the quantity of matter in living things
changes along a food chain.
Biomass pyramid
The base of the pyramid
represents the matter in
producers. The next
level shows biomass of
1st order consumers
and so on.
Biomass pyramid
At each level in the pyramid biomass is smaller
than in the trophic level below. At each level
biomass is lost.
An energy pyramid shows the total energy in
trophic levels and how that energy is lost
along a food chain.
Energy pyramid
Decomposers
Organisms that use the organic matter of
dead plants and animals are called
decomposers. They release digestive enzymes
to break down organic matter and then absorb
the products of digestion. Decomposers include
fungi and bacteria. Decomposers do not fit
readily into one trophic level.
Competition for resources
Competition is a relationship in which two
organisms compete for a limited resource.
In the short term this results in a decrease in the
abundance of one of the species. In the long
term it can result in extinction of the less
successful species.
Competition for resources.
Competition is one pressure that influences the
evolution of organisms. For example,
competition is one of the factors that results in
organisms adapting to occupy distinct niches.
Adaptations
All organisms have adaptations that help them to
survive. Organisms that are adapted to their
environment are able to:
 obtain air, water, food and nutrients
 cope with physical conditions such as
temperature, light and heat
 defend themselves from their natural enemies
 reproduce
 respond to changes around them
Adaptations



Structural adaptations are the physical
characteristics of an organism (e.g., skin color,
shape, body covering).
Behavioral adaptations are the ways in which an
organism behaves.
Physiological adaptations are those that allow
an organism to perform certain biochemical
reactions (e.g., making venom, secreting slime,
being able to keep a constant body
temperature).