Download Ecology 2

Ch.23 INTER-RELATIONSHIPS OF
ORGANISMS WITH EACH
OTHER AND WITH THEIR
ENVIRONMENT
Part II
Study after Field Study has been
completed
Ch. 27 Inter-relationship of organisms with
each other and with their environment
23.1 The syllabus
An understanding of the terms ‘biosphere',
'biome' and 'ecosystem'. The concept of
habitat and niche of an organism. A
general understanding of the interaction
of organisms with the abiotic and biotic
factors of the environment with reference
to ONE local habitat such as grassland, a
stream, a rocky shore, a mangrove and
an urban ecosystem.
Producers, consumers and
decomposers. Energy flow, food
chains, food webs and trophic Levels.
The pyramid of numbers, pyramid of
biomass and pyramid of energy. Water,
nitrogen and carbon cycles. (Names of
individual bacteria are NOT required.)
Predation, competition, commensalism,
mutualism and parasitism. A simple
account of ecological succession.
23.2 DEFINITIONS
What is an ecosystem?
An ecosystem is a functioning, interacting
system which consists of two main parts:
Biotic (living) components - these refer to
all the living organisms, e.g., plants and
animals.
Abiotic (non-living) components - these
refer to the physical environment, e.g.,
soil, climate, etc.
According to the size, ecosystems can be
classified as (starting from the biggest):
largest
smallest
biosphere ¾ biomes ¾ habitats ¾
microhabitats
e.g. the Earth,
a tropical rain forest,
a rocky shore,
a rock pool
Within each ecosystem, there are
populations made of different species and
23.4
Within a stable system, there are always
1 Energy flow
Energy flows from organism to
organism in the form of food and
is eventually lost as heat.
Nevertheless, there is constant
input of energy from the sun into
the ecosystem. This balances
the lost energy so that a stable
system is maintained.
2
Cycling of materials
Useful elements such as carbon
and nitrogen inside organisms
are mostly not lost from the
ecosystem when the organisms
respire, excrete or die. They are
recycled so that they can
become available again.
3
Interdependence of
organisms
Organisms within an
ecosystem develop special
relationships with each other.
Several major types of
relationships have been
identified , for example,
d ti
titi
t
4
Interactions between
physical factors and
organisms
The physical conditions affect
the organisms in the
ecosystem in many ways. On
the other hand, organisms
may affect the physical
i
ti
t
23.5 Ecological categories of
biotic components in a typical
ecosystem, e.g. rocky shore
Producers (autotrophs)
Producers are mainly green plants
which are able to produce their
own food through the process of
photosynthesis.
Consumers (heterotrophs)
Consumers are mainly animals which
obtain their food by eating plants or
other animals. They can be further
divided into several groups according to
their feeding habits:
(a) Herbivores - animals which only feed on
plants, e.g., chiton,
(b) Carnivores - animals which only feed on
herbivores, e.g., tiger, fox.
(c) Omnivores - animals which feed on
both plants and herbivores and
carnivores, e.g., man.
Decomposers
Decomposers are certain bacteria
and fungi their function is to
break down the dead bodies of
both plants and animals.
23.6 The trophic structure of a food
chain
23.7
Energy loss within food chains and food webs
Energy within organisms in a trophic
level can be lost by
• respiration
• excretion (not much in plants)
• death and
• predation by predators in the next
trophic feeders
from the members in that trophic level.
Energy losses from all trophic levels
Below is an energy flow diagram showing the losses
Members in a higher trophic level always
receive less energy as some of the energy
always leaves any trophic level:
(R for respiration; E for excretion & egestion
and D for death)
e.g.
ox
Æ
man
energy input in ox = 3060 kJ (p.a.)
energy input in man = 130 kJ (p.a.)
Energy loss from all trophic levels
Ecological pyramids
–graphical representation of a food
chain expressed
in terms of each trophic level’s
•number,
•biomass or
•total energy content
Ecological pyramid
Pyramid of number
(they can have any shape)
Pyramid of biomass
Pyramid of energy
Figures:
energy flow in kJ m-2 yr-1
(energy input)
A comparison of Ecological
pyramids
• pyramid of numbers
• pyramid of biomass
• pyramid of energy
NB. In nature, most carnivorous
consumers occupy a few trophic levels
in a food web so that it is difficult
to assign them to trophic levels.
Food web
Grasshoppers
lizards
earthworms
B
birds
C
hawks
grass
A
A: first trophic level進食層
B: second trophic level
C: third trophic level
D: fourth trophic level
D
pyramid of numbers
It is a bar diagram of numbers of
individuals in each trophic level
observed at any one time
Provided that each upper member
feeds on many lower ones, the
upper level must contain fewer
members than the lower one.
Drawbacks
1. All organisms are equated, regardless
of their sizes. For example, An oak tree
is counted as one individual in the
same way as an aphid.
2. The numbers of some individuals are
so great that it is impossible to
represent them accurately on the same
scale as other species in the food chain.
pyramid of biomass
It is a bar diagram which shows
the total amounts of dry masses
(of standing crops) of all the
organisms in each trophic level
at any one time.
Upper members’ total biomass
may be greater if
• they absorb calcium from the
sea water to build calcarious
shells or
• there is seasonal fluctuation of
biomass, e.g. much fewer algae
in winter while the algae feeders
can remain in greater number.
Drawbacks
1. It is almost impossible to
measure exactly the biomass of
all individuals in a population. A
small sample is normally taken
and measured. This sample may
not be representative of the
habitat studies.
2. The time at which a sample is
taken may affect the result.
Drawbacks
3. Weight for weight, two
species do not necessarily
have the same energy
content so that comparison
based on biomass may be
misleading, e.g. a crab may
be heavier than a fish bigger
in size but the crab’s weight
mainly comes from the shell
Drawbacks
4. The great importance
of soil bacteria in terms
of energy flow is not
obvious form their small
biomass.
pyramid of energy
It is a bar diagram with each
bar length (for each of the
trophic levels) drawn
proportional to the amount of
energy per unit area or
volume that flows through
each of the trophic levels in a
given time period
-2
-1
(in KJ m yr )
The pyramid’s shape must be
erect:
the lower level must contain a
greater energy content than the
upper one so that there can be
enough energy for flowing to the
upper level both for them to
build their bodies and for them
to lose.
Drawbacks
The energy data are very
difficult to obtain and it
requires combustion
(killing) of representative
sample organisms.
Advantages
1. It takes into account the rate
of production for the
members
2. The great importance of soil
bacteria in terms of energy
flow can be obviously shown.
3. The input of solar energy
can be added as an extra
rectangle at the base of a
Cycling of materials
Some elements are cycled through
organisms in an ecosystem many
times. The cycling elements such as
carbon and nitrogen, in their
elemental forms or in the form of
organic or inorganic compounds
flow from one stations to the next
and will eventually flow back to
these stations so that they are not
exhausted.
(However, solar energy cannot be
recycled in an ecosystem and must
The carbon cycle
Stations and the
input/output paths :
The carbon cycle
The carbon cycle
The nitrogen cycle
How nitrogen, in the form of nitrate, is added
to the soil :
N-cycle stations
How nitrogen, in the form of nitrate,
is removed from the soil
The nitrogen cycle
The five TYPES OF ECOLOGICAL RELATIONSHIP
SYMBIOSIS
–commensalism
–mutualism
–parasitism
predation
competition
(Symbiosis is where two different types of
organism live together in close
association.)
Ecological Succession生態繼位
A community is all the plants and
animals which occupy a particular
area. The individual populations
within the community interact with
one another.
The community is a constantly
changing dynamic unit, which
passes through a number of stages
from its origin (pioneer community)
to its climax. The transition from one
stage to the next is called
succession
Imagine an area of bare rock. The first
group of organisms capable of surviving
is the lichens. The mutualistic
relationship between an alga and a
fungus which makes up a lichen allows it
to survive in considerable drying out. As
the first organisms to bring about
colonization of a new area, the lichens
are called pioneers or the pioneer
community.
Mutualism in lichen (a fungus + alga)
The weathering of rocks produces sand or
soil, but in itself this is inadequate to
support other plants. With the
decomposing remains of any dead
lichens after many years, however,
sufficient fertilizers are made available
to support a community of small plants.
Mosses are typically the next stage in the
succession, followed by ferns.
With the continuing erosion of the rock
and the increasing amounts of organic
material available from these plants, a
thicker layer of soil is built up. This will
then support smaller flowering plants
such as grasses and, by turns, shrubs
and trees. Animals also come to live here.
The ultimate community is a
woodland.
The stable state thus formed
comprises a balanced equilibrium of
species with few, if any, new
varieties replacing those established.
This is called the climax community.
Within the climax community there is
normally a dominant plant and animal
species, or sometimes two or three
co-dominant species. The dominant
species is normally very prominent and
has the greatest biomass.
The succession described above, where
bare rock or some other barren terrain
荒廢苔原 is first colonized, is called
primary succession.
A typical primary succession on bare rock
lichen
mosses
ferns
grasses and other herbaceous plants
shrubs
trees
woodland of diversified organisms
(a stable climax community)
secondary succession
If, however, an area previously
supporting life is made barren,
the subsequent
recolonization is called
secondary succession.
Secondary succession occurs
after a forest fire or the clearing
of agricultural land.
Spores, seeds and organs of
vegetative propagation may
remain viable in the soil, and
there will be an influx of animals
and plants through dispersal
and migration from the
surrounding area. In these
circumstances the succession
will not begin with pioneer
species but with organisms from
subsequent successive stages.