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Ecology
Ecology is the study of how plants and animals interact with each other and their (nonliving) environment.
Biotic factors
living parts of the environment
e.g.
predation, bacteria
food availability,
competition
Abiotic factors
non-living parts of the environment
e.g.
rainfall,
temperature,
soil pH
Community – made up of all the different plants and animals in a given area (i.e. habitat).
Energy is the basis of every community. Of course, the origin of all energy is the sun.
The soil depends on organic matter for minerals (e.g. decomposing plants or animals)
An ecosystem consists of all the organisms in a community and the non-living part of the
environment and their interaction.
Many individuals
of same species
=
Population
+
Population of
other species
=
Community
+
=
ECOSYSTEM
Non-living part of
the environment
The environment is the surroundings of an organism and everything that influences it
The habitat is where an organism usually lives
The population is the number of single species in a given area.
All ecosystems contain:
producers (green plants)
consumers (animals)
decomposers (bacteria / fungi)
Energy flow in an ecosystem
The source of all energy in an ecosystem is the sun. Energy from the sun is trapped in
chlorophyll in green plants to produce carbohydrates (e.g. glucose) in the process of
photosynthesis.
The carbohydrates produced provide a source of energy for animals. A lot of energy is lost
to the environment by transfer of one species to another.
Therefore, the flow of energy in an ecosystem is always linear (i.e. degrades progressively)
but the flow of matter is cyclic (i.e. re-occurs).
Matter within an ecosystem
The material for living organisms is derived from the soil, rock and the atmosphere. It has a
limit. It is recycled by the process of growth and decay. Therefore, the flow of matter is
cyclic.
Cycles
Materials are continuously exchanged between the earth and the space surrounding it. The
exchanges occur in cycles between organisms and the physical environment.
For example, oxygen, carbon dioxide, water and minerals are all exchanged between
organisms as well as the environment. These are constantly absorbed by organisms and
replaced by natural processes such as photosynthesis, excretion, respiration and
decomposition.
The losses = the replacements – so it is all balanced.
Recycling in an ecosystem
CONSUMERS
(animals)
die
eaten
light energy
die
PRODUCERS
(green plants)
DECOMPOSERS
(bacteria, fungi)
decomposition
water and minerals
Food chains
-
SOIL
(minerals and humus)
series of eaters and things that are eaten
summarises the feeding relationship between organisms
begins with a green plant (producer)
ends with a carnivore
arrow shows flow of energy – it points to the eater
Generalisation food chain
Green plant →
die
Herbivore
die
→
Carnivore
die
→
Top carnivore
die and decompose (by saprophytes)
Sapprophytes
live on dead decaying organic matter (e.g. bacteria / fungi)
they break down decaying matter into ammonium compounds
There are rarely more than 5 stages in a food chain because energy is lost at each stage.
The energy transfer from producer to herbivore is low because we do not have the enzymes
to break down xylem (fibre) and cellulose.
Food webs are a series of interlocking food chains. The disruption of any one chain can
effect the whole food web.
Pyramid diagrams - used to represent feeding relationships. The sun is the ultimate source
of energy. All plants are the basic food supply for all animals – directly or indirectly.
(a)
Pyramid of numbers
Problems
-
scale is unmanageable
accuracy of the count at each trophic level is not accurate
many eat more than one food source
Example:
1 sparrow hawk
4 birds
100’s of invertebrates
100’s of green leaves
relative number
(b)
Pyramid of biomass
dry-mass at each trophic level
water variable
dry the organism / sample in oven at 100ºC
biomass – biological material – more likely to indicate energy at each
trophic level
energy lost by:
Advantages
-
energy
respiration
movement
heat
conversion into mass
(So, obviously, energy loss can be reduced by
keeping at warm temperature and also
restricting the movement of some of the
animals)
manageable scale
efficiency of energy transfer between trophic level can be calculated
energy wasted at each level can be seen
gives more information: indicates energy present
Disadvantages
sampling is destructive (sample has to be dead)
all organisms contain dead material that would not be eaten
not actually energy (but an estimate)