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Ecology
Ecology – Greek = oikos meaning home and logos meaning study
Define – You MUST use the definitions in the syllabus and give examples of;
Ecology
ecosystems populations community species
habitat
Food chain
trophic level food web
autotroph
heterotroph carnivore
Detritivore (detritus) saprophyte (saprotroph)
herbivore
omnivore
producer
decomposer chemoautotroph
consumer
decomposer
**Check syllabus
• be able to draw three food chains, each with four organisms in them – specific names→ grass,
tree and bird won’t work
• construct a food web with 10 organisms (bacteria can act as an Autotroph, heterotroph and
detritivore
food web is better as it shows more links more realistic, the more links, the more stable – WHY
trophic level - position in food chain determined by number of energy transfers - as not all
animals stay in one category like a bear is a herbivore but will eat meat if.. Organisms can be both
primary and secondary consumers
V
W
X
Y
Z
Make sure you know which way the arrows are going and the flow detritivore (decomposers)
and detritus not shown on chains
Detritivore – organisms that feed on the detritus (wastes) and decomposing organic material of
living organisms. Eg. dung beetle
Saprotrophs or decomposers – organisms that feed on dead organisms and products of living
organism. They secrete enzymes…. Extracellular digestion so they do not ingest whole food but
absorb. Eg. bacteria and fungi. * Extremely vital for the recycling of nutrients
Discuss the pyramids of biomass, pyramid of numbers and energy.
Energy is lost as you go up the food chain or pyramid. Energy transformations are not 100%
efficient. (Discuss the transducers and what energy changes and laws of thermodynamics) 1020% energy transfers per transfer. Rest is used for; catching animal – cellular respiration, not
eating all parts, heat energy etc.
More efficient to eat grass but culture dictates ?.
This is why food chains are rarely more than four links long and why the pyramid of energy is the
shape it is.
Note units for pyramid are J/m2/yr or J m-2 yr-1 or kJ m-2 yr-1 Discuss
Biological Amplification – higher tropic levels are a good indication of problems in the
ecosystem
•Light is the main, initial source for almost all communities. Remind about photosynthesis.
Chemosynthesis is rare
How energy enters and leaves a community = sunlight → light energy → chemical energy →
consumers energy lost to decomposers and as heat may stay in the community but not eaten.
Energy is NOT recycled. Remember your second law of thermodynamics – energy cannot be
created or destroyed – but is changed into an unusable form. – heat (which is more disorganised)
Principle of allocation – each organism has a limited amount of energy that can be allotted to
obtaining food, escaping from predators growing, repair, reproducing etc. Energy expended on
homeostasis can not be used on other activities. (winter animals live on the edge)
Greenhouse Effect
Energy drives all biotic and abiotic cycles. Energy does NOT recycles. It is changed into a form
that is not useable to life and radiated off.
Albedo – describes the ability to reflect, snow albedo is high, cloud cover and dust from
volcanoes have a high albedo as can reflect light back to earth. A cloudy evening is warmer
than a clear night, which is why desert is cold at night.
Organisms withdraw elements form the environment in order to build and maintain cells. Six
elements are responsible for over 95% of the mass of all living things –carbon, hydrogen, oxygen,
nitrogen, phosphorous and sulphur. The movement of these material through the biosphere is
termed their biogeochemical cycles. We will look at carbon in the form of carbon dioxide.
Carbon cycle – be able to draw, photosynthesis, respiration, fossilization, carbons are coming
from carbohydrates like glucose
CO2 in air
respiration
photosynthesis
C in animals
fossilization
feeding
combustion
C in plants
fossilization
Fossil fuels
CO2 taken in by plants is same as given off in respiration – direct correlation.
Fossil fuels are reservoir of energy-bearing organism, occurred when decay is slow and allowed
to accumulate, Saprophytes release CO2 into air. We can measure over time (CO2 trapped in
glaciers)
Increase in CO2 due to burning of fossil fuels and deforestation (30% increase in [CO2] since
1850 due to burning (before 1850 was 274/1000000 (ppm) and 1981 was 357 ppm)
The greenhouse effect – is a natural, normal phenomenon. We need it or else all the heat that is
“lost’ or radiated off would leave and the Earth would be too cold. Mechanism – Check text –
incoming waves are shorter waves of radiation. Reflect off the Earth and loss some energy and
re-radiated as a longer wave. A lot of this longer- lower energy wave can’t leave the atmosphere
due to greenhouse gases. And what are greenhouse gases you ask??? Methane, CO2, oxides of
nitrogen (NO2)
Problem – too much man made CO2. Note [CO2] will fluctuate normally with the seasons due to
different rates of photosynthesis
Pros – will increase photosynthesis and increase producers and first order consumers etc. Also
will increase temperature, which will increase reaction rates and increase metabolism.
“Under existing laws, most chemicals are considered innocent until proven guilty and estimating
their toxicity to establish guilt is difficult, uncertain and expensive” APES textbook.
Precautionary Principle – when there is reasonable but incomplete scientific evidence of
significant harm to humans or the environment from a proposed or existing chemical or
technology, we should take action to prevent or reduce the risk instead of waiting for more
conclusive evidence.
“some human induced changes can have catastrophic consequences so those responsible for the
change must prove it will cause no harm before proceeding – this is the reverse of historical
practices
SEE SYLLABUS
Eg. Fishing industry – science of how the ecosystem works and what affects it and how much
fishing is sustainable is still unclear. Precautionary principle – sharply reduce fish harvest and
close some over fished areas until they recover and we have more information about what levels
of fishing are sustainable.
Invasive species – Australia and New Zealand no longer assume that a potential invasive species
is innocent until proven guilty. Species not on an approved list are denied entry into the country.
NOTE – 5.2.5 Discuss
And 5.2.6
TEXT has very good questions – DO.
Increased rates of decomposition of detritus trapped in permafrost
Populations
Review definition of population
Change in population size is by the process of adding new members or subtracting  natality,
morality, immigration, emigration
Natality > mortality and immigration > emigration then – go through possibilities
Exponential growth rate – bacteria do fission every 20 minutes if factors are favorable. If
this continued for 11/2 days, there would b enough bacteria to form a layer one foot deep
over the entire Earth. But other organisms have slower potential like elephants that
produce a maximum of 6 kids/lifetime and a lifetime is 100 years. Even still, a single mating
pair could produce 19 million offspring in 750 years. What are the limits to this? We
know there is a struggle to survive.
Carrying capacity – maximum number of members of a species that an environment can hold. If
a population exceed it by overproduction  struggle for survival and factors will decrease the
size. These factors can be divided into two groups – density- dependent and density independent.
(like food, space, competition, emigration, disease)
Populations tend to overshoot or overproduce which leads to natural selection. Really, everything
related to natural selection – go though the requirements for it and relate.
Plot growth on graph giving sigmoid curve with an exponential growth phase, plateau phase and
transitional phase.
Be able to explain all;
During exponential phase - pop is increasing, natality rate is higher than mortality. The resources
needed by the population such as food and space are abundant and diseases and predators are rare.
Most offspring survive and live to reproduce.
Transitional phase- birth rate begins to decrease, natality is still larger than mortality but the
difference between them is slowing decreasing as resources start to decrease, wastes leading to
diseases and predation start to take hold.
Plateau phase -is reached as pop levels off, natality = mortality, resources become so low that no
further reproduction can take place
Carrying capacity reached –caused by limiting factors
Transitional phase is when the limiting factors start effecting growth
List some limiting factors – available resources, disease, space, predators
What is the Earth’s carrying capacity for us? Earth can support more herbivores than carnivores
(why)
Man’s exponential growth is the major reason for the degradation of the populations and biomes.
Due to lack of habitat, pollution, hunting, unstable food webs, monocultures, loss of species
diversity ….
Some great questions, data analysis in tiger book on whole ecology, greenhouse
and populations. They MUST be done.