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Ecology - Unit 2 - Change and Stability in Ecosystems
.
The focus of this unit is to understand the cycling of
organic substances within living things
Organic substances always contain atoms of carbon
and hydrogen as well as oxygen and nitrogen.
Matter that does not contain a combination of
carbon and hydrogen atoms is called inorganic.
To maintain life on Earth matter must be recycled
Decomposers break down complex organic molecules
into inorganic matter, which may be used by plants.
Plants reassemble these inorganic substances (also
called nutrients) to make food for themselves. In
turn, animals may eat the plants, continuing the cycle
of matter.
Copy Figure 3 page 51 into your notes.
2.2 Case Study of Pesticides
Pesticides are chemicals designed to kill pests. A pest is an
organism that people consider harmful or inconvenient, such
as weeds, insects or rodents.
Pesticides can be grouped into 4 different categories:
Type of Pesticide
Target
Example
Persistence
Insecticide
insects
DDT
high 2-15 years
Malathion
Herbicide
weeds
2,4-D
moderate 1-12 wks
low days to wks
Round Up
Fungicide
moulds and fungus
Captan
low days
Bactericides
Bacteria
Penicillin
low
Bioamplification – Pesticides that contain chlorine, like DDT,
are soluble in fat but not in water. As a result, these toxins
cannot be released in urine or sweat, so they accumulate in the
fatty tissues of animals. As primary consumers are eaten by
secondary consumers and these are in turn eaten by tertiary
consumers more and more toxins are consumed. The higher
the trophic level the greater the concentration of toxins. This
process is referred to as Bioamplification. Copy Figure 4 page
54 into your notes.
One of the animals most affected by bioamplification is
the Bald Eagle
- Pesticides are used to kill insects (DDT)
- DDT is washed into the lakes as rivers as runoff
- DDT is eaten by small insects and fish
- Larger fish feed on the insects and small fish
- Bald Eagles feed on the large fish
- Lifespan of a bald eagle is 25 years which helps increase the
amount of toxins consumed
- Result is that the toxins weaken the egg shell of the bald eagle
making them easily broken when the female
tries to incubate the eggs.
Fewer eggs survive = fewer bald eagles
2.5 The Carbon Cycle
Carbon is the key element for life on Earth
Carbon can be found in:
- atmosphere as carbon dioxide
- dissolved in ocean water as carbon dioxide and
bicarbonates
Each year 50 to 70 billion tonnes of carbon is
recycled by the process of Photosynthesis.
Plants use light to combine carbon dioxide from the
atmosphere and water, into more complex organic substances
in the process we call photosynthesis:
Carbon dioxide
+ water + light energy
sugar (glucose)
+ oxygen
Some organic carbon is released back into the environment by
cellular respiration as carbon dioxide.
Sugar (glucose) + Oxygen
Water
+ Carbon Dioxide +
Energy
Because photosynthesis and cellular respiration are
complementary processes, and because the carbon they use is
repeatedly cycled through both processes, this relationship is
often called the Carbon Cycle.
Reservoirs (pools) of Inorganic Carbon
- Storage areas of carbon not in an organic form
- The oceans (dissolved CO2)
- Earth’s Crust (limestone, bicarbonate)
- The atmosphere ( CO2)
- Industry and vehicles(gasoline)
- fossil fuels ( oil and natural gas)
-Reservoirs (pools) of Organic Carbon
-The bodies of living things – animals, bacteria + fungi, vegetation
- decomposing material in bogs ( peat moss)- litter and waste
Human impact on the Carbon Cycle
human industrialization has increased the amount of CO2 being
released into the atmosphere and at the same time decreasing
the reserve of organic carbon as we burn fossil fuels
The Carbon Cycle Game
Carbon Cycle Terminology
• Carbon Cycle – Movement of carbon atoms
through the environment
• Combustion – burning carbon based materials
(wood,gas,coal) to do work, releasing carbon
dioxide as a byproduct into the atmosphere
• Humification – changing organic matter that is too
complex to breakdown by bacteria and fungi,
becomes carbon in the soil
• Inorganic – molecules that are not of biological
origin (carbon dioxide, bicarbonates)
Carbon Cycle Terminology
• Organic – molecules that are biological in
origin(wood, leaves, sugars, starches)
• Organic matter – various molecules and pieces of
dead tissue that are biological in origin
• Photosynthesis – conversion of carbon dioxide
into sugars by plants using the sun as a source of
energy
• Respiration – conversion of sugars into carbon
dioxide to release energy used by organisms
2.6 The Nitrogen Cycle
Life depends on the cycling of nitrogen. Nitrogen atoms are needed so
that animals can make proteins like muscle and also DNA in cells.
Nitrogen that is moved through the air and soil is called the nitrogen
cycle
Nitrogen cycling in the air
- 79% of air is nitrogen
- atmospheric nitrogen is unusable by animals
- to be useful it must be turned into nitrates (NO3-)
- 2 methods can change atmospheric nitrogen into useful nitrates by
a process called nitrification
1) nitrogen fixation by lightening
2) nitrogen fixation by bacteria in soil
Nitrogen Cycling in the soil
- once the nitrogen has been fixed into the soil in the
form of nitrates it is then available to be used by plants
(natural fertilizer).
- Plants convert the nitrates into proteins
- Animals eat the nitrogen rich plants making more
proteins
- Animal either dies and decays or poops releasing
ammonia (NH3) into the soil
Nitrogen fixing bacteria then turn that ammonia back into
useful nitrates by a process called nitrification
Denitrification – at certain stages in the decaying process,
denitrifying bacteria can break down nitrates into nitrites
(NO2-), and then nitrites into nitrogen gas which eventually is
released back into the atmosphere.
Copy Figure 1 Page 66 into your notes
1.9 The Nitrogen Cycle Extension Activity
2.9 Monitoring Changes in Populations
Human population increase has had a major impact on the ecosystem and
the cycling of matter in the ecosystem.
Human population is increasing exponentially
Year
1650
1850
years
Population
Doubling Time
500 million
1 billion
200
1650
1850
1850
1930
1850
1 billion
2 billion
80 years
1930
1975
1930
2 billion
4 billion
45 years
1975
2014
1975
4 billion
8 billion
39 years
Changes in population size in a community occur when individuals are
added to or removed from a population
-
Natality – Births or number of offspring born in one year
- Mortality – deaths or the number of individuals of a species that die
in one year
- Immigration – number of individuals of a species moving into and
existing population
- Emigration – number of individuals of a species moving out of and
existing population
Population growth formula
Population growth = (births + immigration) – (deaths + emigrations)
Open populations are populations where all of the above
factors are allowed to occur
Closed populations are populations in which only natality
and mortality affect their population size
1.12 Case Study: Populations
2.10 Limits on Population Size
The maximum number of offspring that a species could produce , if
resources are unlimited is called biotic potential
Biotic potential is regulated by 4 factors:
1) birth potential – maximum # of offspring per
birth
2) capacity for survival – # of offspring that reach
reproductive age
3) procreation - # of times a species reproduces
each year
4) length of reproductive life – age of sexual maturity
and the number of years the individual can reproduce
Limiting Factors to Population
-
Abiotic factors:
O Amount of light
o
Temperature
o
Chemical environment
Biotic factors:
O
food
o
predators
o
disease and parasites
o
competition for resources
Carrying Capacity
The maximum number of individuals of a species that
can be supported indefinitely by an ecosystem.
The carrying capacity is determined by:
- the availability of water
- availability of food
If a species exceeds the carrying capacity of the
ecosystem poplations will decline.
Limits of Tolerance
There are 2 laws that control the survival and
reproduction of an organism
1) Law of Minimum – the nutrient in least
supply is the one that limits growth
2) Law of Tolerance – an organism can survive within
(tolerate) a certain range of an abiotic factor.
Above or below the limit it cannot survive
Factors that cause changes in population
Density Independent Factors – affect members of a population
regardless of population density (i.e. # of animals/area)
- flood
- fire
- pesticides
- change in climate or temperature
- loss of habitat
- drought
Density Dependent Factors – affect a population
because of the density of the population
-
food shortage
competion for mates
-
disease
-
introduction of an exotic species
-
increased predation
-
competion for water and other resources