Ecology Part 3

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Ecology Part 3
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Food chain is the sequence of organisms including
producers (autotrophs), primary consumers
(herbivores), secondary consumer, (herbivore
eating carnivores), tertiary consumers (carnivore
eating carnivores), and decomposers, through
which energy and materials may move in a
community. In most communities the food chain
are called trophic levels.
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These are 2 food chains for two different
environments, terrestrial and marine.
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In most communities the food chains are
completely intertwined to form a food web. The
direction of the arrow indicates the movement of
energy and material.
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The successive levels of food and energy in the
food chains are called trophic levels. The
producers constitute the first trophic level, and

the primary consumers, the second and so on.
Since many species eat a varied diet, trophic
levels are not hard-and-fast categories. At each
trophic level there is a loss of energy from the
system. Only a small percentage of the energy
at one trophic level is available for the next.
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Less than 10 of the energy can make it from
level to the next. There are reasons why only
10 of the energy can move from one level to the
next.
1. Lack of complete consumer harvest of available
biomass. 2. The inability to assimilate all
that is consumed. 3. Loss of energy due to
dissipation of heat energy. 4. Energy used for
growth and reproduction.
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This is represented by the pyramid of
productivity with the producers at the base and
the last consumer at the top. Usually producers
are engage in photosynthesis but includes
chemosynthesis. In general only 10 of the
energy from one level can move to a successive
level. The right is showing the flow of energy.

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The pyramid of productivity is the basis that a
pyramid of biomass exists. In general the
decrease of energy at each successive trophic
level means that less biomass can be supported at
each level. Hence the total mass of carnivores
in a given community is almost always less than
the total mass of herbivores. However the size,
growth rate, and longevity of the species at
various trophic levels are important determining
factors.
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Because of the energy flow, in general moving
from the producers to the tertiary consumers,
there is a decrease in biomass. However in
certain aquatic ecosystems this is not the case
because the reproduction of the algae occurs at a
fast rate, and consumed at a fast rate. In
addition it has a small size.
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The pyramid of productivity and the pyramid of
biomass support the pyramid of numbers. This is
because in general, carnivores are larger than
the herbivorous prey . Since total biomass tends
to decline at successive trophic levels, it
follows the number of individuals must decline at
each level (except decomposer which outnumber
all other groups combined).
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Gross primary productivity is the ability of
producers to fix or convert carbon dioxide into
organic material. Consumers reduce gross primary
productivity by consuming the producers.
Producers also reduce gross primary productivity
because they also engage in cellular respiration.
Net primary productivity is the amount of
organic material that is produced beyond what is
needed by the living organisms in an ecosystem.
A dominant species in an ecosystem are species
which are present in the greatest numbers or
greatest biomass. A keystone species is one that
exert an important species that can exert an
effect on regulating other in a community.
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Sea otters are considered to be a keystone
predator species. Sea otters prey on sea
urchins. Sea urchins eat kelp. Where sea otters
are plentiful, sea urchins are rare and kelp beds
are plentiful. Where sea otters are population
is low, sea urchins are plentiful and kelp beds
are almost absent.
Whales in the last 20 years have been preying on
sea otters, this has increased the sea urchin
population and decreased the kelp beds off the
coast of western Alaska.
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Foundation species are species that exert their
effect by changing their environment profoundly.
Ex. Beavers can profoundly change the environment
by damming a creek or river.
Species diversity refers to the different number
of species in a given area. One should also
looks at relative numbers of each species as
well. This factor is called species richness. In
general, the greater the species diversity of an
ecosystem, the more stable the ecosystem. An
ecosystem with fewer species may be more
susceptible to damage from some sort of
disturbance, however it may recover quickly. An
ecosystem with more species may be more stable
and less resistant to change from a disturbance,
however it may be more difficult for the
ecosystem to recover when a serious disturbance
does occur.
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While both of these ecosystems have the same
number of species of trees, the first community
is more stable because of the relative number of
individual trees is almost equal unlike the
second community where one species dominates.
This first community is described as having
species richness.
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Succession is the process of change in which
one community of organisms replaces another. This
happens after some sort of change- volcano, fire,
tornado, etc has disturbed the environment. As
each community is established, the environment is
modified and change making it possible for
another community to become establish.
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Primary succession begins with bare rock or sand
and involves first the building of soil. Once
organisms colonize an area, they change it so
that other organisms may follow. Examples
include what happens after a volcano erupts or
glacier retreats.
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Primary succession begins with bare rock or sand
and involves first the building of soil. Once
organisms colonize an area, they change it so
that other organisms may follow. e.g.The first
organisms to colonize the area may be mosses and
lichens. These plants may produce acids as a
waste produce to break down rocks in the
formation of soil.
Once soil formation is begun, ferns may come in
and colonized the area. Its rhizoids helping to
form more soil, and as they die and decompose,
the soil may become more rich suitable for
different types of organisms. It is easy to see
that organisms can change the environment they
interact with.
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Another example of succession is that found in a
pond. First the pond is barren but then the
aquatic plants die and sediments begin to fill in
and begins to be ringed by vegetation.
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2 yrs. the pond is ringed by vegetation including
cotton wood saplings.
The beginnings of pond succession. It is barren
with little vegetation.
150-200 yrs. the pond has become a meadow, the
pond is ringed by vegetation.
50 yrs. the pond is bordered by mature cottonwood
trees.
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Secondary succession- Soil is present and occurs
at a much more rapid rate. Can be the result of
fire, tornados, floods and other like events.
Examples abandoned crop lands, unused rail roads
etc.
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Ecological succession may lead to a stable
community of plants and animals called the climax
community. Catastrophic events (hurricanes,
volcanoes, fires, etc.) may disturb a climax
community, causing the process of succession to
occur again. A biome is an environment that has a
characteristic climax community. The earth has
two main types of biomes, land biomes and aquatic
biomes.
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Most land biomes are named for their climax
community or dominant type of plant life. The
major types of biomes are the tundra, taiga,
temperate deciduous forest, grassland, tropical
rain forest, and desert.
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TUNDRA Where Found northern North America,
Europe, Asia Plants mosses, lichens, grasses, a
few stunted trees Animals caribou, reindeer,
wolves Other Characteristics permafrost
creates freezing and thawing cycle
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TAIGA Where Found most of Canada and Asia
Plants pine trees Animals bears, wolves,
moose, elk, voles, wolverines, Characteristics
long and cold winter, summers completely thaws
the soil.
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TEMPERATE DECIDUOUS FOREST Where Found southern
Canada, eastern U.S., Europe, and
Japan Plants trees that lose their leaves (oak,
maple, birch) Animals huge variety, including
fox, deer, moose, etc. Characteristics lands
cleared by hunting and farming
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GRASSLANDS Where Found interior of many
continents Plants grasses and small leafy
plants Animals grazers and browsers Characterist
ics Large variation in temperature and seasonal
changes. Grazing and prairie fires halts
succession.
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TROPICAL RAIN FORESTS Where Found South
America, S.E. Asia, Central Africa,
Central America Plants rich vegetation in
canopy and undergrowth Animals colorful
insects, lizards, amphibians, reptiles,
small mammals Characteristics 200 400 cm
rain, constant (25o C)
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DESERTS Where Found northern Africa, southern
Asia, central Australia Plants cactus
and other non-leafy plants Animals lizards,
small rodents Other Characteristics very little
rainfall, although some deserts have
seasonal rain
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Nutrients are recycled into the ecosystem unlike
energy. The major nutrient cycles are water,
carbon, nitrogen and phosphorus.
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In the carbon cycle, carbon is recycled mainly
through the process of photosynthesis, cellular
respiration and burning of fossil fuels.
In the carbon cycle, carbon is recycled mainly
through the process of photosynthesis, cellular
respiration and burning of fossil fuels. Carbon
dioxide (CO2) and carbon monoxide emissions have
been increasing and increasing in the atmosphere.
It allows light energy in but traps the
reflected heat energy in atmosphere so that it
does not go back into space. It causes global
warming.
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Nitrogen used for proteins and nucleic acids.
The air is over 75 N2, but this nitrogen can not
be used because of its triple bond. N2 is broken
down by bacteria into NH4 (ammonia), then NO2
(nitrite) and finally NO3 (nitrate). Plant roots
absorb this NH4, NO2 or NO3 and then make amino
acids and then proteins. Animals get their
nitrogen from eating plants or other animals.
Nitrogen also gets into the soil when man uses
fertilizers made from factories. Nitrification
is the process of putting N2 into the ecosystem.
Another way to get nitrogen into the ecosystem is
through decaying organisms and wastes.
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Plants absorb water through their roots. Land
animals absorb water from their food or drink it.
Aquatic animals are bathed in it. Water gets
into the atmosphere from cellular respiration,
transpiration and evaporation from the oceans.
Water vapor condensing will result in
precipitation (rain or snow). The excess
nitrogen and sulfur in the air (pollution)
combines with the water. This results in acid
rain. This leech minerals from the soil killing
plants.
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The phosphate cycle is the one nutrient that does
not have an atmospheric component. It cycles
through the soil and water. The main source of
phosphorous is the weathering of rocks.
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There are times when unwanted chemicals
accumulate in organisms through the food chain.
In the 1960's, cities sprayed with DDT, a
chemical to get rid mosquitoes. This chemical
accumulated in the lakes. It found It found its
way into the aquatic plants. Fish ate the plants
and DDT accumulated in the fish. Eagles ate the
fish. DDT accumulated in the eagles. It
affected their eggs as the shells were not hard.
The chicks would not hatch. As a result, eagles
became endangered. This process is called
biological magnification.
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