Transcript Ecology Part 3

Ecology Part 3
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.
These are 2 food chains
for two different
environments, terrestrial
and marine.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
The beginnings of pond succession. It
is barren with little vegetation.
50 yrs. the pond is bordered
by mature cottonwood trees.
2 yrs. the pond is ringed by vegetation
including cotton wood saplings.
150-200 yrs. the pond has become a
meadow, the pond is ringed by
vegetation.
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.
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.
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.
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
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.
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
GRASSLANDS
Where Found: interior of many continents
Plants: grasses and small leafy plants
Animals: grazers and browsers
Characteristics: Large variation in temperature and seasonal
changes. Grazing and prairie fires halts succession.
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
o
Characteristics: 200 – 400 cm rain, constant (25 C)
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
Nutrients are recycled into the ecosystem unlike energy. The
major nutrient cycles are water, carbon, nitrogen and phosphorus.
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.
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.
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.
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.
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.