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CONCEPTUAL UFE SCIENCE
Ecology
DEFINITION OF ECOLOGY
Ecology is the science that deals in the interrelationships between organisms and
their environment. The environment contains physical factors and living factors.
THE ENVIRONMENT
Physical factors
The physical environment consists of the soil and rocks in the surroundiDp of the
organism. The light, heat and water in the surroundings are also part of the physical
environment.
living factoJs
The living environment consists ofall plants and animals nearby which interact
with the organism. This is a community. AJ] of the organisms of the same species withiB
the community constitute a population.
Energy in the environment
Prime., Consu.e...
(Insects)
Pri.e., Produce...
(Green Plants)
Figure B-1. The pyramid ofenergy in ecology.
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Food chains
All energy OD 1he surface of1he Earth is derived from the S1m. Photosynthesis
occurs in the primary producelS that are green plants. Primary consumers eat the plants.
PredatOR eat the primary consumers. The predatOR m secondary consmners. This
constitutes a food chain. There are higher levels of a food chain. There may be tertiary .
or quaternary consumers. In North America most food chains end with a predatory bird
such as"the eagle.
Flow of energy in the food chain
Energy in food chains always begins with the Sun. SUDlight is absorbed by green
plants. The green plant uses photosynthesis to trap solar energy and convert it to glucose.
The glucose molecule contains stored chemical energy.
The primary consumer eats the green plant and gains some of the energy from it.
The primary consumer is a herbivore because it eats the plants. Most of the energy in the
plant is lost when it is eaten.
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The secondary CODSlDDer eats the primary consumei'. It is a carnivore. The
carnivore obtains some of the energy stored in the anima) it eats but most ofthe stmed
energy is lost. thus, energy is lost as the food chain grows longer. In order to obtain the
maximum amount of energy stored by the originaJ producer pl8Dt, you have to eat the
plant dircctJy.
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Food webs
Food webs m more complicated than food chains because some CODSlDDers may
be eaten by several predators. This causes branches in food chains.
Figmc £-2.
DiasraJn of a food web.
Succession ofplants
Newly exposed rock will first be colonized by lichens. These are joined by small
plants like mosses and liverworts. After some soil begins to fmm, fems and grasses
move in. More soil fonns and then slnubs and pine 1n:eS begins to grow. The thickness
of the soil continues to increase. The sluubs and pine 1Jees are replaced by oak t=s,
beech trees and finally maple trees. In the temperate forests of the United States, the
climax vegetation win be maple trees. The sequence from bare rock to mature forest
takes about 100 years.
Table xm. Ecological succession.
Early (Pioneer) Plants
1.
Lichens
2.
3.
liverwortS and mosses
Ferns
Grasses and shrubs
Intermediate Plants
S.
PiDeuees
6.
Oaktrees
7. . Beech trees
Climax Forest Plants
4.
8.
Maple trees
Biomes
A biome is a collection ofmany commUDities which is characteri7al by the same
ofclimax vegetation. Terrestrial biomes are listed in Table XIV. 'The climax
vegetation is a botanical community. For example, the nortbeastem United States is in
the biome known as the Temperate Deciduous Forest. "Deciduous" means that the leaves
fall oft'tbe trees in the autumD.
fODD
The terrestrial biomes depend on climate. Tbe climate changes as you travel
toward the North Pole. It changes in a similar fashion as you 10 high up into the
mountains. Climates similar to Tundra and Taip are found on high mountaiDs.
The marine biome includes aU of the communities that are found in the ocean.
The types of Jiving things that are present in a Biven part of the marine biome depend on
the water temperature, availability offood BDd nutrients for the Bell life, and other factors.
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Table XIV. Terrestrial biomes.
Biome
T1Dldra
Taiga
Temperate Deciduous Forest
Grassland
Desert
Tropical Rain Forest
Climate
Very cold, JODS winters,
very sbon growing season,
onlY the tOPSOil thaws
Cold Winters, moderate growiDg
Vegetation
Lichens, mosses, gruses,
smalJ floweriDg pllDls
season (no
fir1nleS)
Deciduous trees
IDIDY
:PlantS
Mainly puses
Cold winters, hot summers., plentiful
Rainfall. long growing season
Cold winters, hot swnmers., DOt
EnouJdJ rainfaD to SUPIXB1 trees
Hot days, cool Digbls
very little ninfaU
Hot days all year Ions; fiequeDt,
Heavy rain, very humid
Conifers (pine, spruce and
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Plants adapted to IfOWin&
with little WIder
Plants with 1Iqe leaves
for heavy rainfall
MATERIAL CYCLES
Nature worlts in cycles. There are a nmnber ofcycles in the ecosystem that serve
to regenerate and renew materials for use by living thiDgs.
__._--r
IPhotosynthesls'
~ OXJgen
I __
ICombustion r
J
Carbon
Dioxide
andW.er
Figure E-1. The carboD-hydrogen-oxygen cycle.
IRespiration I
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The carbon-bydrogen-oxygen cycle
Photosynthesis by green plants releases oxygen into the atmosphere because
oxygen is the waste product ofphotosynthesis. Living things use oxygen for their
respiration and release water and carbon dioxide into the atmosphere. These materials
are thep used by the plants for more photosynthesis.
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The nitrogen cycle
Nitrates from the soil are absorbed by the green plants and are used to make plant
proteins. Animals make proteins from aminO acids derived from plant pro1eins. Dead
plant and animal tissue is decomposed by bacterial action. Other bacteria in the soil
transform nitrogen products to produce more soil nitrates for plants.
Eaten
Anlme.
Proteins
(p.ant Protelnsl
IAmmonlal
INltratesl
Nitrifying
Baeterle
o
Figure E-2. The Nitrogen cycle.
RELATIONSHIPS BETWEEN ORGANISMS
Between organisms oftbe same species there can be SexuaI contact, cooperation
and social organization, especially in a large population. Between different species, the
interactions are commenslliism, mu1IIlI1ism, parasitism and predotioli. All of these
interactiODS are fmms of symbioN.
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Symbiosis
"Symbiosis" means living together. The tenn does not indicate the nature of the
relationship. Life scientists prefer to use one ofthe other terms that give a more precise
indication of the relationship.
Commensalism
Commensalism is where one organism benefits but does DOt cause any harm to
the other. An example is Spanish Moss. ]t hangs from 1I'ees in Florida. ]t is Dot a
parasite; all it needs is a place to bang. ]t gets its water from the air.
Mutualism
In mutualism, a mutuaUy beneficial relationship exists where both partners
benefit. An example is the relationship between the legumes (beans, peas, clover, alfalfa)
and the nitrogen-fixing bacteria. The bacteria produce usable ni1rogen for the plant and
the plant gives them a place to live.
Termites eat wood that they cannot digest. There are bacteria and protozoa in
their digestive systeJils that can digest cellulose to produce glucose. The microorganisms
benefit because they have a place to live and a constant supply ofceUulose to digest. The
termites get the benefit from the glucose released from the cellulose by the bacteria and
protozoa.
A cow eats grass that it cannot digest. In the multichambered stomach of1be cow
are bacteria and protozoa that digest the cellulose for the cow. In return they let a place
to live and a food supply.
. Parasitism
In parasitism, the parasite benefits but the host" does not. Parasites are generally
internal. In the lower phyla of the animal kingdom, most sroups contain one or more
parasites ofvarious kinds. Parasites require the host for reproduction.
A predator is a free-living aDd feed on other organisms. Some, like lions, IdJl and
eat an entire organism. Others, like mosquitoes, take only 8 small part.