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Second Law of Thermodynamics (Law of Energy Degradation)
- in all conversions of heat energy to work, some of the energy is degraded to a
more dispersed & less useful form (usually heat); no conversion is 100%
- heat always flows spontaneously from hot to cold
- any system & its surroundings as a whole spontaneously tend toward increasing
randomness or disorder (entropy = measure of disorder or randomness)
Food Chain - sequence of transfers of energy in the form of food from organisms in one
trophic (feeding) level to organisms in another, when one eats or decomposes another
- only ~10% of the high quality chemical energy available at one trophic level can be
transferred to the next; this is known as the 10% Rule & is due to the 2nd Law of
Thermodynamics which states that in all conversions of heat energy to work, some of the
energy is degraded to a more dispersed & less useful form. So, the shorter the food chain,
the less loss of usable energy &, in addition, the biomass (total combined weight of any
group of organisms) decreases at higher trophic levels
Food Web - complex, interlocking series of food chains
Biogeochemical Cycles
hydrologic (water - hydrogen & oxygen).
gaseous (carbon, oxygen, nitrogen),
sedimentary (phosphorus, sulfur, etc.)
Hydrologic - water comes down to the Earth via precipitation. It then either enters the ground to
become groundwater or stays on the surface to become surface water. Either way it eventually
enters the oceans & lakes to be returned to the atmosphere via evaporation. Some of the water is
taken up by the plants, which in turn return the water through the process of transpiration
Carbon-Oxygen - carbon enters the atmosphere by respiration, volcanic eruptions, burning of
fossil fuels, etc. Plants use sunlight & incorporate the CO2 via photosynthesis into organic
molecules which are used as food by animals
Nitrogen - is found in the bodies of organisms as dissolved gas & dissolved organic matter.It is
bound with free oxygen or hydrogen into usable chemical forms by specialized organisms. It
enters the ocean through rivers & precipitation. After being assimilated by plants, the nitrogen is
recycled when animals eat them & excrete ammonium & urea
Phosphorus - is weathered from rock, washed into the rivers & ends up in the ocean. Plants
absorb it & when they are eaten it gets passed to the animals. Eventually it returns to the soil as
waste & decay products.
Sulfur - enters the atmosphere from natural sources ; returns to the Earth via precipitation where
it is taken up by plants & passed to the animals. Eventually it returns to the soil as waste & decay
products
Ecosystems are dynamic & not static systems; they are constantly changing
Ecological Niche - a species total structural & functional role in an ecosystem
- what a particular species does in the ecosystem & how it responds to &
modifies its biotic & abiotic environment
- do not confuse with habitat (location where an organism lives & grows)
- habitat & niche are analogous to address & occupation/life-style
Competitive Exclusion Principle - no 2 species in the same ecosystem can occupy exactly
the same ecological niche indefinitely
The number of “niche-spaces” available for a species in a particular ecosystem determines its
carrying capacity - maximum number of individuals of each species that can live in a particular
ecosystem
Ecological Succession - repeated replacement of one kind of natural community of
organisms with a different natural community over time
Primary Succession - ecological succession that begins on area that has never been
occupied by a community of organisms
Secondary Succession - ecological succession that begins on area that had been occupied
by a community of organisms
Biotic Potential - capacity of a species for reproducing itself (due to reproductive rate,
defense mechanisms, migration, etc.)
Environmental Resistance - combination of all factors that limit the survival of a species’
members (lack of food, water, habitat, predators, disease, etc.)
An example of the above is the predator-prey relationship
Ecosystems have Stability - ability of a living system to withstand or recover from
externally imposed changes or stresses
a) inertia stability (persistence) - ability of a living system to resist being disturbed
or altered
b) resilience stability - ability of a living system to restore its structure & function
to an original condition following a natural or human-induced stress, provided the
outside disturbance is not too drastic
Species Diversity - number of different species & their abundance in a given area; it affects
the inertia stability. high species diversity tends to increase long-term persistence. It
has more ways of responding to most environmental stresses.
(Exceptions: coastal salt marshes with low species diversity have high persistence;
rocky intertidal seashores with high species diversity have low persistence)
Range of Tolerance - range or span of conditions that must be maintained for an organism
to stay alive & grow, develop & function normally
Limiting Factor Principle or Law of Tolerance
- the existence growth, abundance or distribution of an organism can be determined by
whether the levels of one or more limiting factors go above or below the levels required by the
organism
In response to changing conditions or stress, organisms can:
1) migrate (move)
2) undergo readaptation (change)
3) become extinct (die)
Threshold Effect - phenomenon in which no effect is observed until a certain level or
concentration is attained
Speciation - splitting of a single species into two different species. It normally occurs when
a species’ population is distributed over many environments. It is a slow process &
normally requires 1000 generations
Biological Magnification - buildup in concentration of a substance in successively higher
trophic levels of the food chain or web
In dealing with ecosystems, we must remember:
1) interdependence
2) diversity
3) resilience
4) adaptability
5) limits