Download Chapter 54 Ecosystem

Chapter 54 Ecosystem
I
Ecosystems, Energy and Matter
A. General Information
1. Ecosystems – all the organisms living in a community as
well as the abiotic factors with which they interact
2. Energy flow and chemical cycling are important in the
study of ecosystem
a. energy enters the system in the form of sunlight
and is converted to chemical energy by autotrophs
and is passed to heterotrophs in the form of food
and dissipated in the form of heat
b. chemical elements such as carbon and nitrogen are
cycled among abiotic and biotic components of the
ecosystems
B. Thermodynamics – the study of energy transformations
1. First Law of Thermodynamics – energy can be
transferred and transformed, but it cannot be created
or destroyed
2. Second Law of Thermodynamics – energy transfer or
transformation makes the universe more disordered
a. energy conversion can’t be efficient, some energy
is lost as heat
b. energy flowing through ecosystems is dissipated
into space as heat
II
Trophic Relationships – each ecosystem has a trophic
structure of feeding relationships that determine the paths
of energy flow and chemical cycling
A. Trophic Levels
1. Primary producers
2. Primary consumers
3. Secondary consumers
4. Tertiary consumers
5. Decomposers (detritivores)
a. prokaryotes, fungi, and animals that get their energy
from detritus
b. detritivores decompose the organic materials and transfer
the chemical elements in inorganic form to soil, water, and air
c. producers recycle the elements into organic compounds
III
Ecosystem energy budget
A. Global energy budget
1. most of the solar radiation is reflected, absorbed, or
scattered by the atmosphere, clouds, and dust
2. only a small amount of solar energy strikes plants
and algae
B. Gross and Primary Production
1.GPP - total primary production in an ecosystem , the
amount of light energy that is converted to
chemical energy by photosynthesis
2. Net primary production – is equal to gross primary
production minus the energy used by the primary
producers for respiration
a. accounts for the organic mass of plants and
represents storage of chemical energy available
for consumers
b. can be expressed as biomass
3. primary productivity varies among ecosystems
a. tropical rainforest are very productive and
contribute large portion to overall productivity
b. estuaries and coral reefs are also productive but make
only a small contribution to productivity
c. open oceans have low productivity but make the largest
contribution to ecosystems
d. deserts and tundra have low productivity
C. Limiting Factors in Aquatic ecosystem productivity
1. light intensity and temperature affect primary
productivity of phytoplankton in the open ocean
-productivity is highest near the surface and
decreases with depth
2. nutrient limitation – in open ocean water there is
low concentration of phosphorus and nitrogen in the
photic zone
3. marine phytoplankton is most productive where updwellings bring nutrient rich waters to the surface
4. freshwater ecosystem productivity varies from the surface
to the depths in relation to light intensity
-biannual turnovers bring nutrients to the surface waters
IV
Biogeochemical Cycles
A. Gen Information
1. Continuation of life depends on recycling of essential
chemical elements
2. Decomposition of wastes and the remains of dead
organisms replenishes the pool of inorganic nutrients
available to autotrophs
3. Biogeochemical cycles = nutrient circuits involving both
biotic and abiotic components of ecosystems
4. Elements such as carbon, oxygen, sulfur, and nitrogen
have gaseous forms, their cycles are global and the
atmosphere serves as a reservoir
a. characteristics that define reservoirs
1. whether they contain organic or inorganic materials
2. whether or not the materials are directly available
for use by organisms
b. available organic reservoirs contains living organisms
and detritus (available when organisms feed on each
other)
c. the unavailable organic reservoir is formed by
organisms that died ( coal, oil, and peat)
d. the available inorganic reservoirs includes all matter present
the soil or air and dissolved in water
B Types of geochemical cycles
1. Water Cycle – occurs between the oceans and the
atmosphere
a. solar energy results in evaporation from oceans
water vapor rises, cools, and falls as precipitation
c. over the oceans, evaporation exceeds precipitation
excess water vapor is moved over land by winds
d. over land, precipitation exceeds evaporation and
transpiration, runoff and ground water balance
the net flow of water vapor to land
e. the water cycle is primarily due to physical
processes, not chemical
b.
2. The Carbon Cycle – autotrophs acquire carbon dioxide
from the atmosphere by diffusion through leaf
stomata, some becomes a carbon source for
consumers, and respiration returns carbon dioxide to
the atmosphere
a. carbon loss by photosynthesis is balanced by carbon
release during respiration
b. atmospheric carbon dioxide is increased by
combustion of fossil fuel
c. the amount of atmospheric CO2 decreases in the
Northern Hemisphere during the summer due to
increased photosynthetic activity and increase in the
winter when respiration exceeds photosynthesis
3. The Nitrogen Cycle – nitrogen is the key chemical in
ecosystems; its found in all amino acids which
comprise the proteins of organisms
a. 80% of the atmosphere is made of N2, but it’s not
available to plants
b. nitrogen enters ecosystems by either atmospheric
deposition or nitrogen fixation
1. atmospheric deposition of nitrogen - NH4+ (ammonium)
and NO3 (nitrate) are added to the soil by being dissolved
in rain or by settling as part of fine dust
2. nitrogen fixation – the reduction of atmospheric
nitrogen to ammonia(NH3)which can be synthesize
nitrogenous organic compounds such as amino acids
a. only certain prokaryotes can fix nitrogen
1. terrestrial – some nonsymbiotic soil bacteria and
symbiotic (Rhizobium) soil bacteria
2. Cyanobacteria fix nitrogen in aquatic ecosystems
b. -NH3 is a gas and can evaporate quickly in the
atmosphere
-NH4 can be used directly by plants
c. the nitrogen cycle also involves
-nitrification – a metabolic process by which aerobic
soil bacteria use ammonium (NH4+ ) as an energy
source by oxidizing it to nitrite (NO2 ) and then to
nitrate (NO3- )
Plants assimilate nitrate and convert it to organic
forms of amino acids and proteins. Animals
assimilate organic nitrogen by eating plants and
other animals
- denitrification – process that returns nitrogen to the
atmosphere by converting NO3 to N2
-Ammonification – the decompositition of organic
nitrogen back to ammonia
Important aspects of the Nitrogen Cycle
1. Prokaryotes serve as vital links in the cycle
2. Most of the nitrogen cycling involves nitrogenous
compounds in the soil and water
3. Many species of plants depend on symbiotic , nitrogenfixing bacteria in their root nodules as a source of nitrogen
in a form that can be assimilated
4. Denitrification only return a small amount of Nitrogen
back to the atmosphere
5. Most assimilate nitrogen comes from nitrate
6. The majority of nitrogen in most ecosystem is recycled
by decomposition and reassimilation
4. The Phosphorous Cycle
-a major component of nucleic acids, phospholipids,
ATP, and a mineral in bone and teeth
-Phosphorous Cycle
a. weathering of rocks adds Phosphorous to the soil
b. producers absorbs the soil phosphate
c. phosphorous is transferred to consumers in organic
forms
d. phosphorous is added back to the soil by excretion
and decomposition of detritus
e. phosphorous may limit algal productivity in aquatic habitat