Ecosystems
Ecosystems
• The sum of all the
organisms living within
particular boundaries
and all the abiotic
factors with which they
interact
• Also encompass energy
flow and chemical cycling
• Transformations largely
occur via photosynthesis
and feeding relationships
Physical Laws
• Conservation of Energy
• 1st law of thermodynamics
• Energy cannot be created or destroyed, but only
transferred and transformed
• 2nd law of thermodynamics
• Every exchange of energy increases the entropy of
the universe (some energy is always lost as heat)
• Conservation of Mass
• Law of conservation of mass
• Matter cannot be created or destroyed
Energy, Mass, & Trophic
Levels • Autotrophs or primary
producers ultimately
support all other trophic
levels
• All other organisms in other
trophic levels are
heterotrophs and ultimately
depend on the autotrophs
• Consumers (primary,
secondary, tertiary, etc.) eat
plants, eat animals that eat
plants or eat other carnivores
that depend on plant eating
organisms
• Detritivores/decomposers are
also heterotrophs that depend
on dead material for nutrients
• Fungi and prokaryotes
Energy Budgets
• Primary production is the amount of light energy that is
converted to chemical energy by autotrophs during a
given period of time
• Primary producers will use light energy to create organic
molecules which eventually generate ATP
• Consumers then acquire their organic fuels via food webs
• The amount of all photosynthetic production sets the
spending limit for the entire ecosystem energy budget
Gross and Net Primary Production
• Gross Primary Production (GPP) is the amount of
light energy that is converted to chemical energy
by photosynthesis per unit time
• Net Primary Production (NPP) is equal to GPP
minus the energy used by the primary producers
for respiration (R) (NPP=GPP-R)
• NPP is generally considered more important because it
represents the stored chemical energy that will be
available to consumers
• NPP would be equal to the amount of NEW biomass of
photosynthetic autotrophs added in a given time rather
than the total biomass of an area
Primary Production in Aquatic
Ecosystems
• Light and nutrients are both
important limiting factors
• Depth of light penetration is important,
but is not as important as nutrients
• This is known because we see no
production gradient between the poles and
the tropics
• The limiting nutrient may vary between
different environments, often nitrogen or
phosphorous
• Limiting nutrient is the element that must
be increased for production to increase
• This is also important for upwelling areas
and areas of eutrophication or algal
blooms
Primary Production in Terrestrial
Ecosystems
• Temperature and moisture
are important limiting factors
in terrestrial ecosystems
• This plays a huge role in actual
evapotranspiration (the annual
amount of water transpired by
plants and evaporated from a
landscape)
• Increases with the amount of
precipitation in a region and the
amount of solar energy
available to drive transpiration
• Mineral nutrients can also be
limiting locally, often nitrogen
and phosphorous
Secondary Production
• The amount of
chemical energy in
consumers’ food that
is converted to their
own biomass during a
given time period
• Only a portion of that
which is consumed will
go to fuel an increase in
biomass
• Also used in completing
cellular respiration and
much is lost as heat
Efficiency
• Production efficiency=(net secondary
production x 100%)/assimilation of
primary production
• Net secondary production is the energy
stored in biomass represented by growth
and reproduction
• Assimilation consists of the total energy
taken in and used for growth,
reproduction, and respiration
• Production efficiency is the percentage
of energy stored in assimilated food that
is not used for respiration
• Vary from organism to organism
• Trophic efficiency is the percentage of
production transferred from one trophic
level to the next
• Will always be less than production
efficiencies
• Generally about 10%, but vary depending
on the ecosystem
Biogeochemical Cycles
• The recycling of nutrients
using biotic and abiotic
means
• There are both global and
local cycles
• Decomposers can play a
huge role in many of these
cycles
• The speed at which things
decompose in different
environments can play a
role at how long these
cycles take
• Disturbance can also have
an impact on the speed of
the cycles as well as
amounts that are available
to be actively cycled
Human Activities and Chemical
Cycles
• Human activities continue to
have a direct impact of
chemical cycling
• Nutrient enrichment – the
movement of nutrients from
one area to another
• Ex: food is grown in California,
but consumed here
• Agriculture – nutrient
enrichment issues related to
movement of crops as well as
use of fertilizers and run-off
• Run-off has led to
contamination of aquatic
ecosystems which leads to
algal blooms and
eutrophication
Human Activities and Chemical
Cycles
• Acid Precipitation – burning of many
fossil fuels leads to the release of
oxides (sulfur and nitrogen) into the
atmosphere that join with air to create
sulfuric and nitric acid
• This creates acid precipitation which
can lead to acid lakes and plant and
animal life die off
• Toxins – there are a variety of toxins
(often synthetic) that are released into
the environment daily
• Some of these toxins accumulate in fat
and other body tissues and
bioaccumulate. This can lead to
biomagnification of the food chain.
(PCBs and DDT
Human Activities and Chemical
Cycles
• Greenhouse gases and global warming
• The largest culprit today is seen as carbon
dioxide which continues to increase largely
as a result of the burning of fossil fuels
• Elevated CO2 levels may change the plant
composition of our planet because C3 plants
will be less limited by CO2 availability
• CO2 also has the ability to absorb more of
the solar radiation thus leading to increased
temperatures
• This increase in temperatures can have
far reaching effects including extreme
weather, shifts in climate, sea-level rise,
and potential mass extinction
Human Activities and Chemical
Cycles
• Depletion of atmospheric
ozone
• Destruction generally as a result
of CFCs (chemical used in
refrigeration and
manufacturing) in the
atmosphere
• Chlorine reacts with ozone,
reducing it to O2
• Decreased O3 leads to more UV
light reaching the Earth’s
surface
• This leads to an increase in
skin cancers, cataracts and
potential ill effects on plants
and phytoplankton related to
DNA damage