Phys 102: Natural Systems

1
Phys 102 Natural Systems
Vincent Conrad
2
Introduction
Lecture 9
Phys 102 Natural Systems
Introduction

• Last Week
• Thermodynamics and the cycle of the lithosphere.
• Classification of oganisims.

• This week - use our knowledge of abiotic and
  biotic systems to look at
• Food Chains/Webs
• Trophic Levels
• Energy Flow and Ecosystems
• Food Pyramids
• Biogeochemical Cycling

Vincent Conrad
3
Food Chain
Lecture 9
Phys 102 Natural Systems
Food Chains

• The sequence of who eats who in an ecosystem is
  called a food chain.
• In a properly functioning ecosystem, there is no
  waste.
• All organisms (both dead and alive) are potential
  sources of food for other organisms.

Vincent Conrad
\beginmyslide1Food Chains
\beginitemize \item The sequence of who eats
who in an ecosystem is called a
\colordgreen food chain. \item In a
properly functioning ecosystem, there is no
waste. \item All organisms (both dead and
alive) are potential sources of food for
other organisms. \enditemize
\begincenter \includegraphicswidth0.9
\columnwidth,height!foodchain.eps\\
an example of a food chain
\endcenter \endmyslide
\
beginmyslide1Trophic Levels
\beginitemize \item Every organism can be
assigned to a \colordgreen trophic
level. \item The trophic (from the Greek word
\em trophos meaning nourishment) level
determines where in the food chain an organism
gets its nourishment. \item \colordgreen
Producers belong to the first trophic level.
\item Primary consumers belong to the second
trophic level, secondary consumers the third
trophic level etc... \item Detritivores are a
special class of consumer. They feed of
detritus materials from all trophic levels.
\enditemize \begincenter
\includegraphicswidth0.7 \columnwidth,height!
\endcenter \endmyslide

\beginmyslide1Food Webs
\beginitemize \item Simple food chains are
very rare in ecosystems. \item Most consumers
feed on several organisms and are fed on
themselves by several organisms higher up the
food chain. \item Most organisms are involved in
a complex network of interlinked feeding
relationships. \item This is called a
\colordgreen food web. \item Trophic levels
can also be assigned to food webs. \item It
should be noted that the food webs in the ocean
has the greatest number of trophic
levels. \item Food webs are a fundamental
component of any attempt to describe how
natural communities are structured or how
complexes of species interact. \enditemize
\begincenter \includegraphicswi
dth0.7 \columnwidth,height!
\endcenter \endmyslide
\
beginmyslide1Terrestrial Food Webs What
do the arrows represent? \begincenter
\includegraphicswidth0.7 \columnwidth,height!
40_07.eps \endcenter \endmyslide

\beginmyslide1Food Web with
Aquatic Components \begincenter
\includegraphicswidth0.6
\columnwidth,height!,angle90food-web.eps
\endcenter \endmyslide

\beginmyslide1Food Webs - in reality can
be very complex \begincenter
\includegraphicswidth0.8 \columnwidth,height!
image010.eps \endcenter \endmyslide

\beginmyslide1Magnification
of toxins \beginitemize \item Toxins
can be magnified by the food chain/web \item
When organisms feed, toxic and radioactive
substances are magnified in the food chain
\item This causes those organisms at higher
trophic levels to receive higher doses of the
substances. \item Many birds of prey became
threatened by consuming DDT, which decreased
calcium in the egg shell. As a result, eggs broke
and populations decreased rapidly in hawks,
owls, eagles, pelicans, etc. \item Mercury
poisoning is another example. Mercury levels are
found to be highest in sharks, which are at
the top of the food chain. \enditemize \endmy
slide
\beginmyslide1
Magnification of toxins
\begincenter \includegraphicswidth0.75
\columnwidth,height!we56.eps
\endcenter \endmyslide
\
beginmyslide1Energy Flow through
Ecosystems \beginitemize \item
Energy flow in ecosystems, as with all other
energy, must follow the two laws of
thermodynamics (From last weeks tutorial)
\beginitemize \item First law
energy is neither created nor destroyed, but
instead changes from one form to another (eg
potential to kinetic). \item The
second law mandates that when energy is
transformed from one form to another, some
usable/useful energy is lost as heat (the
exergy increases). Thus, in any food chain, some
(in fact a large proportion of) energy must
be lost as we move up the chain.
\enditemize \item Food chains/webs represent
the path of energy flow through an ecosystem.
As natural ecosystems have numerous
interconnected food chains, energy flow can
be very complex. \enditemize
\endmyslide
\beginmyslide
1Energy Flow through Ecosystems
\begincenter \includegraphicswidth0.8
\columnwidth,height!Fig56-7.eps
\endcenter \endmyslide

\beginmyslide1Energy Flow through
Ecosystems \sidebyside0.40.45
\beginflushleft \includegraphicswidth1.3
\columnwidth,height!0855al.eps
\endflushleft The greater number of
trophic levels is a food web/chain, the greater
the loss of usable high quality energy.
\beginitemize \item Between 5\ and 20\
of energy available from a trophic level is
passed to the next available level. \item On
average it is about 10\ \\\to \em the 10\
rule. Why? \beginitemize \item Some
plant material uneaten \item Some remains
undigested \item Some is respired to produce
energy to live and ends up as heat \item
Some herbivores die without being predated
\enditemize \enditemize \endmyslide

\beginmyslide1Food
Pyramids \beginitemize \item Food chains
and food webs can show the relationship between
organisms in a community but they do not give
any kind of indication of how many living
organisms are involved. \item Example it
takes a huge number of grass plants to produce
enough rabbits to support a single fox because
the amount of energy that is transferred
along a food chain rapidly decreases.
\item We can obtain a greater understanding of
the functioning of the ecosystem by using
graphs called \colordgreen Food Pyramids
\enditemize \endmyslide

\beginmyslide1Food Pyramids There are
two types of Food Pyramids. The first is
\colordgreen pyramid of numbers
\beginitemize \item Here the \em number of
organisms at each trophic level are shown. A
typical example is \begincenter
\includegraphicswidth0.35 \columnwidth,height!
pyramid_numbers2.eps \endcenter \item
If the producer was an oak tree, or a rose bush,
then the pyramid would look quite different.
The oak/rose only counts as one organism
\begincenter \includegraphicswidth0.35
\columnwidth,height!pyramid_numbers3.eps
\includegraphicswidth0.35\columnwidth,height
!pyramid_numbers4.eps \endcenter
\enditemize \endmyslide

\beginmyslide1Pyramids 2nd type of Food
Pyramid is \colordgreenpyramid of biomass
\beginitemize \item As pyramids of numbers
show number of organisms, and the size of
each organisms can vary, they do not show you the
amount of energy that is being transferred
from one trophic level to the next. \item
To show this the pyramid of biomass is used.
Biomass is the dry weight of of living
material that is available as potential food.
And thus the energy stored in that trophic
level. \item Do produce a pyramid of biomass
requires intensive effort Need to collect a
sample of organisms from each trophic level,
weigh them (strictly speaking we would then dry
at 100\degree C to get rid of the
water).Then multiply the mass by the number of
organisms in the whole community you are
studying. \item The pyramid of numbers for the
rose bush then becomes \enditemize
\begincenter \includegraphicswidth0.3
\columnwidth,height!pyramid_biomass1.eps
\endcenter \endmyslide
\
beginmyslide1Pyramids \beginitemize
\item The biomass of carnivores is significantly
less than the biomass mass of the
herbivores. \item The numbers of herbivores are
significantly less than producers the
numbers of carnivores are significantly less
than the numbers of herbivores. \item It is
very inefficient to eat just meat to get our
matter and energy because there is less
numbers of animals available. \item A greater
number of individuals can be supported if we
change our diets from a meat-eating society
to a plant-eating society. \enditemize
\begincenter \includegraphicswidth
0.6 \columnwidth,height!we28.eps
\endcenter \endmyslide
\
beginmyslide1Biomass Pyramids
\beginitemize \item Another example of how
biomass pyramids can change in different
ecosystems. \item An aquatic ecosystems, the
producers are microscopic phytoplankton.
\item These organisms can grow and reproduce
very rapidly. \item Thus a smaller total biomass
of phytoplankton can supply the primary
consumers, than with slow growing terrestrial
plants. \enditemize \begincenter
\includegraphicswidth0.6 \columnwidth,height
!biomass-p.eps \endcenter \endmyslide

\beginmyslide1Relative
productivity \beginitemize \item The
rate at which an ecosystem's producers cature and
store a given amount of energy as biomass is
a given amount of time is called the
ecosystem's \colordgreen Primary
Productivity. \item Ecologists cab
estimate the average annual productivity per
square meter of producers for ecosystems in the
different biomes. \item Though the size of
the size and prevalence of the ecosystem needs
to be taken into account. \item See page 96-98
in the Ecosystem reading. \enditemize
\endmyslide
\beginmysl
ide1Relative productivity
\vspace-7mm \begincenter
\includegraphicswidth0.8 \columnwidth,height!
product.eps \endcenter \endmyslide

\beginmyslide1Biogeochemical
Cycling \beginitemize \item The patterns
of cycling nutrients in the biosphere involves
metabolism by living organisms, as well as a
series of strictly abiotic chemical
reactions. \item Understanding the cycle of a
single element requires the knowledge of a
process that depends jointly on the biology of
all organisms that utilize the element, its
geological availability, and its organic and
inorganic chemistry. \item Understanding the
cycling of biologically important elements is
truly interdisciplinary in nature. \item We
generally call this process biogeochemical
cycling. \item Living organisms are tied to the
nonliving environment through the
Biogeochemical Cycles. \item Living organisms
require the availability of about 20 to 30
chemical elements for the various of metabolic
processes that take place in their bodies.
\enditemize \endmyslide
\b
eginmyslide1Biogeochemical Cycling
\beginitemize \item Some products that are
metabolized by organisms require relatively
few nutrients for their production. (example,
carbohydrates are photosynthesized from just
water and carbon dioxide.) \item Some
organic substances, like amino acids and
proteins, are more complex in their chemical
make up and therefore require a number of
different nutrients. \item The types of
nutrient needed by life is often categorized
into two groups \colordgreen
Macronutrients and \colordgreen
Micronutrients. \beginitemize \item
\colordgreen Macronutrients are required in
relatively large amounts. Examples are
carbon, oxygen, hydrogen, nitrogen and
phosphorus which each constitute more than 1 \
of dry weight of an organism. Sulfur,
chlorine, potassium, sodium, calcium,
magnesium, iron, and copper are macronutrients
that constitute 0.2 to 1 \ of dry organic
weight. \enditemize
\enditemize \endmyslide
\
beginmyslide1Biogeochemical Cycling
\beginitemize \item \beginitemize
\item \colordgreen Micronutrients are
elements that often constitute less than
0.2 \ of dry organic matter. They include
aluminum, boron, bromine, chromium, cobalt,
fluorine, gallium, iodine, manganese,
molybdenum, selenium, silicon, strontium,
tin, titanium, vanadium, and zinc.
\enditemize \item We will look at some of
the macronutrient cycles. These are driven
either directly or indirectly by the sun and
gravity. The cycles we will examine are
\beginitemize \item Carbon (C) Cycle
\item Nitrogen (N) Cycle \item Oxygen (O)
Cycle \item Phosphorus (P) Cycle \item
Sulfur (S) Cycle (Micronutrient)
\enditemize \enditemize \endmyslide

\beginmyslide1A
Generalized Cycle \begincenter
\includegraphicswidth0.6 \columnwidth,height!
nutrientcycling.eps \endcenter \endmyslide

\beginmyslide1Carbon
Cycle \beginitemize \item All life is
based on the element carbon. \item Carbon is
the major chemical constituent of most organic
matter, from fossil fuels to the complex
molecules (fats proteins, DNA and RNA) that
control genetic reproduction in organisms.
\item By weight, carbon is not one of the most
abundant elements within the Earth's crust.
The lithosphere is only 0.032 \ carbon by
weight while oxygen and silicon make up 45.2 \
and 29.4 \ of the Earth's surface rocks.
\item Ecosystems gain most of their carbon
dioxide from the atmosphere. (Remember that
CO_2 is 0.03\ of the atm by vol. is also
dissolved in water) \enditemize
\endmyslide
\beginmyslide
1Carbon Cylcle \beginitemize \item
Autotrophic organisms \colordgreenabsorb
CO_2 to produce carbohydrates via
photosynthesis. Organic matter produced in
plants is passed down to heterotrophic animals
through consumption. \item Carbon is
\colordgreenreleased from ecosystems as
carbon dioxide gas by the process of
respiration. \item Respiration takes place in
both plants and animals and involves the
breakdown of carbon-based organic molecules into
carbon dioxide gas and other compounds as by
products. \item The detritus food chain
contains a number of organisms whose primary
ecological role is the decomposition of organic
matter into its abiotic components.
\enditemize \endmyslide

\beginmyslide1Carbon Cylcle
\begincenter \includegraphicswidth0.8
\columnwidth,height!carboncycle.eps
\endcenter \endmyslide
\be
ginmyslide1Carbon Cylcle
\beginitemize \item Carbon dioxide is
\colordgreenabsorbed by the waters of the
ocean by simple diffusion. \item In seawater,
the \cdiox can remain as is, or can be converted
into carbonate (CO_3-2) or bicarbonate
(HCO_3-). \item Ocean organisms
biologically fix bicarbonate with calcium
(Ca2) to produce calcium carbonate
(CaCO_3). \item This is used to produce
shells, skeletons, coral, etc... \item The
organisms die, shells and body parts sink to the
ocean floor where they accumulate as
carbonate-rich deposits. \item After long
periods of time, these deposits are physically
and chemically altered into sedimentary
rocks. \item Limestone (CaCO_3) found in
sedimentary rock is the largest reservoir for
carbon. \item Oceans are the 2nd largest
reservoir. \enditemize \endmyslide

\beginmyslide1Carbon Cylcle
\begincenter \includegraphicswid
th0.9 \columnwidth,height!carboncycle2.
eps \endcenter \endmyslide

\beginmyslide1Carbon Cycle and Global
Temperature \beginitemize \item The
quantity of \cdiox found in the atmosphere has
been steadily decreasing over the last
several billion years. \item Researchers
theorized that this change is in response to an
increase in the sun's output over the same time
period. \item Higher levels of \cdiox meant the
Earth's temperature was slightly higher than
today. \item This allowed for the flourishing
of plant life despite the lower output of
solar radiation due to the green house effect.
\item As the sun grew more intense, several
biological mechanisms gradually locked some
of the atmospheric carbon dioxide into fossil
fuels and sedimentary rock. \item Thus the
Earth's global average temperature essentially
constant over time. \item This regulating
process has kept the Earth's global average
temperature essentially constant over time. (more
evidence for Gaia hypothesis??)
\enditemize \endmyslide

\beginmyslide1Human
Impact on the Carbon Cycle \beginitemize
\item Since the 1950s humans have greatly
increased the quantity of carbon dioxide found
in the Earth's atmosphere and oceans. \item In
the early 1700s \cdiox was 275 parts per million
(ppm) to just over 365 PPM today. (see graph
lectures 3 \ 4) \item Scientists estimate that
future atmospheric levels of carbon dioxide
could reach an amount between 450 to 600 PPM by
2100. \item Sources are fossil fuel combustion
(65 \ of \cdiox) and the modification of
natural plant cover found in grassland,
woodland, and forested ecosystems (35
\). \item Researchers have shown that natural
ecosystems can store between 20 to 100 times
more carbon dioxide than agricultural land-use
types. \enditemize \endmyslide

\beginmyslide1Nitrogen Cycle
\beginitemize \item Nitrogen is used by
living organisms to produce a number of
complex organic molecules like amino acids,
proteins, and nucleic acids. \item The
complete nitrogen cycle is very complex!! \item
The largest store of nitrogen is found in the
atmosphere (78 \ of atm is N_2 gas) but
this cannot be absorbed by organisms
directly. \item This is because most plants
can only take up nitrogen in two solid forms
ammonium ion (NH_4) and the ion nitrate
(NO_3-). \item Most plants obtain the
nitrogen they need as inorganic nitrate from
the soil. Ammonium is used less by plants for
uptake because in large concentrations it is
extremely toxic. \item The conversion of
atmospheric N_2 into NH_4 and NO_3-
is carried out by certain kinds of bacteria and
is called \colordgreen nitrogen
fixation. \enditemize \endmyslide

\beginmyslide1Nitrogen
Cycle \beginitemize \item Nitrogen
fixation is carried out by \beginitemize
\item Cyanobacteria which live in soil
\item The bacteria rhizobium which lives in the
nodules (small swellings of the roots of
legumes (such as peas beans alfalfa etc)
\enditemize \item Nitrate is very
soluble, easily lost from soil by leaching.
Can be returned to oceans where it can be
returned to the atmosphere by
denitrification. \item Animals receive the
required nitrogen they need for metabolism,
growth, and reproduction by the consumption of
living or dead organic matter containing
molecules composed partially of nitrogen.
\enditemize \begincenter
\includegraphicswidth0.22 \columnwidth,height!,
angle90alder8s.eps \includegraphicswid
th0.37\columnwidth,height!nodules.eps \\
examples of nodules \endcenter \endmysli
de
\beginmyslide1Nitro
gen Cycle \beginitemize \item
\colordgreenAmmonification N is also added
to the soil from animal biomass and manures.
This detritus materials containing N is
broken down by specialised decomposer bacteria.
It enters the soils as ammonia ammonium ions
(NH_4) or atmosphere as gas (NH_4).
This recycles large amounts of nitrogen to
the soil. \item Lightning also plays a
role in N fixation. It causes chemical
reactions that result in solid nitrate compounds
entering the soil through precipitation.
\item \colordgreen Denitrification is
carried out by bacteria that get the oxygen
they need for metabolism from nitrates (rather
than O_2) under anaerobic (O_2 free)
conditions. They convert NO_3- into N_2
or nitrous oxide (N_2O) gas. Both of these
gases then diffuse into the atmosphere.
\enditemize \endmyslide

\beginmyslide1Nitrogen Cycle
\vspace-5mm \begincenter
\includegraphicswidth0.8 \columnwidth,height!
nitrogen.eps \endcenter \endmyslide

\beginmyslide1Nitrogen
Cycle The activities of humans have severely
altered the nitrogen cycle. Some of the major
processes involved in this alteration
include \beginitemize \item Application of
nitrogen fertilizers to crops has caused
increased rates of denitrification and leaching
of nitrate into groundwater. This also comes
from discharge of treated and untreated sewage
and livestock waste. When this excess supply of
nutrients reaches rivers/lakes it can stimulate
rapid growth of algae and other aquatic
plants. \item Large quantities of nitric oxide
(NO) are released into the atm when wood or any
fuel is burned. (NO forms when O and N are
combined at high temps.) NO O_2 \to
NO_2 H_2O \to HNO_3 (nitric acid).
This is one components of acid rain, kills trees
and fish. \item Burning grasslands and clearing
forests removes nitrogen from the soil as well
as producing nitrogen oxides into the
atmosphere. \enditemize \endmyslide

\beginmyslide1Oxygen Cycle
\begincenter \includegraphicswidth0.
7 \columnwidth,height!oxy-cycle.eps
\endcenter \endmyslide
\
beginmyslide1Phosphorus Cycle
\beginitemize \item Phosphorus is essential
for the body's energy transport molecules and
for holding DNA and RNA molecules together.
\item It is used in living organisms as phosphate
ions (PO_43- and HPO_42-) \item The
phosphorous cycle is an example a cycle that does
not have a gas as part of its cycle. Bacteria
are also far less important than in the N
cycle. \item Phosphate are only slightly
soluble in water. Thus often only small
amounts in the soil \to can be a limiting
factor in plant growth. \item Phosphorus
released from breakdown/weathering of phosphate
rock deposits. Carried by water through soil and
is taken up by plants. phosphate particles can
also be carried by wind. \item Animals get
phosphorus from eating producers or primary
consumers. \item By decomposing animal
waste/biomass, producers return P to the
soil. \item Finally through leaching P can end up
in oceans and via sedimentation forms new
phosphate rock deposits. \enditemize \endmys
lide
\beginmyslide1Phos
phorus Cycle \vspace-5mm
\begincenter \includegraphicswidth0.65
\columnwidth,height!phosphoruscycle.eps
\endcenter \endmyslide

\beginmyslide1Phosphorus Cycle There are
two main ways we intervene in the phosphorus
cycle \beginitemize \item Mining large
quantities of phosphate rocks. This is to
produce commercial fertilizers and
detergents. \item Heavy uses of
fertilizers in crop farming can cause large
amounts of phosphates in the runoff water. This
can also come from animal wastes. \item
Since phosphorus is a limiting growth factor, as
with nitrates and ammonium ions, excesses
supply may cause explosive growth of algae
and other kinds of plants that live in water.
\enditemize \endmyslide
\
beginmyslide1Sulphur Cycle
\beginitemize \item The S cycle involves many
physical, chemical and biological agents.
\item S is essential in proteins and vitamins in
organisms. \item Most of the Earth's sulphur
exists in underground rocks. \item It enters
the atm from three main sources
\beginitemize \item Hydrogen sulfide
(H_2S). A poisonous gas with a rotten egg
smell. Comes from active volcanoes and the decay
of organic matter in swamps tidal flats by
anaerobic decomposers. \item Sulphur dioxide
(SO_2) a colourless suffocating gas from
active volcanoes. \item Particles of sulfate
(SO_42-) salts such as ammonium
sulphate, from sea spray. \enditemize
\enditemize \endmyslide

\beginmyslide1Sulphur Cycle
\beginitemize \item Circulates from rocks
deep under the ocean sediment. \item
Sedimentation of organic matter forms fossil fuel
deposits containing S. \item This also
produces sulphates in the soil which are taken up
by plants. \item The action of microorganisms
releases the sulphates in the soil via reduced
sulphur (H_2S). \item In the atm SO_42-
O_2 \to SO_3 (sulphur trioxide) H_2O
\to H_2SO_4 (sulphuric acid) \item
Sulphuric acid is a component of acid rain,
killing trees and fish. \item We intervene in
a major way! About 1/3 of all sulphur compounds
reaching the atm come from human activities.
(99\ SO_2 entering atm from human
activities!) \enditemize \endmyslide

\beginmyslide1Sulphur Cycle
\begincenter \includegraphicswi
dth0.8 \columnwidth,height!ESwe34.eps
\endcenter \endmyslide
\be
ginmyslide1Temperature Regulation
\sidebyside0.40.45 \beginflushleft
\includegraphicswidth1 \columnwidth,height!
we35.eps \endflushleft
\beginitemize \item Dimethyl sulfide (DMS)
produced by oceanic phytoplankton \item It may
provide feedback to regulate global climate
\item It helps form more clouds. \item
Climate warmer \to more DMS \to more clouds
blocking sunlight \to lowering surface
temperatures. \item Was one of initial
precesses that inspired Lovelock's Gaia
Theory of the self regulating earth.
\enditemize \endmyslide

\beginmyslide1Next week
\beginitemize \item Will put the reading for
next week on the web site. So check that
towards the end of the week. \item May be from
the reader, of maybe readings from web sites.
\enditemize \endmyslide

http//www.agen.ufl.edu/chyn/age2062/lect/le
ct.htm
\beginmyslide1
\sidebyside0.40.45
\beginflushleft \includegraphicswidth
1.2 \columnwidth,height!
\endflushleft \beginitemize
\item \enditemize \endmyslide

\beginmyslide1
\beginitemize \item \enditemize
\begincenter \includegraphicswidth
0.7 \columnwidth,height!
\endcenter \endmyslide

\enddocument Local Variables mode
latex TeX-master t End
4
Trophic Levels
Lecture 9
Phys 102 Natural Systems
Trophic Levels

• Every organism can be assigned to a trophic
  level.
• The trophic (from the Greek word trophos
  meaning nourishment) level determines where in
  the food chain an organism gets its nourishment
• The first trophic level is occupied by producers.
• The second trophic level is the primary
  consumers, secondary consumers the third trophic
  level etc...
• Detritivores are a special class of consumer.
  They feed of detritus materials from all trophic
  levels.

Vincent Conrad
5
Food Webs
Lecture 9
Phys 102 Natural Systems
Food Webs

• Simple food chains are very rare in ecosystems.
• Most consumers feed on several organisms and are
  fed on themselves by several organisms higher up
  the food chain.
• Most organisms are involved in a complex network
  of interlinked feeding relationships.

• This is called a food web.
• Trophic levels can also be assigned to food webs.
• Oceanic food webs have the highest number of
  trophic levels.
• Food webs are a fundamental component of any
  attempt to describe how natural communities are
  structured or how complexes of species interact.

Vincent Conrad
6
Food Webs
Lecture 9
Phys 102 Natural Systems
Food Webs
What do the arrows represent?
Food webs can get complex very quickly.
Vincent Conrad
7
Magnification of Toxins
Lecture 9
Phys 102 Natural Systems
Magnification of Toxins

• Toxins can be magnified by the food chain/web
• When organisms feed, toxic and radioactive
  substances are magnified in the food chain.
• This causes those organisms at higher trophic
  levels to receive higher doses of the substances.
  
• Many birds of prey became threatened by consuming
  DDT, which decreases calcium in the egg shell. As
  a result, eggs broke and populations decreased
  rapidly in hawks, owls, eagles, pelicans, etc.
• Mercury poisoning is another example. Mercury
  levels are found to be highest in sharks, which
  are at the top of the food chain.

Toxin magnification effects humans too.
Vincent Conrad
8
Magnification of Toxins
Lecture 9
Phys 102 Natural Systems
Magnification of Toxins

• Toxin magnification effects humans too.
• From 1953 to 1957 the british government carried
  out atom bomb tests in Australia.
• Most of the scientific community encouraged the
  testing, but not Hedley Marston
• Under threat from ASIO he fought to make the
  public aware of the widespread nuclear fall out
  from the tests.
• By analysing cows organs he proved Strontium
  levels across the continent were being magnified.
• The education dept. had a policy at the time of a
  glass of milk everyday for school children.
• Documents which became available in 2001 show
  increased Strontium in the bones of 20 000
  (mostly childrens) corpses collected in secret
  from 1957-1979.

Marston then went on to show radiation was being
circulated around the globe from the nuclear
powers tests. His work lead to the global
nuclear testing bans imposed in the 1980s.
Vincent Conrad
9
Energy Flow Through Ecosystems
Lecture 9
Phys 102 Natural Systems
Energy Flow Through Ecosystems

• Energy flow in ecosystems, as with all other
  energy, must follow thelaws of thermodynamics.
• First law energy is neither created nor
  destroyed, but instead changes from one form to
  another (eg potential to kinetic).
• The second law mandates that when energy is
  transformed from one form to another, some
  usable/useful energy is lost as heat (the exergy
  increases). Thus, in any food chain, some (in
  fact a large proportion of) energy must be lost
  as we move up the chain.

• Food chains/webs represent the path of energy
  flow through an ecosystem. As natural ecosystems
  have numerous interconnected food chains, energy
  flow can be very complex.

Vincent Conrad
10
Energy Flow Through Ecosystems
Lecture 9
Phys 102 Natural Systems
Energy Flow Through Ecosystems

• The greater number of trophic levels is a food
  web/chain, the greater the loss of usable high
  quality energy.
• Between 5 and 20 of energy available from a
  trophic level is passed to the next available
  level.
• On average it is about 10 Why?
• Some plant material uneaten
• Some remains undigested
• Some is respired to produce energy to live and
  ends up as heat
• Some herbivores die without being predated

Vincent Conrad
11
Food Pyramids
Lecture 9
Phys 102 Natural Systems
Food Pyramids

• Food chains and food webs can show the
  relationship between organisms in a community but
  they do not give any kind of indication of how
  many living organisms are involved.
• Example it takes a huge number of grass plants
  to produce enough rabbits to support a single fox
  because the amount of energy that is transferred
  along a food chain rapidly decreases.
• We can obtain a greater understanding of the
  functioning of the ecosystem by using graphs
  called Food Pyramids

Vincent Conrad
12
Food Pyramids
Lecture 9
Phys 102 Natural Systems
Food Pyramids
There are two types of Food Pyramids. pyramid
of numbers Here the number of organisms at each
trophic level are shown.
If the producer was an oak tree, or a rose bush,
then the pyramid would look quite different. The
oak/rose only counts as one organism
Vincent Conrad
13
Food Pyramids
Lecture 9
Phys 102 Natural Systems
Food Pyramids

• pyramid of biomass
• As pyramids of numbers show number of organisms,
  and the size of each organisms can vary, they do
  not show you the amount of energy that is being
  transferred from one trophic level to the next.
• To show this the pyramid of biomass is used.
  Biomass is the dry weight of living material that
  is available as potential food. And thus the
  energy stored in that trophic level.
• This takes a lot of work though.

• Need to collect a sample of organisms from each
  trophic level
• Weigh them (strictly speaking have to dry them
  first).
• Multiply the mass by the number of organisms in
  the whole community.

Vincent Conrad
14
Food Pyramids
Lecture 9
Phys 102 Natural Systems
Food Pyramids

• The biomass of carnivores is significantly less
  than the biomass mass of the herbivores.
• The numbers of herbivores are significantly less
  than producers the numbers of carnivores are
  significantly less than the numbers of
  herbivores.
• It is very inefficient to eat just meat to get
  our matter and energy because there is less
  numbers of animals available.
• A greater number of individuals can be supported
  if we change our diets from a meat-eating society
  to a plant-eating society.

Vincent Conrad
15
Food Pyramids
Lecture 9
Phys 102 Natural Systems
Food Pyramids

• Another example of how biomass pyramids can
  change in different ecosystems.
• An aquatic ecosystems, the producers are
  microscopic
• phytoplankton.
• These organisms can grow and reproduce very
  rapidly.
• Thus a smaller total biomass of phytoplankton can
  supply the
• primary consumers, than with slow growing
  terrestrial plants.

Vincent Conrad
16
Relative Productivity
Lecture 9
Phys 102 Natural Systems
Relative Productivity

• The rate at which an ecosystem's producers
  capture and store a given amount of energy as
  biomass in a given amount of time is called the
  ecosystem's primary productivity.

• Ecologists can estimate the average annual
  productivity per square meter of producers for
  ecosystems in the different biomes.
• Though the size and prevalence of the ecosystem
  needs to be taken into account.

Vincent Conrad
17
Phys 102 Natural Systems
Vincent Conrad