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7/30/2019 Carter. Human Decomposition Ecology
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Organisms and their environment, including other
organisms
Ecology investigates:Resource colonization
Resource decomposition and distribution
Competition
Succession
Reproduction and development
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6CO2 + 6H20 C6H1206 + 6O2
C6H1206 + 6O2 6CO2 + 6H20
Production
Decomposition
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Energy =
carbon (C)
Ultimately measured in kilocalories/calories
Nutrients =
nitrogen (N)
phosphorus (P)
potassium (K)
magnesium (Mg)
Several other elements and compounds
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Autotroph
Acquires energy throughphotosynthesis
Plants, algae
Heterotroph
zymogenous
autochthonous
Acquires energy through
eating
Humans, mammals, birds,
bacteria, fungi, insects,
etc.
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Can be viewed from two perspectives:
1. Taxonomy: what is doing the decomposing?
2. Taphonomy: what processes are takingplace?
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Most decomposition is biologically mediated
(minimum 80%)
Microorganisms (bacteria, fungi)
Insects (flies, beetles)
Scavengers
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Catalysisenzymatic and chemical reactions
transforming complex to simple.
Comminutionphysical breakdown of
resource.
Leachingsoluble material moved by water
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Resource Quality
Decomposer
CommunityPhysicochemical
environment
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Physicochemical Environment
Four primary modulators of decomposition:
Moisture
TemperatureAeration (oxygen, carbon dioxide)
pH
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A high quality
resource
An ephemeralresource
patch/disturbance
A source of waterA habitat for
microorganisms
carbon:nitrogen
Wood 145:1
Straw 100:1
Leaf litter 50:1
Manure 25:1
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Stages of Decomposition
1. Fresh
2. Bloated
3. Active Decay
4. Advanced Decay
5. Skeleton
In reality:
Stages do not exist
Stage
characteristics canblend from one
stage into another
Stages provide a
convenient meansfor taphonomists to
assess
decomposition
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Autolysis starts: abiotic breakdown of cells and
tissues
Associated with start ofmortis triad
Little release of fluids and disturbance of
surroundings
Flies first colonize: looking for place to lay eggs.
If too cold: microbes and scavengers dominate
If outside: vegetation and soil surface covered.
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The mortis triad
Algor mortisbody temperature changes to
ambient temperature
Rigor mortistemporary stiffening of the joints
Livor mortissettling and pooling of blood; blood
will become fixed after a period of time.
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Gunn (2009)
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Gunn (2009)
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Fresh Stage (biological
changes)
Initial insect colonization (response tochemical disturbance, i.e. presence ofcorpse)
Release of ammonia, sulphuric acid, carbondioxide, nitrogen
Increased microbial activity (response tophysical disturbance)
Initial shift in bacterial and fungal communitystructure (response to physical disturbance)
F h St ( h i l
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Fresh Stage (chemical
changes) Increase in
atmospheric
carbon dioxide
(CO2) methane (CH4)
hydrogen sulfide
(H2S)
nitrogen (N2) ammonia (NH3)
Increase in gravesoil
ammonium (NH4+)
nitrate (NO3-)
phosphorus (P)
soil pH
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Bloat Stage Decomposition
Enteric microbial community produces gases(putrefaction)
Purge fluids released from orifices: mouth,nose, anus, etc.
Buildup of gas can cause rupturing, fluidsreleased from ruptures in skin.
Fly larvae (maggots) are active
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Gunn (2009)
Bl t d (bi l i l
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Bloated (biological
changes)
Maggot activity
Elevated microbial activity (CO2 respiration)
Shift in bacterial community structure
Bl t d ( h i l
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Bloated (chemical
changes)Increased in gravesoil:
ammonium
calcium
chloridefatty acids (butyric, propionic, valeric)
magnesium
organic N, ammonium, nitrate
phosphorus
potassium
sodium
sulphate
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Active Decay
Maggot activity at its peak
Increased release of fluids
Increased marbling, slippage of skin
Exposure of internal organs
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A ti D (bi l i l h )
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Active Decay (biological changes)
Peak insect activity
Death of associated vegetation (not
sure why)
Elevated microbial activity
Shift in bacterial community structure
A ti D ( h i l
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Active Decay (chemical
changes)Same elevated concentrations as observed in
the bloated stage.
Increased:
Lipid phosphorus
Enzyme activity
Protease activity
Phosphodiesterase activity
Total nitrogen
Total phosphorus
Ad d D (bi l i l
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Advanced Decay (biological
changes)
Maggots have migrated.
Corpse comprises skin, organs, hair and
bone.
Declining microbial biomass and activity, but
still greater than non-gravesoil.
Fruiting of postputrefaction fungi.
Shift in bacterial community structure.
Advanced Decay (chemical
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Advanced Decay (chemical
changes)Same as observed during bloated and
active decay.
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Postputrefaction fungus
Skeleton Stage
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Skeleton Stage
Decomposition Can persist from weeks to millenia
Materials present: bone, teeth, hair, dried
skin
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Gunn (2009)
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Gunn (2009)
Time
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Fresh Bloated Active DecayAdvanced
DecaySkeleton
Gravesoil
Biology
Gravesoil
Chemistry
Initial
disturbance
Increased
microbial
activity
Shift in
bacterial and
fungal
community
structure
Increased
microbial
activity,
biomass
Shift in
bacterial
community
structure
Increasedmicrobial
activity
Shift in
bacterial
community
structure
Declining
microbial
activity andbiomass
early phase
postputrefactio
n fungi
Shift in
bacterial
community
structure
Increased
microbial
activity,biomass
Succession of
fungi from early
phase to late
phase
Shift in
bacterial
community
Initial
disturbanceIncreased
ammonium,
carbon dioxide,
nitrate,
phosphate
Increased
ammonium,
butyric acid,
calcium,
chloride,
magnesium,
ninhydrin-reactive N,
nitrate,
potassium,
phosphate,
propionic acid,
sodium,
sulphate,
valeric acid
Increased pH
See Bloated
Increased lipid
phosphorus,
proteaseactivity,
phosphodiester
ase activity,
total nitrogen,
total
phosphorus
See Bloated
Increased
ammonium,
electrical
conductivity,ninhydrin-
reactive
nitrogen, lipid
phosphorus,
total nitrogen,
total
phosphorus
Increased
amino acids,
nitrate,ninhydrin-
reactive
nitrogen, total
nitrogen, total
phosphorus
Decreased pH
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Gunn A (2009) Essential Forensic Biology. Wiley-
Blackwell.
Hopkins DW (2008) The role of soil organisms in
terrestrial decomposition. In: Tibbett M, Carter DO; Soil
Analysis in Forensic Taphonomy. CRC Press: 53-66.