Download Human Decomposition Ecology

Organisms and their environment, including other
organisms
Ecology investigates:
Resource colonization
Resource decomposition and distribution
Competition
Succession
Reproduction and development
Production
6CO2 + 6H20  C6H1206 + 6O2
Decomposition
C6H1206 + 6O2  6CO2 + 6H20
Energy =
carbon (C)
Ultimately measured in kilocalories/calories
Nutrients =
nitrogen (N)
phosphorus (P)
potassium (K)
magnesium (Mg)
Several other elements and compounds
Autotroph
Acquires energy through
photosynthesis
Plants, algae
Heterotroph
zymogenous
autochthonous
Acquires energy through
eating
Humans, mammals, birds,
bacteria, fungi, insects,
etc.
Can be viewed from two perspectives:
1. Taxonomy: what is doing the decomposing?
2. Taphonomy: what processes are taking
place?
Most decomposition is biologically mediated
(minimum 80%)
Microorganisms (bacteria, fungi)
Insects (flies, beetles)
Scavengers
Catalysis—enzymatic and chemical reactions
transforming complex to simple.
Comminution—physical breakdown of
resource.
Leaching—soluble material moved by water
Resource Quality
Decomposer
Community
Physicochemical
environment
Physicochemical Environment
Four primary modulators of decomposition:
Moisture
Temperature
Aeration (oxygen, carbon dioxide)
pH
A high quality
resource
An ephemeral
resource
patch/disturbance
A source of water
A habitat for
microorganisms
carbon:nitrogen
Wood
145:1
Straw
100:1
Leaf litter
50:1
Manure
25:1
Stages of Decomposition
1. Fresh
2. Bloated
3. Active Decay
4. Advanced Decay
5. Skeleton
In reality:
Stages do not exist
Stage
characteristics can
blend from one
stage into another
Stages provide a
convenient means
for taphonomists to
assess
decomposition
• Autolysis starts: abiotic breakdown of cells and
tissues
• Associated with start of mortis 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.
The mortis triad
Algor mortis—body temperature changes to
ambient temperature
Rigor mortis—temporary stiffening of the joints
Livor mortis—settling and pooling of blood; blood
will become “fixed” after a period of time.
Gunn (2009)
Gunn (2009)
Fresh Stage (biological
changes)
Initial insect colonization (response to
chemical disturbance, i.e. presence of
corpse)
Release of ammonia, sulphuric acid, carbon
dioxide, nitrogen
Increased microbial activity (response to
physical disturbance)
Initial shift in bacterial and fungal community
structure (response to physical disturbance)
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
Bloat Stage Decomposition
• Enteric microbial community produces gases
(putrefaction)
• Purge fluids released from orifices: mouth,
nose, anus, etc.
• Buildup of gas can cause rupturing, fluids
released from ruptures in skin.
• Fly larvae (maggots) are active
Gunn (2009)
Bloated (biological
changes)
Maggot activity
Elevated microbial activity (CO2 respiration)
Shift in bacterial community structure
Bloated (chemical
changes)
Increased in gravesoil:
ammonium
calcium
chloride
fatty acids (butyric, propionic, valeric)
magnesium
organic N, ammonium, nitrate
phosphorus
potassium
sodium
sulphate
Active Decay
• Maggot activity at its peak
• Increased release of fluids
• Increased marbling, slippage of skin
• Exposure of internal organs
Active Decay (biological changes)
Peak insect activity
Death of associated vegetation (not
sure why)
Elevated microbial activity
Shift in bacterial community structure
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
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
changes)
Same as observed during bloated and
active decay.
Postputrefaction fungus
•
Skeleton Stage
Decomposition
Can persist from weeks to millenia
• Materials present: bone, teeth, hair, dried
skin
Gunn (2009)
Gunn (2009)
Time
Fresh
Gravesoil
Biology
Gravesoil
Chemistry
Bloated
Active Decay
Advanced
Decay
Skeleton
•Increased
microbial
activity,
biomass
•Succession of
fungi from early
phase to late
phase
•Shift in
bacterial
community
•Increased
amino acids,
nitrate,
ninhydrinreactive
nitrogen, total
nitrogen, total
phosphorus
•Decreased pH
•Initial
disturbance
•Increased
microbial
activity
•Shift in
bacterial and
fungal
community
structure
•Increased
microbial
activity
•Shift in
bacterial
community
structure
•Increased
microbial
activity,
biomass
•Shift in
bacterial
community
structure
•Declining
microbial
activity and
biomass
•early phase
postputrefactio
n fungi
•Shift in
bacterial
community
structure
•Initial
disturbance
•Increased
ammonium,
carbon dioxide,
nitrate,
phosphate
•Increased
ammonium,
butyric acid,
calcium,
chloride,
magnesium,
ninhydrinreactive N,
nitrate,
potassium,
phosphate,
propionic acid,
sodium,
sulphate,
valeric acid
•Increased pH
•See Bloated
•Increased lipid
phosphorus,
protease
activity,
phosphodiester
ase activity,
total nitrogen,
total
phosphorus
•See Bloated
•Increased
ammonium,
electrical
conductivity,
ninhydrinreactive
nitrogen, lipid
phosphorus,
total nitrogen,
total
phosphorus
Gunn A (2009) Essential Forensic Biology. WileyBlackwell.
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.