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.

Documents

Carter. Human Decomposition Ecology