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Human Decomposition Ecology

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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 Heterotroph zymogenous Acquires energy through autochthonous photosynthesis Acquires energy through Plants, algae 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 Physicochemical Community environment Physicochemical Environment Four primary modulators of decomposition: Moisture Temperature Aeration (oxygen, carbon dioxide) pH A high quality carbon:nitrogen resource Wood 145:1 Straw 100:1 An ephemeral Leaf litter 50:1 resource Manure 25:1 patch/disturbance A source of water A habitat for microorganisms Stages of Decomposition In reality: 1. Fresh Stages do not exist 2. Bloated Stage 3. Active Decay characteristics can 4. Advanced Decay blend from one stage into another 5. Skeleton 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 Increase in gravesoil atmospheric + • ammonium (NH4 ) • carbon dioxide - • nitrate (NO3 ) (CO ) 2 • phosphorus (P) • methane (CH ) 4 • soil pH • hydrogen sulfide (H2S) • nitrogen (N2) • ammonia (NH3) 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 Advanced Fresh Bloated Active Decay Skeleton Decay •Declining •Increased •Initial microbial microbial disturbance •Increased •Increased activity and activity, •Increased microbial microbial biomass biomass microbial activity, activity •early phase •Succession of Gravesoil activity biomass •Shift in postputrefactio fungi from early •Shift in •Shift in Biology bacterial n fungi phase to late bacterial and bacterial community •Shift in phase fungal community structure bacterial •Shift in community structure community bacterial structure structure community •Increased ammonium, butyric acid, •See Bloated calcium, •See Bloated •Increased •Increased chloride, •Increased lipid ammonium, •Initial amino acids, magnesium, phosphorus, electrical disturbance nitrate, ninhydrin- protease conductivity, •Increased ninhydrin- Gravesoil reactive N, activity, ninhydrin- ammonium, reactive nitrate, phosphodiester reactive Chemistry carbon dioxide, nitrogen, total potassium, ase activity, nitrogen, lipid nitrate, nitrogen, total phosphate, total nitrogen, phosphorus, phosphate phosphorus propionic acid, total total nitrogen, •Decreased pH sodium, phosphorus total sulphate, phosphorus valeric acid •Increased pH 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..
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