2. Abiotic Factors and Physical Processes Flashcards
Biotic factors
living organisms found in an ecosystem
Abiotic factors
non-living organisms found in an ecosystem
Examples of biotic factors
Insects Root and fungal tunnelling Bacterial action Rodent gnawing Small carnivore damage Large carnivore damage Human modification
Examples of abiotic factors
Winnowing
Aggradation
How do insects and predators affect decomp?
In correct circumstances, maggots can reduce a body to bones within days
Cold weather slows maggot activity
Flies can being laying eggs within minutes of death occurring if access is not blocked
Predators cause loss of soft tissue and increased access for insects
How does scavenging impact remains?
Reduces soft tissue very quickly
Predators cause loss soft tissue and increased access for insects
Can damge bone (may not)
Depends on access
How does animal activity affect bone?
Can cause loss or damage to bone which mimics perimortem trauma
-8% spiral or green fractures caused by carnivore activity
-5% spiral or green fractures caused by trampling
Smaller species can cause up to 50% bone fracturing
Examples of canidae scavengers?
Domestic dogs Fox Wolf Coyote Jackal
Examples of felidae scavengers?
Domestic cat Lynx Lion Tiger Leapord
Examples of ursidae scavengers?
Brown/black/grizzly bears
Examples of hyaenidae scavengers?
Brown/spotted/striped hyaena
Properties of canid scavenging?
Feeding begins at face and neck
Moves to thorax (especially chest)
Upper extremities disarticulated from trunk
Lower extremities disarticulated from trunk
Finally trunk disarticulated and eaten
How does plant activity affect decomposition?
Roots can ‘etch’ the surface of bone since they secrete humic acid
Roots can perforate cortex causing mechanical damage as they grow
Roots may be attracted to dug area because soil is looser or due to decomposition process
Can stain the surface of bone brown(plant decomp) or green(algae)
Can move bones
Abiotic effects on decomposition
Physical/Chemical processes: temperature, humidity, oxygen, pH acid/alkali Winnowing/Aggrading: water, gravity Fracture patterns Post-depositional damage Burning/thermal effects
Examples of different climates
Hot and wet (fastest decomposition gets rid of soft tissue in 6/7 days)
Hot and dry
Cold and wet
Cold and try
How does weather affect decomposition?
Temperature/humidity affects insect activity
Cold slows bacterial reproduction and chemical proceses
Heat/high humidity speeds processes
Low humidity = mummification
Indoors/outdoors heat increases decomp of soft tissue
10 degree rise in temp doubles rate of chemical reactions
Define mummification
Mummification involves the transformation of a once-living body or tissue into a state of arrested decay
Define dessication
Removal of all water from tissues via heat, osmosis and evaporation
Requires warmth/cold and no predation
Dry conditions mean no putrefaction occurs
How do chemicals effect decomp?
Heavy metals can help to preserve tissue e.g. mercury, arsenic, lead and copper
Chelating agents can combine with heavy metals making them unavailable to bacteria e.g. sphagnum produced by moss in bogs
Define bone weathering
The process by which the original microscopic organic and inorganic components of bone are separated from each other and destroyed by physical and chemical agents operating on the bone either on the surface or within the soil zone
e.g. loss of collagen and hydroxyapatite
What are Behrensmeyer’s 5 stages of bone weathering?
Stage 0 - fresh, defleshed bone
Stage 1 - cracks to appear along the length of the bone, some soft tissue may still be present
2a - top layer of bone begins to flake, some soft tissue may still be present
2b - top layer of bone almost completely flaked off
3 - top layer of bone gone, deeper layers of compact bone are fibrous (1-1.5mm)
4 - compact bone continues to look fibrous, rough to touch, splintering of bone may occur, inner cavity begins to show wear
5 - inner trabecular bone exposed, bone falling apart and losing original shape
Other factors affecting decomposition
Burial - slows rate of decomp, restricts access of carnivores and insects
Mass burial - produces differentiating rates of decay, faster on edges
Water - slows rate of decay, temperature and salinity are both important
How does shallow water/floods affect decomp?
Can act to move disarticulated remains or single bones
What are the effects of immerision in water on soft tissue?
Goose skin (anserina cutis) - roughening or pimpling of skin Skin maceration (washer womans skin) - swelling and wrinkling of skin Adipocere - transformation of fatty layer beneath skin into soap like material (requires 3 or more weeks)
How do bodies in water lie?
Face down
Head hanging when bloating brings them to surface
How does depth affect burial?
Less than a foot = insects can access body
Over two feet = temperature drops and becomes consistent
What factors of soil type affect burial?
pH
Type - clay/sand etc
Moisture content
Soil organisms
Define the process of saponification
Hydrolysis of triglycerides by bacterial enzymes which separates the fatty acids from the glycerol molecule which continues until there are no triglycerides left
Produces mixture of saturated and unsaturated fatty acids
Hydrogenation of unsaturated fatty acids into saturated fatty acids occurs
Examples of unsaturated fatty acids
palmitoleic
oleic
linoleic
Examples of saturated fatty acids
myristic
palmitic
stearic
What does saponification produce?
Formation of a waxy, fatty substance (adipocere)
Properties of adipocere
Off white in colour but can be reddish, greyish or grey/green
Needs the presence of adipocere
Can occur in dry conditions as well as amp conditions
What conditions slows/speeds saponification?
Speeds up - body covered in clothes, early activity by anaerobes
Slows down - in cold water
How does burning affect remains?
Reduces body to relatively small fragments
Destroys DNA evidence at moderate temperature
Leads to heat-induced morphological change - warping/distortion/fracturing/cracking
Destroys odontological evidence and many personal markers of identity
