Biotic Factors

• Environmental Factors

  •Biotic

  •Relates to living biological factors

  •Abiotic

  •Factors that are environmental but not biological in origin
• Biotic Factors

  Biotic factors are those that relate to living things and include:

  •Insect activity

  •Animal scavenging

  •Human interaction/intervention

  These factors act independently and co-dependently with abiotic factors to influence the pattern and rate of decomposition
• Insect Activity

  -Insect activity, and the study thereof (entomology), is central to the biotic factors involved in decomposition

  -Commencing with oviposition, insects and other necrophagous species including beetles, will be attracted to the remains as a food source and as a habitat.

  -Oviposition is the process of egg-laying. This will commence within minutes of death, primarily in areas that are easy to access and that will provide access to the larvae once hatched e.g. orifices and the eyes.

  
• Insect Activity – The Life Cycle

  The life cycle of an insect will depend on the species, however there is a broadly similar pattern which includes:

  •Egg

  •Larva – several instar stages

  •Pupa – variable pupation times

  •Adult

  All stages of the life cycle will interact with the remains in a variety of ways, although primarily using them as a food source.

  
• Insect Activity – Affect on decomposition

  -As the number of larvae present on the remains increases, the rate of decomposition will increase.

  -A larval (maggot) mass will form, which will maintain or even increase the ambient temperature of the remains

  -The larval mass will cause further exposure of tissues, enabling more access for insects, increasing the level of insect activity further.

  -This process is continuous until the soft tissue (food source) is expended.

  
• Animal Scavenging

  Animal scavenging can influence decomposition in a number of ways, both increasing and decreasing the rate at which the process occurs.

  Animals, including small and large carnivores, birds and omnivores, will feed on the remains, removing soft tissue. They can however also feed on the insects present. While the former may increase the rate of decomposition, the latter will delay it.

  
• Animal Scavenging

  Scavengers vary depending on country however in the UK can include:

  •Domestic dogs

  •Foxes

  •Cats

  •Badgers

  •Deer (primarily on bone)

  •Squirrels

  •Rabbits

  •Rodents (rats, mice and voles)

  •Birds

  
• Animal Scavenging – Order of Scavenging

  The order in which animals (primarily carnivores) will scavenge remains is relatively similar between species and can be generalised to:

  •Face and Neck

  •Thorax (heart and lungs)

  •Upper extremities (disarticulated from trunk)

  •Lower extremities (disarticulated from trunk)

  •Trunk (disarticulated and eaten)
• Rodent scavenging

  In contrast to large carnivores, rodents will primarily target the distal extremities (fingers and toes) and the soft areas around the face.

  Once bone is exposed, rodent gnawing can be seen on any element and is characterised by a parallel set of striae