The effect of cadavers on soil ecology: biotic and functional responses (CADAVER)
Project responsable Edward Mitchell
Team member Enrique Lara
Ildiko Szelecz
Abstract Cadaver decomposition has a clear impact on the soil ecosystem due to large, localised inputs of nutrients, especially C, N & P, as well as microclimatic effects. Cadaveric materials are rapidly introduced into the soil environment and assimilated by soil communities to form a “cadaver decomposition island (CDI)”. This “pulse of resources” affects the soil biota and functions drastically; yet these effects are not well understood. This natural perturbation contributes to biological and functional diversity through the contrasted responses of different taxa and associated processes and the spatial and temporal heterogeneities caused by the presence of cadavers. Once the decomposition process is completed the soil ecosystem is thought to gradually return to a “normal” condition. These patterns and processes are relevant to general soil biology and application in forensic science, yet there is little data on cadaver decomposition effects on the soil biota and functions and the patterns and pace of secondary succession leading back to the initial condition. We plan to study the effects of cadavers on the soil biota in both fundamental (disturbance and nutrient pulses impact on soil biota) and applied (potential of soil biota and functions as indicators for forensic applications) perspectives. A key aspect of forensic research is to develop tools to determine if a cadaver has decomposed in a certain place and how long ago the death occurred (the post-mortem interval – PMI). Forensic pathology uses several tools (e.g. body temperature, rigor mortis, insect infestation) but is usually not precise beyond 3-4 weeks. Hypothesised dynamic changes in the soil biota over a longer period (months to years) both in the disturbance and the recovery phases should allow the developing new tools in forensic taphonomy for estimating the time since death and the location of graves (e.g. if corpses were removed). We plan to conduct a fully factorial experiment to assess how a pig (standard model in forensic science) cadaver influences the soil biota and functioning and how the soil environment recovers from this perturbation. In addition to the cadavers and control treatments, fake pigs (i.e. filled cloth bags of equivalent size, but without cadaveric fluids) and pigs decomposing 2m above the soil (to test the influence of cadaveric fluids without the weight of the corpse) will be used to separate microclimatic and chemical effects, the latter being hypothesised as having a stronger influence. Soil samples from real forensic cases (if available) and nearby control soil will also be studied to test the broader applicability of the newly developed indicators and expand the range of natural conditions studied. As insects are supposed to be a major driving force regarding the speed and amount of decomposition (and much better understood than the soil biota), classical forensic entomology analyses will also be performed for comparison with the changes in the soil biota. This research addresses fundamental soil ecology (disturbance, resilience and succession – linkages among taxa, abiotic variables and functions) and applied forensic science (bioindication, PMI estimation) that have never been addressed in the same study. The project is divided into 5 tasks. 1) Insect succession on cadavers in relation to microclimate. 2) Soil physico-chemical characteristics. 3) Molecular diversity and community structure of soil Bacteria, micro-Eukaryotes and mesofauna assessed by pyrosequencing. 4) Morphological characterisation of testate amoebae and mesofauna communities. 5) Community and ecosystem ecology modelling (species/species traits-environment-function correlations, path analysis to explore cause/effects relationships, and testing if the nutrient pulse leads to phylogenetic clumping in soil communities) and definition of abiotic and biotic (bio)indicators of post-mortem interval.
Keywords soil ecology, ecological succession, forensic science, community ecology, soil microorganisms, cadaver decomposition, bioindication, soil invertebrates, soil protozoa, microbial ecology
Type of project Fundamental research project
Research area Ecologie
Method of financing FNS - Encouragement de projets (Div. I-III)
Status Completed
Start of project 1-8-2012
End of project 31-7-2015
Overall budget 315'000.00
Additional info http://p3.snf.ch/project-141188#
Contact Edward Mitchell