Chemical ecology

Chemical ecology concerns the use of specific molecules and/or compound specific stable isotope techniques (e.g. δ13C, δ15N, δD) to investigate the behaviour of living organisms in either complex systems where their action and function are difficult to observe, or in the past where the organism(s) in question are now extinct.

The functional behaviour of various soil invertebrate species is an example of the former scenario, whilst determining the diets of extinct animals is an example of the latter. The OGU continues to investigate both scenarios.

Surprisingly little is known about the role that invertebrates play within the soil environment. They constitute a rich pool of species that exhibits a wide range of functional diversity. Some soil animals are true herbivores feeding directly on the roots and/or roots exudates of living plants but most live on dead plant matter and/or microbes associated with it. Others may be carnivores, parasites, or even top predators.

Despite our lack of knowledge concerning these fauna, we do know that they play a crucial role in the transfer of organic matter to soils and its subsequent mineralisation or long term stabilisation. For example, in the top F layer of a typical forest soil up to as much as 90% of the residual organic matter will exist in the form of arthropod faecal material.

Indeed, for the majority of soils the importance of these larger organisms in the pre-processing and comminution of deadfall cannot be overstated. Through a number of laboratory studies, using isotopically labelled substrates, work conducted by the OGU has provided new insights into the trophic preferences of the soil collembola Folsomia candida and Proisotoma minuta.

The diet and digestive processes of extinct animals have long been the subject of much research and speculation. Biomarkers are organic molecules with distinctive chemical structures or stable isotope signatures, which are diagnostic for particular groups of organisms or processes. Biomarkers present in animal faeces are derived from the animal itself, its food and its gut microbial community.

Previous research has characterised some of these biomarkers in modern and archaeological contexts and this work has been extended to fossil materials by researchers in the OGU. Coprolites are fossilised faeces and can preserve direct evidence of the digestive biology of the animals that produced them (as can fossilised gut remains).

By comparing the results obtained from fossilised materials with those derived from contemporary organisms we are able to reconstruct the dietary preferences of extinct species and, on a wider scale, provide information about the role played by extinct species in ancient ecosystems.

Further reading

Chamberlain, P. M., Bull, I. D., Black, H. J., Ineson, P. and Evershed, R. P. (2006) Collembolan trophic preferences determined using fatty acid distributions and compound-specific stable carbon isotope values. Soil Biology and Biochemistry 38, 1275-1281.

Gill, F. L., Crump, M. P., Schouten, R. and Bull, I. D. (2009) Lipid analysis of a ground sloth coprolite. Quaternary Research 72, 284-288.

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Surprisingly little is known about the role that invertebrates play within the soil environment. They constitute a rich pool of species that exhibits a wide range of functional diversity. Work conducted by the OGU has provided new insights into the behaviour of various soil invertebrate species.
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