Investigations of indirect relationships in ecology and environmental sciences: a review and the implications for comparative theoretical ecosystem analysis

The understanding of complex interactions involving ecosystem components is indispensable for sustainable development of humankind. To date, ecological research has mainly concentrated on investigations of direct relationships, whilst indirect interactions (and in particular the less obvious, e.g. delayed ones) have often been overlooked. Investigation of mechanisms underpinning complex indirect relationships in ecosystems is greatly aided by mathematical techniques, including correlation, multiple regression and factor analysis, simulation modelling, path analysis and methods of network analysis, etc. This paper provides a brief review of the recent relevant studies. Mathematical modelling techniques may be especially useful if used in concert on a range of ecosystems, thus integrating the information obtained in a comparative theoretical ecosystem analysis (CTEA). A methodological framework for CTEA is given, limitations of the review are acknowledged and possible implications discussed.