Ecosystem processes, mechanistic level

Evidence of causality is perhaps the most concrete and also the most elusive aspect of the data assessment process. At the single organism or species level, it is often possible to assign specific mechanistic connections for mortality or other impact. Unfortunately, it is not clearly understood how prevalent and pervasive these impacts are at the community level. Correlational data may be all that are available for impacts at the level of interspecies interactions. Correlations are difficult to assess because correlation does not denote cause and effect. In a system as complex as an ecosystem, multiple correlations due to chance may occur. It may also be difficult to separate cause and effect without firmly established criteria. 

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