No single factor/s whether molecular or morphological is/are important in a sustainable maintenance of any system, is an indication of failure in reductionist approach or otherwise successful in an integral interpretation.
Intelligent question Dr Senapati. I feel , species diversity , either it is functional, compositional or metabolic nature , they compliment each other at different levels of ecosystem functioning with varied implications , and always successful in better interpretation ....all a part of sustainable system..
The question has the philosophical/strategical background which is pointed to the nature of the Systems Context involving "the function of a system is more than the sum of the total components". In this way it is obvious that the function is not the algebraic sum of the total components but it is the synergy achieved among the total components like as molecular components and species diversity.