The evolution of ecosystem organisation
The concept of self-organisation and its role in governing complexity and stability of an ecological network is a fundamental topic in theoretical ecology. The hypothesis of a relationship between ecosystem self-organisation, functionality and energy circulation within the system has a long history and integrative information theoretic measures have been proposed to capture ecosystem growth, development and organisation. Previous studies have ascribed prevailing intermediate degrees of organisation to trade-offs between autocatalytic feedbacks and adaptability in the light of environmental variation. However so far, no consideration has been given to the role of functional and evolutionary constraints on energy transfer and topological properties of a food web.
This work investigates the impact of functional and structural constraints on the topological structure of food webs when selecting for efficiency and organisation respectively. The latter indicators are defined by the pattern of network flows and captured by information theoretic measures. The structural properties of the evolved food webs are assessed and the degree of organisation of real world food webs is compared to theoretical food webs which follow the same constraints.
Irrespective of the functional and structural constraints imposed on the ecological networks, selection for either efficiency or streamlined organisation leads to unrealistic network structures such as plain food chains or very broad webs; selection for both efficiency and streamlined organisation evolves more intermediate network structures. Comparing the structure of real world food webs to their computationally evolved equivalents reveals the fundamental role of the number of primary producers and top consumers as well as the number of interaction links in the food web to yield realistic structure in the simulated networks, which suggest the potential reflection of developmental and historical constraints of ecosystem development in the structural constraints on evolving food webs. It is shown that given functional and structural constraints, a large number of real world ecosystems exhibits degrees of organisation in the upper 5% of possible organisation patterns, indicating a tendency of ecological networks to evolve toward states of higher organisation and efficiency.
The findings support the hypothesis of the interplay between efficiency and organisation as systemic optimisation principles, highlight the system’s dependence on functional, evolutionary and developmental constraints and may help shed light on the role of bottom-up and top-down control during ecosystem evolution.