Complex repeated interactions create ecostructures

Complex repeated interactions are fundamental in creating "ecostructures"—the intricate architectures or networks seen within ecological systems. These structures are not the product of simple, isolated pairwise species interactions, but rather emerge from layered and often high-order interactions that can involve several species simultaneously, with effects often propagating across spatial and temporal scales.

Key points include:

• Ecosystem Dynamics: In high-diversity systems, complex and repeated interactions generate persistent, non-equilibrium states where populations fluctuate rather than stabilize. Such dynamic states enable more species to coexist than would be possible in equilibrium, with asynchronous population changes across different locations acting as a buffer against extinction. Migration among spatial patches helps maintain diversity by rescuing local populations from extinction, thus keeping the entire system in a fluctuating but stable state1.

• Multi-layered Structures: Ecosystems often display multi-layer (or multi-tier) interactions, such as vertical stratification in marine systems or soil communities, where competitive interactions within the same layer tend to stabilize the ecosystem. In contrast, competition between different layers can have destabilizing effects. The overall stability or resilience of eco-structures thus depends on how these interactions are distributed across layers and scales2.

• High-order (non-pairwise) Interactions: Beyond simple two-species interactions, many ecosystems are structured by higher-order interactions, where the relationship between two species is modified by the presence of a third (or more). For example, in microbial communities, a third species may change the effects between an antibiotic producer and its target by degrading the antibiotic. Such high-order associations are crucial, as they can invert classical predictions: instead of destabilizing, they can actually require—and benefit from—greater diversity for stable coexistence3.

• Ecostructure Example: Physically, ecostructures can be seen in biogenic habitats like kelp forests. Here, the three-dimensional complexity from living structures (e.g., kelp holdfasts, tree canopies) physically modifies the habitat and creates myriad interaction opportunities, structuring entire communities and fostering robustness against change4.

• Emergent Properties: These complex networks and feedbacks lead to emergent properties—characteristics of the whole system that cannot be predicted from individual parts alone. For example, biodiversity maintenance, resilience to stressors, and the formation of stable, self-organizing eco-structures all result from this web of interactions13.

In summary, ecostructures arise because repeated, complex, and multi-level interactions among organisms and their environments create dynamic, self-organizing, and often surprisingly stable ecological networks123.

1. https://journals.plos.org/ploscompbiol/article?id=10.1371%2Fjournal.pcbi.1007827
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC9943886/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC4974637/
4. https://onlinelibrary.wiley.com/doi/10.1111/ddi.13140
5. https://www.sciencedirect.com/science/article/abs/pii/S0169534725000576
6. https://www.biorxiv.org/content/10.1101/2024.11.25.624858v2
7. https://animalecologyinfocus.com/2024/01/10/key-concepts-in-ecology-complex-interactions-and-foodwebs/
8. https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12495
9. https://ecostructureproject.aber.ac.uk/wp-content/uploads/2022/11/Ecostructure-Output-Guide.pdf