Understanding how species interactions shape ecosystems and affect biodiversity, resilience, and ecosystem functioning is a key goal in ecology. Until now, most studies on ecological complexity have focused on specific species interactions that mediate a single ecological function, such as pollination, overlooking the combined impact of multiple functions. To fully capture the richness of ecosystem interactions, it is necessary to shift from unifunctionality to multifunctionality. In this study, we introduce a novel mathematical framework that integrates multiple observed interactions into a single model. Moreover, we capitalize on an unprecedented sampling effort based on direct observations on the islet Na Redona in the Balearic Islands (Spain), reporting 1,537 interactions between 691 species of plants, animals, and fungi across six different functions. What’s truly exhilarating is that this framework transcends our specific case study—it has the potential to revolutionize approaches across a multitude of fields. This exciting development not only showcases the power of interdisciplinary collaboration but also opens doors to fresh insights and applications everywhere!
Who's behind
Just as our research explores into the duality of species and functions in ecosystems, the team behind this work embodies a similar duality—two complementary disciplines, Ecology and Physics of Complex Systems, coming together to tackle complex ecological questions. This integration of expertise from different fields serves as a clear advantage—not only in formulating the right questions but also in interpreting the results from both ecological and physical perspectives, two essential components of this study. Bridging the divide between physicists and ecologists was no small feat, but it was a thrilling journey that proved essential to our discussions on the analyses. Through persistence and collaboration, ecologists managed to illuminate the ecological significance of the work to the physicists, who then harnessed their deep expertise to create an innovative mathematical framework.
This dual approach also influences how each of us experiences the 'behind the scenes' process. We are Sandra Hervías-Parejo and Mar Cuevas-Blanco, the two first authors of this research, with backgrounds in Ecology and Physics, respectively. Here, we provide a brief overview of our individual research journeys. Although our journeys are quite different, much of the richness of this study lies in successfully integrating both disciplines, fostering a deeper understanding of the ecosystem's functioning.
Collaboration Team.
Exploring The Ecosystem: An Ecologist's Journey
In October 2018, Anna Traveset (the project's principal investigator at IMEDEA-CSIC), Manuel Nogales (IPNA-CSIC), Ruben Heleno (U. Coimbra), and I (Sandra Hervías-Parejo, IMEDEA) set out, united by a strong passion for islands. Having explored many islands around the world together, we were filled with excitement as we headed to Na Redona, an uninhabited islet in Cabrera National Park that lacks a proper landing site. However, our enthusiasm quickly turned to disappointment when adverse sea conditions thwarted our plans to access Na Redona.
At that time, much like the multiple roles species play in an ecosystem, I also wore many hats in the project, preparing systematic sampling and field sheets, organizing materials, managing permits, and coordinating logistics for the team. After much planning and perseverance, we finally set foot on the islet! Before diving into our systematic surveys, we conducted an initial assessment to evaluate the availability of resources (plants) for our consumer groups, including animals and fungi. For instance, we counted flowering species for pollinators and fruit-bearing plants for seed dispersers. This groundwork allowed us to allocate our time effectively, ensuring we devoted equal effort to studying each type of interaction.
Despite the challenges of fieldwork—long hours in the sun, extended periods of standing, trekking significant distances, and carrying heavy equipment—what I enjoy most is the thrill of observing the unique interactions within these island ecosystems, which are often crucial for their functioning.
After wrapping up our field campaigns, I eagerly plunged into the laboratory work that awaited me. This involved transcribing field data, organizing the samples, and ensuring everything was properly labeled and preserved—all crucial steps before diving into analysis. Given the sheer volume of samples we handle, this process can be incredibly time-consuming. Picture this: examining over 1,000 droppings and pellets in search of seeds, plus nearly 100 pollen samples! We were fortunate to have the expertise of Susana Rodríguez-Echeverría from the University of Coimbra, a fungi specialist, who streamlined the analysis of our root samples. Additionally, a local entomologist helps us identify the invertebrates we collected, making the entire process much more efficient and insightful.
We were thrilled to have all the samples identified! The next step was to prepare the data for analysis. I cleaned the raw data and normalized it based on the effort involved. Ultimately, I was able to set up multilayer networks to analyze all types of interactions together, which provided a better understanding of ecosystem dynamics. At this stage, we face a crucial and challenging step: comparing five plants visited by a pollinator with five plants that host fungi on their roots. This task is essential for making fair comparisons across different ecological functions and for minimizing issues related to observational biases.
Modeling Complexity: A Physicist's Journey
Dear reader, I’m Mar Cuevas-Blanco, currently a PhD student at the Institute for Cross-Disciplinary Physics and Complex Systems (IFISC) in Mallorca, Spain. Growing up in the Canary Islands in Spain, I developed two strong passions, among others: physics and nature. Surrounded by rich natural environments like the Laurisilva forests, I’ve always been fascinated by the complexity of the natural world and deeply committed to its conservation. It has been a privilege to combine these interests in my research and make them the focus of my PhD. Under the supervision of Dr. Víctor M. Eguíluz and Dr. Lucas Lacasa, two leading researchers in network science and complex systems, I’ve had the chance to learn great deal from their expertise in these fields.
At IFISC, our research revolves around complex systems—where interactions between interconnected parts give rise to collective phenomena that can’t be understood by examining individual components alone. From traffic jams and bird flocks to ecosystems, all these phenomena share this core principle. Complex networks have been instrumental in representing complex systems, shifting the focus from individual components to the relationships between them. To incorporate multiple ecological functions into a single model, we turned to multilayer networks, which allowed us to better capture the complexity of these systems by accounting for multifunctionality.
Our journey in developing this mathematical framework took about two years of intense work, shaped by the intriguing questions that kept emerging. It involved countless hours in front of a whiteboard for brainstorming, followed by many more hours of programming, running simulations, and trying to deeply understand the results and their implications. In the end, these discussions and iterations, both within our team and with the rest of the group, were critical to refining the framework and reaching our final conclusions.
What we Discovered
All species are permanently involved in a myriad of entangled interactions with other coexisting species, playing multiple and simultaneous ecological roles. But how do we capture this? Traditionally, ecological research has focused on species alone (a species-centric perspective). In our study, however, we examine both species and functions, focusing on how they are interconnected. Applied to our Na Redona community, we found that the species-function network displays a nested structure—previously observed in mutualistic networks—suggesting that both species and functions play heterogeneous and dual roles and participate into each other in a non-random way.
Have you ever thought about how plants 'multitask' in an ecosystem? By including function connectivity, we extended the concept of keystone species to a multifunctional one, considering both (i) the species’ participation in various ecological functions and (ii) how well species connect different functions. For Na Redona, we found that plant species contribute heterogeneously to multiple ecological functions — essentially, they are the multitaskers of the natural world! What’s particularly intriguing is that the top six species in the keystoneness hierarchy, boasting the highest multitasking indices, are all woody shrubs. The dominance of woody shrubs in diverse roles likely stems from their longer lifespans, which allow them to forge connections with a wider array of species across different interactions.
Are there ecological functions that better connect species? In this study we introduce the concept of 'function keystoneness,' that naturally emerges from the species-function duality. Interestingly, our research highlights that interactions between plants and fungi—especially saprotrophic and pathogenic fungi—are key players in shaping this intricate multitrophic network. This further supports the recent shift in interest toward the importance of underground interactions for ecosystem functioning.
Conceptual framework.
We capture the richness of ecosystem interactions in a Resource (plant species) - Consumer (animal/fungal species) - Function tensor that can be visualized as a multilayer (multifunctional) ecological network. Integrating our the consumer index, we obtain a Resource-Function matrix that encapsulates how plant species and functions are intertwined in the ecosystem. Further projections of this matrix yield Function-Function/Plant-Plant network that characterize how each plant species/function connects different functions/species.
Why It Matters
Diving into the intricate world of plant interactions can feel like navigating a complex web of relationships. Imagine trying to unravel how a single plant species is pollinated by two different animals while simultaneously interacting with a myriad of fungi! It’s not always a straightforward task, but it’s an essential one. Understanding these dynamics allows us to make fair comparisons of ecological functions and tackle the biases that can arise from mere observation.
By quantifying the probability of these diverse interactions (instead of using more traditional) raw weights that measure the actual number of observed occurrences), we can shine a light on fascinating comparisons—like determining whether a plant thrives through pollination or establishes vital saprophytic relationships. These insights are not just academic; they pave the way for deeper analyses that can transform our understanding of ecosystems. In our latest paper, this foundational comparison proved to be a game-changer, opening up new avenues for exploration in the complex dance of nature.
What’s even more fascinating is the identification of key species and key functions that serve as vital connectors within the ecosystem. Their roles appear to be fundamental to maintaining the ecosystem's overall functioning and stability. This insight not only reshapes our understanding of ecological dynamics but also emphasizes the importance of both species and functions in sustaining the intricate web of life. The web of life is more interconnected than we often realize, and understanding these dynamics can pave the way for more effective conservation strategies.
Looking Ahead
But what drives this multitasking magic? To unlock the mysteries behind these relationships, we need more in-depth studies—such as incorporating more detailed data, including competition between plants, animal-fungi interactions, or insect trajectories. Additionally, it will be essential to apply this framework to other ecosystems to confirm the generalization of our results.
Importantly, the innovative mathematical framework we've developed is not limited to our ecological case study; it can be applied across diverse systems—biological, ecological, and even social or technological. This versatility allows for a deeper understanding of interactions within many complex systems, paving the way for insights that can enhance research and practices in various fields.
By applying this framework, we can better understand the intricate networks that exist not only in nature but also in human-designed systems, from urban ecosystems to economic models. The potential for interdisciplinary collaboration is immense, and we invite researchers from all domains to explore how this framework can illuminate patterns and functions within their own systems. As we continue to investigate these dynamic relationships, we stand on the cusp of groundbreaking discoveries that will not only enrich our understanding of ecological dynamics but also inform more effective strategies for sustainability and conservation in an interconnected world.