Nature has an uncanny way of finding balance, and nowhere is this delicate dance more apparent than in the intricate choreography of ecological succession. As ecosystems evolve and transform over time, species jostle for dominance, competing for resources and space. Yet, there exists a nuanced interplay between different mechanisms that include competition, facilitation, interactions with enemies, and domination — a trade-off that shapes the trajectory of community development.

Many ecosystems are the arena for a tug-of-war between species, as at the heart of ecological succession (especially whether a primary succession) lies the struggle for supremacy. As pioneering species lay claim to new habitats, they engage in competition for limited resources — sunlight, water, nutrients, and more. This competition can be both intraspecific (within a species) and interspecific (between different species), each species vying for a slice of the ecological pie.

However, as the succession unfolds, the dynamics shift, revealing a more intricate web of interactions. Some species begin to assert dominance, often due to specific traits that grant them an edge in the race for survival (as described in the works of Rees and colleagues, since 2001).

In the initial stages of succession, as multiple species scramble for resources, a variety of adaptations emerge. This diversity of traits contributes to a vibrant and resilient ecosystem. Think of a rainforest teeming with a multitude of species, each finely tuned to a specific niche. The intense competition among these species fosters continuous innovation and specialization, ultimately enhancing the overall health of the ecosystem.

Amid the competition and quest for domination, the concept of facilitation emerges as a crucial player. Certain species pave the way for others, creating favorable conditions that nurture new beginnings. These facilitators, often early colonizers, modify the environment in ways that make the habitat different from the habitat before the colonization by influencing the resources availability.

The Resource Ratio Hypothesis proposed by ecologist David Tilman in the 1980s has since played a crucial role in understanding species interactions and their effects on community dynamics. This hypothesis suggests that the relative availability of multiple resources in an environment (i.e., light and soil nitrogen) determines the outcome of competition among species. Tilman proposed that the growth of a species depends not only on the absolute amount of one key resource, but also on the ratio of different resources available. According to the hypothesis, one resource is usually in excess, while another is limiting. Changes in the availability of resources can lead to shifts in species dominance, especially if there is an excess of produced biomass which is not exported.

While species engage in this “ecological ballet”, they must also navigate interactions with enemies. Predators, herbivores, and pathogens become part of the intricate tapestry, exerting their influence on the succession process. The presence of such enemies can shape the dominance of certain species, as those with effective defenses gain an upper hand. This interplay adds yet another layer of complexity to the competition-domination trade-off, influencing the composition and resilience (or a regime shifting) of the community.

While competition, facilitation, interactions with enemies, and dominance each offer unique benefits, an excess of either can tip the ecological scales. Too much competition can lead to a constant turnover of species, preventing any one group from gaining a foothold and hindering the establishment of a stable community. Conversely, unchecked dominance can lead to a lack of diversity, leaving the ecosystem vulnerable to sudden changes and disturbances.

This is where the competition-domination trade-off, along with the influence of facilitation and interactions with enemies, steps in. As certain species assert dominance, the competition among them lessens, allowing space for other species to thrive. The dominance of a few key species provides stability, while the presence of multiple competitors maintains innovation and adaptability, all the while interacting with enemies and facilitators.

To disentagle a little this complex pattern, as a scholar starts to be fascinated by the ecological successions, he or she becomes keen on predicting the evolution of a succession. It was this curiosity that pushed the ecologist Horn to develop the Markov chain model of successional stages. All started with the recording of the proportional abundance of staplings beneath an adult tree: according to Horn and the resulting proportionality matrix, the abundance of a species at the time of observation represents the probability of that species to replace the older tree in a successive stage of the community.

To better understand the Markov model in ecology, imagine each stage of a succession as a unique state in a dynamic process. Just as a chessboard transitions through a series of positions with each move, an ecosystem evolves through various stages, with species succeeding one another with a probability depending on their abundance at a certain reference time.

However, there is a lot of work still to be done on this topic: the full picture of spatial and temporal variability in ecological succession is far to be fully depicted.

Ecological succession is a mesmerizing tapestry woven from the threads of competition, facilitation, interactions with enemies, and domination. This intricate dance between species and their allies or adversaries shapes ecosystems, guiding them from barren landscapes to thriving communities. The competition-domination trade-off, along with the subtle influence of facilitation and interactions with enemies, ensures that no single species takes the spotlight for too long, fostering resilience, stability, and the awe-inspiring diversity that defines our natural world. But disturbances, randomness and chaotic dynamics are part of the ecosystems and make everything more complex. Such factors have just started to be taken into account by some ecologists (including me) and the studies, modelizations and simulations – along with theoretical calculations – are getting really challenging (…finger crossed for my results, please 🙂 !)

So, the next time you stroll through a forest or gaze at a meadow, remember the silent struggle, partnerships, and conflicts that have played out over centuries. It’s a symphony of life, an eternal tango of competition and cooperation, working in harmony to create the wondrous spectacle of dynamic ecosystems.