Prof. Ehud Meron - Research

Drylands showcase fascinating spatial self-organization phenomena involving partial plant mortality and the rearrangement of the remaining plants in regular patterns (Fig. 1). Mathematical models and pattern formation theory have played crucial roles in uncovering the mechanisms that drive vegetation patterning (Meron, Nonlinear Physics of Ecosystems 2015; Physics Today 2019).

Model studies predict wide precipitation ranges of multi-stability, where two or more alternative stable states, spatially uniform or patterned, coexist (Hardenberg et al., Phys. Rev. Lett. 2001; Zelnik et al. Phil. Trans. R. Soc. A 2013; Getzin et al. PNAS 2016). Multi-stability of states implies possible state transitions when environmental conditions change. When a state transition is accompanied by a loss of biomass production, it is commonly referred to as desertification. State transitions can be abrupt and irreversible or gradual and reversible. The former case occurs when a stress threshold or “tipping point” is crossed, and the transition encompasses the whole system with the same process co-occurring everywhere (Scheffer et al. Nature 2001). The latter case occurs when the transition is local but expands by front propagation as a domino effect (Bel et al., Theoretical Ecology 2012; Bel et al., PNAS 2015; Zelnik et al. J. Theor. Biol. 2017; Zelnik & Meron, Ecological Indicators 2018).

We are interested in understanding how spatial self-organization affects ecosystem functioning (Meron, Mathematical Biosciences 2016; Meron, Annu. Rev. Condens. Matter Phys. 2018), addressing in particular burning questions such as how to evade tipping points and thereby increase the resilience of ecosystems to climate change (Rietkerk et al. Science 2021; Zelnik et al. PLOS Computational Biology 2021), and how to reverse desertification fronts (Fig. 2 and 3; Fernandez-Oto et al. Phys. Rev. Lett. 2019), or fronts of exotic-species invasion (Ferré et al. Chaos Solitons and Fractals 2022). We are also interested in extending these questions to savanna and tundra biomes, where woody-plant encroachment into grasslands is of deep concern because it often involves loss of ecosystem services and can feed back on the climate (Eldridge et al. Ecology Letters, 2011; Mekonnen et al. Environ. Res. Lett. 2021).

These questions can be addressed at different levels of complexity, taking into account the interplay between spatial self-organization – a population-level response – with mechanisms operating at other levels of ecological organization, such as phenotypic changes at the single-plant level or plant-community re-assembly (Fig. 3; Meron, Mathematical Biosciences, 2016; Bera et al., eLife 2021). Another element of complexity is the interaction of plants with different trophic levels, such as herbivores or soil biota (Inderjit et al., Physics of Life Reviews 2021).

We address these questions using mathematical models of increasing complexity, importing concepts of nonlinear physics, such as front instabilities (Zelnik and Meron, Ecological Indicators 2018; Fernandez-Oto et al. Phys. Rev. Lett. 2019), homoclinic snaking (Zelnik et al., PNAS 2015; Zelnik et al. J. Theor. Biol. 2017); spatial resonances (Mau et al. Phys. Rev. Lett. 2012; Mau et al., Phys. Rev. E 2015) and others, and applying state-of-the-art methods of pattern-formation theory. This allows us to shed new light on old questions in ecology and ask new questions of ecological interest that have never been asked before.

We further confront theoretical predictions with empirical observations from satellite images, field studies, and laboratory experiments by collaborating with ecologists (Sheffer et al. Ecology Letters 2013; Getzin et al. Ecography 2015; Getzin et al. PNAS 2016; Bennett et al. PNAS Nexus 2022).

Intensive further collaboration with ecologists is expected in the framework of our new ERC-Synergy project RESILIENCE on “Pathways of resilience and evasion of tipping in ecosystems,” which will start in 2023 for six years and will focus on savanna and tundra ecosystems. More about this project in the website of RESILIENCE.