Browsing by Author "Kefi, Sonia"

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    AN OPEN-SYSTEM APPROACH TO COMPLEX BIOLOGICAL NETWORKS
    (2019) Rebolledo, Rolando; Navarrete, Sergio A.; Kefi, Sonia; Rojas, Sergio; Marquet, Pablo A.
    Biological diversity is essential for the maintenance of the ecosystem functions that support life on the planet. Inherent to this diversity is the seemingly endless way in which the biological entities of a natural system interact and affect each other at local and regional scales, conforming complex ecological networks permeable to external forcing. Existing approaches to capture and model such complexity typically make unrealistic or excessively restrictive assumptions. Here we use concepts from open dynamical systems and metacommunity theory to develop a framework in which the system dynamics is a function of both interspecific interactions in the focal system (e.g., a local community of coexisting species) and unobserved biotic and abiotic interactions with the local and regional environment (e.g., the metacommunity). Species in the vital system interact through direct exchanges of biomass (i.e., trophic interactions), as well as through altering the acquisition and/or transformation of biomass by other species (nontrophic interactions). Interactions are affected by environmental fluctuations and by migration and emigration processes, which can take place at different time scales and can be modeled by stochastic differential equations driven by a mixture of continuous and discontinuous processes. In this manner, the proposed framework provides a wider and more flexible representation of the complexity of ecological systems, in comparison with the closed-system paradigm that isolates the system from the environment. Because the core model explicitly recognizes the existence of local and regional processes, it is also a natural starting point to examine spatially structured networks.
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    Self- organization as a mechanism of resilience in dryland ecosystems
    (2024) Kefi, Sonia; Genin, Alexandre; Garcia-Mayor, Angeles; Guirado, Emilio; Cabral, Juliano S.; Berdugo, Miguel; Guerber, Josquin; Sole, Ricard; Maestre, Fernando T.
    Self- organized spatial patterns are a common feature of complex systems, ranging from microbial communities to mussel beds and drylands. While the theoretical implications of these patterns for ecosystem - level processes, such as functioning and resilience, have been extensively studied, empirical evidence remains scarce. To address this gap, we analyzed global drylands along an aridity gradient using remote sensing, field data, and modeling. We found that the spatial structure of the vegetation strengthens as aridity increases, which is associated with the maintenance of a high level of soil multifunctionality, even as aridity levels rise up to a certain threshold. The combination of these results with those of two individual - based models indicate that self- organized vegetation patterns not only form in response to stressful environmental conditions but also provide drylands with the ability to adapt to changing conditions while maintaining their functioning, an adaptive capacity which is lost in degraded ecosystems. Self- organization thereby plays a vital role in enhancing the resilience of drylands. Overall, our findings contribute to a deeper understanding of the relationship between spatial vegetation patterns and dryland resilience. They also represent a significant step forward in the development of indicators for ecosystem resilience, which are critical tools for managing and preserving these valuable ecosystems in a warmer and more arid world.
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    Species diversity promotes facilitation under stressful conditions
    (2024) Danet, Alain; Bautista, Susana; Genin, Alexandre; Beckerman, Andrew P.; Anthelme, Fabien; Kefi, Sonia
    Climate change is expected to lead to a drier world, with more frequent and severe droughts, constituting a growing threat to biodiversity, especially in drylands. Positive plant-plant interactions, such as nurse plants facilitating beneficiary communities in their understorey, could mitigate such climate-induced stress. However, testing the real-world relevance of nurse facilitation under drought requires accounting for interactions within the diverse beneficiary communities, which may reduce, or amplify the buffering effect of a nurse. Here, we investigated when and how the interactions among nurse plants and beneficiary community members buffered drought effects in a Mediterranean semiarid abandoned cropland. We transplanted sapling beneficiary communities of either one or three species either under a nurse or in open microsites for different soil moisture levels through watering. Net facilitative effects on survival and biomass were only observed when beneficiary communities were species-diverse and under drought (without watering), meaning that under these conditions, facilitation provided by the nurse had larger positive effects than the negative effects stemming from competition with the nurse and among beneficiary species. Nurses appear to be generating these increases in survival and biomass in drought conditions via two mechanisms commonly associated with watering in open sites: they generate complementarity among the beneficiaries and shift traits to lower stress profiles. Contrasting with watering, which was found to enhance competitive hierarchy, our study shows that nurses appear to alter species dominance, favouring the less competitive species. Our results highlight three mechanisms (complementarity, competitive dominance, and trait plasticity) by which nurse species could mitigate the loss of biodiversity and biomass production due to water stress. Maintaining and supporting nurse species is thus a potentially pivotal approach in the face of projected increase in drought conditions for many drylands across the world.Keywords: biodiversity, dryland, ecosystem functioning, facilitation, functional traits, plant-plant interactions