Browsing by Author "Rojas, Sergio"

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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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    The complexity of a “simple” predator–prey system: non-trophic positive interactions generate unsuspected dynamics and dependencies
    (2025) Valencia, Daniel E.; Génin, Alexandre; Rojas, Sergio; Navarrete, Sergio A.
    In natural ecosystems, many species engage simultaneously in both trophic and non-trophic interactions (NTIs), influencing each other's population growth and patterns of local coexistence. However, in coastal marine systems, where the larvae of most benthic adults disperse and frequently settle into populations distant from their origin, populations do not experience feedback from local reproduction. This implies an apparent decoupling between local dynamics and regional-scale dispersal processes. Here, we explore the consequences of positive NTIs for the coexistence and dynamics of a predator and its prey. Inspired by two species studied in the Chilean intertidal zone, we developed a predator–prey model in which the prey also facilitates the recruitment of and provides refuge to the predator, while larval subsidies externally control the population growth of both species. The predator–prey dynamic was simulated at different levels of species recruitment, with and without NTIs. Overall, NTIs led to density dependence of the predator on the prey, coupling their abundances across varying levels of larval subsidies. Furthermore, the impact of NTIs on predator abundance was non-additive, with the magnitude of these effects depending on recruitment rates. In addition to determining population growth, recruitment rates also modulate the extent to which the predator is facilitated by the prey. These results suggest that incorporating NTIs into dynamic models and ecological theory is necessary for a more complete understanding of the mechanisms of species coexistence and spatial variability. This knowledge is critical for understanding ecosystem responses to ongoing climate and global changes.
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    THE OUTGOING TIME-HARMONIC ELECTROMAGNETIC WAVE IN A HALF-SPACE WITH NON-ABSORBING IMPEDANCE BOUNDARY CONDITION
    (2019) Rojas, Sergio; Muga, Ignacio; Jerez-Hanckes, Carlos
    We show existence and uniqueness of the outgoing solution for the Maxwell problem with an impedance boundary condition of Leontovitch type in a half-space. Due to the presence of surface waves guided by an infinite surface, the established radiation condition differs from the classical one when approaching the boundary of the half-space. This specific radiation pattern is derived from an accurate asymptotic analysis of the Green's dyad associated to this problem.