Strongly Deterministic Population Dynamics in Closed Microbial Communities
Zak Frentz, Seppe Kuehn, and Stanislas Leibler
Phys. Rev. X 5, 041014 – Published 26 October 2015
Source/Fonte: Eurekalert
ABSTRACT
Biological systems are influenced by random processes at all scales, including molecular, demographic, and behavioral fluctuations, as well as by their interactions with a fluctuating environment. We previously established microbial closed ecosystems (CES) as model systems for studying the role of random events and the emergent statistical laws governing population dynamics. Here, we present long-term measurements of population dynamics using replicate digital holographic microscopes that maintain CES under precisely controlled external conditions while automatically measuring abundances of three microbial species via single-cell imaging. With this system, we measure spatiotemporal population dynamics in more than 60 replicate CES over periods of months. In contrast to previous studies, we observe strongly deterministic population dynamics in replicate systems. Furthermore, we show that previously discovered statistical structure in abundance fluctuations across replicate CES is driven by variation in external conditions, such as illumination. In particular, we confirm the existence of stable ecomodes governing the correlations in population abundances of three species. The observation of strongly deterministic dynamics, together with stable structure of correlations in response to external perturbations, points towards a possibility of simple macroscopic laws governing microbial systems despite numerous stochastic events present on microscopic levels.
FREE PDF GRATIS: Physical Review X
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APS Physics Excerpt/Excerto do APS Physics:
[...] the dynamics of this ecosystem seems to follow a prescribed “program.”
What might this program be then? Theoretical ecologists may feel compelled to build a model; after all, the three-species ecosystem is just a trophic chain that can be described by three differential equations, one for each species. Wrong. The deterministic dynamics of the system depend on a multitude of microscopic factors. Algae, bacteria, and ciliates can swim, aggregate, and change their size and behavior. All of these factors contribute to shift the species abundance in a reproducible yet unpredictable manner. The upshot is that we know there is a program, but we don’t know its rules.
[...] the dynamics of this ecosystem seems to follow a prescribed “program.”
What might this program be then? Theoretical ecologists may feel compelled to build a model; after all, the three-species ecosystem is just a trophic chain that can be described by three differential equations, one for each species. Wrong. The deterministic dynamics of the system depend on a multitude of microscopic factors. Algae, bacteria, and ciliates can swim, aggregate, and change their size and behavior. All of these factors contribute to shift the species abundance in a reproducible yet unpredictable manner. The upshot is that we know there is a program, but we don’t know its rules.
Researchers could try and find some set of rules by measuring all the microscopic processes that take place in the closed ecosystem. But that exercise would most likely result in a model for this specific experiment, rather than in the scientific synthesis of the ecological forces that drive the system to its deterministic behavior. Experience from other complex systems shows that, to find a useful scientific synthesis, we need to identify order parameters, or “collective variables,” that capture the macroscopic behavior that emerges from a myriad of microscopic details.
Finding those variables remains a challenging problem, and it is one of the main scientific frontiers in the physics of life. However, for physicists, as for biologists, it should be clear that despite the great advances in molecular systems biology, the most ambitious questions in biology remain at the highest levels of organization.
Source/Fonte: APS Physics
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NOTA DESTE BLOGGER:
Diversidade, complexidade, organização é tema recorrente na literatura científica que Darwin e sua teoria da evolução não respondem cientificamente. E mais uma vez um simples micróbio coloca em questão as explicações darwinistas simplistas tidas como explicação final e grandiosa do fato, Fato, FATO da evolução. Nada mais falso! A ciência é bem outra!
Darwin kaput! desde 1859!
Darwin kaput! desde 1859!
