Contingency and Statistical Laws in Replicate Microbial Closed Ecosystems

Abstract

Contingency, the persistent influence of past random events, pervades biology. To what extent, then, is each course of ecological or evolutionary dynamics unique, and to what extent are these dynamics subject to a common statistical structure? Addressing this question requires replicate measurements to search for emergent statistical laws. We establish a readily replicated microbial closed ecosystem (CES), sustaining its three species for years. We precisely measure the local population density of each species in many CES replicates, started from the same initial conditions and kept under constant light and temperature. The covariation among replicates of the three species densities acquires a stable structure, which could be decomposed into discrete eigenvectors, or "ecomodes." The largest ecomode dominates population density fluctuations around the replicate-average dynamics. These fluctuations follow simple power laws consistent with a geometric random walk. Thus, variability in ecological dynamics can be studied with CES replicates and described by simple statistical laws.

Stability of two-species communities: Drift, environmental stochasticity, storage effect and selection

“…Environmental stochasticity is almost always quite strong in biosystems (see, e.g. [37], where environmental stochasticity dominates system fluctuations even under extremely stable external conditions. See also [12][13][14] for an analysis of "standard" high diversity ecosystems, showing that the main driver is environmental noise).…”

Community history affects the predictability of microbial ecosystem development

“…Microcosms provide a powerful tool for microbial ecology (Jessup et al, 2004), as they make it possible to perform replicate laboratory experiments under manipulable conditions. Many important advances have been made using 'simple' microcosm communities with relatively few species (Weatherby et al, 1998;Langenheder and Székely, 2011;Hekstra and Leibler, 2012). In contrast, in this study we aim to preserve the key features of natural microbial ecosystems-high microbial diversity, nutrient cycling, community-environment feedbacks, strong interspecies interactions and spatial structure.…”

Stochastic multiplicative population growth predicts and interprets Taylor's power law of fluctuation scaling

“…TL is one of the most widely tested empirical patterns in ecology and is the subject of an estimated thousand papers [1,2]. It has been confirmed for hundreds of species or groups of related species in field observations [3][4][5] and laboratory experiments with stem cells [6] and ecological microcosms [7][8][9]. Numerous models have been proposed to explain TL under various assumptions [10][11][12][13][14][15][16] and probability distributions compatible with TL have been analysed [17][18][19][20][21][22][23][24].…”