A basic community dynamics experiment: Disentangling deterministic and stochastic processes in structuring ecological communities

Community dynamics are governed by two opposed processes: species sorting, which produces deterministic dynamics leading to an equilibrium state, and ecological drift, which produces stochastic dynamics. Despite a great deal of theoretical and empirical work aiming to demonstrate the predominance of one or the other of these processes, the importance of drift in structuring communities and maintaining species diversity remains contested. Here we present the results of a basic community dynamics experiment using floating aquatic plants, designed to measure the relative contributions of species sorting and ecological drift to community change over about a dozen generations. We found that species sorting became overwhelmingly dominant as the experiment progressed, and directed communities towards a stable equilibrium state maintained by negative frequency-dependent selection. The dynamics of any particular species depended on how far its initial frequency was from its equilibrium frequency..., Source community
The source plant community was isolated from a eutrophic pond adjacent to fallowed agricultural fields on the Macdonald campus of McGill University, Quebec, Canada (45° 42’ N, 73° 94’ W). The pond sustains a diverse community of floating macrophytes, the four most abundant being Lemna minor (Lm), Lemna trisulca (Lt), Spirodela polyrhiza (Sp) and Wolffia columbiana (Wc), all in the family Lemnaceae. Large samples consisting of hundreds of thousands of individuals were taken in June 2020 and manually separated into the constituent species.
Experimental design
The experiment was conducted at the LEAP (Large Experimental Array of Ponds) facility at  Gault Nature Reserve of McGill University in Quebec, Canada (45° 32’ N, 73° 08’ W), (Fugère et al. 2020) (Fig. 1). 48 large mesocosms (surface area=2.43m2) were filled each with 500L of water piped from Lac Hertel, a mesotrophic lake on the reserve, 1km upstream of the experiment. The water was sieved to remove fish, tadpoles, m...,