Experimental setup
All meta-ecosystems consisted of a heterotrophic and an autotrophic patch (ecosystem), respectively. The heterotrophic ecosystems consisted of a community of nine, mostly heterotrophic ciliates (Blepharisma sp., Colpidium sp., Euplotes aediculatus , Loxocephalus sp., Paramecium aurelia ,Paramecium caudatum , Spirostomum sp., Spirostomum teres , and Tetrahymena cf. pyriformis) , and one rotifer (Cephalodella sp.). The autotrophic ecosystem consisted of a photosynthesising mixotrophic flagellate (Euglena gracilis ). We subsequently refer to all these organisms as “protists”. Before the experiment, the protists were individually cultured in pre-autoclaved bottles with protist medium (0.46 g of Protozoa Pellet by Carolina per L of water) and bacteria (Serratia fonticola , Bacillus subtilis , and Brevibacillus brevis ) acting as food for protists and constituting 5 % of the total volume of the culture. See Altermatt et al. (2015) for further details and protocols.
At the beginning of the experiment (day zero), we prepared two large bottles either containing E. gracilis or the mix of the 10 heterotrophic protists (the latter at 1/10 of their carrying capacity). From these large bottles, we prepared 60 cell flasks (40 mL volume) with different culture volumes—20 flasks of small ecosystem size (7.5 mL), medium ecosystem size (22.5 mL), and large patch size (37.5 mL) (3 sizes x 2 trophic types x 2 connection treatments x 5 replicates = 60 flasks). Subsequently, the position of the cultures was randomised within an incubator, maintained at a constant temperature of 20 °C with continuous illumination.