Fig. 2. Dynamic of interactions.

Oscillations in nutrient availability (red gradient) considerably affects the community composition over time. A vitamin B₁₂ auxotroph (shown in blue) relies on other members of the community or external sources to obtain this amino acid. In turn, the vitamin B₁₂ auxotroph provides lysine to a member in the community that is a lysine auxotroph (shown in green). When vitamin B₁₂ becomes limited, the abundance of B₁₂ auxotrophs decreases (blue line). As a result, lysine auxotrophs in the community interact with other members in the community (shown in purple) to obtain lysine and to maintain growth (green line). Thus, the decrease in abundance of one member (blue line) can be beneficial for competitors (purple line) and leads to changes in community composition and the interaction network.