Fig. 1 Different ecological interaction types and vertical cross-sectional spatial patterns of microorganisms with model predictions (adapted from Momeni et al, 2013a). A, Different forms of interaction between two bacterial populations, with solid arrows indicating increased net fitness benefits (+), dashed connectors indicating decreased net fitness benefits (-), and no arrows indicating no fitness benefits (0). B, Two bacterial populations formed different distributions patterns in the vertical direction of the community. a-f corresponding to competition, commensalism, amensalism, parasitism, mutual antagonism and cooperation, respectively. The red and green colors indicate different bacterial populations, denoted by the R and G, respectively. The symbols in parentheses close to the alphabet represent fitness benefits: + indicates an increase in net fitness, - represents a decrease in net fitness, and 0 means no change in net fitness. For example, R [+ -] G describes a parasitic interaction in which the net fitness of the red colony increases while the net fitness of the green colony decreases.

Fig. 2 Representative horizontal surface spatial patterns of different ecological interactions with computer simulation (adapted from Blanchard & Lu, 2015). The red and green colors indicate different bacterial populations, denoted by the R and G, respectively. The symbols in parentheses close to the alphabet represent fitness benefits: + indicates an increase in net fitness, - represents a decrease in net fitness, and 0 means no change in net fitness. For example, R [- +] G describes a parasitic interaction in which the net fitness of the red colony decreases while the net fitness of the green colony increases. Two bacterial communities form different types of horizontal surface spatial patterns during expansion with different forms of ecological interactions.

Fig. 3 Spatial self-organization process of competition and cooperation interactions. Different colors represent different bacterial species. Bacteria initially distribute randomly in the environment. During growth and dispersal, competitive interactions will lead to spatial segregation of different species, while cooperation among them allows different species to mix with each other spatially.

Fig. 4 Schematic diagram of spatial pattern of the cheater invading the cooperative system. This figure was adapted from the study of Momeni et al (2013b). According to the experimental results of Momeni et al (2013b), the blue area represents the cooperative partner, the yellow area represents the cooperator, and the green area represented the cheater. Cooperators tend to mix with each other, while cheaters are crowded out of the community. This spatial pattern effectively increases the frequency of interaction of cooperators and avoids being exploited by cheaters.