Table 1. Description of parameters used in the models.

Parameter (general)	Description
Gene loss ($l$)	Rate at which carrier cells lose the beneficial gene
HGT rate ($h$)	Rate at which non-carriers are transformed into carriers (when interacting with carrier cells)
Benefit of gene ($b$)	Growth rate benefit for carrier cells (or penalty for negative b)
Costs of HGT ($c$)	Growth rate penalty for the rate of HGT
Parameter (IBM only)	Description
Grid size ($n$)	The simulation is done on a square grid of n x n cells
Mixing rate ($d$)	Every time step, the grid is mixed $d$ times using the Margolus Diffusion algorithm (Toffoli and Margolus, 1987). Alternatively, the population was well-mixed by assigning new positions at random every time step.
Competition range ($s$)	Sub-population of s x s cells surrounding focal grid point that compete for reproduction
HGT distance ($t$)	Sub-population of t x t cells surrounding focal grid point from which a random potential donor is sampled for HGT
Influx genes ($f$)	A small probability for any cell to discover a gene de novo
Benefit of influxed gene (b*)	Growth rate benefit for carrier cells (or penalty for negative b)
Influx SGEs ($i$)	A small probability for any cell to be infected by an SGE de novo
Fitness penalty of SGE ($\beta$)	The fitness penalty imposed by the SGE
Mutation rate (u)	Chance of mutating the evolvable HGT-rate
Mutation step ($m$)	Uniform step size of mutations