Figure 3.

Increasing population structure hurts the beneficial strain under fixed rewards from the host. The plot gives the combinations of host choosiness and relatedness between the symbionts that allow the beneficial symbiont to invade when rare and go to fixation when common in the population. Grey, beneficial symbiont can neither fix nor invade; red, beneficial symbiont can fix but cannot invade; white, beneficial symbiont can both invade and fix. For a given choosiness (going along a horizontal line), increasing relatedness between symbionts only makes the invasion and fixation conditions harder to satisfy. For all values depicted here, the selection differential changes sign at most once. Parameter values are: h₀=1, h₁=0, k = 0.4, n = 100.