Figure 2.

Influences of model parameters on the evolutionarily stable amount of help offered by helpers (h*, thick solid line) and the tolerance threshold of breeders, below which they will evict helpers (p*, thin lines). Tolerance thresholds are shown for two values of brood sizes in the absence of help (solid line: F₀=1.0; dotted line: F₀=1.5). Help offered does not change with F₀. Density dependence acts through the probability of inheriting a territory. Parameters shown are: (a) g, the cost of helping on helper survival; (b) c, the reduction in brood size resulting from the presence of a subordinate; (c) s, the cost of eviction for breeders; (d) δ, a parameter that influences the likelihood of mistakenly evicting or tolerating a helper; (e) S_b, the survival rate of breeders; and (f) S_n, the survival rate of subordinates if they do not help. For all panels, parameters that are not varied are g=1, c=0.3, s=0.05, δ=0.05, S_b=0.95, S_n=0.7, S_f=0.1, α=0.3, K=0.4.