Fig. 2

Large population size limit. Relative abundances of two genotypes of host h₁ and h₂ and parasite p₁ and p₂ over time (left) and 2D representation (right) in the deterministic equivalents of the Evo ⁺ and Evo process with constant population size. Top: Intraspecific competition within the whole population (+) results in an attracting fixed point which is reached eventually and does not changed once reached, leading to stasis (also EcoEvo ⁺). Bottom: Pairwise competition between individuals allows for a neutrally stable fixed point which neither attracts nor repulses the dynamics resulting in continuous co-evolution in the form of negative frequency-dependent selection dynamics (NFDS) around the internal fixed point (also EcoEvo). Method: integration of ordinary differential equations, the adjusted replicator dynamics (Evo ⁺) and the replicator dynamics (Evo), which are the deterministic limits of the respective stochastic processes. Parameters: selection strength w_H=w_P=1, matching allele parameters α=1 and β=0