Figure 1.
Effect of various mixes of facilitation and competition on the within-host dynamics of coinfecting species. A,
Equilibrium densities of parasite A (A*). B, Equilibrium densities of parasite B (B*). C, Virulence such that V = aA*+bB*. The red region represents the region where all equilibria are destabilized (i.e. xy>z, x<0 and y<0). Darker regions indicate lower values. The values on the contour lines indicate the relative densities of parasite at equilibrium. The line x = 0 defines the density of parasite A alone, and y = 0 defines the density of parasite B alone. The parameter values used are a = b = z = 1.
Figure 2.
Effect of asymmetric (a ≠ b) and symmetric (a = b) parasites’ contribution to total virulence (V).
Given a pair of values (a, b) the contour lines in each figure represent the total virulence on the host (V = aA*+bB*) for different values of x (parasite B competition/facilitation of parasite A) and y (parasite A competition/facilitation of parasite B). Lighter the region higher the virulence. z = 1 (i.e., symmetric intraspecific competition). The dashed white line exemplifies a situation where virulence is largely defined by parasite A (a>>b) and parasite B inhibits parasite A (x>0). Moving along this line by increasing −y (i.e. increasing facilitation to B) may decrease the overall virulence.