Figure 2.
Bifurcation diagrams and bifurcation phase portrait for the cancer–immune dormant state. The bifurcation parameter, predation strength, has a physical range of a0 ∈ [0, α/Ie], as larger values correspond to negative (and unphysical) dormant cancer populations. The immune recruitment parameter, μ, controls the behaviour of the dormant state. In (a), the dormant cancer population increases as predation strength decreases, but it is ultimately limited in size if the recruitment is strong enough. In (b), the dormant immune population increases without bound as predation strength decreases, but will be ultimately limited in size if the recruitment is too weak. The relation between the immune and cancer dormant sizes as predation strength weakens is shown in (c). Each curve is the progression of (Id, Cd) as predation strength weakens. Small dormant cancer populations will be maintained even though predation weakens provided that recruitment is strong enough to grow an infinitely large immune response.