The resident strikes back: Invader-induced switching of resident attractor

The aim of this paper is two-fold: (a) by way of example, we elucidate the phenomenon of invader-induced switches in a resident attractor; (b) we expo se in detail how resonance and phase have a strong impact when semelparous organisms (as, e.g. Pacific salmon) with different life-cycle lengths compe te in a self-induced periodically fluctuating environment. We analyse a sim ple model for the competition between annuals and biennials, focusing on th e situation that the annual population in isolation converges to a two-cycl e. Well-tinned biennial mutants sample the periodically varying environment more efficiently than the annual resident. They can invade successfully ev en when they are inferior to the resident, in the sense that they have lowe r viability and/or fertility. Successful invasion can lead to resonance-med iated coexistence if the invader is rather inferior to the resident. Remark ably, for mutants that are less inferior to the resident, successful invasi on by a mutant strategy will inevitably be followed by the extinction of th e former invader and concurrent re-establishment of the resident. The expul sion of the invader is brought about by an invasion-induced phase shift or attractor switch. We call this phenomenon "the resident strikes back" and s ay that the resident strategy is invisible, yet invincible. After the resid ent has struck back, other mutants can successfully invade again. On a long er time-scale, this might lead to an intermittent occurrence of ultimately inferior strategies. The results show that even in a deterministic setting, successful invasion does not necessarily lead to establishment and that mu tual invisibility is not always sufficient for coexistence. (C) 2001 Academ ic Press.