BAKERS LAW REVISITED - REPRODUCTIVE ASSURANCE IN A METAPOPULATION

Baker's Law states that it is more likely for self-compatible than for self-incompatible individuals to establish sexually reproducing colon ies after long-distance dispersal, because only the former can do so w ith a single individual. This hypothesis, proposed by H. G. Baker 40 y ears ago is based largely on the observation that self-compatability i s particularly frequent among colonists of oceanic islands. Here we ar gue that the principle of Baker's Law applies equally in the context o f a metapopulation in which frequent local extinction is balanced by r ecolonization of sites by seed dispersal: metapopulation dynamics will select for an ability to self-fertilize. We review several studies th at support this hypothesis and present a metapopulation model in which the seed productivity required by obligate outcrossers for their main tenance in a metapopulation is compared with that of selfers. Our mode l also estimates the reduction in the advantage of reproductive assura nce to selfers as a result of perenniality and seed dormancy. In gener al, selection for reproductive assurance is greatest when the colony o ccupancy rate, p, is low and is much reduced when p approaches its max imum. This provides an explanation for the observation that many highl y successful colonizers, in which p is often high, are self-incompatib le. The basic model we present also lends itself to comparisons of met apopulation effects between unisexuality and cosexuality and between d ifferent modes of self-incompatibility.