For nonfluctuating environments, births were given a special role in the bookkeeping. This focus allowed a considerable simplification of the calculations thanks to the fact that at birth individuals usually pass through a subset of states that is much smaller than the h-state space as a whole. Birth thus provides a bottleneck for the passing on of information from previous stages through the life cycle. Such bottlenecks may sometimes also occur elsewhere. For example, when in (2) families may split only when above a certain size, the most parsimonious calculations result from treating the reaching of the size threshold as if this were the birth events. There often is considerable freedom in the compounds that can be chosen for the role ofmetaindividual. In making such choices, it pays to build in the severest possible bottlenecks.
In metapopulations consisting of clonally reproducing individuals, the calculations are simplest for meta-life-cycles going from new disperser to local colonies founded by dispersers to the dispersers produced by such colonies. This leads to taking as fitness proxy for constant environments (of the metaindividuals) the probability of surviving dispersal times the average number of dispersers produced over the lifetime of an invader colony. For diploid metapopulations with small local population sizes the new dispersers are no longer equal but should be distinguished according to their birth state: heterozygote or homozygote.
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