Finegrained Heterogeneity

An individual often experiences environmental heterogeneity within its own lifetime. Because an individual can only be at one place at any given time, an individual experiences both spatial and temporal heterogeneity within its own lifetime as a temporal sequence. Hence, for purposes of microevolutionary modeling, no distinction is necessary between fine-grained spatial and temporal heterogeneity. In many situations, fine-grained heterogeneity needs no special consideration as it can be folded into the constant-fitness models given in Chapter 11. To see this, consider two extreme situations: the case in which every individual in the population experiences the same temporal sequence of fine-grained heterogeneity and the case in which every individual experiences an independent sample of temporal sequences of environments within its lifetime.

The first case would apply to the situation in which an organism has one generation per year but in which seasonal variation influences the viabilities of the genotypes within the population. Thus, every individual in the population experiences the seasonal variation within its own lifetime, and every individual experiences exactly the same sequence of this seasonal heterogeneity. In the previous section, Hoekstra's (1975) model of coarsegrained seasonal variation was given, and Hoekstra also modeled the case of fine-grained seasonal variation. Table 14.4 gives the two-season fine-grained model in which the fitness effects within a season are identical to those given in Table 14.3, the two-season coarse-grained model. Note that Table 14.4 is just the standard, constant-fitness model (Figure 11.2) with the constant viabilities of t aa = waa = w1w2 and taa = waa = v1v2. Hence, all of the equations and conclusions of Chapter 11 apply to this case of fine-grained seasonal variation. In particular, the frequency-dependent dynamics that emerge from the

Table 14.4. Hoekstra's (1975) Model of Fine-Grained Cyclical Selection at One Locus with Two Alleles (A and a) over Two-Environment Cycle with Each Environment Experienced by All Individuals within Single Generation


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