Effects of Delayed Reproduction on Survival, Fecundity, and the Rate of Population Increase

However, gene flow does have the expected result of swamping out local chance differentiation of the sort one associates with isolation-by-distance models (Rohlf and Schnell 1971). We agree with Endler (1973) that there is no easy way to explain an observed pattern of geographic differentiation. As can be seen in figure 1, only with large N and G would one expect observed lines which accurately reflect linear selection gradients (if such actually exist). It would be very difficult o estimate empirically the extent of nonmonotone dines of selective coefficients in nature (which are undoubtedly quite probable) without knowing details of the population biology of a species which are probably unobtainable today except in laboratory populations.