Latitudinal variation in the fruiting phenology of a bird-dispersed plant (shape Crataegus monogyna) in Western Europe

Abstract

A number of fleshy-fruit-bearing plants of temperate regions are dispersed by migratory frugivorous birds. It has been suggested that the more southerly populations of such species should produce ripe fruits later than more northerly populations, to ensure that fruit is available when the birds arrive. I will call this the ‘adaptive delay’ hypothesis. To test this hypothesis, I monitored fruiting phenology of Crataegus monogyna Jacq. at ten sites (in all of which fruit consumption is very largely by redwings, Turdus iliacus, and fieldfares, Turdus pilaris) between northern Spain (42° N) and northern Scotland (59° N). There was no negative correlation between latitude and date of fruit ripening (earliest recorded date on which ripe fruits had appeared, or earliest recorded date by which all fruits had ripened). My results thus argue against the adaptive delay hypothesis.