Evidence of microevolution in an escaped pear population

Abstract

A population of 87 wild pears (Pyrus communis L.) of fruiting age, growing in a relatively homogeneous old field environment, was found to be highly variable, with coefficients of variation up to 40%. Generally, variability was greater in size than in meristic characters, in meristic characters than in shape characters, and floral traits were less variable than vegetative. Tree trunk core samples showed the population to have been founded circa 1905 to 1908, by three trees. Establishment of progeny began about 19 years later. The population is high in 1975 and still expanding logarithmically. Numerical taxonomic clustering techniques using morphological characters showed the population to contain two very diverse groups. Trees of both groups are of all age classes and are distributed randomly over the site. Trees phenetically like and unlike the oldest trees were analysed as to growth rates. Those trees similar to the oldest trees were significantly slower in growth rate than trees that were morphologically dissimilar. This suggests that natural selection is operating to remove the less fit genotype from the population.