HUMAN IMPACT ON PLANT GENE POOLS AND SAMPLING FOR THEIR CONSERVATION

Many human activities distort the sample of genes that pass from one generation to the next of a plant population. These activities affect genetic structure either by markedly altering - usually decreasing - the level of genetic diversity, or by causing large changes in specific allele frequencies. The former changes are due to such stochastic evolutionary forces as reduced population size, increased migration and recombination, and the latter changes are due to systematic selection pressure. The leading examples of each are habitat destruction and environmental degradation. Interaction between stochastic and deterministic evolution is well displayed by introduced colonizing weeds. To combat unwanted evolutionary changes in plant population genetic structure, conservation measures - both in situ and ex situ - should employ sampling strategies that meet both stochastic and systematic needs.