Genetics and demography of rare plants and patchily distributed colonizing species

Abstract

In California, two herbaceous plant genera of vernal pools, Limnanthes and Orcuttia have been studied for genetic structure, breeding systems, and life histories under population size changes over several seasons. Limnanthes show genetic variation patterns to be predictable from the geographical range of various metapopulation units and breeding systems; the wide-ranging species (L. alba, L. douglasii) are more variable and heterozygous than the inbreeding and narrowly distributed species (L. floccosa, L. bakeri). Life history comparisons showed a critical role of seed bank and early flowering in the lower amplitude of population numbers, correlated with greater persistence of even small populations in L. floccosa than its closest outbreeding relative L. alba. Populations of several Orcuttia species provided evidence for the critical role of early seeding establishment in their persistence. Conservation programs have focused on the habitat protection by setting up several nature reserves and on monitoring the vernal pool communities. Populations of the introduced rose clover Trifolium hirtum have been studied during their colonizing phase of pastures and along roadsides. Pollinators account for gene flow among such colonies and genetic variation is significantly ubiquitous even under higher rates of selfing. Input high levels of variability helped in colony success. Gynodioecy seems to have evolved and increased in relative frequency in the areas of new range expansion. The serpentine sunflower Helianthus exilis has become a sort of cause celebre due to its biosystematic status change. Several populations have been lost and the remaining few are small and need protection. -from Author