XVI International Botanical Congess

Metapopulation persistence depends on colonization and extinction. Population size is important for both, affecting founder success and extinction risk. We studied effects of population size on viability in several threatened species. In small populations of most perennial species, we found clear examples of (1) stochastic (accidental) extinctions, (2) genetic erosion and limited gene flow, (3) reduced offspring fitness as a result of inbreeding, and (4) low reproductive success owing to pollination limitation. Annual and biennial species tended to be habitual selfers and had very little genetic variation in both small and large populations. Environmental stochasticity may be a more important risk for these species. We conclude that beyond the effects on local populations, habitat fragmentation must have lowered metapopulation viability as well.