Conservation of endemic giants in serpentine landscapes

Serpentine outcrops in northern California occur in a variety of configurat ions, from scattered small patches to extensive landscapes covering hundred s of square kilometers. These areas support a. distinctive flora with numer ous uncommon or rare endemic species. I studied the reproductive ecology of two endemic plant species on large and small serpentine outcrops. The pere nnial herb, Calystegia collina, exhibited significantly lower reproductive success on small outcrops, partly because compatible pollen was not availab le from other, nearby populations. Local populations are more likely to pro duce seeds, and therefore potential colonists, when they occur in clusters of populations. Number of alleles and average heterozygosity were not signi ficantly different between C. collina patches in small versus large outcrop s. Vegetative reproduction enables small patches to persist for many years and apparently maintains genetic diversity despite low levels of seed produ ction. Pollinators and insect herbivores of C. collina were not significant ly less numerous on small outcrops than on large outcrops, suggesting that species interactions are not directly responsible for reproductive failure on small outcrops. The annual herb, Helianthus exilis, was entirely absent from small outcrops. This locally distributed serpentine endemic is restric ted to moist seeps, a specialized microhabitat found only within large serp entine outcrops. Transplant experiments showed that H. exilis survives poor ly or not at all outside these narrow conditions. Results from these invest igations illustrate the need to protect serpentine landscapes that contain multiple local populations and the full range of microhabitats that are inh abited by serpentine endemic plants. (C) 2001 Elsevier Science Ltd. All rig hts reserved.