Debra R. Ayres

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Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to the California native Spartina foliosa. Our goal was to map the location and extent of all non-native Spartina in the estuary. Hybrids of S. alterniflora and S. foliosa are by far the most numerous exotic and are spreading rapidly. Radiating from sites of(More)
The emergence of hybrids between native and introduced species is an increasingly widespread problem which can alter entire ecosystems. We present a general model for the hybridization of two plant species to investigate the conditions under which hybrid invasions can occur, and the ecological and genetic consequences of such hybridizations. We find that(More)
Rapid evolution in contemporary time can result when related species, brought together through human-aided introduction, hybridize. The significant evolutionary consequences of post-introduction hybridization range from allopolyploid speciation to extinction of species through genetic amalgamation. Both processes are known to occur in the perennial(More)
Plant hybridization can lead to the evolution of invasiveness. We wished to determine whether hybrids between the largely self-sterile Atlantic Spartina alterniflora and California native S. foliosa had evolved self-fertility during their ca 30 year existence in San Francisco Bay, CA. In pollination experiments we found that neither of the parental species(More)
Spartina alterniflora, introduced into the UK in the 1800s, was the seed parent in an interspecific hybridization with S. maritima. The sterile F1 hybrid S. ×townsendii gave rise to the fertile allopolyploid S. anglica by chromosomal doubling. Previous chromosome, isozyme, and cpDNA surveys did not reveal notable genetic variation within either the parental(More)
Wyethia reticulata is an edaphic endemic in the Sierra Nevada foothills. Its sympatric congener, W. bolanderi, is also restricted to the foothills, but has a north-south range of 275 km, compared to 14 km for W. reticulata. The goals of this study were to determine clonal diversity, population size, genetic variation, and spatial and generic structure for(More)
We report the discovery and spread of a dwarf ecotype of Spartina alterniflora in San Francisco Bay. Relative to typical S. alterniflora, this dwarf ecotype has one-fifth the tiller height (∼21 cm), tenfold the tiller density (∼4000 tillers/m(2)), and is restricted to growth in the upper intertidal zone. Chromosome counts of the dwarfs are identical to(More)
Diversity in the tRNALEU1 intron of the chloroplast genome of Spartina was used to study hybridization of native California cordgrass, Spartina foliosa, with S. alterniflora, introduced to San Francisco Bay approximately 25 years ago. We sequenced 544 bases of the tRNALEU1 intron and found three polymorphic sites, a pyrimidine transition at site 126 and(More)
Compared to the vast theoretical literature on the dynamics of single species invasions, relatively few models have dealt with the emergence of invasive hybrids. Here, we review the variety of modeling approaches that have been used to study the dynamics of hybridization, outlining the underlying assumptions and highlighting their advantages and(More)
Invasive hybrids and their spread dynamics pose unique opportunities to study evolutionary processes. Invasive hybrids of native Spartina foliosa and introduced S. alterniflora have expanded throughout San Francisco Bay intertidal habitats within the past 35 years by deliberate plantation and seeds floating on the tide. Our goals were to assess spatial and(More)