Population-level genetic variation and climate change in a biodiversity hotspot.

INTRODUCTION: Estimated future climate scenarios can be used to predict where hotspots of endemism may occur over the next century, but life history, ecological and genetic traits will be important in informing the varying responses within myriad taxa. Essential to predicting the consequences of climate change to individual species will be an understanding of the factors that drive genetic structure within and among populations. Here, I review the factors that influence the genetic structure of plant species in California, but are applicable elsewhere; existing levels of genetic variation, life history and ecological characteristics will affect the ability of an individual taxon to persist in the presence of anthropogenic change. FACTORS INFLUENCING THE DISTRIBUTION OF GENETIC VARIATION: Persistence in the face of climate change is likely determined by life history characteristics: dispersal ability, generation time, reproductive ability, degree of habitat specialization, plant-insect interactions, existing genetic diversity and availability of habitat or migration corridors. Existing levels of genetic diversity in plant populations vary based on a number of evolutionary scenarios that include endemism, expansion since the last glacial maximum, breeding system and current range sizes. REGIONAL PRIORITIES AND EXAMPLES: A number of well-documented examples are provided from the California Floristic Province. Some predictions can be made for the responses of plant taxa to rapid environmental changes based on geographic position, evolutionary history, existing genetic variation, and ecological amplitude. CONCLUSIONS, SOLUTIONS AND RECOMMENDATIONS: The prediction of how species will respond to climate change will require a synthesis drawing from population genetics, geography, palaeontology and ecology. The important integration of the historical factors that have shaped the distribution and existing genetic structure of California's plant taxa will enable us to predict and prioritize the conservation of species and areas most likely to be impacted by rapid climate change, human disturbance and invasive species.

Do invasive species perform better in their new ranges?

A fundamental assumption in invasion biology is that most invasive species exhibit enhanced performance in their introduced range relative to their home ranges. This idea has given rise to numerous hypotheses explaining "invasion success" by virtue of altered ecological and evolutionary pressures. There are surprisingly few data, however, testing the underlying assumption that the performance of introduced populations, including organism size, reproductive output, and abundance, is enhanced in their introduced compared to their native range. Here, we combined data from published studies to test this hypothesis for 26 plant and 27 animal species that are considered to be invasive. On average, individuals of these 53 species were indeed larger, more fecund, and more abundant in their introduced ranges. The overall mean, however, belied significant variability among species, as roughly half of the investigated species (N=27) performed similarly when compared to conspecific populations in their native range. Thus, although some invasive species are performing better in their new ranges, the pattern is not universal, and just as many are performing largely the same across ranges.

Population genetics of Howellia aquatilis (campanulaceae) in disjunct locations throughout the Pacific Northwest.

Howellia aquatilis A.Gray (water howellia) is a federally-listed threatened aquatic plant species with limited distribution in four states: California, Idaho, Montana, and Washington. Previous studies have shown a lack of genetic variation within the species; these studies, however, have excluded samples from one or more states. There have been no published studies on the population biology or genetics of the six known California populations or their evolutionary relationship to the other Pacific Northwest populations. We used Amplified Fragment Length Polymorphisms to identify genetic variation within and among the California populations, and to compare the California populations to the Idaho, Montana, and Washington populations. Analysis of molecular variance of 92 individuals from the six California populations show that 83.8% of genetic variation is found within populations and 16.2% among populations (P < 0.001). All sampled populations from all states provide 83.7% variation within and 16.3% variation among populations (P < 0.001). A UPGMA analysis confirms there is no clear clustering of Howellia aquatilis populations within California, that the Montana populations cluster within the California populations, and, although with limited population sample sizes, the Idaho and Washington populations are distantly related to all other populations. Waterfowl migration patterns support a hypothesis for avian dispersal as a primary factor in gene flow in Howellia aquatilis.

Genetic variation and phylogeographic analyses of two species of Carpobrotus and their hybrids in California.

Despite the commonality and study of hybridization in plants, there are few studies between invasive and noninvasive species that examine the genetic variability and gene flow of cytoplasmic DNA. We describe the phylogeographical structure of chloroplast DNA (cpDNA) variation within and among several interspecific populations of the putative native, Carpobrotus chilensis and the introduced, Carpobrotus edulis (Aizoaceae). These species co-occur throughout much of coastal California and form several 'geographical hybrid populations'. Two hundred and thirty-seven individuals were analysed for variation in an approximate 7.0 kb region of the chloroplast genome using PCR-RFLP (polymerase chain reaction - restriction fragment length polymorphism) data. Phylogenetic analyses and cpDNA population differentiation were conducted for all morphotypes. Historic geographical dispersion and the coefficient of ancestry of the haplotypes were determined using nested clade analyses. Two haplotypic groupings (I and II) were represented in C. chilensis and C. edulis, respectively. The variation in cpDNA data is in agreement with the previously reported allozyme and morphological data; this supports relatively limited variation and high population differentiation among C. chilensis and hybrids and more wide-ranging variation in C. edulis and C. edulis populations backcrossed with C. chilensis. C. chilensis disproportionately contributes to the creation of hybrids with the direction of gene flow from C. chilensis into C. edulis. The cpDNA data support C. chilensis as the maternal contributor to the hybrid populations.