This journal frequently contains papers that report values of F-statistics estimated from genetic data collected from several populations. These parameters, FST, FIT, and FIS, were introduced by Wright (1951), and offer a convenient means of summarizing population structure. While there is some disagreement about the interpretation of the quantities, there is considerably more disagreement on the method of evaluating them. Different authors make different assumptions about sample sizes or numbers of populations and handle the difficulties of multiple alleles and unequal sample sizes in different ways. Wright himself, for example, did not consider the effects of finite sample size. The purpose of this discussion is to offer some unity to various estimation formulae and to point out that correlations of genes in structured populations, with which F-statistics are concerned, are expressed very conveniently with a set of parameters treated by Cockerham (1 969, 1973). We start with the parameters and construct appropriate estimators for them, rather than beginning the discussion with various data functions. The extension of Cockerham's work to multiple alleles and loci will be made explicit, and the use of jackknife procedures for estimating variances will be advocated. All of this may be regarded as an extension of a recent treatment of estimating the coancestry coefficient to serve as a mea-

https://www.jstor.org/stable/pdfplus/2408641.pdf

Estimating F-statistics for the analysis of population structure.

Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

Although the potential genetic risks associated with rare or endangered plants and small populations have been discussed previously, the practical role of population genetics in plant conservation remains unclear. Using theory and the available data, we examine the effects of genetic drift, inbreeding, and gene flow on genetic diversity and fitness in rare plants and small populations. We identify those circumstances that are likely to put these plant species and populations at genetic risk. Warning signs that populations may be vulnerable include changes in factors such as population size, degree of isolation, and fitness. When possible, we suggest potential management strategies.

/pdf/population-genetic-consequences-of-small-population-size-3onkvtfxng.pdf

POPULATION GENETIC CONSEQUENCES OF SMALL POPULATION SIZE: Implications for Plant Conservation

Tree taxa shifted latitude or elevation range in response to changes in Quaternary climate. Because many modern trees display adaptive differentiation in relation to latitude or elevation, it is likely that ancient trees were also so differentiated, with environmental sensitivities of populations throughout the range evolving in conjunction with migrations. Rapid climate changes challenge this process by imposing stronger selection and by distancing populations from environments to which they are adapted. The unprecedented rates of climate changes anticipated to occur in the future, coupled with land use changes that impede gene flow, can be expected to disrupt the interplay of adaptation and migration, likely affecting productivity and threatening the persistence of many species.

http://science.sciencemag.org/content/sci/292/5517/673.full.pdf

Range shifts and adaptive responses to Quaternary climate change.

Seven two-trait combinations (e.g. breeding system and seed dispersal mechanism) of five life history characteristics were used to analyse interspecific variation in the level and distribution of allozyme genetic diversity in seed plants. Highly significant differences were seen among categories for all seven comparisons. Life form and breeding system had highly significant influences on genetic diversity and its distribution. Regardless of other traits, outcrossing species tended to be more genetically diverse and had less genetic differentiation among their populations. Similarly, woody plants have less among population differentiation and somewhat more genetic diversity than non-woody species with similar life history traits. An analysis of twelve plant families indicated that species within families with predominately outcrossing, woody species had more genetic diversity and less interpopulation differentiation than species within families with predominately herbaceous species.

Effects of life history traits on genetic diversity in plant species

Allozyme diversity in plant species

Plant populations are not randomly arranged assemblages of genotypes but are structured in space and time (2, 29, 49, 58, 84, 112). This structure may be manifested among geographically distinct populations, within a local group of plants, or even in the progeny of individuals. Genetic structure results from the joint action of mutation, migration, selection, and drift, which in tum must operate within the historical and biological context of each plant species. Ecological factors affecting reproduction and dispersal are likely to be particularly important in determining genetic structure (2, 31, 58). Reproduction is the process that translates the current genotypic array into that of subsequent generations, while the dispersal of pollen and seeds determines the postreproductive pattems of gene dispersion within and among populations. Although the concept of genetic structure has been used in various ways (58, 130, 154), we limit our definition to the nonrandom distribution of alleles or genotypes in space or time and disregard genome organization and meiotic processes that can also affect allele and genotype frequencies. Because of the limited mobility of plants, their genetic structure implies spatial structure, or the actual physical distribution of individuals. While spatial pattems often have genetic implications, nonrandom genetic pattems can exist without a nonrandom distribution of individuals. Conversely, a population may have a nonrandom spatial distribution without any accompanying genetic structure. Spatial and genetic patterns are often assumed to result from environmental heterogeneity and differential selection pressures (22, 53, 131, 132). Selection is a ubiquitous feature of natural populations; it alters gene and

Ecological determinants of genetic structure in plant populations

The plant allozyme literature was reviewed to: (1) compare genetic diversity in long-lived woody species with species representing other life forms, and (2) to investigate whether the levels and distribution of genetic diversity in woody species are related to life history and ecological characteristics. Data from 322 woody taxa were used to measure genetic diversity within species, and within and among populations of species. Woody species maintain more variation within species and within populations than species with other life forms but have less variation among populations. Woody species with large geographic ranges, outcrossing breeding systems, and wind or animal-ingested seed dispersal have more genetic diversity within species and populations but less variation among populations than woody species with other combinations of traits. Although life history and ecological traits explain a significant proportion (34%) of the variation among species for the genetic parameters measured, a large proportion of the interspecific variation is unexplained. The specific evolutionary history of each species must play an important role in determining the level and distribution of genetic diversity.

Factors influencing levels of genetic diversity in woody plant species

Numerous studies of morphological and physiological traits (reviewed in 3, 57, 95, 132, 135) as well as the more recent studies of enzyme loci (reviewed in 21, 52, 63) have generally shown the existence of significant amounts of genetic variation both within and between plant populations. These reviews (21, 52, 63) have also demonstrated considerable variation among species in intrapopulation allozyme variation. For instance, Hamrick (63) found that populations of woody plants contained higher levels of genetic variation than did populations of herbaceous species; Gottlieb (52) and Brown (21) demonstrated that predominantly outbreeding species maintain higher levels of intrapopulation genetic variation than predominantly inbreeding species. Nevo (111) found that habitat generalists and animal species with cosmopolitan or tropical distributions were typically more variable than species with specialized habitat preferences or temperate distributions. While these results are interesting and informative, they consider the influence of only a few evolutionarily important characteristics on the main-

https://www.jstor.org/stable/info/2096789

J. L. Hamrick

Papers

Allozyme diversity in plant species

Effects of life history traits on genetic diversity in plant species

Ecological determinants of genetic structure in plant populations

Factors influencing levels of genetic diversity in woody plant species

Relationships Between Life History Characteristics and Electrophoretically Detectable Genetic Variation in Plants