Knowledge of the life history and ecological characteristics of woody plant species allow predictions of the level and distribution of genetic diversity within and among populations. Generalizations developed from such analyses can be used to develop sampling strategies for the preservation of genetic diversity.Abstract.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.

No abstract

Estimates of genetic diversity maintained by plant species and its distribution within and among populations allows plant geneticists to predict, in a general way, the evolutionary potential of species. Single-gene markers, particularly allozymes, have been used to measure the genetic diversity of species. In this paper, the plant allozyme literature was reviewed to compare levels of genetic variation maintained by crop and non-crop species. Crop species (plant species intentionally cultivated by humans) have more allozyme diversity as a whole than other seed plant species, although the mean genetic diversity partitioned within populations of crop species was similar to that of other plant species. Populations of crop species were more genetically heterogeneous, an observation that was probably due to the higher proportion of crops that reproduce by self fertilization. Dicotyledonous crops have much less genetic diversity than monocotyledonous crops at the species and the population level and exhibit more inter-population genetic differentiation. Annual and perennial crop species had similar levels of genetic diversity and partitioned genetic diversity in similar ways. Predominantly selflng crops had somewhat less genetic diversity than outcrossing or mixed-mating species. Selflng crops exhibited more population-to-population variation in genetic diversity and allele frequency differences were much greater among their populations. High population-to-population variation in genetic diversity increases the importance of empirical data for the design of sampling protocols. B IOLOGISTS define evolution as a change in the genetic composition of populations (Dobzhansky, 1970). Since the availability of genetic variation is a necessity for evolutionary change, a central question in evolutionary biology has been how much genetic variation occurs within species or populations. Of equal importance is the distribution of genetic diversity among populations. Applied evolutionary biologists, particularly crop breeders, are constantly concerned with the availability of genetic variation for desirable traits in commercially important species. Thus, the development and maintenance of a reservoir of genetic variation for commercially valuable species has been a major concern. To this end, crop breeders have been actively involved with the collection, preservation, and maintenance of landraces, cultivars, and accessions of crop species and their wild relatives. In fact, plant geneticists with crop-breeding backgrounds have played a major role in the development of plant conservation genetics (e.g.,

Allozyme diversity was examined in four rare, high‐montane plant species from the Appalachian Mountains of southeastern North America. These species may represent relictual members or descendants of an alpine community that was more widespread during the late Pleistocene. We sampled five populations of Geum radiatum (Rosaceae), Carex misera (Cyperaceae), Trichophorum cespitosum (Cyperaceae), and the four known populations of Calamagrostis cainii (Poaceae). Genetic diversity was low for all species but was typical of that found for plant species with limited ranges. Low genetic diversity may reflect historical events associated with changes in the species’ biogeography. As the Pleistocene climate warmed, suitable habitat decreased in areal extent and became fragmented, probably resulting in smaller, more‐isolated populations. In recent times these species, which co‐occur in fragile rock outcrop habitats, have been adversely affected by human activities. Genetic analyses revealed reduced diversity in populations of decreasing size for three species. Estimates of gene flow were low (Nm < 1.0) in all four species. Positive associations between genetic diversity and population size, evidence of recent population declines, and the low estimates of gene flow suggest that genetic drift may play a prominent role in shaping the present‐day genetic composition of these species. Furthermore, these data suggest that the genetically depauperate populations are unlikely to regain genetic variation without human intervention.

No abstract