Hamrick (1983) and Loveless and Hamrick (1984) used several life history and ecological traits to determine whether inter-population neutral genetic heterogeneity was related to the species' characteristics. They found that life form, geographic range, breeding system and taxonomic status had significant effects on the partitioning of genetic diversity within and among plant populations. For detailed information on how breeding system, floral morphology, mode of reproduction, pollination mechanism, seed dispersal, seed dormancy, phenology, life cycle, timing of reproduction, successional stage, geographic range, population size/density and population spatial distribution may affect the genetic variation within populations—as well as the genetic structure within and among populations—see a literature review of several case studies undertaken by Loveless and Hamrick (1984).
In addition, Hamrick and Godt (1996) performed two-trait combination analyses on five different life history characteristics (breeding system, seed dispersal mechanism, life form, geographic range and taxonomic status) in order to study how genetic diversity varies in seed plants. They analyzed inter-specific variation of allozyme genetic diversity to determine the percentage of polymorphic loci within the species (P), the genetic diversity within the species (Hardy-Weinberg expected heterozygosity, Hes, Weir 1990) and the proportion of total genetic diversity among populations (GST).
The life history traits studied were:
- Breeding system: outcrossing, selfing and mixed mating.
- Seed dispersal mechanism: attached, gravity, animal, wind.
- Life form: annual, short-lived and long-lived perennial taxa.
- Geographic range: endemic, regional, narrow, widespread.
- Taxonomic status: gymnosperm, dicotyledon, monocotyledon.
The authors concluded that all examined traits have significant effects on the genetic parameters considered, but life form and breeding system have the most significant influence on the levels and distribution of genetic diversity. Their main conclusions were:
- Regardless of other traits, outcrossing species tend to be more genetically diverse and have less genetic differentiation among populations.
- Woody plants have less differentiation among populations and more genetic diversity than non-woody species with similar life history traits.
- Species in families with predominately outcrossing and woody species had more genetic diversity and less inter-population differentiation than species within families with predominately herbaceous species.
- Species with low inter-population genetic differentiation tend to have more overall genetic diversity.
- Woody plants have lower GST values and somewhat higher P, and Hes values than herbaceous plants with the same combinations of life history traits, regardless of their phylogenetic relationship.
