Introduction - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 2

Much attention has been devoted to the effects of founder number
and the rate of population growth on the population genetics of nascent
stands (e.g., see Frankham et al. 2002; Allendorf and Luikart 2007). While
the effects of founding geometry on population expansion and genetic
diversity retention have been less thoroughly investigated, some studies
have been conducted. For example, Lacy (1987) demonstrated by computer
simulations that, in some cases, subdivision of founders leads to increased
loss of heterozygosity within subpopulations but increased retention of
genetic variation across all subpopulations compared to introduction
of founders in one undivided group. Margan et al. (1998), working
with laboratory-manipulated Drosophila populations, determined that
subdivided populations can in some, but not all, cases maintain higher
levels of genetic diversity (estimated heterozygosity) than populations
initiated with the same number of founders introduced and maintained
as one continuous population.
Geometry and Founding Effects in Artifi cial Populations
Spationumeric founding effects are not merely of theoretical interest, but
also of considerable practical and economic import in human-infl uenced
populations. For example, newly establishing, isolated populations are
created in plant or habitat restoration projects, whether to protect rare
species or to support the provisioning of ecosystem services (Benayas et
al. 2009). While such projects are likely to increase in the future, there has
been little work on ways in which introduction of founders in different
numbers in different spatial patterns can affect the preservation of genetic
diversity. For example, conservation practitioners who want to restore or
introduce a plant species to a nature preserve lack tools to help them decide
how best to spationumerically establish founders in order to maximize
the conservation of genetic diversity in the future. Most texts and papers
on conservation biology offer very general advice, such as “Introduce as
many individuals as possible” (e.g., Falk et al. 1996; Frankham et al. 2002;
Primack 2006). Planting densities and introduction geometry are usually
vaguely addressed, if even mentioned, with regard to conserving genetic
diversity.
However, since it is costly to introduce a species, it would be prudent
to plan carefully so as to maximize population growth and conservation of
genetic diversity. Introduction costs can include the following:
1. Harvesting seeds and, sometimes, harvesting or growing seedlings
to be introduced. For rare species, this can involve extensive travel
and searching time. In most cases for rare species, contracts must be
established with government agencies or private concerns.