Conclusions and Discussion - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 335

the population genetic characteristics of resulting populations, these effects
often having different trajectories that carry on through several generations.
If many or even most populations in nature have at least a partial history
of differing local founding geometric characteristics, then this may obscure
the sought-after correlations of life history features with population genetic
diversity patterns. It must be kept in mind that, when sampling across plant
populations to examine how various evolutionary forces may have acted
to modify the genetic diversity of populations, one may be sampling across
a patchwork of “subpopulations” that have patterns of genetic diversity
affected by very different local founding and expansion patterns.
Implications for Conservation and Restoration Biology
Numerous in situ and ex situ projects aimed at restoring population
numbers and species while conserving adequate genetic diversity are
now underway or in the planning stages (e.g., Falk et al. 1996; Guerrant
et al. 2004). In some cases, such projects may involve very low numbers
of wild source plants (in the tens or hundreds) and equally low numbers
of reintroduced plants (Cochrane et al. 2007). When possible, planting
available offspring of rare species at more than one site is desirable as a
means of “bet hedging” against localized losses due to fi re, pathogens, or
other factors, diminishing the number of offspring available per site. High
mortality rates often accompany introductions, further lowering the size
of initial restoration populations (Primack and Miao 1992; Allen et al. 2001;
Primack 2006; Cochrane et al. 2007).
In the introduction, it was pointed out that conservation and restoration
projects involving population establishment and maintenance can be
expensive for a host of reasons. The costs will vary with the situation. For
genetic diversity preservation, different issues may be involved for different
species. For example, one species may be especially sensitive to inbreeding
and increased homozygosity, while another project aims at conserving
a broad complement of distinct alleles from several small and isolated
subpopulations that were once contiguous. In almost all conservation and
restoration projects, rapid growth and expansion of populations will be
desirable. Ongoing projects may also need various types of management
as populations develop. This could include supplementation or removal
(e.g., thinning) of individuals, mixing of individuals, harvesting of seed or
pollen, fi re management, or pest control. As shown in this topic, another
central issue is that the placement of founders must be optimized in terms
of their spacing, degree of subdivision, and distance from borders, barriers
(e.g., a habitat that is of lower quality or unoccupiable), or corridors, to
promote both the greatest protection against genetic diversity erosion and