Monitoring Endangered Species Populations: Gene Dispersal Can Have Pronounced Effects on the Relationship between Census Size and Genetic Diversity

Abstract

Anthropogenic activities are increasing habitat fragmentation, as well as the number of threatened and endangered spe cies. Thus, isolated fragments with natural remnant stands, or in situ or ex situ endangered species rescue populations, are on the rise. The most common method for assessing the “conservation health” of such populations is to determine or estimate the census size. However, while it is known that the census size of a population does not always correlate with its genetic diversity, methods for modeling how different factors can drive variation in the relationship of census size to genetic diversity in plant populations are needed. Here we use the computer program NEWGARDEN to investigate how the relationship of stand size versus genetic diversity (measured as both the percent of the founding alleles retained and F IT ) can be extremely variable depending on founder number, founder density, and gene dispersal distances. Popu lations of endangered species that appear to have the same conservation health in terms of similar population numbers may differ greatly in their conservation health as indicated by the genetic diversity they retain. NEWGARDEN can be used to explore how different founding and intra- or interspecific life history characteristics can affect genetic diversity relative to census size. If proper historical data exist, NEWGARDEN can also be used to estimate the percent of found ing genetic diversity remaining in a given stand.