Integrating demographic and genetic approaches in plant conservation

Abstract

We summarize the problems that populations of formerly common plants may encounter when habitat fragmentation isolates them and reduces population size. Genetic erosion, inbreeding depression, Allee-effects on reproductive success, catastrophes and environmental stochasticity are illustrated with studies on species that have recently become rare in The Netherlands due to habitat fragmentation. These clearly indicate that population viability is negatively affected. We also show that in the recent literature (since 1980), most studies on the conservation of rare plants have addressed population genetic structure and relationships between genetic variation and population size. Though important, these studies are not suitable for assessing the importance of genetics for population viability. In turn, demographic studies can detect changes in vital rates in small populations, but cannot reveal underlying genetic causes. Fitness and demographic studies are also well-represented in the literature, but remarkably few studies have attempted to integrate empirical demographic and genetic studies. We discuss two approaches to fill this very important lacuna in our knowledge. One of these constructs matrix-projection models on the basis of demographic censuses of—if possible—large and viable populations, and combines these with the results of experiments to determine inbreeding effects on demographic transitions and, subsequently, population growth and extinction. The other approach is to demographically monitor experimentally created small and large populations with low and high genetic variation and measure their actual growth rates and probabilities of extinction. We conclude that demography and demographic-genetic experiments should play a central role in plant conservation genetics.