Genetic and ecological consequences of small population size in Lychnis viscaria

Abstract

Human induced changes in the landscape and resulting habitat destruction is endangering the survival of numerous plant species. In this thesis I used Lychnis viscaria (Caryophyllaceae), a perennial herb, as a model plant to study some of the genetic and ecological factors related to habitat fragmentation that may influence the viability of small plant populations. L. viscaria is common in Southern Finland but occurs in small, endangered populations in Central Finland. Small and isolated populations had less genetic variation, measured with allozymes, but the viability of individuals in these populations (germination rate, seedling mass or seed yield) was not lower than in large populations. However, in longer time scale the loss of genetic variation in small populations may endanger their ability to adapt to changing environment. Although levels of allozyme variation do not necessarily reflect the levels of adaptively significant variation, in L. viscaria a relationship between levels of allozyme variation and morphological variation was found. However morphological population differentiation did not reflect the allozyme differentiation. Habitat fragmentation can also affect the mutualistic plantpollinator interactions. The pollinator visitation rates were higher in large and, surprisingly, sparse populations. Higher visitation rates in sparser populations were probably due to their larger area and inflorescence size. Pollinator behaviour was also affected by plant density. The changes in the plantpollinator relationship did not directly affect reproductive success of the plants, but probably lowered the quality of seeds by increasing inbreeding depression. The study on the expression of inbreeding depression revealed that inbred populations may be adapted to inbreeding, expressing less inbreeding depression at early life stages (germination), but may still express relatively high inbreeding depression at later stages. This study provides information to be applied in modern conservation biology, when designing management plans and policies for endangered plant populations.