Evolutionary consequences of habitat fragmentation: selection on plant phenotypic traits

Habitat fragmentation is considered to be one of the major threats to biological diversity worldwide. Plant-animal interactions have often been found to be disrupted by habitat fragmentation, and mutualists are known to exert selective pressures on plant phenotypic traits. The two major aims of this thesis were to investigate fragmentation effects on phenotypic selection on plant traits and to determine if fragmented plant populations are able to respond to such selection pressures. The study was conducted with the perennial, self-incompatible plant species Phyteuma spicatum, which occurs in highly fragmented deciduous hardwood forests in north-western Germany. Results of the four studies integrated in this thesis show, that selection pressures on plant phenotypic traits may be stronger in small or low-density populations and small populations may suffer from reduced heritable trait variation compared to large populations. However, patterns were quite variable within this study system.