Reduced colonization capacity in fragmented populations of wind-dispersed grassland forbs
Article first published online: 11 DEC 2002
Journal of Ecology
Volume 90, Issue 6, pages 1033–1043, December 2002
How to Cite
Soons, M. B. and Heil, G. W. (2002), Reduced colonization capacity in fragmented populations of wind-dispersed grassland forbs. Journal of Ecology, 90: 1033–1043. doi: 10.1046/j.1365-2745.2002.00729.x
- Issue published online: 11 DEC 2002
- Article first published online: 11 DEC 2002
- Received 21 February 2002 revision accepted 10 September 2002
- habitat fragmentation;
- population size;
- seed production;
- site productivity;
- wind dispersal
- 1Habitat fragmentation as a result of intensification of agricultural practices decreases the population size and increases the site productivity of remnant populations of many plant species native to nutrient-poor, species-rich grasslands. Little is known about how this affects the colonization capacity of populations, which is highly important for regional species survival. We studied the effects on four wind-dispersed forbs that represent two major dispersal strategies in grasslands: Cirsium dissectum and Hypochaeris radicata, which have plumed seeds and are adapted to long-distance dispersal by wind, and Centaurea jacea and Succisa pratensis, which have plumeless seeds and are adapted to only short-distance dispersal by wind.
- 2Colonization capacity decreased with decreasing population size. This was due to lower seed germination ability in all species, and a lower seed production and a narrower range of seed dispersal distances in the species with plumed seeds. Inbreeding depression is the most likely cause of this. We found no evidence for a stronger selection for reduced dispersal in smaller populations.
- 3Increasing site productivity changed the colonization capacity of all species. The capacity for colonization of nearby sites increased, due to higher seed production and seed germination ability, but the capacity for colonization of distant sites decreased, due to a lower long-distance dispersal ability.
- 4Seed dispersal ability and germination ability were negatively correlated in the species with plumeless seeds, but not in the species with plumed seeds. The dispersal ability of individual plumed seeds remained constant under changes in population size and site productivity. This indicates a strong selection pressure for long-distance dispersal ability in these species.
- 5When habitat fragmentation results in a simultaneous decrease in population size and increase in site productivity, both the local survival probability and the colonization capacity of remnant populations of wind-dispersed grassland forbs are likely to be severely reduced. This increases regional extinction risks of the species.