Testing for ecological and genetic Allee effects in the invasive shrub Senna didymobotrya (Fabaceae)
- For an introduced plant species to become invasive, it must be able to reproduce even in initially small populations We tested for Aliee effects (reduced reproductive performance of individuals in small populations) in the nonclonal, NW-pollinated shrub Senna didymobotrya in its invasive range in South Africa. The species is self-compatible. but we found that in its invasive range in South Africa it requires pollinators to set seed. Nearly all stigmas (90%) received pollen. but natural fruit set has very low (3-20%), Pollen receipt and fruit set were not significantly correlated with population size. We thus found no evidence for an ecological Alice effect arising from pollen limitation in small populations. Offspring seedling performance, measured in terms of stern volume and leaf area, was also not significantly correlated with the number of plants in the source population. indicating that genetic Alice effects, such as inbreeding depression, are either absent or of such a small magnitude that they would be unlikely to limit furtherFor an introduced plant species to become invasive, it must be able to reproduce even in initially small populations We tested for Aliee effects (reduced reproductive performance of individuals in small populations) in the nonclonal, NW-pollinated shrub Senna didymobotrya in its invasive range in South Africa. The species is self-compatible. but we found that in its invasive range in South Africa it requires pollinators to set seed. Nearly all stigmas (90%) received pollen. but natural fruit set has very low (3-20%), Pollen receipt and fruit set were not significantly correlated with population size. We thus found no evidence for an ecological Alice effect arising from pollen limitation in small populations. Offspring seedling performance, measured in terms of stern volume and leaf area, was also not significantly correlated with the number of plants in the source population. indicating that genetic Alice effects, such as inbreeding depression, are either absent or of such a small magnitude that they would be unlikely to limit further spread of S. didymobotrya in South Africa…
