Modelling seed dispersal in restoration and invasions

[摘要] Dispersal plays an essential role in determining the distribution of populations of species,especially species expanding their ranges. Two disciplines are concerned with gainingunderstanding of spread of species, namely restoration ecology and invasion biology. Con-ceptual understanding of dispersal, its mechanisms and its management is essential to bothdisciplines. Nevertheless, the disciplines have quite opposite objectives: in restoration ecol-ogy, spread of indigenous species into transformed landscapes is promoted, while invasionbiology aims to prevent the (further) spread of alien species into pristine or restored habi-tats. Despite these two opposite objectives of facilitating spread and preventing spread oftheir respective target species, these disciplines have essentially the same requirements interms of information needed for restoration. In this thesis, I will present two modellingstudies-one looking at the impact of two different seed-feeding alien control agents onthe spread of Hakea sericea, the other investigating the recolonisation by Dicerothamnusrhinocerotis of an old field dominated by Cynodon dactylon. Based on these studies, Iwill draw conclusions for the management in each case. In a second step, I will comparethese two seemingly-different studies and draw conclusions on how these two disciplinescan learn from each other, and how conclusions drawn and management recommendationsdeveloped for the one discipline can be translated for the other. The invasion biologystudy concluded that seed-feeding biocontrol agents do have a considerable impact on thevelocity of the spread of the target species. In addition, management recommendationsincluded the possibility of substituting seed-feeding biocontrol agents with an increasedfire frequency where the negative impact on natural vegetation, on the site invaded by thetarget species, is acceptable. The restoration study concluded that the main impact on thevelocity of spread, and the speed of the return of the shrub species onto the old fields, isthe availability of micro-sites. A sensitivity analysis showed the even a slight change from1% to 2% increases the velocity and pattern of spread dramatically. The other parametersplaying an important role are the mean rate of establishment and the time span between

[发布机构] Stellenbosch University