Modelling seed dispersal in restoration and invasions
Date
2008-03
Authors
Krug, Rainer Michael
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
Dispersal plays an essential role in determining the distribution of populations of species,
especially species expanding their ranges. Two disciplines are concerned with gaining
understanding of spread of species, namely restoration ecology and invasion biology. Con-
ceptual understanding of dispersal, its mechanisms and its management is essential to both
disciplines. Nevertheless, the disciplines have quite opposite objectives: in restoration ecol-
ogy, spread of indigenous species into transformed landscapes is promoted, while invasion
biology 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 of
their respective target species, these disciplines have essentially the same requirements in
terms of information needed for restoration. In this thesis, I will present two modelling
studies—one looking at the impact of two different seed-feeding alien control agents on
the spread of Hakea sericea, the other investigating the recolonisation by Dicerothamnus
rhinocerotis of an old field dominated by Cynodon dactylon. Based on these studies, I
will draw conclusions for the management in each case. In a second step, I will compare
these two seemingly-different studies and draw conclusions on how these two disciplines
can learn from each other, and how conclusions drawn and management recommendations
developed for the one discipline can be translated for the other. The invasion biology
study concluded that seed-feeding biocontrol agents do have a considerable impact on the
velocity of the spread of the target species. In addition, management recommendations
included the possibility of substituting seed-feeding biocontrol agents with an increased
fire frequency where the negative impact on natural vegetation, on the site invaded by the
target species, is acceptable. The restoration study concluded that the main impact on the
velocity of spread, and the speed of the return of the shrub species onto the old fields, is
the availability of micro-sites. A sensitivity analysis showed the even a slight change from
1% to 2% increases the velocity and pattern of spread dramatically. The other parameters
playing an important role are the mean rate of establishment and the time span between
Description
Thesis (PhD (Conservation Ecology and Entomology))--Stellenbosch University, 2008.
Keywords
Seed dispersal, Ecological restoration, Invasion biology, Ecological modelling, Dissertations -- Conservation ecology and entomology, Theses -- Conservation ecology and entomology