MSc., Faculty of Science, University of the Witwatersrand, 2011 / This research investigated the susceptibility of South African indigenous aquatic
plants to competition from invasive species, using the competitive interactions of
two sets of aquatic plants as a potential indicator. These interactions were
studied in two separate experiments: the submersed weeds, Hydrilla verticillata
(L.F.) Royle (Hydrocharitaceae) and an indigenous species, Lagarosiphon major
(Ridley) Moss (Hydrocharitaceae) and; the floating weeds, Azolla filiculoides
Lamarck (Azollaceae) and the indigenous Spirodela polyrhiza (L.) Schleid
(Lemnaceae). Plants were grown under differing nutrient levels, and in an
addition series of eight different densities, using the reciprocal yield model to
estimate competitive ability. The invasive Hydrilla outcompeted Lagarosiphon in
terms of mean length, dry mass, and survival. Major algal infestation in the high
nutrient level of the Hydrilla/Lagarosiphon experiment altered light and nutrient
conditions, which may have played a significant role in the lack of establishment
of Lagarosiphon and the poor growth performance of Hydrilla. The invasive
Azolla and indigenous Spirodela both performed well in terms of plant mass and
increase in number. While Azolla was affected by intraspecific competition, it
showed a steady increase in growth and multiplication with an increase in
nutrients. The individual mass of Spirodela plants was highest in the low nutrient
level, and multiplication rates were greatest in the high nutrient level. Results
indicate that the susceptibility of indigenous plants may be increased in highnutrient
systems, and that a continuous monitoring programme of aquatic alien
species is vital in protecting our indigenous plants from extinction. This research
recommends that the method of investigating competitive interactions between
alien and indigenous plants be repeated with a variety of aquatic plants, as a
means of anticipating susceptibility to invasions.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/11238 |
| Date | 02 February 2012 |
| Creators | Taylor, Kelly May |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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