| Summary: | Large areas of moist upland grassland in KwaZulu-Natal are severely fragmented
due to large scale farming of exotic trees. The aims of this thesis were to
determine whether habitat fragmentation of these grasslands has a detrimental
effect on plant-pollinator interactions and hence the reproductive output of the
wildflower species occurring there and whether the magnitude of this effect can be predicted by breeding and pollination system characteristics.
The 24 wildflower species included in this study appear to support a rich
and diverse pollinator community, including long-tongued solitary bees, long-tongued
flies, hawkmoths and sunbirds. Two thirds of the wildflower species
appear relatively specialised in terms of pollination, with six species entirely
dependent either on a single species or a specific functional type of pollinator for
pollination. The majority of wildflower species (90%) were found to be incapable
of autonomous self-pollination and thus dependent on pollinators for fruit and
seed set. At least six species are obligately xenogamous. Little evidence was
found for pollen limitation in undisturbed moist upland grassland, suggesting that
these grasslands are characterised by high levels of pollinator activity. Greater
levels of pollen limitation of reproductive output in habitat fragments was
evident in two species, suggesting that depressed reproductive output in habitat
fragments may be the consequence of a decrease in the quantity and/or quality of pollinator services.
Significant detrimental effects of habitat fragmentation on reproductive
output were evident in two thirds of the wildflower species, with 94% of the
species exhibiting overall declines in seed set per flower from the continuous
grassland site to the habitat fragments. The median decline in seed set per
flower for the wildflower species was found to be 33.0%. Significantly more
species experienced overall declines in reproductive output than would have been
expected by chance alone. Only specificity of the pollination interaction in terms
of number of pollinator taxa involved was found to be significantly related to
percentage change in seed set from continuous to fragment habitats. This effect
was diminished when other factors were included in a multiple regression.
Results support Bond's (1994) hypothesis that degree of specificity in pollination
systems is important in determining extinction risk of a given plant species.
Declines in reproductive output of a range of wildflower species in grassland
habitat fragments may affect the local persistence of these populations,
particularly if recruitment is seed-limited. === Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.
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