Freshwater amphipods in southern Africa are divided into three distinct elements. Five ingolfiellid species occur in Namibia, six Sternophysinx species are found in the northern Cape Province and Transvaal, while 12 Paramelita species are restricted to the south-western Cape. The crangonyctoid genus Paramelita was last reviewed in 1981 based mainly on a reassessment of museum material. Thus, large scale field surveys of these amphipods have not been undertaken since they were first described by Barnard in 1916 and 1927. In addition, little is known about the ecology of these amphipods. This thesis examines the systematics, distribution and aspects of the ecology of Paramelita. After an extensive sampling programme in 1989 and 1990, several new species were discovered. Four new species, whose affinities with the known species were not immediately evident, were initially described, and later, after further analyses .of morphological and genetic differentiation amongst Paramelita populations, eight other new species were recognised. A phenetic analysis of the 24 Paramelita species revealed the existence of three distinct groups. The new genus Afrocrangonyx was proposed to accommodate seven of these species, whilst a single species was placed in the new genus Aquadulcaris. Sixteen species remained in Paramelita. Based on a cladistic analysis of morphological data, a fully resolved phylogenetic tree was obtained for Afrocrangonyx, but not for Paramelita, suggesting that the latter genus is not monophyletic. A population of P. nigroculus in Window Stream, Table Mountain, was selected for a detailed ecological study. P. nigroculus occurred at high densities, and showed no seasonal breeding patterns. An investigation of thermal acclimation and tolerances to high temperatures in P. nigroculus individuals showed that their acclimation rates and lethal limits were similar to many other crustaceans. P. nigroculus individuals feed mainly on allochthonous input. An investigation of the nature, timing and magnitude of this input indicated that litter was dominated by abscissed leaves which fall throughout the year, peaking in summer. Leaf fall values and benthic detritus standing stocks were within the range reported for headwaters worldwide. A study of leaf retention capabilities of two similar headwaters revealed that amphipod abundances were positively correlated with leaf retention characteristics. Leaf retention was strongly influenced by discharge, with increasing discharges resulting in decreases in retention and stream bed complexity. Thus the stream with higher discharges was less favourable for colonisation by amphipods. Since P. nigroculus occurred at such high densities, it was expected to play a significant role in breakdown of detritus. Breakdown of three riparian leaf species in litter bags submerged in two streams was investigated. Litter bags were designed to allow amphipod access, yet retain fragments which resulted from physical abrasion and feeding activity. Breakdown was rapid, and the decomposition rate of one of the leaf species was the highest ever recorded for a riparian leaf species. Thus, it was concluded that where they occur at high densities, Paramelita individuals play a major role in the detritus dynamics of the stream.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/18334 |
| Date | January 1991 |
| Creators | Cook, B A |
| Publisher | University of Cape Town, Faculty of Science, Department of Biological Sciences |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, Doctoral, PhD |
| Format | application/pdf |
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