Browsing by Author "Taylor, Stuart."

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Complementarity between two metrics which use invertebrates to assess riparian conditions of rivers.
(2005) Smith, Jenny.; Samways, Michael John.; Taylor, Stuart.
Conservation of streams involves an understanding of their physical , chemical and biological entities. SASS5 is a biomonitoring method developed to monitor the habitat quality of a water body. It is based on differential scores attributed to various macroinvertebrate families with varying degrees of sensitivity to anthropogenic impact. This method , however, does not assess impacts on particular species. Odonata are good candidates for study at the species level as they are well researched and males are easily identified . As adults, they are known to be sensitive indicators of both riparian and river conditions. Yet Odonata cannot be an umbrella taxon for all other taxa . Therefore, the main aim of this study is to determine the complementarity of the two metrics (Odonata assemblages and SASS5), establishing whether Odonata assemblages offer additional information on, or insight into, riverine habitat quality as portrayed by SASS5. To accomplish this, certain objectives were addressed . 1) The variation of SASS5 scores and 2) Odonata assemblages between river systems, structural habitat types (open or closed canopies) and compositional habitat types (indigenous or alien vegetation). 3) Whether SASS5 scores vary to the same extent, and, 4) on the same spatial scale (river system and point localities) as Odonata abundance and species richness . The relationship between these two metrics was determined along three rivers in the Pietermaritzburg basin. Sampling units (SUs) with extremes in vegetation structure (sunlight and shaded SUs) and vegetation composition (alien or indigenous) were selected. Using this range of environmental conditions placed environmental extremes on the macroinvertebrate populations at point localities and having three different river systems added the dimension of variation over a broader scale, thus stretching the two metrics to investigate whether both responded similarly or in different ways. Results indicated that both metrics provide a similar portrait of overall river conditions. At the smaller spatial scale, the Odonata assemblage, unlike SASS, was highly sensitive to the riparian vegetation. Odonata species were less sensitive to vegetation composition but differentially sensitive to vegetation structure. However, landscape context is also important, with point localities being affected by the neighboring dominant habitat type. Larval Odonata alone did not provide this information. Overall, aquatic macroinvertebrates and adult Odonata provide a highly complementary pair of metrics that together provide large spatial scale (river system) and small spatial scale (point localities) information on the level of impact of stressors such as riparian invasive alien trees.
On the behavioural ecology and vocal communication of the brown-headed parrot (Poicephalus cryptoxanthus)
(2002) Taylor, Stuart.; Perrin, Michael Richard.; Lawes, Michael John.
The Brown-headed Parrot (Poicephalus cryptoxanthus) is a poorly known species inhabiting open woodland in south-eastern Africa. This study elucidates critical aspects of the species ecology and although each of these categories impinge on one another, it concentrates on two broad biological aspects, diet and breeding biology, and vocalizations. The species has a generalist diet, switching from one suite of food species to another as and when those species become available, with no species critical for its survival. Analysis of dietary items throughout the year and comparison with handling times and availability reveals that at no time is the species under dietary constraint. Evidence from association indices and behavioural observation shows that the popular view that the Brown-headed Parrot forms pairs just before breeding is erroneous. Birds retain pair bonds and the bond is long-term, lasting at least throughout the year. Congregations are therefore of a classical fission/fusion type with the sub-units being the paired males and females. A mathematical model of the growth of captive chicks is presented, as a guideline to alert potential breeders of Brown-headed Parrots of malnutrition or disease. The species is a secondary cavity hole nester and whilst, the breeding biology of the species is summarised, the importance of large and old trees for breeding opportunities of the species is emphasised. This theme is continued by testing various adaptive hatching hypotheses as possible explanations of asynchronous hatching in the species. It is suggested that asynchronous hatching may be an adaptive strategy moderating against the number of suitable nesting cavities. The vocalization repertoire of the Brown-headed Parrot is described and seven separate vocalizations are recognized. None of these are associated with sexual situations, offering further evidence of a long-term pair bond. Evidence is offered that Brown-headed Parrot chicks can recognise their parents from individual vocal signatures supporting previous evidence from a number of species where chicks may mingle with unrelated chicks. Conversely, parents seem to be unable to recognise their chicks in the same way. It is concluded that this inability may be a result of strong one-way selection pressure, where the costs outweigh the benefits for parents with more than one chick or may be related to the experimental design. Individual recognition by voice implies individual voice differences and the adult double chip contact call is analysed using multivariate statistical techniques. The analysis separates individuals on the basis of frequency and temporal patterns and it is concluded that these parameters may allow individual voice differentiation. Finally, high frequency aspects of the double chip contact call are examined. These frequencies lie above the normally accepted upper threshold of avian hearing. From laboratory and field experiments, behavioural evidence is presented suggesting that the Brown-headed Parrot reacts to these frequencies and may use their degradation as a means of ranging distances to conspecifics.
Rodent damage control in commercial forestry in the Natal Midlands, South Africa.
(1996) Taylor, Stuart.; Perrin, Michael Richard.
Rodents cause damage in commercial forests by gnawing at the bark of the trees. It is currently estimated that rodent damage in commercial forestry costs the industry R50 million per annum. The species of rodents which cause the damage are not known, neither is the reason behind this behaviour. Through stomach analysis it has been established that 3 species are involved Otomys irroratus, Rhabdomys pumilio and Mastomys natalensis, however this behaviour is confined to the winter. Chemical analysis of the bark reveals that the percentage concentration of nitrogen varies seasonally. The period of high concentration correlates with periods when the natural food of the rodents is restricted and when bark gnawing is most prevalent. In the past the industry's response to the damage has been to treat the areas with rodenticides. Using standard CMR methods, the two commercially-licensed rodenticides and raptor perches were tested to examine their efficacy as rodent control strategies. It was found that at a lower application of I block of rodenticide every third tree there is little difference in the effectiveness of the rodenticide brands and there is also little reduction in the abundance of the rodents. At a higher application rate of I block per tree, the abundance of rodents is reduced but termination of the treatment results in the rodent numbers quickly recovering, indeed they surpassed their original population numbers within 4 months. Apart from the environmental dangers of applying such concentrations of poison, this is clearly an uneconomic solution. My results indicate that at first planting, the sites should be provisioned with raptor perches at a density of 16 ha⁻². Contrary to accepted policy the perches do not require cross pieces, which add to the expense and offer no advantage in raptor residency time. In areas of very high rodent abundance the provisioning of tree collars provide physical protection to the trees. An additional benefit of the collars is that the collars cause a beneficial microclimate around the tree which enhances its growth rate. When the tree is around 2 years old it should be pruned to a height of I ffi, the slash being left in the inter-row. Results show that trees treated in such a way experience no further attack and the rodents browse on the prunings. As the cost of the perches is reduced and the cost of pruning is non-recurring the recommendations provide an economical and environmentally sympathetic alternative to rodenticide application.