Doctoral Degrees (Zoology)

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Environmental stochasticity and African elephant population dynamics : investigating limitation through juvenile mortality.
(2008) Woolley, Leigh-Ann.
The successful conservation management of African elephants depends largely on understanding the fundamental processes driving the population regulation of this species. Southern Africa’s increasing populations have raised concern over the impact of high elephant densities on the system, in stark contrast against the elephant’s more precarious position in other parts of Africa. As we search for solutions from the processes of historical elephant regulation, we realise that there is a decided lack of empirical evidence to explicitly direct our efforts. In this PhD, I attempt to investigate the application of the classic pattern of large herbivore population limitation, which mainly involves high juvenile mortality in response to stochastic environmental events, to African elephant population dynamics. Firstly, I evaluated the magnitude and frequency of mortality events that would be required to prevent elephant population growth. The death of 85 % of infants and weaned calves would need to occur twice a generation, while a single severe mortality event (causing the death of all infants and weaned calves and 10 % of the rest of the population) once a generation would be sufficient. However, the severity of these events is not matched in natural occurrence in Africa today and only a single recorded event in Tsavo National Park, Kenya, in the 1970’s has come close when more than 7 000 died during a very severe drought. Secondly, I evaluated the potential role of fire as a stochastic, massmortality event limiting elephant populations. I found that fire functions in a similar manner to other environmental catastrophes and primarily causes high juvenile mortality. However, this catastrophic event also highlighted the extreme behavioural and physiological impacts experienced by the elephant population involved. The potential role of these types of events on long-term female fecundity needs further investigation. In isolation, this type of mortality event would need to occur with high frequency to prevent population growth. However, in combination with a decrease in female fecundity, these stochastic events may have a much greater impact on population demography than first thought. Thirdly, I investigated a potential mechanistic link between stochastic mortality events and juvenile susceptibility to resource limitation. Allometric relationships dictate that juveniles select a diet of higher quality than adult elephants. We found that this was achieved by weaned calf selection of higher quality plant parts, although use of plant types and plant species was similar to that of adult females, who they move across the landscape with. The strong sexual dimorphism exhibited by this species was reflected in adult male use of lower quality forage than adult females (or juveniles) in both dry and wet seasons. Diet quality scaled negatively with body size, but adult females consistently selected a higher quality diet than adult males, irrespective of body size. The nutritional and reproductive demands placed on an individual during different life-history stages therefore influence foraging strategies, together with nutrient requirements, e.g. phosphorus for pregnancy/lactation selected consistently by females when unrestricted in the wet season, protein for growth selected consistently by weaned calves. Competitive displacement of adult females to feed at higher levels in the canopy by calves also influenced feeding behaviour. Therefore intraspecific body size, nutritional requirements (in terms of nutrients and energy) and competition had a strong influence on foraging strategy employed by age-sex classes of elephants in response to seasonal environmental change. More selective juvenile foraging requirements means that juveniles are most susceptible to resource limitation, for example during stochastic environmental events such as droughts. In small, closed systems, juvenile mortality is likely to have a strong influence on elephant population regulation, with a slight, temporary decrease in female fecundity possibly acting in conjunction with juvenile mortality effects. Therefore, stochastic environmental events such as drought and fire may be the only natural incidence of population regulation to occur in these systems, where populations continue to grow exponentially and there is no evidence of density-dependence (as in the case of many small, fenced reserves in South Africa). In large, open, high-density systems in other parts of southern Africa, density dependence acts strongly on female fecundity and causes low levels of juvenile mortality in areas of local population aggregation. Therefore, in isolation, natural juvenile mortality is unlikely to regulate African elephant populations, but in conjunction with decreased female fecundity in response to density-dependent feedbacks and stochastic environmental events, population regulation may occur. The management of long-lived megaherbivore species with similar demographic drivers must include an appreciation of the complexity of population response to manipulation of mortality or fecundity effects. Small changes can potentially result in large shifts in population dynamics. Further insight into the mechanisms driving these processes will allow sound scientific support of megaherbivore management decisions to be made throughout Africa.
Effect of soil factors on parasitic nematodes of sugarcane in KwaZulu- Natal, South Africa.
(2004) Dana, Pelisa.; Cadet, P.; Spaull, Vaughan William.; Appleton, Christopher Charles.
Nematicides are not only expensive and unaffordable to small-scale farmers but are also harmful to the environment as they kill both the target organisms and non-target micro and macro-organisms, thereby destabilising the ecosystem. Most developed countries have or are in the process of banning use of chemicals for pest management, implying that agricultural products from developing countries using pesticides will not be marketed in the developed countries. In former studies, it was shown that plant parasitic nematodes posed serious problems in sugarcane fields as their attacks on sett roots during germination period decreased sett root weights, delayed bud germination or led to fewer buds germinating as most buds abort. Those that germinate later are then faced with competition for food, space and light from the "older" shoots and often die. The attacks on shoot roots may lead to inefficient uptake of water and nutrients by the plant thereby leading to stunted plants. Fewer and shorter sugarcane stalks due to nematode attacks result in poor yield. In this study, it has been shown that a large number of endoparasites would be needed to reduce sett root weights. Agricultural systems based on monoculture are rarely successful in the long term and because sugarcane fields have been monocultured for a very long time, they are losing their productive capacity and this is termed "Yield Decline". Instead of using nematicides, alternative methods can be used for the management of nematode communities. Research has shown on other plants that nematode communities dominated by Helicotylenchus dihystera are less pathogenic to the plants than other ectoparasitic nematodes, e.g., Xiphinema elongatum and Paratrichodorus spp. A study conducted as a pot experiment showed that sugarcane grown in soil with high H. dihystera grew taller and produced greater root and aerial biomass than one grown in X elongatum infested soil. To induce a nematode community dominated by H. dihystera in the field, two strategies were followed: (i ) abiotic factors that influence the nematode's environment were identified. Certain elements found in soil and sugarcane leaves were found to be correlated to certain species, e.g., H. dihystera was negatively correlated to soil sulphur, medium and coarse sand while X elongatum was positively correlated to these soil types and soil elements. Sugarcane leaves with high levels of Ca, Zn, Cu and Fe were found in areas with high percentages of H. dihystera while the reverse was true for X elongatum. (ii) organic amendments were used to improve the sugarcane growth, modify the environment and decrease competition among species within a community. Application of organic matter to the soil improves soil properties such as water infiltration, water holding capacity, erodibility and nutrient cycling, increases suppressiveness of soils to plant parasitic nematodes and stimulates other anti-nematode micro-organisms, e.g., nematode-trapping fungi. Organic amendments were therefore used in this study not only as screens to protect sugarcane roots from nematode attacks but also to manipulate nematode communities for the less pathogenic species, H. dihystera. In a field study where organic amendments were used, plots treated with filter cake, thume + filter cake, trash + filter cake, filter cake + furfural and Temik (aldicarb) had high percentages of H. dihystera while control plots had high percentages of X elongatum. However, the change in relative proportion of H. dihystera by certain treatments was not followed by an average increase in yield, probability because of the overall variability. The yield results, however, showed that for all treatments, including control, the highest yields corresponded to plots with higher H. dihystera proportions, conflicting the initial hypothesis. As a result, if an organic amendment that can substantially increase the relative proportions of H. dihystera can be found, a substantial increase in yield can be expected. Although the organic amendments did not successfully manipulate the nematode communities for the less pathogenic species, H. dihystera, plots with higher yield were those that had high H. dihystera percentages in their nematode communities.
Population genetics of the striped-mouse, Rhabdomys Pumilio (Sparrman, 1784)
(1999) Mahida, Harendra.; Campbell, Glen Kerry.; Taylor, Peter John.
The striped-mouse, Rhabdomys pumilio, is widely distributed throughout southern Africa within a variety of habitats and rainfall regimes. It is found at sea level in the Eastern and Western Cape regions and at altitudes above 2700 m in the Drakensberg mountains. The attraction of R.pumilio to cultivated land and crops has resulted in extensive damage to plants and cultivated crops. A study of the genetic variation between populations of R.pumilio from different regions of southern Africa was undertaken by protein electrophoresis and randomly amplified polymorphic DNA using the polymerase chain reaction (PCR-RAPD). A cytogenetic study was also undertaken. The mean heterozygosity (H=0.074) for R.pumilio was more than twice that estimated for mammals (H=0.036) while the mean percent polymorphism (P=16.1%) was only slightly higher than the mean percent polymorphism obtained for mammals (P=14.7%). The highest heterozygosities were recorded in the Potchefstroom (H=0 .145) and Zimbabwe (H=0 .118) samples and the lowest mean heterozygosity was recorded in the peninsular Western Cape (H=0. 032). A mean Fst value of 0.459 was obtained, suggesting a high degree of genetic differentiation between the samples of R.pumilio but the negative Fis (-0.01) value emphasized that R.pumilio retained an outbreeding population structure. The similarity coefficient between the samples of R.pumilio using PCR-RAPD's ranged between 0.471 and 0.853 and substantiated the argument for genetic divergence between the samples of R.pumilio. An isolation by distance model for the population genetic structure of R.pumilio was supported by the allozymes (r=0.58, p<0.00l) and PCR-RAPD's (0.75, p<0.00l). Temperature and rainfall also had an influence on the allelic frequency distribution of certain loci of R.pumilio. Rogers (1972) genetic similarity varied between 0.796 and 0.988 while the values for Nei's (1978) unbiased genetic distance varied between 0.000 and 0.189 for the different samples of R.pumilio. Subgrouping of the KwaZulu-Natal samples, the peninsular Western Cape and Eastern Cape samples of R.pumilio was evident with the allozymes. With the PCR-RAPD' s the Zimbabwe sample showed the least similarity to the other samples with a KwaZulu-Natal/Potchefstroom subgroup separating from the less well defined Eastern Cape and Western Cape subgroup. Cytogenetic studies of specimens of R.pumilio from some of the localities in southern Africa revealed a chromosomal number of 2n=48 , while the Potchefstroom and Zimbabwe specimens displayed a chromosomal number of 2n=46. Homology in G-and C-banding was recorded. The allozymes, PCR-RAPD's and chromosomal studies suggested subspecies status for the Zimbabwe population of R.pumilio. The Potchefstroom sample displayed a greater genetic similarity to the remaining South African samples of R.pumilio than the Zimbabwe samples and therefore could not be considered for subspecies status. Although the South African samples of R.pumilio displayed a certain degree of genetic divergence, it was insufficient to warrant subspecies status although evolution in this direction was suggested.
Thermoregulation in free-ranging African-endemic small mammals : the rock elephant shrew, Elephantulus myurus and the lesser bushbaby, Galago moholi.
(2005) Mzilikazi, Nomakwezi.; Lovegrove, Barry Gordon.; Masters, Judith C.
Endothermy in birds and mammals is invariably associated with homeothermy. However, homeothermy can only be maintained if sufficient energy is obtained to meet the animals' maintenance budget. In mammals, daily torpor and hibernation have evolved to conserve energy when energy inputs from the environment are insufficient to meet maintenance requirements. Several studies have suggested that daily torpor and hibernation do not represent distinct physiological responses but are components of a continuum of heterothermy. Under laboratory conditions, even within phylogenetically ancient eutherian mammals, such as elephant shrews, it is unclear whether daily torpor or hibernation is used. Furthermore, an interpretation of the torpor patterns observed under laboratory conditions is complicated by the fact that torpor patterns often differ between laboratory and free-ranging conditions. Within the more recent mammal lineages, torpor has been observed in strepsirrhine primates. The occurrence of torpor in strepsirrhines is interesting as it pertains to arguments relating to the colonization of Madagascar by strepsirrhine primates as well as implications for human physiology. The first aim of this study was to investigate and quantify parameters that characterize torpor in a phylogenetically ancient eutherian mammal (Macroscelidae: Elephantulus myurus) under free-ranging conditions. This was done mainly to resolve whether daily torpor and hibernation were physiologically discrete responses. The second aim was to investigate torpor occurrence in a more recently evolved eutherian mammal (Primates: Galago moholi). The objective was to gain insights into the phylogenetic distribution of torpor and to provide a physiological verification of torpor occurrence in a mainland strepsirrhine relative to arguments about the colonization of Madagascar. I measured body temperatures in three monthly cycles between May 2001 - May 2002 in 22 free-ranging E. myurus. I recorded a total of 467 torpor bouts throughout the study period. The elephant shrews were capable of daily torpor throughout the year, with torpor most prevalent during winter and correlated with ambient temperature, photoperiod and invertebrate abundance. Only two torpor bouts were observed during summer. I suggest that although torpor use was most prevalent during winter, summer torpor might also be important for energy conservation in this species during drought years. This highlights the need for long-term physiological data in free-ranging animals. The mean torpor Tbmin and the mean bout length for the whole year were in the range expected for daily heterotherms. However, there was some marginal overlap with hibernation characteristics; a few torpor bouts were longer than 24 hrs in duration indicating that the animals were capable of opportunistically extending torpor bouts longer than 24 hours in response to unpredictable energetic shortfalls. Tbmin also decreased below 10°C. However, a consideration of behavioural and ecological factors argues against hibernation in E. myurus. Instead, these results support the idea of a physiological continuum for heterothermy. A return to normothermic body temperatures requires considerable energy expenditure, and this is perceived to be one of the major disadvantages of torpor. E. myurus offset the high cost of arousal from low body temperatures by using exogenous passive heating. This is achieved by coupling of the timing of arousal with ambient temperature cycles. Laboratory studies that quantify torpor energetics are usually conducted under constant temperature conditions and are likely to underestimate the energetic benefits accrued through the use of ambient temperature cycles during arousal. Torpor is often displayed during the animal's rest phase. However, nocturnal small mammals that utilize passive heating to assist arousal from torpor may enter torpor during the nighttime, thus effectively advancing the onset of the rest phase. I investigated the functional significance of daily and seasonal rhythms of body temperature in normothermic and torpid free-ranging E. myurus. Daily patterns of Tb, in normothermic E. myurus suggested polyphasic Tb patterns that nevertheless indicated a rest phase coincident with the daytime. I suggested that the principal benefit of a flexible daily rhythm of Tb, is that it facilitated torpor use during the nighttime and arousal by passive exogenous heating using ambient temperature cycles. It has been suggested that the evolution of endothermy precluded the need for homeothermic mammals to be sensitive to Ta cycles because they could maintain physiological function despite fluctuations in the ambient temperature. Elephant shrews utilize passive heating and provide excellent models with which to investigate whether mammals can entrain their body temperature rhythms to ambient temperature cycles. I experimentally tested whether food restricted E. myurus can entrain torpor cycles to shifts in the Ta cycle while holding the light-dark cycle constant. Food restriction and short photoperiod were only sufficient to induce torpor in E. myurus if photoperiod and Ta, cycles are in phase with each other. Shifting the cold T, into the photophase prevented the expression of torpor. I concluded that the body temperature rhythm is most probably tightly coupled with the photoperiod cycle and that although Ta and photoperiod usually act synergistically in nature, photoperiod is probably the stronger zeitgeber. The evolution of endothermy is thought to have been facilitated by the advent of endothermic energy sources such as brown adipose tissue (BAT), the principal site of nonshivering thermogenesis (NST). Rock elephant shrews are amongst the smallest members of the Afrotheria, the most basal of the eutherian lineage. I determined whether the phylogenetic placement of E. myurus and reliance on passive heating might result in a decreased capacity for NST relative to other eutherians. I investigated the capacity for NST in winter acclimated E. myurus by measuring the thermogenic response to noradrenalin (NA) injection. I used phylogenetically independent analyses to compare E. myurus NST capacity with other eutherians. E. myurus had an NST capacity that was no different from other eutherian mammals. Although they displayed a NST capacity that was 74% of that expected on the basis of body mass, this value was not significantly different from phylogenetically independent allometric predictions. Although heterothermy is almost always considered in the context of how the environment affects function , its use may offer insights into topics such as island biogeography and species dispersal. For example, there have been suggestions that heterothermy might have played an important role in the successful colonization of Madagascar by strepsirrhine primates. To my knowledge no studies exist as yet that provide a physiological verification of this suggestion. Currently no data exist on thermoregulation and heterothermy in any free-ranging African strepsirrhines. The lesser bushbaby, Galago moholi, is a small nocturnal strepsirrhine primate that experiences severe winters and drastic food reduction during winter and is a candidate employer of torpor. I measured body temperatures of 11 free-ranging lesser bushbabies, Galago moholi, captured at different times between February 2002 - September 2003. I did not record any incidents of heterothermy throughout the study period. Why does G. moholi not employ heterothermy? I consider several alternatives; phylogenetic placement, physiological and ecological factors that might preclude the use of torpor in this species. I suggest that the breeding pattern observed in G. moholi obviates torpor use whilst increasing fecundity, which would be adaptive if the animals are confronted with high predation risks. Much is currently known about the advantages of torpor use. This study highlights the need to consider and investigate those physiological, ecological and phylogenetic factors that might constrain species from utilizinq heterothermy. Furthermore, this study highlights the potential for thermoregulatory studies to offer insights into topics as widely separated as evolution of endothermy to species dispersal and island biogeography.
Chromosomal evolution in the Vlei Rat Otomys irroratus.
(1996) Contrafatto, Giancarlo.; Meester, Jurgens Anthonie Jansen.; Campbell, Glen Kerry.; Grace, James H.
Proponents of the recognition concept of species hold that isolating mechanisms, including chromosome rearrangements, play no role in speciation while the more commonly accepted biological species concept proposes that isolation mechanisms are instrumental in the formation of new species. Moreover, some adherents of the biological concept of species, reject the hypothesis that chromosomal rearrangements can be instrumental in causing reproductive isolation and, hence, speciation. Evidence to the causative role played in speciation by chromosome changes can be obtained from cytogenetic investigations of sibling species, in parallel with analyses of gene products, DNA polymorphism and premating behaviour. This study reports the results of a cytogenetic investigation of 97 specimens of the vlei rat 0. irroratus, from 18 South African localities, and 11 samples of the Angoni vlei rat 0. angoniensis from two geographically distant populations. All 0. angoniensis individuals showed a constant karyotype with 56 acrocentric chromosomes but extensive variation was detected in 0. irroratus. Five cytotypes could be recognized within the latter. In the south-eastern parts of its South African range, 0. irroratus had a diploid number (2n) of 30 chromosomes in whicll all autosomes were acrocentric (cytotype A) while further east (cytotype A2), the diploid number was 30-32 with, again, acrocentric autosomes, A further acrocentric cytotype (AI) with 2n = 24-27 occupied the southern and south-eastern slopes of the Drakensberg range. A type with 2n = 28-30 (cytotype B), with eight pairs of biarmed autosomes, was found in the southern Cape region while in the Cape of Good Hope and in the north-eastern parts of South Africa, 0. irroratus had 2n = 28 with only four pairs of biarmed autosomes (cytotype C). Most of the numerical changes were due to variation in the number of copies of Bchromosomes which were small, biarmed and partly heterochromatic. C-banding analysis revealed that the short arms of bianned autosomes were totally heterochromatic. On the other hand, G-banding patterns of acrocentric autosomes were, with two exceptions (AI and A2 types), similar in all cytotypes while G~banding of the long arms VII of biarmed chromosomes matched the pattern of their homologues in acrocentric cytotypes. A potentially heterotic rearrangement was detected in the Al localities where a unique acrocentric autosome was identified as the product of a fusion between chromosomes 7 and 12. The geographic distribution of these groups of karyotypes correlated, by Discriminant Function Analysis, with bioclimatic regions of South Africa. The Al cytotype was shown to occupy the coldest and wettest region of the montane Drakensberg while the B type is found in the hot area of the eastern Cape with an unpredictable rainfall pattern: group C occupies regions of intermediate climate. Gene product analysis was carried out using the novel approach of subjecting liver homogenates to "Western blotting". This method was first assessed at supraspecilic level using specimens of various southern African rodents, and allowed the generation of phylogenies essentially similar to those produced by allozyme studies of the same taxa. At intraspecilic level, immunobloHing analysis did not reveal synapomorphies congruent with karyotype groups. This was interpreted, in conjunction with available allozyme data from the same populations, as evidence of low genetic differentiation between 0. irroratus cytotypes, A measure of genetic divergence was indicated in two populations from the Cape province and this was in agreement with existing data from allozyme electrophoresis and mitochondrial DNA polymorphism. The cytogenetic results were related to available data on breeding and premating behaviour concerning some of the O. irroratus populations investigated here. The presence of the 7/12 chromosome fusion in the Al cytotype correlated with a dramatic reproductive impairment of FI individuals originated from Al/A2 and Al/B cytotype crosses. Evidence of partial premating behavioural barriers has been reported by others, but information on premating behaviour between populations which are not chromosomally isolated is lacking. Therefore, it was not possible to establish if behavioural premating barriers preceded, or followed, the fixation of negatively heterotic chromosomal rearrangements. It was, nevertheless, suggested that the existence of such impaired mate recognition may be an example of reproductive character displacement which may have followed the fixation of the t(7: 12) typiVIII cal of the Al populations. In conclusion, the existence of chromosome changes in the AI, and possibly A2, populations accompanied by low genetic divergence and severely impaired hybrid reproductive success, are consistent with a hypothesis whereby chromosomal reproductive isolation causes speciation. Nonetheless, other speciation mechanisms mediated by genetic divergence and/or mate recognition failure, are possible in other populations where no chromosome changes of negatively heterotic potential were found.
The analysis of erythropoiesis and other early developmental events in the chick embryo using mesodermal-inducing factors.
(1994) Gordon-Thomson, Clare.; Fabian, B.
The causal and temporal aspects of blood tissue specification in the chick embryo were investigated in this study. The main focus was on the role of basic fibroblast growth factor (bFGF) in the determination of the erythropoietic tissue, particularly in context with its representation as a non-axial mesodermal derivative which arises in the posterior domain of the chick embryo. The initial strategy employed in this study was the use of agents that are known to block the activity of bFGF, and to determine their effects on erythropoiesis. Treatment of unincubated chick embryo explants with heparin, which binds specifically to the FGF family, was found to inhibit primitive streak formation and erythropoiesis, and also inhibited the formation of other mesodermal tissues. These initial findings suggested that one or more growth factors had become bound to the heparin, and that their activity is important for the specification of primitive streak formation and mesodermal patteming. The development of the erythropoietic tissue was assayed by a cytochemical test for haemoglobin using 0dianisidine; and by histological examination for blood islands and red blood cells in serial sections of the embryos after 48 hours incubation. Microscopic examination of the embryos at the stages of gastrulation on the first day of incubation revealed that heparin caused holes to appear in the ventral layer; and although a primitive streak did not form, a middle layer of mesenchymal cells were seen to accumulate between the ectodermal and ventral "endodermal" layers. It was significant that heparin's inhibitory effect on erythropoiesis could be reversed after the addition of a recombinant bovine bFGF to the heparin-treated embryos. However, the exogenous bFGF did not neutralize the inhibitory effect of heparin on the primitive streak and other mesodermal derivatives (Chapter Two). The inhibition of erythropoiesis by heparin was also reversed by the addition of a mesodermal-inducing factor extracted from a Xenopus embryonic cell line, namely XTC. The XTC mesodermal-inducing factor (MIF), which belongs to the transforming growth factor-B family and is a homologue of activin, could also reverse the inhibitory effect of heparin on primitive streak formation; but no recognizable axial mesodermal structures subsequently developed. Of consequence, was that both bFGF and XTC-MIF blocked heparin's effect on the ventral layer, preventing the gaps forming. Therefore, it is suggestive that the VI development of an intact ventral layer is important for the determination of the erythropoietic sequence (Chapter Three). By taking a more specific approach using antisera to bFGF (anti-FGF) and the bFGF receptor (anti-FGFR) on whole embryo explants, it was found that anti-FGP and anti-FGFR were able to inhibit erythropoiesis, but not primitive streak formation. However, these antisera caused defects in the posterior region of the embryonic axis. These embryos not only lacked posterior blood tissue, but heart and somites were missing; whereas the anterior head structures were well formed. These results therefore suggest that bFGF signalling is important for the development of the posterior body plan, which includes erythropoiesis (Chapter Four). Further evidence for the role of bFGF in the determination of the blood mesodermal tissue line was reached in an in vitro bioassay. In this part of the investigation, specific pieces of the blastoderm, namely pieces dissected from the posterior marginal zone (PMZ) and inner core of the central disc (lCD) were able to form haemoglobin under particular conditions. The PMZ components were found to have the capacity to form haemoglobin when dissected from blastoderms of stages X to xm when cultured in serum-free medium. This commitment to form haemoglobin could be blocked by treatment with anti-FGP at stages X and XI, but not at the later stages of xn and XIII. The ICD components were found to have a commitment to form haemoglobin only if this component was dissected from embryos at stage XIT and XITI, but not before. These results suggest that a determinative event for the haemoglobin differentiative pathway occurs between stages XI and XII. It was also found that the stage X central disc component could be induced to form haemoglobin if a stage xm hypoblast was added to it in tissue recombination sandwich cultures, or if bFGF (75 - 150 ng/ml) was added to the medium. These results lend further support that bFGF plays an important role in the determination of erythropoiesis; and furthermore, suggest that the hypoblastic tissue is the source of this induction (Chapter Four). Finally, immunocytochemical labelling with a polyclonal antibody to bFGF has revealed that bFGF increases significantly from stage XI in cells within the developing hypoblast layer and in the middle mesodermal layer. These cells are located predominantly in the posterior domain of the embryo. This polarized distribution of bFGF with the high value of bFGF concentration in the posterior area, is presumably responsible for inducing the overlying epiblast to form the posterior horseshoe-shaped region from which blood tissue is seen to arise. An immunocytochemical analysis of the distribution of the FGF receptor was vu assessed, as an indicator of the possible competence of the cells to respond to the bFGF signal. The bFGF receptor was found to be expressed at stage XII in cells that appeared to be in register with those immunoreactive to the bFGF ligand; therefore suggesting an autocrine function. It was interesting that at stage Xli an intense immunostaining with the anti-FGFR developed in the nuclei of cells within the epiblast layer (Chapter Five). In conclusion, this study has demonstrated that the initial determination of the erythropoietic cell lineage in the chick is at the time when the hypoblast is in the process of forming beneath the epiblast, Le. between stages XI and XII. Furthermore, it was found that an induction by an FGF-like signal from the hypoblast layer (or middle mesodermal cells that may be closely associated with the hypoblast) induces "competent" cells (Le. FGFR-positive cells) in the epiblast to form blood tissue in the posterior domain of the chick embryo.
Black rhinoceros (Diceros bicornis) habitat selection and movement analysis.
(2010) Morgan, Simon.; Slotow, Robert Hugh.
Many aspects of habitat selection have been largely ignored in conservation planning of large mammals, including variation between day and night movement patterns, inter-individual niche variation of conspecifics and translocated individual‟s responses to new environments in relation to the influence of ecogeographical variables. Being a solitary moving animal with a known tendency to move through the night, the black rhino Diceros bicornis is a perfect species to test theories about individual spatial and temporal variation in habitat utilisation. I tested the appropriateness of using carrying capacity (CC) estimates as a tool for population conservation planning, and as an indicator of habitat utilisation for black rhino. I found individual selection was not related to the value of the habitat according to modelled CC. I therefore do not recommend the use of a priori calculations of resource quality and abundance of habitats (CC estimates), which do not take into account the factors that influence an animal‟s selection of a habitat, as indicators of species habitat use. Secondly I tested whether current methods of analyzing mainly diurnal location data of animals result in accurate ecological or conservation conclusions. I found a circadian variation in habitat use for different behaviours, and that excluding nocturnal data from home and browsing range analyses would provide inaccurate results for black rhino habitat use. I then tested for inter-individual niche variation amongst two populations of black rhino at various scales of selection, ranging from habitat through to browse selection. I showed that black rhino, a selective browser, had a significant degree of inter-individual habitat and dietary niche variation. Consequently, pooling habitat location data and diet selection data for black rhino individuals in a population does not reflect the actual selection of any, or many, individuals. To clarify which ecogeographical variables might influence this selection I ran maximum entropy models on individual‟s diurnal locations across the landscape. I was then able to develop a habitat suitability model which was based on the individual rather than population, providing a more accurate prediction. I repeated the individual models in phases, from the initial post-release phase after the release of individuals onto a new reserve through to their „settled‟ phase, allowing me to explore the effect of habitat variables on different settling phases of translocated animals. The results indicate that all the rhinos‟ acclimation phase lasted no longer than 25 days and that to minimize disturbance to the settling process all individuals in a newly released cohort should be released within this period. This study as a whole provides conservation managers with a better ecological understanding of black rhino in conjunction with a number of management tools. This will enable conservation managers to better understand the way animals utilise and perceive their environment, allowing for better monitoring and analyses of animal movements. This will aid in the development of strategic management plans in the conservation of not only animal species but also the ecosystems that they reside in and the identification of suitable areas for future conservation of animal species.
The use of Cape gannets Morus capensis in management of the purse-seine fishery of the western Cape.
(1987) Berruti, Aldo.; Maclean, Gordon Lindsay.
A large purse-seine fishery is located in the highly productive southern Benguela System off the western Cape. Purseseine fisheries have been prone to collapse worldwide and management practices have met with limited success. Predators offer potential as biological indicators yielding information on the status of fish stocks. The rationale behind this proposed usage was previously loosely-defined. The premise that some variable of seabird biology is related to some aspect of fish biology about which information is required was critically examined. The diet of the Cape Gannet was monitored monthly at Lambert's Bay and Malgas Island in the western Cape from 1977 to 1986. Gannets ate shoaling fishes (mainly Cape Anchovy, South African Pilchard and Saury) , measuring 29-429 mm Lc, which were available during the day at the surface and hake offal scavenged from demersal trawlers. Comparison with purse-seine fishery catches and the distributional ecology of the fishes suggested that the contributions of epipelagic fishes to the diet of the Cape Gannet were related to their availability and abundance, but that the occurrence of mesopelagic fishes (adult Redeye Roundherring and Onderbaadjie) in the diet of gannets was not related to their availability or abundance. Availability of epipelagic fishes was apparently lowest during late winter and spring; at longer time scales, availability was apparently lowest between 1983 and 1985 during the period from 1978 to 1986. Differences in the diets of breeding and nonbreeding gannets were small. Gannets from the colony at Lambert's Bay fed primarily north of Cape Columbine. These birds fed in cool inshore waters on juvenile fishes (mainly Cape Anchovy). Gannets from Malgas Island fed primarily south of Cape Columbine. They fed in cool inshore waters on juvenile epipelagic fishes (mainly Cape Anchovy), in warmer waters offshore on large epipelagic fishes (Saury and adult pilchard) or scavenged hake at trawlers offshore. Adult South African Pilchard were preferred prey. Epipelagic prey were selected in preference to mesopelagic fishes and hake. Significant correlations between the percentage of pilchard in gannet diet and purse-seine fishery catches suggested that gannets were reliable monitors of the trend in pilchard stocks at low biomass levels. The Saury is a poorly known species and its availability to gannets was reviewed as an example of the indirect use of the diets of predators in understanding the ecology of prey species, and functioning of ecosystems. Future directions for research were suggested. However extensive use of data from predators in fisheries management awaits the development of techniques which can use qualitative data. Nevertheless, it was concluded that the species composition and length of prey in gannet diet and the mass of regurgitations and the proportion of birds which regurgitated food were related to the abundance of epipelagic fish prey generally and South African Pilchard in particular.
The ecology and conservation biology of the Black-cheeked Lovebird Agapornis nigrigenis in Zambia.
(2003) Warburton, Louise Sarah.; Perrin, Michael Richard.
This study was undertaken to investigate the ecology of the Black-cheeked Lovebird Agapornis nigrigenis in the wild. Prior to this study little was known about the ecology of this parrot or other members of the genus Agapornis. The Black-cheeked Lovebird is classified as Vulnerable and has suffered a severe population decline and reduced distribution, from which, for largely speculative reasons, it has never recovered. The overall aim of this project was to elucidate the basic biology of the Black-cheeked Lovebird and determine the conservation actions which are necessary to conserve the species in the wild. Fieldwork was conducted across the species' range in south-west Zambia over twenty-two months between May to December 1998; March to December 1999; and February to May 2000. An education project focussing on Black-cheeked Lovebird conservation was conducted with local schools, villagers and Zambia Wildlife Authority scouts during September 2001. Historical records pertaining to distribution of the Black-checked Lovebird, both within and beyond Zambia are few, anecdotal and often discredited, and it is suggested that the species should be considered as endemic to Zambia. Within its core range the species has a clumped and localised distribution, associated with Mopane woodland and permanent water sources. Two sub-populations occur and appear to be distinct. Black-cheeked Lovebirds were most active, in the early morning and late afternoon, forming the largest daily flocks sizes during these times, which correlated with drinking and feeding activities. The smallest flock sizes occurred when roosting. Overall flock sizes were significantly larger during the dry (non-breeding) season. Black-cheeked Lovebirds were observed feeding on 39 species. Food items included seeds, leaves, flowers (especially nectar), fruit pulp, invertebrates, bark, lichen, resin, and soil. Various foraging techniques were used. Terrestrial foraging was dominant, with little temporal or spatial variability. Arboreal foraging in plants varied seasonally and by availability. Feeding preferences were not specialised and there was no dependence on a limited food resource. Black-cheeked Lovebirds fed on two agricultural crops. There was no evidence to suggest an extended foraging range during the crop-ripening season, or the reliance on crops for survival. The crop-ripening season coincided with the lovebird breeding season. The species is widely perceived as a crop pest, with 18% of seed heads of millet crops suffering more than 20% damage during the ripening season. Local farmers attempted to protect their crops in a variety of ways, however, these were largely ineffective and rarely lethal to lovebirds. The importance of elevating local tolerance for the species through education programmes is highlighted. This study presents the first collection of breeding data on the species. Breeding occurred from midlate January to early May. A single clutch was raised by most pairs per breeding cycle. Seventy-eight nests were found and characteristics measured. Fidelity to nest-sites is suspected. Although breeding behaviour was non-cooperative most nests were found in a loosely clumped distribution. No nesting requirement appeared to be in limited supply, or had reason to affect the population's reproductive output. Behavioural data on nest location, building, defence and predation are presented. In addition courtship, copulation, parental care and juvenile behaviours are reported. Data on clutch size, laying intervals and hatching success with captive birds are included. One nestling tested positive for Psittacine Beak and Feather Disease Virus (PBFDV). Other observations suggest PBFDV is present in the wild population. Implications for research and conservation are discussed. Black-cheeked Lovebirds roosted inside naturally formed cavities in live Mopane trees. Roost cavities were found in a loosely clumped distribution. No roosting requirement appeared to be in limited supply. Black-cheeked Lovebirds are highly dependent on surface water supplies and need to drink at least twice daily. The lovebirds are highly cautious drinkers that will not drink if the water resource was actively disturbed by humans or livestock. Water availability is a limiting factor to the Black-cheeked Lovebird. The gradual desiccation of its habitat appears to be the major cause behind the reduction of occupancy within its small range. Over the last 45 years (1950 - 1997) the annual rainfall in the Black-cheeked Lovebird's habitat has decreased resulting in further reduction of its already highly localised distribution increasing the species dependence on artificial water supplies. The conservation management of the species should be prioritised towards maintaining and creating water resources with minimal external disturbance; upholding the wild-caught trade ban in the species, continuing environmental education with local schools promoting lovebird conservation, and monitoring populations through dry season water source counts.
Dragonfly assemblage dynamics and conservation at small reservoirs in KwaZulu-Natal, South Africa.
(2004) Suh, Augustine Niba.; Samways, Michael John.; Piper, Steven Edward.
A study of the odonate fauna was carried out at the edge of a major escarpment, in eastern South Africa, using the same methodology as has been used in the temperate regions to obtain a sub-tropical perspective. The study used the macroecology approach to compare patterns and responses of these animals (at the developmental stages of larva, tenerals and adults) to seasonal, topographical and anthropogenic disturbances. The habitats used were small, but well-established reservoirs located at five elevational gradients: Stainbank Nature Reserve (100 m), Krantzkloof Nature Reserve (450 m), National Botanical Gardens Pietermaritzburg (790 m) Cedara (1050 m) and Mondi Goodhope Estate (1350 m). Although this is essentially a local component of a larger macroecological study, it is shown that even though species and identities differ between temperate, tropical and sub-tropical ecoregions, the general pattern of community response to these variables is similar. Odonate species phenologies in this sub-tropical study showed great similarity to their tropical counterparts by reason of their adults being highly elevation-tolerant, with long flight periods and over-lapping generations. Yet they also show temperate characteristics by over-wintering principally as larvae and eggs. The Libellulidae, followed by the Coenagrionidae were the most abundant, elevationtolerant families, with national endernics constituting only 6.5% of the total species sampled. Classification and ordination methods identified and characterised sub-sites to ecologically meaningful biotopes for odonates . This also allowed inferences as to how the various landscape disturbances at the five elevations affect species richness and abundance. Species that responded to these impacts were potential indicator groups that can assist in the planning and management of the landscape for conservation of biodiversity. Some management recommendations for these landscapes are given. Individual odonate species developmental stages and their environmental relations were investigated using both univariate and multivariate analyses. The solutions to these analyses were then used to describe how odonate species are distributed along major environmental gradients. It was shown that regional processes e.g. elevation and insolation alongside local variables e.g. pH, marginal grasses, percentage shade, exposed rock, marginal forest, marsh and flow greatly accounted for adult (aerial stage) assemblage variation and distribution. Turbidity, floating/submerged vegetation and water depth (also influenced by regional factors), highly explained larval (aquatic stage) variation. Elevation has therefore, an indirect effect in that it determines climate, which in turn, determines soil and vegetation types which then determine species presence and absence. Also, although these artificial water bodies do not increase the 'extent of species occurrence', they are important in increasing their 'area of occupancy'. Dragonflies play a major role in conservation. The Japanese culture has strongly illustrated how dragonflies feature in everyday life more than any other country in the world. While many parks and Botanical Gardens feature dragonfly trails in their nature trails in Britain, this does not necessarily cater for threatened species . Conservation of invertebrates in urban environments in South Africa for example by ecological landscaping designed to encourage dragonflies has been particularly rewarding. A core of regularly occurring odonate species occupied the dragonfly trail at the National Botanical Gardens in Pietermaritzburg, while other species visited the study site at irregular periods . This is likely to be the case for a longer term, say ten years or more. Also, the trail, with updated information on species phenologies, variability and habitat preferences continues to play a valuable role in sensitising an increasingly urbanised population to biodiversity and conservation issues. Odonates remain a major component when assessing ecological components of aquatic biotopes, with the assemblage composition at anyone locality capable of changing over time. This has been extensively illustrated in the northern hemisphere. Medium to longer term changes in odonate population at established reservoirs as demonstrated in this study at the National Botanical Gardens in Pietermaritzburg, South Africa, makes it possible to determine whe[t]her a species in a conservation area is being given enough protection from local anthropogenic impacts and effects of unpredictable weather conditions. This in turn enables one to understand how concepts of residency and succession underpin conservation management decisions. In conclusion, this study has addressed some salient aspects of species inventory, monitoring and conservation practice at a local scale that also play a central role in conventional biodiversity conservation practice of a global nature. Information on species phenologies enhances their awareness-raising in addition to providing valuable insights into their population dynamics and conservation, especially for those under threat. In addition, baseline data from this study and similar ones is useful in conserving biodiversity (as subjects) or in multi-taxa studies (as tools) in conserving ecosystems and/or landscapes. Finally, the macroecological approach employed in this study has great potential for teasing apart local effects from regional and/or global ones, and can contribute to the conservation of biodiversity at both small and large scales.
The evolution and socio-ecology of two populations of the Vlei Rat, Otomys irroratus.
(1993) Pillay, Neville.; Cooke, John Anthony.; Willan, Kenneth Brian Ronald.
This work investigated two important evolutionary processes - speciation and adaptive variation - in two chromosomally-distinct allopatric Natal Midlands populations of the vlei rat Otomys irroratus. The two populations, at Kamberg and Karkloof, differ in the presence of a tandem fusion between chromosomes seven and 12 in the Kamberg karyotype. Speciation studies considered possible reproductive isolating mechanisms. In studies of adaptive variation, socio-ecological characteristics of both populations were investigated. Data on breeding and postnatal development provided evidence of post-zygotic barriers. Interpopulation pairs had reduced breeding success compared to intrapopulation pairs, and some hybrids died before weaning. Surviving hybrids had reduced growth rates, and almost all were sterile. In tests of pre-mating reproductive isolation, ethological barriers were emphasized. Individuals preferred same-population mates, suggesting the existence of mate recognition, which was achieved by means of population-specific courtship behaviour and communication, particularly olfactory, tactile and visual cues. No evidence of population-specific acoustic signals was found, although acoustic cues were associated with agonistic interaction, complementing other communicatory cues to promote increased aggression during interpopulation pairings. Laboratory studies of behaviour and morphology and field work (trapping and habitat assessment) provided information about socio-ecological parameters. The Kamberg habitat was harsher than the Karkloof one, as revealed by differences in seasonal and spatial availability of food and·cover. Cover was the key determinant of the level of sociability of both populations. Sparse, patchy cover selected for a partially communal social system in Kamberg o. irroratus: females were intrasexually tolerant and males were intrasexually highly aggressive. This, in conjunction with male-biased sexual dimorphism, implied that mating was polygynous. Abundant, uniform cover selected for a dispersed social system in Karkloof o. irroratus: females were intrasexually less tolerant than males. Ritualized aggression between males and a low degree of male-biased sexual dimorphism suggested that male may have overlapping home ranges in nature and that mating is promiscuous. Females possibly mated with dominant males, however. Contrasting social systems suggest that adaptation to local environmental circumstances has occurred in allopatry, and that Kamberg and Karkloof o. irroratus are undergoing adaptive speciation. Post-zygotic and pre-mating reproductive barriers appear to have evolved independently in both populations, and could potentially impede gene flow between the populations should they become sympatric. The presence of the tandem fusion in the Kamberg karyotype which, together with genetically-determined factors, may have caused hybrid sterility, suggests that this population is a chromosomally-determined incipient sibling species.
The biology, ecology and conservation of four Flufftail species, Sarothrura (Aves: Rallidae)
(1994) Taylor, Peter Barry.; Maclean, Gordon Lindsay.
The distribution, status, biology and ecology of four flufftail species were investigated in South Africa and Zimbabwe. The Redchested Flufftail is a successful and widely distributed species, occupying a wide range of dense vegetation, from seasonally wet grassland and sedges to permanently shallowly flooded reedbeds. It colonizes artificially created wetland patches and occupies very small patches of suitable habitat. Redchested Flufftails maintain a permanent pair bond and are permanently territorial and entirely sedentary. Their habitat is relatively stable but unpredictable catastrophic events such as burning may force temporary emigration in winter or spring. Displaced birds move a short distance, occupy often marginally suitable habitat and recolonize burned areas as soon as vegetation cover becomes adequate. Periodic burning improves habitat quality, and recommendations are formulated for the management of wetland habitats by burning. The size of the winter territory is larger than the minimum required for survival and provides an insurance against forced emigration, while immatures often share parental territories in winter. The Striped Flufftail's grassland habitats in Natal are decreasing and its numbers are declining. Striped Flufftails are sedentary in low-altitude grassland habitats, but in high-altitude sourveld the decrease in invertebrate food forces emigration in April-June, when the birds move to unknown wintering destinations (movements are possibly altitudinal). Return time to unburned vegetation is dependent upon invertebrate food availability. Return time to burned vegetation is governed by the development of suitable cover, which may occur too late in the breeding season to permit occupation. The species is well adapted to frequent burning of its habitats, which serves to maintain suitable fire-climax grassland, but is also adapted to post-fire-climax vegetation types. The Whitewinged Flufftail is rare but its occurrence was regularly noted during the summer at four sites in Natal and the Transvaal. Habitat preferences and movement patterns were clarified, as was the bird's ecological segregation from the Redchested Flufftail. No conclusive evidence was found for breeding in South Africa and it is suggested that lack of suitable breeding habitat (possibly as a result of its being occupied by breeding Redchested Flufftails) may account for this. Some aspects of the bird's behaviour and calling were investigated. In view of this bird's threatened status and the continuing destruction of its wetland habitats, further surveys are urgently required to clarify the bird's status and the full extent of suitable habitat in South Africa, while a captive breeding programme is recommended to study breeding behaviour. The Buffspotted Flufftail inhabits a wide variety of forested and bushed habitats, and in Natal is a successful colonist of exotic vegetation in gardens. Its breeding biology, territorial and aggressive behaviour, and feeding ecology, were investigated in detail. It has regular seasonal movements in Natal, probably both altitudinal and coastal, although birds may remain throughout the year in areas where conditions are suitable. Seasonal departures are correlated with decreasing invertebrate food availability, while return time is largely governed by food availability, although cover development in exotic vegetation delayed recolonization at one site. The pair bond and the territory are maintained throughout the breeding season, and possibly throughout the year under suitable conditions. Adult mortality is probably high and the species' breeding strategy emphasises fecundity, this being achieved by a large clutch size, a very restricted period of parental care and rapid re-nesting. Juvenile mortality is high. The plumage, behavioural and vocal development of the young were studied in detail.
The ecology and conservation of blue duiker and red duiker in Natal.
(1990) Bowland, Anthony Ernest.; Perrin, Michael Richard.; Melton, D.
The ecology of blue duikers Philantomba monticola and red duikers Cephalophus natalensis was studied in three lowland coastal evergreen forests in Natal. Variation in population densities, estimated with numerous census techniques and between and within study areas permitted comparisons of habitat parameters. Both species are strictly diurnal, and are active between 18 and 40% of the nycthemeral cycle. Usually a pair of blue duikers occupy a permanent territory of about 0,7ha while red duiker home ranges, between 2 and 15ha, overlap extensively with each other and those of blue duikers. Habitat quality of both species is determined by canopy cover (stem densities, spatial patterning, and, diversity of the tree and shrub layers), tree to shrub ratios, and, bedsites. The main dietary item, freshly fallen leaves, is not that of a highconcentrate feeder as hypothesised. Food appears to be abundant while condensed tannins have no influence on duiker densities. Management recommendations include land acquisition, forest ecology research, monitoring interaction with other species, genetic aspects, translocations and captive propagation.
Infraspecific systematics of the yellow mongoose Cynictis penicillata.
(1990) Taylor, Peter John.; Meester, Jurgens Anthonie Jansen.; Rautenbach, Ignatius Lourens.
Geographic variation was analysed in morphological (colour, morphometric) and genetic (electrophoretic, chromosomal) characters in the yellow mongoose cynictis penicillata, a diurnal, colonial, burrow-dwelling viverrid, endemic to and widespread throughout Southern Africa. The causal bases of observed geographic patterns were investigated, and a taxonomic revision of the species was undertaken. Three physical properties of pelage colour (hue, value and chroma) were measured independently using Munsell colour charts and a tristimulus colorimeter. Hue and chroma varied from yellowish (hue) and bleached (chroma) in the north to a brighter, (chroma) tawny-orange (hue) in the south. A zone of rapid colour change separated northern and southern groups. Specimens from the drier western areas were paler (in value) than specimens from more easterly localities. Colour patterns were interpreted in terms in the principle of metachromism. Environmental correlates of colour were analysed. Non-geographic (age, sex, individual) and geographic variation was analysed in 14 cranial and two external characters, using multivariate and univariate techniques. The species does not show secondary sexual dimorphism. Multivariate analyses resulted in the description of four parapatric subspecies, three of which were distinguished on the basis of skull size (which accounted for 93% of geographic variation). Subspecies were separated by continuous zones of craniometric differentiation (transition zones). Craniometric overlap (intergradation) occurred across transition zones. The geographic pattern of craniometric variation in C. penicillata could be explained by either an allopatric or a parapatric mode of speciation. A cladistic analysis of coded cranial characters was used to infer the historical pattern of range expansion in the species. The population genetical structure, based on electrophoretic analysis of 28 loci in eight populations of yellow mongooses, was characterised by the absence of genetic divergence between morphometrically-defined subspecies, a mean expected heterozygosity of 3.4%, low genetic distances between populations (0.000--0.105 for Nei's genetic distance), and a surprisingly high fixation index (FST) of 0.585. The basic karyotype of the yellow mongoose was invariant geographically (2n = 36, NF = 72), although a single, supernumerary microchromosome was detected in four out of the five populations sampled. G- and C-banded karyotypes are presented. Evolutionary relationships among eight Southern African viverrid species, including the yellow mongoose, were inferred from phenetic and cladistic analyses of allelic variation at 18 protein loci. These data suggested the separate evolution of social and solitary lineages of mongooses.
A herpetological survey of the Transvaal.
(1989) Jacobsen, Niels Henning Gunther.; Poynton, John Charles.
This report discusses the taxonomy, distribution and ecology of the herpetofauna of the Transvaal based on a survey conducted over the past 10 years. Seventeen new forms, apart from four new taxa described during the course of this study, are discussed in the section on Systematics. The distribution of many species has been considerably amended. A total of 265 species and subspecies were recorded from the province. The biogeography of the herpetofauna is discussed in the light of past and present climatic events, as determined by palynological record. Factors affecting reptile and amphibian distributions are incorporated in an attempt to elucidate current distribution patterns. The conservation status of each species and subspecies is discussed and a final chapter on threats and conservation recommendations are incorporated.
The herpetology of south-east Africa.
(1966) Broadley, Donald George.; Poynton, John Charles.
No abstract available.
Fleshy-fruited invasive alien plants and frugivores in South Africa.
(2011) Jordaan, Lorinda A.; Downs, Colleen Thelma.; Johnson, Steven Dene.
South Africa is one of the world's most biologically invaded countries and has spent billions of rands on efforts to eradicate alien invasive plants. Chemical and mechanical control methods have varied in success and the need for integrated management strategies has been realised. This requires a better understanding of all aspects of the invasion process. Some of the most invasive plant species rely on vertebrate dispersers which facilitate long-distance seed dispersal. Frugivory is based on a mutualism in which the frugivores gain a resource and the plants benefit from seed dispersal away from the parent plant. Seed germination itself may either be enhanced, reduced or not affected at all after gut passage. The first aim of this study was to determine if generalist avian frugivores and a fruit bat species (Epomophorus wahlbergi) enhance or decrease seed germination of invasive alien plants in South Africa, by either pulp removal or seed coat abrasion, or if they serve as dispersers only. The second aim was to determine if avian frugivores are able to meet their energetic demands by feeding on a specific alien fruit diet. Finally, we also quantified the nutritional content and morphological characteristics of fleshy fruits of various invasive alien and exotic plant species. Avian frugivores: Red-winged Starlings (Onychognathus morio), Speckled Mousebirds (Colius striatus), and Dark-capped Bulbuls (Pycnonotus tricolor), varied in their effects on the germination success of seeds of four invasive alien species, namely: Lantana camara, Solanum mauritianum, Cinnamomum camphora, and Psidium guajava. However, this was not associated with differences in seed retention times. Similar germination success was observed for avian ingested and de-pulped seeds. This was also observed for fruit bat spat and depulped seeds of Psidium guajava, Melia azedarach, Eriobotrya japonica, and Morus alba. Therefore seed coat abrasion was not important for the germination of these fleshy-fruited invasive alien plants. Pulp removal resulted in significantly earlier seed germination as well as higher seed germination percentages than in the case of whole fruit controls for some of these invasive species. Gut passage is thus important for long-distance dispersal, and in some cases, for enhanced germination of seeds. The invasive Solanum mauritianum and indigenous congener S. giganteum showed similar germination responses, with both ingested and depulped seeds germinating profusely. However, S. giganteum benefited from pulp removal as seeds from whole fruits had less germination. Avian frugivores varied significantly in most energetic parameters calculated when given diets of invasive alien fruit. Speckled Mousebirds and Dark-capped Bulbuls were able to maintain body mass and efficiently process fruits of all four alien invasive plants, while Red-winged Starlings were only able to do so on lipid-rich C. camphora and sugar-rich S. mauritianum. Furthermore, frugivores also adjusted their feeding behavior by eating more nutritionally poor fruit and less energetically rewarding fruit. Fruit bats consumed more fruit per gram body mass than avian frugivores did. They therefore process proportionately more seeds than avian dispersers and thus their role in invasive seed dispersal, which has previously been underestimated particularly in South Africa, is highlighted. Fruits of invasive plant species were similar in morphology, but greater in nutritional content, than fruits of indigenous species. These fruits also contained small, light seeds with approximately only 30% having more than 10 seeds per fruit. The ability of frugivores to efficiently process these fruits and the greater nutritional rewards offered by these provide new insights into why these invasive fruits are preferred by frugivores. In addition, invasive alien plants may have a competitive edge over indigenous species because of their larger reproductive outputs and not necessarily because of greater germination success.
Grasshopper ecology and conservation in the Nama-Karoo.
(2001) Bekele, Solomon Gebeyehu.; Samways, Michael John.
This study was undertaken in the Karoo, a semi-arid grazing land in South Africa, to elucidate the interaction between grasshopper assemblages and various aspects of the Karoo landscape. It falls into four sections, the first of which was a three-year study which was undertaken on and around a prominent South African mesa to determine its role as an elevational conservation refugium for grasshoppers in a sea of grazed flatlands (Chapter 2). The number of grasshopper species and individuals on the summit, slopes and flatlands varied significantly, in relation to measured environmental variables. The summit, through inaccessibility to livestock grazing, was effectively a conservation refugium for one grasshopper species, Orthochtha dasycnemis. There was no significant difference in species richness between years of sampling, although there were significant variations in grasshopper abundance between years. The difference in rainfall between years was significant and appeared to be the key factor influencing grasshopper population dynamics. This clearly shows that a mesa can act as a conservation island and refugium supporting an insect assemblage that would be otherwise altered by heavy livestock grazing on the surrounding flatlands. This summit assemblage is strongly linked with that on the slopes and below, and is determined not so much by an island effect per se, but by low grazing intensity and associated soil and vegetation structure. The second part of the study focussed on the interaction between grasshopper assemblage response and three hill sizes at a regional scale (Chapter 3). Small hills contained a significantly higher grasshopper species richness and abundance than medium and large hills. There were significantly higher number of small-sized grasshopper species and individuals than medium and large-sized ones. Flatlands surrounding small hills had significantly higher grasshopper species richness and abundance than those surrounding medium and large hills. The slopes of the three hill sizes did not show significant difference in species richness and abundance. There was no significant variation between the summits of the three hill sizes in species richness but they varied in grasshopper abundance. The summits of small hills had significantly higher grasshopper abundance than the summits of medium and large hills. Detrended Correspondence Analysis showed two clear grouping of sampling site and grasshopper species. While the flatlands of small hills formed a separate assemblage of several grasshopper species, slopes and summits of all hills formed another clump of few grasshopper species. Canonical Correspondence Analysis revealed that flaltands surrounding small hills occurred along increasing gradients of shrub cover whereas those surrounding medium and large hills occurred along increasing gradients of grass cover, vegetation density and greenness of grasses. Slopes and summits of all hill sizes occurred along increasing gradients of rock cover, cragginess, grass height and soil temperature. Patterns of grasshopper dominance were markedly variable among sites. There were low dominance patterns on flatlands of small hills where most species were rare. The distributional patterns varied of higher taxonomic groups varied among the three hill sizes. Small hills contained species from four families and nine subfamilies, but medium and large hills had only members of Acrididae in five subfamilies. About 50% of the total grasshopper abundance were associated with small hills. The study revealed the patterns of grasshopper assemblages at regional scale, and showed that variability in hill sizes across the Karoo has marked role in grasshopper conservation, and that grasshoppers interact differentially with variable hill sizes across the Karoo. The third part of the study was undertaken at twelve grassland sites in the Mountain Zebra National Park (MZNP) and the surrounding farms to assess changes in grasshopper assemblages to grazing by indigenous mammals inside the park in comparison with grazing by domestic cattle outside (Chapter 4). The MZNP has been restored from cattle-grazed farmland to indigenous mammal parkland for 62 years. The number of grasshopper species and families inside the park was not significantly different from outside the park, but the number of individuals inside the park was significantly higher. Multivariate statistics did not reveal any strong site groupings based on simple inside/outside comparisons, but there were clear groupings of sites based on vegetation characteristics and other environmental variables. The park boundary, therefore, does not significantly determine grasshopper assemblages, although intensity of grazing does. The indigenous mammals inside the park had the same effect as the domestic cattle outside, and it was the level of defoliation and trampling that was important rather than type of mammal. Very intensive livestock grazing and trampling leads to bush encroachment and reduction in cover and/or disappearance of several grass species. In response to this pressure, grasshopper populations dropped, with localized extirpation of some species. Vegetation composition and structure showed a significant influence on grasshopper assemblages, particularly grass height and percentage cover. The MZNP is thus a localized area of elevated grasshopper abundance in comparison with the surrounding farm landscape, and presumably represents a situation prior to the current, intensive farming activities. Such elevated grasshopper The significantly lower population of grasshoppers on the surrounding farms, with local extirpation of some species also suggests that the MZNP could be viewed as a local centre to which species with higher capacity for mobility may seek refugia from anthropogenic pressures. Hence the MZNP serves as a reference showing the difference between restored through- natural-succession and anthropogenically-disturbed habitats, and compares desirable with undesirable ecosystem changes for herbivorous invertebrates such as grasshoppers. The fourth part of the study was on grasshopper assemblage response to seasonal grazing (including summer, winter, spring and autumn grazing), rotational grazing, continuous resting and continuous grazing at a long-term experimental site (Chapter 5). Rotationally grazed sites supported the highest number of grasshopper species and abundance, while continuously-grazed sites had the lowest. Cluster analysis revealed that spring-grazed and winter-grazed sites were the most similar, with continuously-rested sites being the next most similar to these. Rotationally-grazed sites showed the lowest similarity to the rest of the sites. DCA showed clear groupings of sites and grasshopper species, with most species associated with rotationally grazed sites. Continuously-grazed sites had a different grasshopper assemblage. CCA showed that the assemblages followed definite gradients of measured environmental variables. Rotationally-grazed sites occurred along gradients of increasing bare ground, while continuously-grazed and summer-grazed sites occurred along increasing gradients of shrub cover and soil temperature. Spring-grazed, autumn-grazed, winter-grazed and rotational1y-grazed sites were characterized by high vegetation density. Grasshopper dominance patterns were very different at different sites. Summer-grazed sites had the highest percent dominance (40%) by Picnodictyaflavipes, while winter-grazed sites showed higher percent dominance (32%) by Pseudogmothela sp. The significance of variable grazing management systems for maintaining floral and grasshopper diversity is discussed. It is recommended that rotational grazing in this arid system is most suited to maintaining plant and insect diversity. These four parts in this study all clearly showed that grasshoppers interact with the landscape in a way that their assemblage patterns are dictated by patch as well as by regional dynamics. Topography in particular contributes significantly to biodiversity patterns at the spatial scale of landscape. But these patterns are also strongly determined by differential grazing pressures from domestic livestock which in turn interact with the various topographical features. These findings enable recommendations to be made on optimal grazing regimes relative to the hilly features of the landscape. The results also show that restoration which incorporates low-pressure grazing regimes and which takes cognizance of topographical features can maintain grasshopper abundance and diversity in the long term.
Ecophysiology and population dynamics of the alien invasive gastropod Tarebia granifera in the iSimangaliso Wetland Park, South Africa.
(2012) Miranda, Nelson Augusto Feranandes.; Perissinotto, Renzo.; Appleton, Christopher Charles.
Tarebia granifera is a prosobranch freshwater gastropod from south-east Asia which has invaded other sub-tropical parts of the world. This snail has recently also invaded the iSimangaliso Wetland Park, often reaching population densities of over 20000 ind.mˉ2 and dominating benthic invertebrate communities. A multiple method approach was used to address several aspects of the biology and ecology of this non-native invasive species (NIS). The tolerance of T. granifera to salinity and temperature was investigated through the experimental manipulation of these factors. T. granifera survived exposure to temperatures between 0 ºC and 47.5 ºC. More remarkably, this snail was able to survive a salinity of 30 for 65 - 75 days. Population density and size structure were monitored in estuaries and coastal lakes. T. granifera successfully invaded estuaries despite frequent exposure to high salinity and desiccation. The persistence of T. granifera was largely ensured due to the wider environmental tolerance of adults (20 - 30 mm shell height) which carried an average of 158 ± 12.8 SD brooded juveniles. Multiple introductions were not essential for the success of this parthenogenetic NIS. Using gut fluorescence and carbon budget techniques it was estimated that T. granifera consumes 0.5 - 35% of the total available microphytobenthic biomass per day, or 1.2 - 68% of the daily primary benthic production. The carbon component estimated from the gut fluorescence technique contributed 8.7 - 40.9% of the total gut organic carbon content. A stable isotope mixing model was used together with gut content analysis to estimate the diet of T. granifera and dominant native gastropod species, potentially competing for resources. Results were used in the formulation of an index of isotopic dietary overlap (IDO, %). This approach yielded detailed information both on general changes in ecosystem functioning and specific species interactions. Before/After-Control/Impact (BACI) logic was used in a multivariate approach to separate human perturbations from natural spatio-temporal variability displayed by communities, and to further separate perturbations due to NIS. Human intensification of drought negatively affected biodiversity and T. granifera may exacerbate this problem by displacing native species from critical refugia and contributing towards biotic homogenization. The present findings constitute a contribution to the scientific knowledge on biological invasions and a useful tool towards adaptive management in the iSimangaliso Park.
The influence of abiotic processes, competition and predation on the community structure of rodents and shrews.
(2012) Delcros, Gwenaelle.; Schoeman, Marthinus Cornelius.; Taylor, Peter John.
Predation and abiotic processes rather than competition should influence the community structure of rodents and shrews with life histories characterised by high fecundity, short longevity and unstable populations. I investigated the influence of abiotic processes, predation and competition on three parameters of community structure (species composition, phenotypic and phylogenetic niches) of rodents and shrews at Mkhuze and Kube Yini, two game reserves in KwaZulu-Natal, South Africa, using null models and multivariate analyses. Rodents and shrews were sampled between 2007 and 2009. Sample-based rarefaction curves indicated that rodent species richness was higher at Mkhuze than at Kube Yini, while shrew species richness was identical at both reserves. Species richness estimators indicated that estimates of species richness were fairly accurate, hence strengthening the results from my null model analyses. I found evidence that immigration and extinction operating at a regional scale influenced rodent species composition. Moreover, habitat filtering operating at a local scale influenced rodent and shrew species composition. These processes produced nested assemblages: species present at species-poor sites were subsets of species present at species-rich sites. Habitat filtering also influenced the phenotypic niche of rodents and shrews: sympatric species showed similar phenotypic adaptations (phenotypic niches were underdispersed), probably in response to similar food requirements. Furthermore, shrew phenotypic traits showed a convergent evolution, and local assemblages comprised distantly related species (phylogenetic evenness), suggesting the influence of habitat filtering on the phylogenetic niche structure of shrews. Predation influenced shrew phenotypes. Bullae and ears were underdispersed and larger than expected by chance, probably to reduce predation risk through increased hearing sensitivity. In contrast, I found no evidence that predation influenced the rodent phenotypic niche. Competition influenced the phenotypic niches of rodents and shrews in species-rich assemblages (phenotypic niches were overdispersed). In these assemblages, the coexistence of species was facilitated by dietary and microhabitat partitioning. Competition also influenced the phylogenetic niche of rodents: phenotypic traits showed a convergent evolution, and local assemblages comprised closely related species (phylogenetic clustering). In conclusion, both abiotic and biotic processes influenced different parameters of the community structure of rodents and shrews. However, despite similar life-history traits, the community structure of local assemblages differed between rodents and shrews. Comparing patterns and processes of community structure across taxa would help find general trends of community organisation.

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