https://commons.ru.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://commons.ru.ac.za/vital/access/manager/Repository/vital:5665 Wed 21 Jul 2021 13:46:25 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5786 Wed 12 May 2021 22:53:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5684 Wed 12 May 2021 22:44:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5704 7mm) were equivalent to ≈10% and ≈5% of body dry weight, respectively. The von Bertalanffy growth curve parameters were empirically identified, by cohort analysis of data collected during 4 years, as K = 0.22239/year, L[subscript]∞ = 14.05789mm, t₀ = -0.05174, L₀ = 0.16083mm. N. marionis can survive up to seven years under natural conditions.]]> Wed 12 May 2021 22:28:01 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5682 Wed 12 May 2021 19:55:48 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5685 l5mm) were calculated as real densities from randomly placed quads i.e. not from areas of 100% cover. Density decreased up the shore; low, mid and high shore zones were significantly different from each other (ANOVA , p<0.0001; followed by multiple range tests). There was no significant difference between the densities of mussels at exposed and sheltered sites within each zone (ANOVA, p=0.7155). Recruit ( Wed 12 May 2021 19:52:56 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5943 Wed 12 May 2021 19:50:45 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5789 Wed 12 May 2021 19:18:34 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5947 Wed 12 May 2021 19:05:52 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5741 15 mm) were positively correlated with recruit densities (1-5 mm) for both shore types (p15 mm) was significantly lower on exposed (mean of 3 348.m⁻²) than on sheltered shores (mean of 4 796.m⁻²) (pO.05). The effect of exposure on growth rate formed the focal point of this study and was determined using three different approaches. The first technique, mark-recapture, involved filing notches on the growing edges of mussels in the field. After 111 days, mussels were removed and the growth measured. The second approach used internal growth bands to measure growth rates, once the periodicity with which these bands were laid down was established. Thirdly, using Shepherd's length composition analysis (SLCA), growth rates were determined from length frequency distributions in 11 samples taken over 15 months. The general conclusion from all three approaches was that growth rate was twice as fast on the exposed shores as on the sheltered shores (p Wed 12 May 2021 18:40:51 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5720 Wed 12 May 2021 17:49:53 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5788 90% in the last 130 years), the cause(s)of which are unknown. There is a paucity of data on this species in the South Atlantic Ocean, therefore their trophic ecology at Tristan da Cunha was studied, specifically focusing on diet, using stomach content analysis and stable isotope analysis (SIA), in conjunction with an analysis of diving behaviour, assessed using temperature-depth recorders. In order to evaluate the influence of gender on foraging, a morphometric investigation of sexual dimorphism was confirmed using molecular analysis. Additionally, plasma corticosterone levels were measured to examine breeding stage and presence of blood parasites as potential sources of stress during the breeding season. Northern Rockhopper penguins at Tristan da Cunha displayed a high degree of foraging plasticity, and fed opportunistically on a wide variety of prey, probably reflecting local small-scale changes in prey distribution. Zooplankton dominated (by mass) the diet of guard stage females, whereas small meso-pelagic fish (predominantly Photichthyidae)dominated diet of adults of both sexes in the crèche stage, with cephalopods contributing equally in both stages. Adults consistently fed chicks on lower-trophic level prey (assessed using SIA), probably zooplankton, than they consumed themselves indicating that the increasing demands of growing chicks were not met by adults through provisioning of higher- quality prey. SIA also indicated that adults foraged in different oceanic water masses when feeding for self-maintenance and for chick provisioning, thus temporally segregating the prey consumed for different purposes. It is possible that adults ‘selected’ these higher quality prey for themselves, or this may be a reflection of opportunistic behaviour. At Tristan da Cunha sexual dimorphism was observed in culmen dimensions (length, depth, width), with males having larger beaks and feeding on larger individuals of squid and fish than females. No sexual segregation in terms of foraging habitat (i.e. different water masses, based on ð¹³N or trophic level ð¹⁵N) during the breeding season or pre-moult period was revealed through SIA, and stomach content analysis revealed no sexual differences in prey species targeted. The results of SIA of feathers indicate that during the pre-moult period birds foraged in different water masses than during the breeding period. The fact that throughout the breeding season birds foraged in similar habitats suggests no intra-specific competition, despite both sexes feeding on the same prey.Birds were generally diurnal, daily foragers (12 – 16 hr trips), with extended trips (maximum duration 35.5 hours) and nocturnal diving recorded in a few individuals. Birds dived well within their physiological limits, predominantly utilising the upper 20m of the water column, employing two different strategies to target different prey items. Long, deep (30 – 40 m), energetically costly dives were performed when targeting energy-rich prey (fish), and a greater number of shorter, shallower (5 – 20 m), energy-efficient dives were performed when targeting prey with a lower energy content (zooplankton). More than half of the sampled study population were infected with the intra-cellular blood parasite Babesia, but infection showed no relationship to body mass, corticosterone levels or breeding success. Fasting birds showed no signs of elevated corticosterone levels, suggesting they had acquired sufficient fat reserves prior to breeding. Failed breeders did not exhibit elevated corticosterone levels. Tristan skuas, Catharacta antarctica hamiltoni, were observed to be a significant cause of egg and chick mortality. The absence of sex-based differences in foraging, and the absence of any signs of stress in relation to body mass, presence of Babesia or breeding stage, suggest that there are no obvious signs of high levels of stress or food limitations during breeding at Tristan da Cunha.]]> Wed 12 May 2021 17:44:40 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5744 Wed 12 May 2021 17:26:42 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5890 Wed 12 May 2021 17:16:57 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5927 Wed 12 May 2021 16:51:18 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:28392 Thu 13 May 2021 07:14:39 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:20500 Thu 13 May 2021 07:01:36 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5679 Thu 13 May 2021 06:52:07 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5733 Thu 13 May 2021 06:47:28 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5926 Thu 13 May 2021 06:33:46 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5814 Thu 13 May 2021 04:51:18 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5925 Thu 13 May 2021 04:23:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5756 Thu 13 May 2021 04:13:04 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5692 Thu 13 May 2021 03:16:35 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:29207 Thu 13 May 2021 03:15:17 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:28686 Thu 13 May 2021 03:01:37 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5847 Thu 13 May 2021 01:12:18 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:31386 Thu 13 May 2021 00:57:15 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5675 Thu 13 May 2021 00:50:01 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:21274 slopes> vertical surfaces> tide pools> crevices. The current study found that, while the pulmonate limpets, Siphonaria capensis and S. serrata, preferred rock pools, sloped, vertical and horizontal rock surfaces, the patellogastropod limpets, Cellana capensis and Scutellastra granularis, preferred rock pools and vertical rock surfaces. Furthermore, the pulmonate limpets were only common on horizontal rock surfaces where specific ameliorating conditions would have mitigated thermal stress there. In addition, C. capensis had similar thermal tolerance limits to the pulmonate limpets in air and the pulmonate limpets had similar and/or higher thermal tolerance limits compared to S. granularis in water. This indicates that the pulmonate limpets did not necessarily prefer warmer microhabitats than the patellogastropod limpets and that there were no differences in the collective upper thermal tolerance limits between the two limpet groups in either medium.Consequently, there was no indication from this study that an assumed superior capacity for oxygen supply translates into greater thermal tolerance and that the hypotheses based on the OCLTT were not supported. Although this was an indirect test of the OCLTT theory, I conclude that this study does not support the notion of its general applicability and that mechanisms other than those outlined by the OCLTT theory may help explain the patterns of thermal limitation observed in the current study.]]> Thu 13 May 2021 00:11:29 SAST ]]>