Browsing by Author "Midgley, Jeremy"

Now showing 1 - 9 of 9
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    A squeaky suspicion : rodent pollination in Protea nana
    (2007) Biccard, Aiden; Midgley, Jeremy
    The pollination syndrome of Protea nana has been described as uncertain throughout the literature. Floral morphology, presence of pendulous inflorescences
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    Community ecology of small-mammal pollinated proteas
    (2013) Kuhn, Nicola; Midgley, Jeremy; Steenhuisen, Sandy-Lynn
    The floral characteristics of small-mammal pollinated (SMP) Protea species have been assessed in a number of previous studies. This study aimed to determine whether the inflorescences of Protea canaliculata, Protea sulphurea and Protea humiflora possess these traits and are pollinated by small mammal species. An additional aim of this study was to determine whether there is a variation in pollinator efficiency of different animal species. Floral characteristics that may influence plantpollinator interactions were measured, including floral dimensions, nectar production and spectral reflectance. Live-trapping was conducted using Sherman traps and mean facial and faecal pollen load was determined for the different species caught. Furthermore pollinators were observed through footage from motion sensor cameras placed facing the inflorescences of SMP proteas. The results of this study confirmed that Protea canaliculata, Protea sulphurea and Protea humiflora are pollinated by small mammal pollinators. The evidence supporting this is that the afore-mentioned species have traits that correspond to those possessed by known small-mammal pollinated proteas including: bowlshaped inflorescences, high nectar concentrations (ranging between 24.1-42.9%), sucrose-rich nectar composition, a "yeasty" scent, floral colours that are visible to small mammals, and a winter flowering season. These proteas were found to have separated peak flowering times, providing a nectar source throughout winter for small mammals at this site. Fifty-eight small mammals of seven different species, were trapped in P. canaliculata and P. sulphurea stands over 98 hours. The average nighttrapping success was 22.7% and day-trapping success was 5.7%, indicating a relatively abundant nocturnal small-mammal population. A separation in pollinator efficiency was observed for different small mammal species, with Elephantulus edwardii identified as the most effective pollinator as it showed the greatest pollen removal (highest faecal pollen load) and spent the longest time foraging on inflorescences (±28 seconds per inflorescence). Another important pollinator was Aethomys namaquensis because it visited flowers 75% more frequently than any of the other pollinators. Camera trapping was shown to be a superior method than conventional trapping for assessing pollination by providing insight into pollinator behaviour, identifying new pollinators of 'trap-shy' species and also due to its more animal-friendly disposition.
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    Crypsis in non-flying mammal pollinated Proteaceae: novel adaptations and evidence of nectarivorous bird avoidance
    (2019) Connolly, Alexandra; Midgley, Jeremy
    A defining feature of the non-flying mammal pollinated (NMP) syndrome is inflorescence crypsis whereby flowers are close to the ground and somewhat hidden within the canopy. A number of species in the Cape Proteaceae are NMP, two of which were chosen as focal species for this study: Protea amplexicaulis and Protea humiflora. This study investigated the two previously suggested hypotheses for crypsis: hidden flowers are more difficult for nectarivorous birds to access, or hidden flowers provide greater cover for small mammal pollinators from aerial predators. Using remote triggered cameras, P. amplexicaulis and P. humiflora inflorescences were observed over the 2017 flowering period, noting visitation by birds and small mammals and assessing the legitimacy of birds as pollinators. In the literature, bird visitation to exposed inflorescences is suggested to be rare, but this study showed that it is considerable. Observations of camera footage suggest that birds are in fact illegitimate pollinators and thus nectar rob. Bird visitation to exposed inflorescences was more than tenfold that of hidden inflorescences, suggesting that crypsis is likely a strategy to avoid nectar robbing by birds. Both P. amplexicaulis and P. humiflora have been observed to retain dead leaves, which may contribute to their cryptic nature. Alternative hypotheses for dead leaf retention in Proteaceae – that it may increase flammability or result in a below canopy spike in nutrients post fire (selfish fertilization) – were assessed and rejected. Sampling of eight local Protea species showed that dead leaf retention is not a consequence of prolonged live leaf retention, with P. amplexicaulis retaining dead leaves for up to 6 years. The removal of dead leaves in 30 P. amplexicaulis individuals resulted in a significant decrease in the number of inflorescences hidden from aerial view, thus suggesting that dead leaf retention may be a strategy to enhance crypsis and thus forms part of the NMP syndrome. This research expands on the knowledge of the NMP syndrome; providing evidence in support of an anti- nectar robbing crypsis function, discovering a novel crypsis adaptation regarding dead leaf retention, and casting doubt on the Restricted Distributions hypothesis for the evolution of the syndrome.
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    Effects of fire and fire intensity on the germination and establishment of Acacia karroo, Acacia nilotica, Acacia luederitzii and Dichrostachys cinerea in the field
    (BioMed Central Ltd, 2004) Walters, Michele; Midgley, Jeremy; Somers, Michael
    BACKGROUND:While fire has been used in some instances to control the increase of woody plants, it has also been reported that fire may cause an increase in certain fire-tolerant Acacia tree species. This study investigated germination of Acacia karroo, A. luederitzii and Dichrostachys cinerea, thought to be increasing in density, as well as the historically successful encroaching woody species, A. nilotica, in savanna grassland, Hluhluwe-iMfolozi Park, South Africa. A. karroo is thought to be replacing A. nilotica as the dominant microphyllous species in the park. We tested the hypothesis that observed increases in certain woody plants in a savanna were related to seed germination and seedling establishment. Germination is compared among species for burnt and unburnt seeds on burnt and unburnt plots at three different locations for both hot and cool fires. RESULTS: Acacia karroo showed higher germination (A. karroo 5.1%, A. nilotica 1.5% and A. luederitzii 5.0%) levels and better establishment (A. karroo 4.9%, A. nilotica 0.4% and A. luederitzii 0.4%). Seeds of the shrub Dichrostachys cinerea did not germinate in the field after fire and it is thought that some other germination cue is needed. On average, burning of A. karroo, A. nilotica and A. luederitzii seeds did not affect germination. There was a significant difference in the germination of burnt seeds on burnt sites (4.5%) and burnt seeds on unburnt plots (2.5%). Similarly, unburnt seeds on unburnt sites germinated better (4.9%) than unburnt seeds on burnt sites (2.8%). CONCLUSION: We conclude that a combination of factors may be responsible for the success of A. karroo and that fires may not be hot enough or may occur at the wrong time of year to control A. karroo establishment in HiP. Although germination and establishment of A. karroo was higher than for A. nilotica a competitive advantage after fire could not be shown.
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    Floral evolution of long-tubed Erica species
    (2023) McCarren, Sam; Midgley, Jeremy
    The genus Erica has undergone an extreme radiation in the Cape and exhibits a diversity of pollination syndromes and floral traits. This makes Erica well-suited to study the evolution of floral traits and how they impact speciation. The first chapter explored the role of ultraviolet colouration by recording its prevalence across Erica pollination syndromes. Ultraviolet was rare in wind-, rodent and small insect-pollinated species, but it was common in bird-pollinated species and ubiquitous in long-proboscid fly (LPF)-pollinated species. Testing their preference revealed that sunbirds can see ultraviolet, but they have no innate preference. LPFs on the other hand were not attracted to flowers where ultraviolet reflectance was removed, thus displaying a strong preference. Chapter 2 focused on the role of stickiness for nectar robbers. I experimentally added stickiness to Erica flowers of one species and further compared stickiness to nectar robbing across several communities. Stickiness appears to reduce damage due to nectar robbing within and between species. Further, I found that stickiness is strongly correlated with pollination by birds and LPFs which might be due to their large nectar rewards. Chapter 3 investigated how the sister species Erica shannonea and Erica ampullacea co-occur despite sharing a pollination syndrome. Pollination experiments and observations showed that they are pollinated by LPFs from two families. The horizontal flowers of E. shannonea are pollinated by a tabanid which has a fixed forward-pointing proboscis, while the vertical flowers of E. ampullacea are pollinated by a nemestrinid which can swivel its proboscis downwards. The nemestrinid in turn has a shorter proboscis which prevents it from accessing nectar in the long-tubed E. shannonea. Due to their different biomechanics, each fly can only access the flower it pollinates resulting in effective reproductive isolation between these species. Chapter 4 compared flower orientation in relation to the two LPF families across all LPF-pollinated species. Using a phylogenetically corrected analysis, I found that flowers pollinated by Tabanidae tend to be horizontal, while nemestrinid flowers are more variable in orientation and more often vertical. This confirms the importance of pollinator biomechanics for the evolution of floral traits. The last chapter investigated how pollen transfer efficiency differs between Erica pollination syndromes. I found that LPF- and bird-pollinated species have higher pollen transfer efficiency in comparison to bee-pollinated species which might have facilitated the shifts from ancestral bee pollination.
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    Heuweltjies : a window into the palaeoclimate and palaeovegetation of the Western Cape?
    (2006) Potts, Alistair; Midgley, Jeremy; Harris, Chris
    Late Pleistocene terrestrial climate information in the Western Cape. South Africa may be preserved in oxygen and carbon isotope ratios in paedogenic calcrete that bas Conned in zeuweltjies (large circular earth mounds). He11weltjles are common landscape features and their potential as palaeoclimatic archives is not known, simply because it has never been investigated. Samples were taken from three depth-profiles down a single hemvcltjie near Worcester. Carbon and oxygen isotope ratios were detennincd. In total, fifty-four samples were analysed. The o13C values vary from -7.4%. to -4.9%0 relative to PDB. whereas 15180 vary from 28.05'160 to 30.91%0 relative to SMOW.
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    Population genetics of South African Protea L. (Proteaceae) species associated with various pollinator guilds
    (2019) Smith, Megan; Midgley, Jeremy; Steenhuisen, Sandy-Lynn; Prunier, Rachel
    South Africa hosts plant species with a large variety of floral traits associated with different pollinator guilds. Suites of specialised floral traits associated with particular pollinators are known as pollination systems or syndromes. However, it is often uncertain how these pollination systems affect gene flow between plant populations, mating system outcome, and subsequent genetic health of plant species. Genetic variability is an important aspect in understanding the long-term survival of a species because excessive homozygosity, as a result of high amounts of inbreeding, may restrict a species’ long-term local adaptive potential. The African genus, Protea, is an ideal study system for exploring the evolution and maintenance of mating systems, because the pollination system for many species have been confirmed by pollinator exclusion experiments. The genus has several pollination systems including birds, insects and non-flying mammals. Comparative estimates of pollinators’ outcrossing abilities are rare and confined to bird and insect guilds. Furthermore, 10 microsatellite markers have been developed for the genus, but have not been used to assess the outcrossing abilities of various pollinators. This study thus had two aims: Firstly, to use microsattelite markers to estimate the outcrossing rates and subsequent genetic diversity of Protea species primarily pollinated by either birds (P. laurifolia and P. roupelliae), insects (P. caffra and P. simplex) or non-flying mammals (P. amplexicaulis and P. humiflora). Secondly, I aimed to understand how birds and non-flying mammal pollinators affect population connectivity and gene dispersal. This was done by comparing indirect estimates of gene flow in the therophilous, P. amplexicaulis, and ornithophilous, P. laurifolia. These estimates included population differentiation (G”st) between subpopulations and spatial genetic structuring within metapopulations of each species. I expected that less vagile pollinators, such NMP’s (non-flying mammal pollinators), would contribute the least to gene flow and cause high selfing rates and low genetic diversity within therophilous populations. Contrastingly, flying pollinators would be able to travel longer distances resulting in more genetic connectivity between plant populations. The high energetic demands and interplant movements of flying animals were predicted to result in high outcrossing rates in ornithophilous and entomophilous species. Non-flying mammal-pollinated (NMP) Protea species had high (> 0.8) and non-significantly different (p > 0.05) outcrossing rates relative to species pollinated by flying animals. Similarly, hand pollen supplementation experiments also revealed that small mammals were effective pollen vectors since P. amplexicualis individuals were not pollen limited. High multilocus outcrossing rates (> 0.80) may have resulted in all sampled Protea species exhibiting high levels of heterozygosity (> 0.7) and low levels of inbreeding. However, some of the outcrossing events were between kin (approximately 14 %), giving evidence for biparental inbreeding. Furthermore, the relationship between geographic distance and genetic distance was significant for sampled P. amplexicaulis individuals. In contrast, sampled P. laurifolia individuals were genetically similar across the landscape. This pattern was reflected in fine-scale (> 500 m) spatial genetic structuring in a sampled metapopulaton of P. amplexicaulis and a homogeneous distribution of P. laurifolia genotypes. Restricted gene dispersal recorded for P. amplexicaulis in this study may have been a result of the high levels of biparental inbreeding. It was not clear whether poor gene flow was primarily a result of restricted pollen dispersal created by NMP’s or restricted seed dispersal. Nevertheless, continuous limited gene dispersal between NMP populations may result in allopatric speciation over time. This provides a hypothesized reason as to why many of the therophilous Protea species are located in small and isolated populations. Additionally, there is a concern that restricted population size in combination with poor gene flow may lead to increased levels of inbreeding over time. This study provided the first evidence for localised gene dispersal, but high outcrossing rates, in NMP proteas.
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    The reproductive biology and ecology of Colchicum (Colchicaceae) in southern Africa
    (2008) Kleizen, Ciara; Midgley, Jeremy; Johnson, Steven
    The observation that many plants have developed sets of structural and functional adaptations that encourage visitation by pollinators has led biologists to define pollination syndromes. These syndromes reflect patterns of convergent evolution and serve to generate hypotheses about potential pollinators based on a plant's morphological characteristics (Faegri and van der Pijl, 1979; Johnson and Steiner, 2000).
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    Understanding the role of fragmentation in informing small mammal diversity and abundance in Rûens Renosterveld
    (2022) Widegger, Abigail; Anderson, Pippin; Midgley, Jeremy
    This thesis engages with the theory of habitat fragmentation through the lens of small mammals within a highly fragmented landscape in the Overberg, South Africa. The study explores habitat features in fragments of Eastern Rûens Shale Renosterveld associated with small mammal diversity and abundance and explores the potential processes driving ecosystem functioning in this region, with the aim of strengthening the knowledge underpinning our understanding of ecological patterns and processes in this critically endangered vegetation type. In the first part of this study, the effect of habitat fragmentation on small mammal communities was investigated by comparing species richness, diversity, and abundance between small, medium, and large fragments of renosterveld within an agricultural matrix. The study shows that medium and large fragments support greater small mammal richness, diversity, and abundance, than small fragments, whilst also harbouring rare, and specialist species. Rhabdomys pumilio was abundant across the study area, and was the only species found in small fragments, albeit at low densities. There was no strong correlation observed between the size of fragments and small mammal species diversity and abundance, with habitat amount across the landscape potentially being a stronger determinant of small mammal diversity. The results suggest that other landscape and local features, such as cover by rocky outcrops and canopy diversity may play a greater role in determining small mammal diversity indices than area of fragment size alone. The second part of the study investigates dietary information of small mammal species in the region through the analysis of stable isotope ratios of carbon ( 13C/12C) and nitrogen ( 14N/15N) in faecal samples. The results are used to compare dietary differences between and within these species as part of understanding the biology of these species and their response to habitat fragmentation. The results do not indicate a clear response in the dietary partitioning in these species, but instead show that the diets of these small mammals appear to be variable, with no clear signal of niche or trophic separation, potentially indicating that the fragmentation in this region has led to these small mammals subsisting on a diet different to what would be expected, with omnivores displaying lower δ 13C than herbivores, and no clear trophic separation based on δ 15N between herbivores, omnivores and insectivores. This work is important for renosterveld conservation, which seeks to implement cost effective and ecologically appropriate restoration methods, through providing much needed information on the status of these ecosystem engineers in fragments where efforts may be prioritised. In addition, it points to the need for a habitat improvement across the region, where fragments are found mainly on private agricultural land, highlighting the need for landowner engagement in any conservation effort.