Browsing by Author "Gihwala, Kirti Narendra"

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    Flamingo foraging plasticity: ecological drivers and impacts
    (2017) Gihwala, Kirti Narendra; Pillay, Deena; Varughese, Melvin
    The consequences of predation have become a central focus of marine ecological research. Numerous studies have emphasized the importance of apex predators in structuring assemblages at various organisational levels and in determining how ecosystems function. However, less appreciated currently is the fact that predators display multiple foraging behaviours, thereby allowing them to overcome problems associated with unpredictability of food resources in space and time. The primary goal of this dissertation is to contribute to growing understanding of the ecological causes and consequences of foraging plasticity displayed by Greater Flamingo Phoenicopterus ruber roseus in intertidal sandflat ecosystems in Langebaan Lagoon, South Africa. P. roseus feeds by either (1) creating pits, which involves flamingos stirring up deep sediments with their feet or (2) creating channels, in which their inverted bills are swept from side-to-side on the sediment surface. The first objective of the study was to quantify the ecological drivers of decisions made by flamingos to feed, and to implement either pit- or channel-foraging strategies. The latter was achieved through RandomForest modelling techniques that identified the prominent ecological drivers from a suite of biotic and abiotic variables. Results indicate that biotic variables, i.e. those associated with flamingo prey assemblages, were key in driving choices made by flamingos to forage and to implement either pit- or channel-foraging strategies. The second aim of this dissertation was to quantify the repercussions of the two different foraging behaviours on benthic assemblages. Comparisons of benthic assemblages in flamingo foraging structures (pits and channels) with adjacent non-foraged sediments (controls) indicated differential effects of both flamingo foraging methods on benthic communities, with channel-foraging eliciting a greater negative impact compared to pit-foraging, for which impacts were negligible. Abundance of macrofauna and surface-dwelling taxa such as micro-algae and the amphipod Urothoe grimaldii were all negatively impacted by channel-foraging. Sizes of channels constructed by flamingos were inversely related to their impacts, with impacts on macrofaunal abundance being greater in smaller channels. Overall, this study has shed light on the differential effects of foraging plasticity on prey assemblages and its importance in enhancing spatio-temporal heterogeneity in intertidal sandflats. The study also emphasizes the need to incorporate foraging plasticity into current thinking and conceptual models of predation in marine soft sediments, in order to appreciate the full spectrum of predation effects on assemblages.
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    Flamingo predation impacts on benthic communities: effects of spatial gradients
    (2014) Gihwala, Kirti Narendra; Pillay, Deena
    Biological disturbances on marine soft sediment ecosystems have been well researched. However, little attention has been paid to the potential ecological role that iconic shore bird predators may have on marine ecosystems. This paper tests the effects of spatial gradients on Greater Flamingo (Phoenicopterus ruber) predation impacts on the benthic macrofaunal community structure in an intertidal sandflat ecosystem in South Africa. P. ruber is a benthic filter-feeder known to feed on benthic dwelling invertebrates through pit formation, where deep sediments are stirred up by trampling their feet. Macrofaunal community structure between flamingo pit foraging structures and adjacent non-foraged sediments (controls) yielded insignificant spatial differences. However, subtle positive and negative effects of flamingo predation on macrofaunal abundance were noted at specific sites. Flamingos in this study were not targeting a specific prey group. Thus of the 19 macrofaunal prey items identified, none were significantly impacted across treatments, except for an unidentified polychaete. However, this was once again site specific. The results suggested this polychaete is generally abundant within the area sampled. Furthermore, its distribution is perhaps affected by the level of intensity employed in pit-foraging, rather than being preyed upon. Greater polychaete abundance in pits relative to controls may be attributed to vigorous flamingo feeding efforts. Pit foraging appears to be an expensive strategy to employ, but the energy investment may be reduced through the use of sophisticated sensory organs to detect accessible prey deep within the sediment. Overall, the study has shown that the impact of flamingo predation on a spatial gradient is small and site specific. However, the study highlights the need for further research on quantifying the ecological role flamingos play as predators on marine ecosystems.