Browsing by Author "Miranda, Nelson Augusto Feranandes."

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Chemical cue interactions between alien invasive and native aquatic gastropods in the iSimangaliso Wetland Park, South Africa.
(2013) Raw, Jacqueline Leoni.; Perissinotto, Renzo.; Miranda, Nelson Augusto Feranandes.
The importance of chemical cues in mediating interactions among individuals and structuring communities is being increasingly recognized in aquatic environments. Chemical cues have been shown to drive predator-prey interactions in which behavioural responses in terms of movement have been reported. The role of chemical cues in mediating interactions between heterospecific competitors, in which there is an observed behavioural response, has not been previously investigated. This research project has used the biological invasion of Tarebia granifera, a caenogastropod endemic to south-east Asia, to determine the role of chemical cues in driving displacement interactions with native gastropods within coastal lakes and estuarine environments of the iSimangaliso Wetland Park, in northern KwaZulu-Natal, South Africa. An experimental approach was used to measure behavioural responses of gastropods to chemical cue treatments by quantifying components of movement. Responses of three dominant native gastropods within Lake St Lucia were tested in a preliminary in situ experiment. The mean Displacement, mean Number of Steps and grand mean Turning Angle were determined from recorded pathways of individual gastropods using image-processing software. Responses to chemical cues released by T. granifera were significantly different and negative in comparison to the control and conspecific chemical cue treatments. Following these results, the experiment was repeated and refined to include responses between native heterospecific gastropods from populations within the larger geographical range of the iSimangaliso Wetland Park. Additionally, the case of whether the observed responses could be attributed to build up of metabolic waste products was also investigated. The results confirmed those of the preliminary in situ study. Negative responses were only reported for gastropods which did not have a shared evolutionary history with T. granifera, irrespective of metabolic waste concentrations Native gastropods moved away from chemical cues released by T. granifera using a directed orientation mechanism. Interestingly, native gastropods did not exhibit this behavioural response to chemical cues of other heterospecifics. This suggests that T. granifera has developed chemical cues under evolutionary pressure, which act as deterrent on naïve gastropods. The implications for these responses are considered within the framework of Movement Ecology with contributions to Chemical Ecology. The potential of this interaction as a mechanism of invasion to be included within spread models is discussed.
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.