Dataset Information

Stable isotope evidence for dietary overlap between alien and native gastropods in coastal lakes of northern KwaZulu-Natal, South Africa.

ABSTRACT: Tarebia granifera (Lamarck, 1822) is originally from South-East Asia, but has been introduced and become invasive in many tropical and subtropical parts of the world. In South Africa, T. granifera is rapidly invading an increasing number of coastal lakes and estuaries, often reaching very high population densities and dominating shallow water benthic invertebrate assemblages. An assessment of the feeding dynamics of T. granifera has raised questions about potential ecological impacts, specifically in terms of its dietary overlap with native gastropods.A stable isotope mixing model was used together with gut content analysis to estimate the diet of T. granifera and native gastropod populations in three different coastal lakes. Population density, available biomass of food and salinity were measured along transects placed over T. granifera patches. An index of isotopic (stable isotopes) dietary overlap (IDO, %) aided in interpreting interactions between gastropods. The diet of T. granifera was variable, including contributions from microphytobenthos, filamentous algae (Cladophora sp.), detritus and sedimentary organic matter. IDO was significant (>60%) between T. granifera and each of the following gastropods: Haminoea natalensis (Krauss, 1848), Bulinus natalensis (Küster, 1841) and Melanoides tuberculata (Müller, 1774). However, food did not appear to be limiting. Salinity influenced gastropod spatial overlap. Tarebia granifera may only displace native gastropods, such as Assiminea cf. ovata (Krauss, 1848), under salinity conditions below 20. Ecosystem-level impacts are also discussed.The generalist diet of T. granifera may certainly contribute to its successful establishment. However, although competition for resources may take place under certain salinity conditions and if food is limiting, there appear to be other mechanisms at work, through which T. granifera displaces native gastropods. Complementary stable isotope and gut content analysis can provide helpful ecological insights, contributing to monitoring efforts and guiding further invasive species research.

SUBMITTER: Miranda NA

PROVIDER: S-EPMC3283693 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Stable isotope evidence for dietary overlap between alien and native gastropods in coastal lakes of northern KwaZulu-Natal, South Africa.

Miranda Nelson A F NA Perissinotto Renzo R

PloS one 20120221 2

<h4>Background</h4>Tarebia granifera (Lamarck, 1822) is originally from South-East Asia, but has been introduced and become invasive in many tropical and subtropical parts of the world. In South Africa, T. granifera is rapidly invading an increasing number of coastal lakes and estuaries, often reaching very high population densities and dominating shallow water benthic invertebrate assemblages. An assessment of the feeding dynamics of T. granifera has raised questions about potential ecological ...[more]

PMID: 22363764

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Project description:BACKGROUND: Estuaries and coastal lakes receive little attention despite being heavily invaded by non-indigenous invasive species (NIS). In these situations, studies of population dynamics in invaded habitats can provide valuable insights into how NIS interact with new environments. Tarebia granifera is a prosobranch gastropod from south-east Asia which has invaded other sub-tropical parts of the world. This study addresses whether a small number of key environmental factors influences gastropod communities, and specifically how the population density and size structure of T. granifera were influenced by environmental change in estuaries and coastal lakes in southern Africa. METHODOLOGY/PRINCIPAL FINDINGS: T. granifera's density, number of brooded juveniles and size structure were measured at the St. Lucia Estuary, Mgobozeleni Estuary, Lake Sibaya and Lake Nhlange. Size structure was classified according to shell height (SH). All dissected individuals were found to be female and free from trematode infection. Salinity, water depth, temperature, and pH were the main factors correlated with population density of gastropod communities. T. granifera often reached densities well over 1000 ind. m(-2), displacing indigenous gastropods and becoming a dominant component of the benthic community. T. granifera successfully invaded estuaries despite frequent exposure to high salinity and desiccation, which could together eliminate >97% of the population. The persistence of T. granifera was ensured due to its high fecundity and the environmental tolerance of large adults (20-30 mm SH) which carried an average of 158±12.8 SD brooded juveniles. Repeat introductions were not essential for the success of this parthenogenetic NIS. CONCLUSION/SIGNIFICANCE: There is a need for a broader study on the reproductive biology of T. granifera (including the previously overlooked "brood pouch ecology"), which affects population dynamics and may be relevant to other parthenogenetic NIS, such as Melanoides tuberculata and Potamopyrgus antipodarum.

Project description:Alien gastropods have caused extensive harm to biodiversity and socioeconomic systems like agriculture and horticulture worldwide. For conservation and management purposes, information on impacts needs to be easily interpretable and comparable, and the factors that determine impacts understood. This study aimed to assess gastropods alien to South Africa to compare impact severity between species and understand how they vary between habitats and mechanisms. Furthermore, we explore the relationship between environmental and socioeconomic impacts, and both impact measures with life-history traits. We used the Environmental Impact Classification for Alien Taxa (EICAT) and Socio-Economic Impact Classification for Alien Taxa (SEICAT) to assess impacts of 34 gastropods alien to South Africa including evidence of impact from their entire alien range. We tested for correlations between environmental and socioeconomic impacts per species, and with fecundity and native latitude range using Kendall's tau tests. Kruskal-Wallis tests were used to compare impact magnitude among mechanisms and habitats, respectively. This study presents the first application of EICAT and SEICAT for invertebrates. There was no correlation between environmental impacts and socioeconomic impacts. Habitats did not differ regarding the severity of impacts recorded, but impacts via disease transmission were lower than other mechanisms. Neither fecundity nor native range latitude was correlated with impact magnitude. Despite gastropods being agricultural and horticultural pests globally, resilience of socioeconomic systems makes high impacts uncommon. Environmental systems may be vulnerable to gastropod impacts across habitats, having experienced multiple local extinctions of wetland island snail fauna. South Africa stands out as the only continental country that follows this trend. The knowledge gained on severity and nature of gastropod impacts is useful in risk assessment, which can aid conservation management. To make impact assessments more realistic, we suggest alternative ways of reporting impacts classified under EICAT and SEICAT.

Project description:ObjectivesResearch on migration and HIV has largely focused on male migration, often failing to measure HIV risks associated with migration for women. We aimed to establish whether associations between migration and HIV infection differ for women and men, and identify possible mechanisms by which women's migration contributes to their high infection risk.DesignData on socio-demographic characteristics, patterns of migration, sexual behavior and HIV infection status were obtained for a population of 11,677 women aged 15-49 and men aged 15-54, resident members of households within a demographic surveillance area participating in HIV surveillance in 2003-04.MethodsLogistic regression was conducted to examine whether sex and migration were independently associated with HIV infection in three additive effects models, using measures of recent migration, household presence and migration frequency. Multiplicative effects models were fitted to explore whether the risk of HIV associated with migration differed for males and females. Further modeling and simulations explored whether composition or behavioral differences accounted for observed associations.ResultsRelative to non-migrant males, non-migrant females had higher odds of being HIV-positive (adjusted odds ratio [aOR] = 1.72; 95% confidence interval [1.49-1.99]), but odds were higher for female migrants (aOR = 2.55 [2.07-3.13]). Female migrants also had higher odds of infection relative to female non-migrants (aOR = 1.48 [1.23-1.77]). The association between number of sexual partners over the lifetime and HIV infection was modified by both sex and migrant status: For male non-migrants, each additional partner was associated with 3% higher odds of HIV infection (aOR = 1.03 [1.02-1.05]); for male migrants the association between number of partners and HIV infection was non-significant. Each additional partner increased odds of HIV infection by 22% for female non-migrants (aOR = 1.22 [1.12-1.32]) and 46% for female migrants (aOR = 1.46 [1.25-1.69]).ConclusionsHigher risk sexual behavior in the context of migration increased women's likelihood of HIV infection.

Project description:BackgroundExclusive breastfeeding (EBF) for six months is the mainstay of global child health and the preferred feeding option for HIV-infected mothers for whom replacement feeding is inappropriate. Promotion of community-level EBF requires effective personnel and management to ensure quality counselling and support for women. We present a costing and cost effectiveness analysis of a successful intervention to promote EBF in high HIV prevalence area in South Africa, and implications for scale-up in the province of KwaZulu-Natal.Methods and findingsThe costing of the intervention as implemented was calculated, in addition to the modelling of the costs and outcomes associated with running the intervention at provincial level under three different scenarios: full intervention (per protocol), simplified version (half the number of visits compared to the full intervention; more clinic compared to home visits) and basic version (one third the number of visits compared to the full intervention; all clinic and no home visits). Implementation of the full scenario costs R95 million ($14 million) per annum; the simplified version R47 million ($7 million) and the basic version R4 million ($2 million). Although the cost of the basic scenario is less than one tenth of the cost of the simplified scenario, modelled effectiveness of the full and simplified versions suggest they would be 10 times more effective compared to the basic intervention. A further analysis modelled the costs per increased month of EBF due to each intervention: R337 ($48), R206 ($29), and R616 ($88) for the full, simplified and basic scenarios respectively. In addition to the average cost effectiveness the incremental cost effectiveness ratios associated with moving from the less effective scenarios to the more effective scenarios were calculated and reported: Nothing-Basic R616 ($88), Basic-Simplified R162 ($23) and Simplified-Full R879 ($126).ConclusionsThe simplified scenario, with a combination of clinic and home visits, is the most efficient in terms of cost per increased month of EBF and has the lowest incremental cost effectiveness ratio.

Project description:Antimicrobial resistance (AMR) is a serious global public-health threat. Evidence suggests that antimicrobial stewardship (AMS) is a valuable tool to facilitate rational antibiotic use within healthcare facilities. A cross-sectional situational analysis using a questionnaire was conducted to determine the current status of antimicrobial stewardship (AMS) activities in all public-sector hospitals in KwaZulu-Natal (KZN). The survey had a 79% (57, N = 72) response rate. A total of 75% of hospitals had an antimicrobial stewardship committee (AMSC), 47% (20, N = 43) had a formal written statement of support from leadership, and 7% (3, N = 43) had budgeted financial support. Only 37% (16, N = 43) had on-site or off-site support from a clinical microbiologist, and 5% (2, N = 43) had an on-site infectious disease (ID) physician. Microbiologist input on pathogen surveillance data (aOR: 5.12; 95% CI: 4.08-22.02; p-value = 0.001) and microbiological investigations prior to the commencement of antibiotics (aOR: 5.12; 95% CI: 1.08-42.01; p-value = 0.041) were significantly associated with having either on- or off-site microbiology support. Respondents that had a representative from microbiology on the AMSC were significantly associated with having and interrogating facility-specific antibiograms (P = 0.051 and P = 0.036, respectively). Those facilities that had access to a microbiologist were significantly associated with producing an antibiogram (aOR: 4.80; 95% CI: 1.25-18.42; p-value = 0.022). Facilities with an ID physician were significantly associated with having a current antibiogram distributed to prescribers within the facility (P = 0.010) and significantly associated with sending prescribers personalized communication regarding improving prescribing (P = 0.044). Common challenges reported by the facilities included suboptimal hospital management support; a lack of clinicians, pharmacists, nurses, microbiologists, and dedicated time; the lack of a multidisciplinary approach; low clinician buy-in; inadequate training; a lack of printed antibiotic guidelines; and financial restrictions for microbiological investigations. The survey identified the need for financial, IT, and management support. Microbiology and infectious disease physicians were recognized as scarce human resources.

Project description:Frugivorous birds play an important role in seed dispersal. Alien plant species' seeds are dispersed by local birds in order to establish populations in new habitats. Alien plant species that produce fruits similar to that of native species have the potential to attract local birds, creating new mutualistic systems that are similar to the local ones. In autumn 2018 and 2019, we studied the seed dispersal systems of an alien plant species, Phytolacca americana, and a native species, Cayratia japonica, in a coastal seawall forest. Both plant species' fruit, frugivorous bird foraging behaviors, seed germination rates, and seedling microhabitats were examined to determine whether the alien species had a similar seed dispersal system to that of the native species. Our results showed that P. americana and C. japonica had similar fruit type, color, and ripening period. There was a positive correlation between the percentage rate of fruit ripening and the percentage rate of fruit missing for both plant species, indicating that local frugivorous birds have the potential to sufficiently disperse the alien seeds to enable its spread in the coastal seawall forest (simple linear regression, P. americana: β = 0.863 ± 0.017, R2 adj = 0.978, P < 0.01; C. japonica: β = 0.787 ± 0.034, R2 adj = 0.898, P < 0.01). Eleven bird species consumed the fruits of the alien species or native species during the study period. Similar results were shown across alien and native species in bird foraging behavior (feeding frequency, feeding duration and first stop distance) indicating that a similar seed dispersal relationship had been established between local frugivorous and both plant species. The alien plant had a higher number of fruits carried by birds, suggesting that P. americana had a slightly higher fruit consumption than that of C. japonica (t-test, P < 0.01). Alien plant seedlings grow more abundant in forest gap microhabitat (t-test, P < 0.01). Our results confirmed that bird digestion promotes seed germination success in both plant species. Our study suggests that in a narrow coastal seawall forest, alien plant species can successfully establish their populations by relying on similar seed dispersal systems as the local species.

Project description:In June 2017, extreme fires along the southern Cape coast of South Africa burnt native fynbos and thicket vegetation and caused extensive damage to plantations and residential properties. Invasive alien plants (IAPs) occur commonly in the area and were thought to have changed the behaviour of these fires through their modification of fuel properties relative to that of native vegetation. This study experimentally compared various measures of flammability across groups of native and alien invasive shrub species in relation to their fuel traits. Live plant shoots of 30 species (10 species each of native fynbos, native thicket, and IAPs) were sampled to measure live fuel moisture, dry biomass, fuel bed porosity and the proportions of fine-, coarse- and dead fuels. These shoots were burnt experimentally, and flammability measured in terms of maximum temperature (combustibility), completeness of burn (consumability), and time-to-ignition (ignitability). Multiple regression models were used to assess the relationships between flammability responses and fuel traits, while the Kruskal-Wallis H test was used to establish if differences existed in flammability measures and fuel traits among the vegetation groups. Dry biomass significantly enhanced, while live fuel moisture significantly reduced, maximum temperature, whereas the proportion of fine fuels significantly increased completeness of burn. Unlike other similar studies, the proportion of dead fuels and fuel bed porosity were not retained by any of the models to account for variation in flammability. Species of fynbos and IAPs generally exhibited greater flammability in the form of higher completeness of burn and more rapid ignition than species of thicket. Little distinction in flammability and fuel traits could be made between species of fynbos and IAPs, except that fynbos species had a greater proportion of fine fuels. Thicket species had higher proportions of coarse fuels and greater dry biomass (~fuel loading) than species of fynbos and IAPs. Live fuel moisture did not differ among the vegetation groups, contrary to the literature often ascribing variation in flammability to fuel moisture differences. The fuel traits investigated only explained 21-53% of the variation in flammability and large variation was evident among species within vegetation groups suggesting that species-specific and in situ community-level investigations are warranted, particularly in regard fuel moisture and chemical contents.

Dataset Information

Stable isotope evidence for dietary overlap between alien and native gastropods in coastal lakes of northern KwaZulu-Natal, South Africa.

Publications

Stable isotope evidence for dietary overlap between alien and native gastropods in coastal lakes of northern KwaZulu-Natal, South Africa.

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