Trophic interactions between two neustonic organisms: insights from Bayesian stable isotope data analysis tools

The by-the-wind sailor Velella velella (Linnaeus, 1758) and its predator, the violet snail Janthina globosa (Swainson, 1822) are both floating neustonic organisms. Despite their global oceanic distribution and widespread blooms of V. velella in recent years, many gaps remain in our understanding about prey/predator interactions between these two taxa. Using stable isotope ratios of carbon and nitrogen, we aimed to study the trophic relationship between V. velella and J. globosa and investigate diet variation of V. velella and J. globosa in relation to individuals’ size. Bayesian approaches were used to calculate isotopic niche metrics and the contribution of V. velella to the J. globosa diet. Our data showed that the isotopic niche of V. velella differed markedly from that of J. globosa. It was larger and did not overlap that of the J. globosa, indicating a more variable diet but at a lower trophic level than J. globosa. The isotopic niche of V. velella also varied according to the size class of the individual. Small individuals showed a larger isotopic niche than larger animals and low overlap with those of the larger individuals. J. globosa displayed very low isotopic variability and very small isotopic niches. In contrast, there were no isotopic composition nor isotopic niche differences between J. globosa of any size. This very low isotopic variability suggested that J. globosa is a specialist predator, feeding, at least in this aggregation, principally on V. velella. Moreover, outputs of a stable isotope mixing model revealed preferential feeding on medium to large ( 500 mm2) V. velella colonies. While our isotopic data showed the trophic relationship between V. velella and J. globosa, many questions remain about the ecology of these two organisms, demonstrating the need for more fundamental studies about neustonic ecosystems.

Feeding Preference of Papilio memnon Linnaeus, 1758 (Lepidoptera) Larvae on Host Plants Citrus aurantifolia and Citrus hystrix (Rutaceae)

This research aimed to investigate the food preference of the Papilio memnon L. larvae on two host plants. This study was conducted by two choice food preference test combination of leaves Citrus aurantifolia Chrism. and Citrus hystrix DC. The result of this study showed that the third instar of P. memnon L. larva significant preferential feeding (P<0.05), while the fourth and fifth instar shown that no significant feeding preference beetwen host plants. Nitrogen and water content of leaves were higher on C. aurantifolia (0.212 % and 70.368%) than C. hystrix (0.04% dan 64.027%). While carbohydrate content was higher on C. hystrix (22.167%) than C.aurantifolia (31.097%).

Fetal and lamb losses from pregnancy scanning to lamb marking in commercial sheep flocks in southern New South Wales

Perinatal lamb mortality is a major challenge for sheep producers worldwide. Lamb losses from ultrasound pregnancy scanning to lamb marking were assessed in 125 mobs of ewes sourced predominantly from sheep flocks in southern New South Wales. In total, 103 086 lambs were marked from100 165 ewes present at joining. Despite the majority of producers undertaking best-practice ewe management, including ultrasound scanning for pregnancy and preferential feeding of multiple bearing ewes, losses were similar to those reported previously (11% and 29% for singles and twins respectively). Non-Merino ewes had significantly lower losses than did Merino ewes, irrespective of ram type (13% versus 21%, P < 0.001). There was a tendency for mob size in twin-bearing ewes to influence survival, with a lower mob size (<200) having lower losses (29% versus 33%, P = 0.07). These results are discussed in the context of existing extension advice about ewe management and perinatal lamb mortality.

Feeding niche preference of the mudsnail Peringia ulvae

The feeding behaviour of Peringia ulvae was studied with the aim of assessing its preferential feeding niche (habit) as well as its potential role in controlling or preventing the occurrence of macroalgal blooms. Both these aspects were studied in the Mondego estuary because of the clear long-lasting eutrophication process that favours the growth of two opportunistic macroalgae, Gracilaria spp. and Ulva spp., over the local beds of the macrophyte Zostera nolteii, which is another potential food source. All three species, both with and without periphyton, were used as a single food source in feeding experiments to assess different feeding parameters of the gastropod. Sediment with microphytobenthos was used together with the latter three species in feeding niche preference experiments. None of the food types provided were resistant to grazing. Higher levels of grazing occurred on Ulva spp. (apical parts) and Z. nolteii, both with periphyton. The presence of periphyton did not change grazing rates. When a choice between each food type was offered, the sediment was clearly the feeding niche preferred by the snails. As P. ulvae spent more time on the sediment (preferred feeding niche), the hypothesis that it has a role in preventing macroalgal blooms was not supported.