Above- and below-ground vertebrate herbivory may each favour a different subordinate species in an aquatic plant community

At least two distinct trade-offs are thought to facilitate higher diversity in productive plant communities under herbivory. Higher investment in defence and enhanced colonization potential may both correlate with decreased competitive ability in plants. Herbivory may thus promote coexistence of plant species exhibiting divergent life history strategies. How different seasonally tied herbivore assemblages simultaneously affect plant community composition and diversity is, however, largely unknown. Two contrasting types of herbivory can be distinguished in the aquatic vegetation of the shallow lake Lauwersmeer. In summer, predominantly above-ground tissues are eaten, whereas in winter, waterfowl forage on below-ground plant propagules. In a 4-year exclosure study we experimentally separated above-ground herbivory by waterfowl and large fish in summer from below-ground herbivory by Bewick’s swans in winter. We measured the individual and combined effects of both herbivory periods on the composition of the three-species aquatic plant community. Herbivory effect sizes varied considerably from year to year. In 2 years herbivore exclusion in summer reinforced dominance of Potamogeton pectinatus with a concomitant decrease in Potamogeton pusillus, whereas no strong, unequivocal effect was observed in the other 2 years. Winter exclusion, on the other hand, had a negative effect on Zannichellia palustris, but the effect size differed considerably between years. We suggest that the colonization ability of Z. palustris may have enabled this species to be more abundant after reduction of P. pectinatus tuber densities by swans. Evenness decreased due to herbivore exclusion in summer. We conclude that seasonally tied above- and below-ground herbivory may each stimulate different components of a macrophyte community as they each favoured a different subordinate plant species

Oportunismo alimentar de Knodus moenkhausii (Teleostei, Characidae): uma espécie abundante em riachos do noroeste do Estado de São Paulo, Brasil

O objetivo deste estudo foi investigar a biologia alimentar de Knodus moenkhausii (Eigenmann & Kennedy, 1903) em riachos do Alto rio Paraná no Estado de São Paulo. Em oito riachos (R1-R8), K. moenkhausii se alimentou de 18 itens, dos quais algas, ninfas de efemerópteros e larvas de dípteros foram os itens autóctones mais freqüentes e dominantes; fragmentos de insetos terrestres, himenópteros e aranhas foram os itens alóctones mais freqüentes e dominantes. No riacho R2, K. moenkhausii apresentou dieta distinta dos demais riachos, principalmente em função da profundidade, tipo de substrato e da presença de vegetação ripária. No riacho R9, amostrado mensalmente durante um ano, foram identificados 15 itens, dos quais insetos terrestres predominaram ao longo do ano; larvas de dípteros e algas foram pouco expressivas nos períodos de dezembro-janeiro (período mais quente e chuvoso) e junho-julho (período mais frio e seco). No riacho R9 foram realizadas observações subaquáticas durante mergulho livre, onde observamos a cata de itens na coluna d'água junto do substrato, da vegetação submersa e na superfície da água. A elevada variedade de itens consumidos - condicionada às variações do hábitat e sazonais - e a prática de diversas táticas nos permitem considerar K. moenkhausii uma espécie oportunista quanto ao uso dos recursos alimentares. Este oportunismo aparentemente se reflete na abundância da espécie, demonstrando boa capacidade em alocar parte significativa de sua energia à reprodução, mesmo em ambientes fisicamente impactados por ação antrópica.In the present investigation we studied the feeding biology of Knodus moenkhausii (Eigenmann & Kennedy, 1903) in streams of the Upper Paraná river system in the state of São Paulo. In eight streams (R1-R8), K. moenkhausii consumed 18 items, of which algae, ephemeropteran nymphs, and dipteran larvae were the most frequent and dominant autochthonous items, as were terrestrial insects, hymenopterans, and spiders regarding allochthonous items. In the R2 stream, K. moenkhausii showed distinct diet, mostly due to depth, substrate type, and presence of riparian vegetation. In the R9 stream (monthly sampled for one year), 15 items were consumed, of which terrestrial insects predominated all year round; dipteran larvae and algae were least relevant during December-January (hot and wet period) and June-July (cold and dry period), respectively. During snorkeling observations in this stream, we recorded individuals performing drift feeding, picking at relatively small preys close to the substrate and submerged vegetation, and surface picking. The large diversity of consumed items - conditioned to habitat and seasonal variations - and the diversity of feeding tactics allow us to consider K. moenkhausii a rather opportunistic fish species. Such opportunism apparently reflects on the species abundance, showing its ability to allocate a significant part of its energy to reproduction, even in physically impacted habitats by human actions

Selected quality parameters of wheat and potato snacks fried in different fats

Coraz większym zainteresowaniem wśród konsumentów cieszą się smażone produkty przekąskowe. Wśród nich wyróżniamy chrupki (prażynki) uzyskane z półproduktów typu pellet. W czasie smażenia pellety ekspandują, dzięki czemu otrzymują specyficzną chrupką i delikatną teksturę. Celem pracy przedstawionej w artykule było określenie wpływu rodzaju tłuszczu użytego do smażenia na jakość smażonych przekąsek pszennych i ziemniaczanych. Smażono pellety pszenne i ziemniaczane w 5 różnych tłuszczach: oleju rzepakowym rafinowanym, oleju rzepakowym tłoczonym na zimno, oliwie z oliwek, smalcu, a w celach porównawczych w tłuszczu palmowym. W smażonych przekąskach oznaczono zawartość wody, tłuszczu, teksturę i mikrostrukturę. Stwierdzono wysoką zawartość tłuszczu w smażonych przekąskach: pszennych od 21,56% w oleju rzepakowym tłoczonym na zimno, do 32,96% w oleju palmowym oraz w przekąskach ziemniaczanych od 19,61% w oleju rzepakowym tłoczonym na zimno, do 38,76% w palmowym. Rodzaj użytego do smażenia tłuszczu nie miał istotnego wpływu na teksturę przekąsek.Nowadays, more and more popular among consumers become fried snacks products. Among them we single out crisps (snacks) obtained from semi-finished type of pellet. During frying pellets are expanding, so why they get a specific crisp and delicate texture. The aim of this study was to determine the effect of type of fat used for frying on the quality of wheat and potato snacks. Wheat and potato pellets were fried in 5 different fats: refined rapeseed oil, rapeseed cold pressed oil, olive oil, lard and for comparative purposes in palm fat. The content of water, fat, texture and microstructure of snacks were determined. There was found a high fat content from 21,56% in wheat snacks fried in cold pressed rapeseed oil to 32,96% fired in palm oil. The content of fat in potato snacks was detected in the range from 19.61% in snacks fried in cold pressed rapeseed oil to 38,76% in snacks fried in palm oil. The type of fat which was used for frying had no significant effect on the texture of snacks