Zooplankton body size is fundamentally affecting productivity, ecosystem respiration, nutrient cycling, and energy transfer and may be controlled by food availability but also water physical and chemical characteristics. However, the differences in control of water physical and chemical characteristics and food availability on zooplankton body size have rarely been investigated in subtropical systems. We tested the hypotheses that: (i) the type of environment, food availability, and water physical and chemical characteristics would influence body size distribution in the Upper Paraná River floodplain and nearby subsystems and (ii) in environments with higher food availability, small‐sized organisms would predominate showing higher abundance, whereas the opposite would occur in environments with lower food availability. To test these hypotheses, we performed partial redundancy and redundancy analyses (RDA). Our results showed that food availability, Secchi depth, and suspended inorganic matter influenced the body size structure of rotifers and cladocerans. Additionally, we observed that greater food availability was related to greater abundance of organisms, which were dominated by small‐sized zooplankton (size classes C2 and C1 in rotifers, and class C2′ in cladocerans). It was possible to associate different zooplankton body size spectra with phytoplankton biovolume and planktonic ciliate abundance. We suggest that large‐bodied cladocerans could have a competitive advantage over rotifers and small‐sized cladocerans when resources are scarce, because the large‐sized group could explore a wider range of resource types.

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ABSTRACT. Processes related to biological invasion of inland waters have become a major issue due to the increasing number of cases associated with the potential effects of invasions. Kellicottia bostoniensis and K. longispina are rotifer species originating from North America and have become invasive in several continents. In this sense, this study carried out a scientometric analysis to analyze the geographical distribution and identify patterns of occurrence as well as to fill gaps on the knowledge of these species. The survey was based on articles indexed in databases from 1896 to 2014. There is a greater scientific knowledge of these species in the temperate region, and these are present in many different environments. In Brazil, there is a very small number of studies, and no record of K. longispina. Therefore, it is noteworthy the importance of studies on the occurrence and abundance of these species in poorly studied areas, such as subtropical and tropical regions, for a better understanding of their invasive potential, given the potential effects on different communities, which can affect the structure and dynamics of environments.Keywords: Rotifera, zooplankton, dispersal potential, time trend.Dispersão geográfica das espécies invasoras Kellicottia longispina (Kellicott, 1879) e K. bostoniensis (Rousselet, 1908): uma abordagem cienciométrica RESUMO. Os processos relacionados à invasão biológica de águas continentais tornaram-se uma questão importante, por causa do crescente número de casos associados aos potenciais efeitos das invasões. As espécies Kellicottia bostoniensis e K. longispina são originárias da América do Norte e tornaram-se invasoras em vários continentes. Nesse sentido, o objetivo deste estudo foi realizar uma análise cienciométrica para verificar a distribuição geográfica e, consequentemente, identificar padrões de ocorrência e preencher lacunas sobre o conhecimento dessas espécies. A pesquisa foi realizada com base em artigos indexados em bases científicas, considerando o período de 1896 a 2014. Foi possível observar que há maior conhecimento científico sobre as espécies na região temperada, e estas estão presentes nos mais diferentes ambientes. No Brasil, foi registrado um número muito reduzido de estudos, e ausência de K. longispina. Portanto, ressaltase a importância de estudos sobre ocorrência e abundância dessas espécies em regiões pouco estudadas, como as subtropical e tropical, para o melhor entendimento de seu potencial de invasão, pelos potenciais efeitos sobre as diferentes comunidades, podendo afetar a estrutura e dinâmica dos ambientes.Palavras-chave: Rotifera, zooplâncton, potencial dispersor, tendência temporal.

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Zooplankton body size shows a strong association with temperature, competition, and predation. Global warming affects all three drivers of body size and is thus expected to lead to substantial changes in zooplankton community composition and body size distributions. To disentangle the isolated and joint effect of temperature, competition, and fish predation on species biomass and community composition in zooplankton, we monitored population biomasses of three Daphniidae species that differ in body size (Daphnia magna, Daphnia pulex, and Ceriodaphnia reticulata) for 20 days, manipulating competition (monoculture, pairwise trials, and three-species communities), temperature (20 C, 24 C, and 28 C) and presence or absence of fish predation. In the absence of predation, D. magna dominated in all competition experiments, even at high temperatures. D. magna went extinct, however, in the predation treatments at 24 C and 28 C. D. pulex outcompeted C. reticulata and was negatively affected by predation and high temperature. C. reticulata did not reduce biomass at high temperatures and was negatively affected by all competition trials, but was positively affected by predation. Our results indicate that the two larger-bodied species are more negatively affected by the combination of temperature and predation than the smallest species. While higher temperatures reduced the biomass of the larger-bodied species, it did not fundamentally change their ability to dominate over the smallest species in competition. The combined effect of warming and predation changed community composition more fundamentally, resulting in the dominance of small-bodied species. This can have important ecosystem-wide impacts, such as the transition to turbid, algae-dominated systems.