INTRODUCTIONLong-term studies are essential for understanding ecological processes such as the influence of stressors and are basic for modeling, but are few in number because of their inherent difficulties, including costs (Jackson and Füreder, 2006;Maberly and Elliott, 2012). In particular, long-term studies of zooplankton can reveal the influence of past factors, including management decisions (Hambright, 2008). Some causes of changes in the zooplankton that are perceptible over a longer period include alterations of abiotic factors or predator invasion (Yan et al., 2008).The factors that affect the diversity and size of zooplankton species are intriguing issues, but still subject to controversy. From the classic paper by Brooks and Dodson (1965) to recent studies, several factors have been contemplated, and temperature has emerged as the preponderant factor for explaining latitudinal differences in zooplankton body size (Gillooly and Dodson, 2000). Gillooly and Dodson compared more than 1100 lakes located between 81°N and 77°S latitude, and found that the size variation of cladoceran species was related to latitude, with smaller sizes in the tropics and the Arctic and a greater difference between the tropics and the temperate zone. According to these authors, the highest mean sizes were observed between 6°C and 8°C, declining at higher or lower temperatures. Havens et al. (2015), comparing 122 lakes located from 6° to 74°N and from 19° to 21°S, showed a relationship between size (as weight) of cladocerans and cyclopoid copepods and temperature. In contrast, Iglesias et al. (2011) suggested that predation by fish is the major factor explaining the smaller size of zooplankton in warm lakes. Hart and Bychek (2011), in their extensive review of the many factors that could potentially influence zooplankton size, addressed extrinsic factors such as temperature, food and predation, amongst others, besides intrinsic ones. The authors concluded, however, that although a general pattern may occur, different results can arise from distinct ecosystems.J. Limnol., 2015; 74(3): 606-617 ORIGINAL ARTICLE DOI: 10.4081/jlimnol.2015DOI: 10.4081/jlimnol. .1132 A long-term study on crustacean plankton of a shallow tropical lake: the role of invertebrate predation
Aim To test the relevance of competition and predation for the two most abundant and frequent cladoceran populations, the medium-sized Ceriodaphnia richardi Sars, 1901 and the large-sized Daphnia gessneri Herbst, 1967, in a tropical shallow lake. Methods Laboratory experiments and weekly samplings in the lake for a year were performed to evaluate: density fluctuations and reproduction; predation on juveniles and adults by larvae of Chaoborus brasiliensis Theobald, 1901; competitive interactions and possible implications of competition and predation on the fluctuations of populations in the lake. Juveniles and adults of both cladocerans were offered to larvae instar IV of chaoborid, for testing selective predation in laboratory experiment. Competitive interaction between the two cladocerans was tested in experiments, with high (0.70 mg C.L-1) and low (0.25 mg C.L-1) concentrations of the edible chlorophycean Desmodesmus spinosus Chodat. Results C. richardi and D. gessneri were more abundant in the cool season, when their densities were inversely correlated, and when invertebrate predators, C. brasiliensis and the water mite Krendowskia sp., were less abundant. Despite higher concentrations of food and larger number of offsprings produced by the cladocerans in the warm season in the lake, their densities were lower, coincident with the increase of invertebrate predators, mainly chaoborid larvae. C. brasiliensis preyed on adult C. richardi and on young D. gessneri. In the competition experiments, the densities and the population growth rates of C. richardi were higher than those of D. gessneri. The competition results support the “small body size” and the “rmax” hypotheses. The exclusion of D. gessneri by C. richardi occurred only in experimental conditions, while they coexist in the lake, but without reaching their carrying capacity. Conclusions Predation is the key factor influencing the populations of cladocerans, whereas competition seems to play a secondary role, probably restricted to some periods of lower food concentration in the cool season.
Citation: Simões LB, dos Santos Ferreira TC, Bichuette ME (2013) Aquatic biota of different karst habitats in epigean and subterranean systems of Central Brazil -visibility versus relevance of taxa. Subterranean Biology 11: 55-74. doi:10.3897/subtbiol.11.5981 AbstractThe karstic area of São Domingos, central Brazil, holds extensive drainage systems. In order to understand its biodiversity, various volumes of water were filtered with planktonic nets in stretches of subterranean and superficial rivers on five different occasions. We sampled four drips (152L), three calcite pools (368L), two subterranean rivers fed mainly by percolation water (6,395L), two subterranean rivers fed mainly by water coming from a sinkhole (4,175L) along different caves, one resurgence (158L), and four epigean rivers (101,690L). Physical and chemical variables were measured at some sites. Canonical Correlation Analysis was used to verify relationships between taxa and environment. The degree of similarity of the biota was assessed by cluster analysis (Sorensen, single linkage). There were records of exclusive taxa in epigean and subterranean samples, mainly in drips, which harbour the most unique fauna. The high richness of taxa presently recorded reveals the potential of the vadose zone biota in the tropical region, which was neglected in studies on Brazilian subterranean biodiversity. According to our results, the unsaturated zone tropical fauna may have different composition compared to that from temperate habitats. The studied communities were dominated by rotifers, while crustacean are predominant in the latter. The hypothesis can be clarified with the increase of long term studies and taxa identification at species level, besides the use of complementary sampling methods.
Tema importante no estudo da ecologia, a competição inter-específica é a demanda ativa por indivíduos de duas ou mais espécies de mesmo nível trófico por um recurso comum que é potencialmente limitante.Esse estudo teve como objetivo avaliar a ocorrência de competição entre espécies de microcrustáceos cladóceros e seu papel na estruturação da Para melhor compreender as razões da superioridade competitiva de C. richardi e o papel da predação com relação a essa espécie, foram feitos experimentos adicionais. Um deles testou a hipótese de que essa espécie pode alimentar-se de outros recursos além de algas, com os tratamentos (3 réplicas): a. água filtrada do lago e b. água filtrada, com adição da alga S.spinosus. Os resultados deram suporte à hipótese. O experimento de predação, com 5 cladóceros e 2 larvas IV de Chaoborus por réplica, mostrou que essa espécie é predada por elas.Flutuações das populações de microcrustáceos zooplanctônicos e dos predadores invertebrados (larvas de Chaoborus brasiliensis e o ácaro aquático Krendowskia sp.) foram acompanhadas semanalmente no lago, durante um ano, entre maio de 2011 e abril de 2012, bem como fatores físicos, químicos e biológicos, como temperatura, oxigênio dissolvido, condutividade elétrica, pH, transparência na coluna d'água e clorofila-a, na tentativa de estabelecer conexão entre os resultados de laboratório e campo.Os resultados mostraram que um período de estratificação térmica mais nítida ocorreu no lago entre outubro e abril (estação quente-chuvosa), sendo mais acentuada a partir de dezembro, enquanto circulação freqüente da coluna d'água foi registrada nos meses mais frios do ano, de maio a setembro (estação fria-seca). A distribuição vertical de outras variáveis ambientais mostrou relação com o padrão de circulação do lago, refletindo na dinâmica populacional das populações zooplanctônicas.Cladóceros foram mais abundantes na estação fria-seca, enquanto copépodos aumentaram no início da estação quente-chuvosa. Porém, ambos os grupos apresentaram as menores densidades entre os meses de fevereiro e abril de 2012. O aumento das larvas de caoborídeos e dos ácaros aquáticos na estação quente-chuvosa parece ser a principal causa do declínio de cladóceros neste período, devido à predação. Já o alimento e temperatura parecem ter maior influência sobre as populações na estação fria-seca. Além da predação, temperatura e alimento, os resultados de competição interespecífica também mostraram ser esse um dos fatores potencialmente controladores da dinâmica populacional do zooplâncton no Lago Monte Alegre, particularmente no período frio, quando o alimento é mais escasso. AbstractCompetitive interactions are an important topic in the study of ecology.The interspecific competition is the demand for active individuals of two or more species of the same trophic level for a common resource that is potentially limiting.This study aimed to evaluate the occurrence of competition between species of cladocerans and their role in structuring the zooplankton community. This is the missing...
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