Is competition an interaction as relevant as predation for tropical planktonic cladocerans?

Abstract

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.

Functional groups of rotifers and an exotic species in a tropical shallow lake

“…Temporal variations of functional groups of rotifers in Lake Monte Alegre indicated the indirect effect of cladoceran predation by invertebrates, such as Chaoborus brasiliensis larvae and the aquatic mite, Krendowskia sp., in 2011-2012 41 . Predation pressure by invertebrates is generally higher in the warm season when their populations increased, resulting in declining cladoceran populations 29,41 . Consequently, there is a decrease in exploitative competition by cladocerans and the possibility of competitive exclusion when resources are limiting.…”

Experiments on invertebrate predation on cladocerans and its relationships with lake data

“…Changes in the composition and density of cladoceran species in Lake Monte Alegre are more evident in the warm season (spring and summer) than in the cool season, along with an increase in Chaoborus density (Arcifa et al, 2015). A sharp reduction in Ceriodaphnia density was observed in this season (Ferreira et al, 2018), while Diaphanosoma remained less abundant throughout the year in the limnetic zone (Ferreira, 2013). The laboratory experiments in the present study provide evidence that Chaoborus predation is of significant importance for lake grazers and that both cladoceran species, D. birgei and C. richardi, can be strongly affected by it, the first being the most affected species.…”

“…Competition could be another important factor, but experiments using seston from the lake as food did not result in clear competition among cladocerans (Ferreira and Arcifa, in preparation), although it occurs when a laboratory alga was offered in limited concentrations. Experiments on competition between Daphnia gessneri and Ceriodaphnia richardi under food limitation showed that C. richardi was a superior competitor to D. gessneri (Ferreira et al, 2018). However, in the lake, the fluctuations of the populations of the two species indicated the prevalence of predation, because although there was a higher carbon concentration and a higher egg production per female in the warm season, their abundance was lower, particularly for C. richardi (Ferreira et al, 2018).…”

“…Water mite predation is considered relevant when their density exceeds 100 ind m -3 (Riessen, 1982). The mite densities recorded in Lake Monte Alegre ranged from 250 ind m -3 to 2000 ind m -3 between 1998 and 2012 (Perticarrari, 2000;Fileto, 2001;Ferreira et al, 2018). Such densities could affect the mortality of cladoceran species (Matveev et al, 1989;Balseiro, 1992).…”

Zooplanctofagia de heterópteros na estrutura da comunidade zooplanctônica em um lago neotropical: análise integrada entre DNA do conteúdo alimentar e experimento em mesocosmo

“…Ou seja, mesmo em densidades menores que outras presas, as presas maiores serão mais frequentemente escolhidas. Esta ideia levou à generalização de que alguns invertebrados aquáticos são predadores seletivos pelo tamanho das presas (Zaret 1980) Ferreira et al 2018). No entanto, esta elevada média em abril (215,9 ind/L) em relação a agosto (44,9 ind/L), está claramente influenciada pela densidade populacional de D. cf.…”