Top-down control by insect predators in an intermittent pond – a field experiment

Abstract

-The role of predation in the regulation of freshwater communities is predicted to decrease along a habitat-duration gradient, from permanent to episodic waters. We tested the role of invertebrate predation in shaping the community structure in a fishless temperate intermittent pond with a three month long hydroperiod by comparing the community structure in two large field enclosures (4.2 m 2 ) with added predators to two enclosures without added predators. The added predators reflected the density and composition of top predators in the pond and comprised weekly additions of dytiscid larvae (for three weeks) followed by weekly additions of odonate nymphs (for five weeks). Compared with the enclosure controls, the predator addition enclosures had fewer dipterans and crustaceans, higher concentrations of benthic ciliates and other protozoans, higher chlorophyll a and bacterial counts, and lower abundance of rotifers. Many treatment effects were temporally variable and this appeared to be linked to predator identity, predator size, and prey availability. Compared with the surrounding pondwater, the enclosed areas had lower abundance of molluscs, ostracods and cladocerans but higher abundance of cyclopoids and higher concentrations of phytoplankton and ciliates. Despite high productivity and seasonally variable predator and prey assemblages, which likely buffered against strong top-down control, we conclude that the top-predators regulate the dipterans and zooplankton in this intermittent pond and that the effects propagated down through the food web to lower trophic levels.

Temporal changes in periphytic meiofauna in lakes of different trophic states

“…As reported by Magnusson, and Williams (2009) and Peters, and Traunspurger (2011), predatory insect larvae as well as grazing macroinvertebrates can negatively affect meiofaunal communities. Whereas several authors established a positive relationship between the meiofaunal abundance and algal biomass of the epilithon Peters, and Traunspurger 2005), this was not confirmed in the present study.…”

Environmental Influence on Flight Activity and Arrival Patterns of Aerial Colonizers of Temporary Ponds

“…Detailed information on the water characteristics of the ponds during the 2001 hydroperiod is available in Magnusson and Williams (2006). Several other food web studies were conducted in these two ponds in 2001 and 2002 (see Andrushchyshyn et al 2003;Andrushchyshyn et al 2006;Magnusson and Williams 2009).…”

“…Moreover, predation is particularly important in the structuring of communities in temporary waters because the inhabitants typically lack adaptations to predation (Wilcox 2001;Petrusek et al 2009). Aerial colonizers can be the main source of top predators in such waterbodies (Schneider and Frost 1996;Wilcox 2001;Anderson and Smith 2004), supplying elements which may act as strong controlling factors on community properties (e.g., Blaustein 1990;Boix et al 2006;Magnusson and Williams 2009). For predatory aerial colonizers, the existence of a pond network together with its characteristics (e.g., distances among ponds; Conrad et al 1999;Wilcox 2001) determine the size of their metapopulations, since predator density and/or food shortage in a pond have been identified as likely cues for initiating dispersal to neighbouring ponds (Ohba and Takagi 2005;Yee et al 2009).…”

Bottom-up processes control benthic macroinvertebrate communities and food web structure of fishless artificial wetlands

“…In wetlands, a historical view that bottom-up controls have greater relative importance than topdown controls in regulating ecosystem structure and function (e.g., Odum and Smalley 1959) has been reconsidered more recently (Sala et al 2008;Moore 2018). Indeed, top predators like fish or invertebrates can significantly control the abundance and the assemblage of their prey (Diehl 1992;Magnusson and Williams 2009;Cobbaert et al 2010;Laske et al 2017) and top-down control of grazers on primary producers play a key role on wetland functioning and stability (e.g., limitation of algal blooms; Hillebrand 2009;Bertness et al 2014). In this context, artificial wetlands, which are increasingly developed to compensate for the loss of natural wetlands (Davidson 2014), could be useful tools for determining the respective roles of bottom-up and top-down forces on community structures because they allow for the selection of systems with distinct productivities.…”