Effects of daphnid size and density on interference between Daphnia and Keratella cochlearis1

Abstract

The cladocerans Daphnia pulex, Daphnia ambigua, Daphnia rosea, Daphnia magna, and Daphnia galeata mendotae were tested in the laboratory for their competency to kill Keratella cochlearis (f. tecta) in the course of their normal filter-feeding behavior. At daphnid sizes > 1.2 mm of body length, all five species killed the rotifers at rates that increased with body length as y = 0.485x -0.588 where y is Keratella killed Daphnia-' h-l and x is daphnid body length in mm. No speciesspecific differences in ability to kill rotifers were detected. Keratella was found in the gut contents of some Daphnia, indicating carnivory and a new pathway in trophic interactions in freshwater ecosystems. Keratella density did not affect Keratella mortality rate within the range tested (125-1,000 liter-l). Daphnia cleared live Keratella from the medium at rates about three times those at which it cleared Cryptomonas from the medium. Relations between Keratella mortality, Daphnia density, and Daphnia size were used to derive a family of curves from which the potential impact of Daphnia-induced mortality on field populations of Keratella can be calculated. When the daphnids are large (>2 mm) and present at densities 2 l-5 individuals liter-', they could have a major impact on the population dynamics of the rotifers. cochlearis f. typica being injured decreased with its age and increased with its residence time in the daphnid branchial chamber. Factors associated with the impact of the cladocerans may include body size, clearance rate, abundance, and species.We examine here the effects of cladoceran factors and rotifer density on interference by testing three hypotheses. The first is that large cladocerans will interfere more with rotifers than will small ones. Rotifers will l This research was supported by National Science Foundation grants DEB 8 1-192 13 and BSR 84-15024 to J.J.G. and carried out while C.W.B. was on sabbatical leave at Dartmouth College. be more likely to be swept into the branchial chambers of large cladocerans because such cladocerans will create stronger inhalant currents and also have wider carapace gapes. The second is that the susceptibility of a rotifer to cladoceran interference will increase as the amount of food available to the cladoceran decreases. At low food concentrations cladoceran clearance rates are maximal (e.g. Rigler 196 1, 197 1) so that rotifers are more likely to be brought into the branchial chamber than they are at high food concentrations when clearance rates are lower. The third hypothesis is that the susceptibility of a rotifer to cladoceran interference will be independent of the population density of the rotifer.To test these hypotheses we used the widely distributed and often abundant rotifer, Keratella cochlearis f. tecta, and several species of Daphnia covering a range of body sizes. We quantify the effects of daphnid size on Keratella mortality rate through interference and derive equations to allow prediction of the potential impact of such

Direct assessment of the independent effects of exploitative and interference competition between Daphnia and rotifers

“…These results show that earlier laboratory studies examining the effects of Daphnia on rotifers were correct in attributing much of the reduction in rotifer numbers to direct interference competition (Gilbert and Stemberger 1985;Burns and Gilbert 1986a;Gilbert 1988b). …”

“…Bums and Gilbert (1986b) suggested that as food decreases, interference competition should have a greater effect on rotifers. I detected no significant food-Daphnia interactions, however.…”

Zooplankton diversity and its relationship with environmental changes after the filling of a temporary saline lake in the semi-arid region of La Pampa Argentina

“…It has also been found that the intensity of competition increases with the increase in density (Gilbert, 1985;Burns & Gilbert, 1986;, such as that observed in El Carancho, together with the fact that rotifers can be damaged and even die by action of the filtering appendages of large cladocerans during feeding (MacIsaac & Gilbert, 1991). On the other hand, although B. poopoensis feeds mainly on small algae, as most of the Argentine species of the genus, it has also been reported that it can feed of ciliates, small nauplii and rotifers (Modenutti et al, 1998;Balseiro et al, 2001;Izaguirre et al, 2003;Vignatti, 2011).…”

Long-term trends in Loch Leven invertebrate communities

“…from physical damage to the rotifer population from Daphnia filtering), as has been suggested for other sites (e.g. Burns & Gilbert, 1986), because experimental studies showed that this does not affect the population dynamics of rotifers and Daphnia in Loch Leven (May & Jones, 1989).…”