Population dynamics and production of Daphnia hyalina in a eutrophic reservoir

A comparison of the population dynamics of Daphnia pulicaria and Daphnia rosea in 1967–1969 and during their decline from Lake Tahoe in 1970 showed that the decline resulted from a combination of increased death rates and decreased birth rates. The remaining cladoceran, Bosmina longirostris, disappeared from the plankton in 1971. The elimination of cladocerans coincided with high densities of the opossum shrimp, Mysis relicta, and the kokanee salmon, Oncorhynchus nerka. Predation by these two introduced species is believed to have increased cladoceran death rates. Changes in the timing of the peaks of primary productivity are a possible cause for the decline in birth rates. A brief resurgence of Bosmina in late 1974 was associated with a dramatic decline of the mysid population and the continued decline of kokanee which began in 1970. The mysids recovered by late 1975 but Bosmina again disappeared and has remained absent since. The failure of Daphnia to reappear suggests that factors in addition to predation by kokanee and Mysis exclude them from Lake Tahoe. Changes in the phytoplankton community composition may have altered the ability of the cladocerans to maintain birth rates sufficiently high to offset increased losses due to predation.

Section: Resultsmentioning

confidence: 99%

A population dynamics analysis of the cladoceran disappearance from Lake Tahoe, California‐Nevada1

Goldman

Morgan

Threlkeld

et al. 1979

“…Gannon and Stemberger 1978;Ferguson et al 1982). Daphnia concentrations varied from 15 liter-l (large adults) to 150 liter-l (neonates); these are also within the range of densities found in field populations (George and Edwards 1974;Threlkeld 1979).…”

Section: Methodsmentioning

confidence: 99%

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

Burns

Gilbert

1986

107

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

“…This situation is due partly to an impression that, in contrast to terrestrial habitats, the pelagic one provides a homogeneous environment for planktonic organisms or that heterogeneity in the environment is ephemeral. Lewis (1978) (Young 1978) defensive aggregation against a predator (Folt 1987) and wind-induced patchiness (George 1989). The stable one implies consistent variation independent of time that results from differences in birth and death rates among sites.…”

mentioning

confidence: 99%

Stable horizontal variation in the zooplankton community structure of a reservoir maintained by predation and competition

Urabe

1990

The zooplankton community of the Ogochi Reservoir was investigated with brief field experiments to examine the mechanisms that maintain a stable horizontal distribution of species in the warm-water season. Daphnia gale&a predominated near the dam site, and its abundance declined toward the headwaters. The abundance of other species increased away from the dam, and Bosmina longirostris was found abundantly at the site near the headwaters. Demographic analysis and field experiments demonstrated that D. galeata had the potential to depress the abundance of other species through exploitative competition and to predominate at sites near the headwaters as well as at the dam site. This potential was never realized, however, at a site near the headwater because of a high mortality rate that could not be explained by food abundance or physical and chemical conditions in the water. The invertebrate predator Leptodora kindtii was abundant at sites nearer the headwaters, but its occurrence was limited temporally. Trammel gill-net samples revealed that planktivorous fish, which prey selectively on the superior competitor D. gale&a and the invertebrate predator L. kindtii, were distributed toward the headwaters in the warm-water season. The high mortality rate of D. galeata at the site near the headwaters apparently was attributable to predation by fish. The data presented demonstrate that the pelagic environment in the reservoir is functionally heterogeneous and that species interactions play an important role in maintaining the stable horizontal pattern in the community structure.