[PDF] Intrazooplankton Predation eBook

Author : Joop Ringelberg
Publisher : Springer Science & Business Media
Page : 360 pages
File Size : 29,74 MB
Release : 2009-12-01
Category : Science
ISBN : 904813093X

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Whatever theory may be advanced to explain diurnal migration, the underlying reactions involved must be demonstrated conc- sively in the laboratory before the explanation can be ?nally accepted George L. Clarke 1933 p. 434 In oceans and lakes, zooplankton often make diel vertical migrations (DVM), descending at dawn and coming up again in late afternoon and evening. The small animals cover distances of 10–40 m in lakes or even a few hundred metres in the open oceans. Although not as spectacular as migrations of birds or the massive movements of large mammals over the African savannas, the numbers involved are very large and the biomass exceed the bulk of the African herds. For example, in the Antarctic oceans swarms of “Krill” may cover kilometres across, with thousands of individuals per cubic metre. These Euphausiids are food for whales, the most bulky animals on earth. Zooplankton are key species in the pelagic food web, intermediary between algae and ?sh, and thus essential for the functioning of the pelagic community. Prey for many, they have evolved diverse strategies of survival and DVM is the most imp- tant one. Most ?sh are visually hunting predators and need a high light intensity to detect the often transparent animals. By moving down, the well-lit surface layers are avoided but they have to come up again at night to feed on algae.

Author : Michael D. White (Ecologist)
Publisher :
Page : 210 pages
File Size : 29,11 MB
Release : 1991
Category : Predation (Biology)
ISBN :

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An investigation was conducted examining the horizontal distribution of zooplankton in relation to predation gradients using both experimental and field systems. In the pond experiment, planktivore refuges were created by placing cages at one end of the experimental pond. Thus a "littoral" zooplanktivore refuge end and a "pelagic" non-refuge area were created. Ponds with no refuges served as controls. All zooplankton sampling was done at night. Zooplanktivores were eliminated by the piscivores in control ponds and were restricted to refuges in refuge ponds. Although no statistically significant differences in abundance were detected, ponds with a zooplanktivore refuge tended to have lower densities of pelagic cladoceran and copepod species and higher densities of littoral cladoceran, littoral copepod, and rotifer species. No effect of the zooplanktivore refuges on the horizontal distribution of zooplankters within the ponds was detected. It was concluded that the influence of planktivorous fish was reduced because they were restricted to the refuge and that daytime horizontal distributions detect the influence of the zooplanktivore refuge on the distribution of the zooplankters. In the field study, the horizontal distribution of zooplankton was determined by collecting samples at fixed stations along three replicate transects. Samples were collected during the day and at night at times of the year in which the abundance of zooplanktivorous fish differed. The results of the field study indicated that large crustacean zooplankters appear to respond to the presence of zooplanktivory gradients created by zooplanktivorous fish that are restricted to the littoral zone by piscivorous fish. Large crustaceans appeared to avoid inshore areas during the day where planktivorous fish were abundant but showed no such avoidance at night or at times of the year when zooplanktivore abundance was reduced. There was no evidence that the diel horizontal migration pattern was a result of sampler avoidance by zooplankton. Rotifers exhibited less seasonal and diurnal variation in their horizontal distributions than did the large crustaceans. This is attributed to the reduced risk of predation that rotifers experience relative to large crustacean zooplankters. A graphical model is proposed to integrate our understanding of diel vertical and horizontal migrations of zooplankton

Author : Bo Ebenman
Publisher : Springer Science & Business Media
Page : 288 pages
File Size : 41,24 MB
Release : 2012-12-06
Category : Science
ISBN : 3642740014

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At last both ecology and evolution are covered in this study on the dynamics of size-structured populations. How does natural selection shape growth patterns and life cycles of individuals, and hence the size-structure of populations? This book will stimulate biologists to look into some important and interesting biological problems from a new angle of approach, concerning: - life history evolution, - intraspecific competition and niche theory, - structure and dynamics of ecological communities.

Author : Hein Rune Skjoldal
Publisher : Fagbokforlaget
Page : 568 pages
File Size : 20,39 MB
Release : 2004
Category : Architecture
ISBN :

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'The Norwegian Sea Ecosystem' elucidates the interaction between the different ecological compartments of the area, with special emphasis on the most important pelagic fish stocks. It deals with mechanisms for ecosystem variability and discusses the challenge of an ecosystem approach to managing the area.