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- Frost, Ingela, et al.
(författare)
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Effects of competition, grazing and cotyledon nutrient supply on growth of Quercus robur seedlings
- 1997
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Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 79:1, s. 53-58
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Tidskriftsartikel (refereegranskat)abstract
- In this greenhouse experiment we examined how competition and herbivory affects the growth of Quercus robur seedlings and if the cotyledon nutrient reserve is of importance for survival and growth during unfavourable conditions. We planted oak seedlings with or without a strong competitor (grass turf) and subjected them to factorial grazing and cotyledon removal, in a split-plot design. After one growing season (20 weeks) we found large negative main effects from competition, grazing and cotyledon removal on all biomass components of the seedling. Seedling mortality was also significantly increased by competition. We observed an additional effect of cotyledon removal if the seedlings were also grazed or were growing in competition with grass. This gives some support to the hypothesis that cotyledon nutrient reserves are used under unfavourable conditions, but the effect was often relatively small and not detectable in the growth of all plant parts.
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- Ehrlen, J
(författare)
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Risk of grazing and flower number in a perennial plant
- 1997
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Ingår i: OIKOS. - : MUNKSGAARD INT PUBL LTD. - 0030-1299. ; 80:3, s. 428-434
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Costs of reproduction may be due to exhaustion of resources or due to increased risk of predation during reproduction. In animals both types of costs have been examined frequently whereas in plants most studies have focused on costs mediated by resource d
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- Persson, Anders
(författare)
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Effects of Fish Predation and Excretion on the Configuration of Aquatic Food Webs
- 1997
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Ingår i: Oikos. - 1600-0706. ; 79:1, s. 137-146
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Tidskriftsartikel (refereegranskat)abstract
- The relative importance for algae of fish excretion and fish predation on zooplankton was studied in experimental pools. Even- (zoo- and phytoplankton) and odd-link systems (planktivorous fish, zoo- and phytoplankton) were established, in which the standing stock of primary producers was expected to follow the predictions from food chain theory sensu Oksanen. Two intermediate treatments (fish predation and nutrient regeneration by fish alone) were used to determine the relative power of fish in affecting the transition from an even-link system to an odd-link system, i.e. their relative power in the trophic cascade. Algal density and production were found to only be enhanced when both fish predation and fish excretion acted together. A reduction in the grazer biomass alone did not increase the algal biomass. Fish excretion alone increased the algal biomass somewhat, but not significantly so compared with the control. The results suggest that both fish predation on zooplankton and the regeneration of nutrients by fish may be necessary to create the difference in algal biomass between an even- and an odd-link system predicted by food chain models, at least in the absence of an external input of nutrients. In addition, the effects of increased nutrient regeneration due to use of non-zooplankton resources by the fish, nutrient maintenance in living biota, and decreased grazing pressure seem to reinforce the cascading effect of planktivorous fish on algae. Consequently, use of a fixed carrying capacity in simple predatorprey models may lead to loss of important information on the dynamics of aquatic food webs, preventing an adequate understanding of cascading trophic interactions from being achieved.
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