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Effect of subsidized predators on coastal food webs in the Baltic Sea area
Stockholm University, Faculty of Science, Department of Botany.
Uppsala Universitet.
Stockholm University, Faculty of Science, Department of Botany.
(English)Manuscript (Other academic)
Abstract [en]

The aim of this study was to examine top-down effects of spiders in subsidized coastal food webs. This was done through a large-scale removal experiment, where spiders were removed from small islands using pitfall traps. Arthropods were sampled using a vacuum sampling device at three occasions each summer 2004-2007. The uniqueness of the study lies in its scale: these types of experiments are typically made using small (one or a few m2) enclosures, in which the food web is manipulated, but this study use islands (20-2000 m2) as natural enclosures. Though the use of islands allows a lesser degree of control of the study system than enclosures, large-scale studies include a large realism by allowing for more natural dynamics. The results suggest that the high spider densities on shores have negative effects on insect predator densities, probably through a combination of competition and intraguild predation. No treatment effects were found on herbivore or detritivore densities, and we suggest that the negative effect of spiders on herbivore and detritivore densities on control islands may be at least partly balanced by an increased effect of insect predators utilizing mainly terrestrial prey on treatment (removal) islands. Our study does not exclude the possibility of top-down effects in the system from spiders on herbivores, but in case they do exist, they are likely behaviour mediated rather than a result of direct spider predation.

National Category
Ecology
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-27223OAI: oai:DiVA.org:su-27223DiVA: diva2:213000
Available from: 2009-04-26 Created: 2009-04-26 Last updated: 2010-01-14Bibliographically approved
In thesis
1. The Spider and the Sea: Effects of marine subsidies on the role of spiders in terrestrial food webs
Open this publication in new window or tab >>The Spider and the Sea: Effects of marine subsidies on the role of spiders in terrestrial food webs
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The purpose of this study was to identify if terrestrial arthropod predators on Baltic Sea shores vary in their use of marine versus terrestrial food items, and to construct a bottom-up food web for Baltic Sea shores. The inflow of marine nutrients in the area consists mainly of marine algal detritus and emerging aquatic insects (e.g. phantom midges, Chironomidae). Diets of coastal arthropods were examined using carbon and nitrogen stable isotope analysis, and a two source mixing model was used to examine proportions of marine carbon to diets. The results suggest that spiders are the terrestrial predators mainly utilizing nutrients and energy of marine origin on Baltic Sea shores, while insect predators such as beetles and hemipterans mainly utilize nutrients and energy derived from terrestrial sources, possibly due to differences in hunting behaviour. That spiders are the predators that benefit the most from the marine inflow suggest that eventual effects of marine subsidies for the coastal ecosystem as a whole are likely mediated by spiders.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University, 2009. 44 p.
Keyword
marine subsidies, food webs, stable isotopes, shore ecosystems, predators, spiders, Pardosa, algae, emerging insects
National Category
Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-27227 (URN)978-91-7155-877-0 (ISBN)
Public defence
2009-06-05, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2009-05-14 Created: 2009-04-26 Last updated: 2009-04-27Bibliographically approved

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