Effect of subsidized predators on coastal food webs in the Baltic Sea area
(English)Manuscript (Other academic)
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.
Research subject Plant Ecology
IdentifiersURN: urn:nbn:se:su:diva-27223OAI: oai:DiVA.org:su-27223DiVA: diva2:213000