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The Spider and the Sea: Effects of marine subsidies on the role of spiders in terrestrial food webs
Stockholm University, Faculty of Science, Department of Botany.
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 [en]
marine subsidies, food webs, stable isotopes, shore ecosystems, predators, spiders, Pardosa, algae, emerging insects
National Category
Ecology
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-27227ISBN: 978-91-7155-877-0 (print)OAI: oai:DiVA.org:su-27227DiVA: diva2:213004
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
List of papers
1. Individual variation between spiders on shores in the utilization of aquatic subsidies
Open this publication in new window or tab >>Individual variation between spiders on shores in the utilization of aquatic subsidies
(English)Manuscript (Other academic)
Abstract [en]

Intrapopulation variation is common in nature, and many generalist species actually consists of individual specialists. In food web ecology, stable isotope analysis is a common tool for examining energy and nutrient flows both between and within ecosystems, but large intrapopulation variation in isotopic values may lead to over- or underestimations of dietary variation between populations or species. Such large intraguild variation is common in spiders, which often are generalist predators. In this study we have used carbon and nitrogen stable isotope analysis to examine diets of shore-dwelling spiders, in relation to aquatic inflows to shore ecosystems. The study was carried out on shores inside and outside a eutrophicated bay in the Baltic Sea, using carbon and nitrogen stable isotope analysis. Aquatic subsidies consisted of inflows of algae (mainly green filamentous algae) and emerging insects (Chironomidae). We found that spiders inside the bay all utilized mainly terrestrial prey, while spiders outside the bay, in particular wolf spiders, were separated into individuals utilizing either terrestrial or aquatic prey. The total population niche width was therefore larger outside than inside the bay. This individual specialization may be related to differences in nutrient enrichment in the aquatic ecosystem and/or salinity between sites inside and outside the bay, and we suggest that eutrophication decreases total niche width by affecting prey availability and prey choice of individual predators. We also conclude that while stable isotope analysis remains a useful tool for examining flows across ecosystem boundaries, caution is needed in the interpretation of data with large intrapopulation variation.

National Category
Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-27224 (URN)
Available from: 2009-04-26 Created: 2009-04-26 Last updated: 2010-01-14Bibliographically approved
2. Coastal niches for terrestrial predators: a stable isotope study
Open this publication in new window or tab >>Coastal niches for terrestrial predators: a stable isotope study
(English)Manuscript (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.

Keyword
stable isotopes, marine subsides, food web, spiders
National Category
Ecology
Identifiers
urn:nbn:se:su:diva-27226 (URN)
Available from: 2009-04-26 Created: 2009-04-26 Last updated: 2010-01-08Bibliographically approved
3. Linking land and sea: Arthropod vectors for marine subsidies
Open this publication in new window or tab >>Linking land and sea: Arthropod vectors for marine subsidies
(English)Manuscript (Other academic)
Abstract [en]

Several studies have shown nutrients and energy derived from marine plants and algae to subsidize shore ecosystems, increasing productivity and affecting food web dynamics and structure. In this study we have examined how the inland reach of such inflow effects depends on vectors carrying the marine inflow inland and on landscape structure. We examined the roles of arthropod vectors in carrying marine derived carbon inland in two very different shore ecosystems: shore meadows in Sweden with marine inflows of algae and emerging chironomid midges, and sandy beaches and shore dunes in Western Australia with marine inflows of algae and seagrass. In both systems we found a larger inland reach of the marine subsidy than could be accounted for by deposited material on shores alone, and that dipterans and spiders functioned as vectors for the inflow. Our results indicate that marine inflows are important for near-shore terrestrial ecosystems well above the water’s edge, and that this effect is largely due to arthropod vectors (mainly dipterans and spiders) in both low productivity sandy beach ecosystems at the Indian Ocean coast of Australia, and more productive shore meadows on the Baltic Sea coast of Sweden.

National Category
Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-27225 (URN)
Available from: 2009-04-26 Created: 2009-04-26 Last updated: 2010-01-14Bibliographically approved
4. Effect of subsidized predators on coastal food webs in the Baltic Sea area
Open this publication in new window or tab >>Effect of subsidized predators on coastal food webs in the Baltic Sea area
(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:nbn:se:su:diva-27223 (URN)
Available from: 2009-04-26 Created: 2009-04-26 Last updated: 2010-01-14Bibliographically approved
5. Edge or dispersal effects - Their relative importance on arthropod densities on small islands
Open this publication in new window or tab >>Edge or dispersal effects - Their relative importance on arthropod densities on small islands
2009 (English)In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 10, 475-484 p.Article in journal (Refereed) Published
Abstract [en]

Abstract Dispersal behaviour and edge effects are two potential factors determining population densities, and both effects are likely to vary with patch size. However, the relative importance of these two effects may be hard to separate because they may produce similar patterns. Here, we separate these two effects on population densities of seven groups of arthropods on small islands. To separate dispersal behaviour and edge effects, we use the fact that the slope of the density–area relationships (DAR-slope) should change with the absolute rates of dispersal, as would occur in response to island isolation, whereas the edge effect is expected not to be dependent on island isolation. For lycosid spiders, parasitic wasps and possibly herbivorous Homoptera DAR-slopes changed between isolated and non-isolated islands, suggesting dispersal behaviour to berelatively more important for explaining variation in their densities. Other arthropods (ants and Collembola), typically those with a predicted low dispersal among islands, showed similar DAR-slopes between isolated and non-isolated islands consistent with dominant edge effects. For two groups (web spider sand Diptera) the results were inconclusive. We conclude that both migratory processes and edge effects should be considered in the evaluation of patch size and isolation on density–area relationships.

Keyword
Lycosidae, Emmigration, Immigration, Metacommunity, Patch area, spatial subsidies
National Category
Ecology
Research subject
Ecological Botany
Identifiers
urn:nbn:se:su:diva-27214 (URN)000268839500010 ()
Available from: 2009-04-24 Created: 2009-04-24 Last updated: 2017-12-13Bibliographically approved

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