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- Title
Interactions between a hunting spider and a web-builder: consequences of intraguild predation and cannibalism for prey suppression.
- Authors
Denno, Robert F.; Mitter, Margaret S.; Langellotto, Gail A.; Gratton, Claudio; Finke, Deborah L.
- Abstract
1. Antagonistic interactions among invertebrate predators such as intraguild predation and cannibalism have the potential to dampen top-down impacts on shared prey at lower trophic levels. Two abundant spider predators, the large wolf spiderPardosa littoralisand the small sheet-web builderGrammonota trivitattaco-occur on the salt marshes of eastern North America where they both attack planthoppers (Prokelisiaspp.), the dominant herbivores on the marsh. Experiments both in the laboratory and field were used to assess the incidence of intraguild predation and cannibalism in these spiders and elucidate how such antagonistic interactions influence planthopper suppression.2. Functional response experiments showed that with an increase in planthopper prey density,Grammonotacaptured more prey but not a higher proportion of that offered.Pardosaexhibited the same response whenGrammonotawere offered as intraguild prey. Both functional responses were type I over the range of prey densities offered.3. Grammonotais moderately cannibalistic, and the presence of planthopper prey reduced the incidence of cannibalism.4. Factorial experiments in the laboratory showed thatPardosabut notGrammonotareduced planthopper prey populations when prey density was low. By contrast, at high prey densities, bothPardosaandGrammonotahad significant adverse effects on planthopper populations. Moreover, there was an interactive effect such thatGrammonotareduced planthopper populations relatively more whenPardosawas absent than when it was present.5. There was direct evidence for the intraguild predation ofGrammonotabyPardosasuch that fewerGrammonotasurvived in the presence ofPardosathan when it was absent. This result occurred whether planthopper prey were abundant or not.6. Field releases ofGrammonotain open plots resulted in significant but small decreases in the density of planthopper prey, both nymphs and adults.7. Enhancing densities ofPardosain open plots resulted inGrammonotasuppression. The intraguild predation ofGrammonotaat this enhancedPardosadensity, however, did not precludePardosafrom significantly reducing planthopper populations.8. Although there was evidence thatGrammonotareduced planthopper populations and that the intraguild predation ofGrammonotabyPardosaoccurred, the strength of these interactions was relatively weak given the low consumption rate of planthoppers byGrammonota(< 3 day–1) andGrammonotabyPardosa(≈ 2 day−1). Thus, weak asymmetric intraguild predation among spiders on the marsh likely dampens but does not eliminate the ability ofPardosato exert significant top-down control on planthopper populations.
- Subjects
CANNIBALISM; PREDATORY animals; MARSHES; SPIDERS; SALT marshes; TIDAL flats
- Publication
Ecological Entomology, 2004, Vol 29, Issue 5, p566
- ISSN
0307-6946
- Publication type
Article
- DOI
10.1111/j.0307-6946.2004.00628.x