Triple interaction network among flowers, flower visitors and crab spiders in a grassland ecosystem

Abstract

This study presents the first description of a tri-trophic interaction network with crab spiders as predators. Monthly observations of flowering entomophilous plant species were recorded between December 2009 and March 2010 and their flower visitors and predators (crab spiders) were caught, with or without prey. Moreover, flower visitors of different orders were caught to evaluate the amount of pollen transported. In order to analyze changes in the plant species and crab spiders, we evaluated the interaction networks in which we had removed different orders of prey (Hymenoptera, Diptera and Lepidoptera) from the original network. Our results indicate that crab spiders select their preys within the community. Furthermore, the Hymenoptera carried higher pollen loads and were the less frequent prey. When the Diptera preys were removed from the initial interaction network, network changes mainly affected the species richness of crab spiders. Decrease in density of Diptera could increase plant resources useful for flower visitors carrying great pollen loads and could promote pollination. Crab spider prey might be restricted to only the more vulnerable flower visitors (e.g. smaller dimensions, without sting or with delicate cuticula) which consume resources and are inefficient as pollen carriers. The selected predation could not negatively affect the fitness of plants.

Keywords:

• tri-trophic interaction network
• pollinator prey
• triple-interaction
• crab spiders

Acknowledgments

Helpful comments by Carolina Quintero, Luciano Cagnolo, Santiago Poggio, Anne Zillikens and three anonymous reviewers contributed to improving this paper. Ramiro Saurral, and Rosemary Scoffield are thanked for revising the language. Field work was supported by ANPCyT (PICT 0851), Argentina. JPT is member of CONICET.