Spiders in rice-paddy ecosystems shift from aquatic to terrestrial prey and use carbon pools of different origin

• Published in: Oecologia Vol. 192; no. 3; pp. 801 - 812
• Main Authors: Radermacher, Nico, Hartke, Tamara R., Villareal, Sylvia, Scheu, Stefan
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Science + Business Media 01.03.2020; Springer Berlin Heidelberg; Springer; Springer Nature B.V
• Subjects: Algae; Animals; Aquatic ecosystems; Arthropods; Biological control; Biomedical and Life Sciences; Carbon; Carbon cycle; Cereal crops; Chironomidae; Cicadellidae; Ecology; Ecosystem; ECOSYSTEM ECOLOGY - ORIGINAL RESEARCH; Ecosystems; Food Chain; Herbivores; Hydrology/Water Resources; Insect pests; Insects; Interspecific relationships; Isotope composition; Isotopes; Landscape; Larvae; Life Sciences; Nitrogen; Oryza; Pest control; Pests; Plant Sciences; Populations; Predation; Predatory Behavior; Prey; Rice; Rice fields; Seasons; Spiders; Stable isotopes; Temporal variations; Web building; Rice field; Generalist predators; Rice insect pest; Stable isotopes; Biological control
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-020-04601-3

Spiders are important bio-control agents of rice insect pests such as plant- and leafhoppers. To investigate temporal changes in spider prey and variations in prey due to landscape structure around rice fields, carbon and nitrogen stable isotopes of rice field arthropods were analysed over three consecutive sampling dates during the rice cropping season. Initial isotope composition of gnats and midges emerging from submersed rice fields indicates a larval algae diet, while later values suggest a switch to rice-derived carbon. Initial δ¹³C values of plant-and leafhoppers were higher in fields of rice-heterogeneous landscapes, indicating migration from source populations feeding on C4 grasses into rice fields; later, their δ¹³C values approached those of rice. Isotope values of web-building and cursorial spiders in the earliest samples indicate aquatic gnat and midge prey. The later shift toward terrestrial herbivore prey was more pronounced for small than for larger species and in rice paddies near permanent vegetation, indicating use of prey from the surrounding landscape. The results suggest that rice field spiders are supported by three different carbon pools: (1) aquatic carbon originating from algae and (2) legacy carbon from previous growing cycles, both incorporated via between-season predation on gnats and midges, and (3) carbon from the current rice season incorporated via herbivore prey. In conclusion, fostering aquatic midge and gnat larvae, e.g. via mulching, and integrating rice fields into rice-heterogeneous landscapes likely strengthens biological control of pest species in rice paddies by supporting high populations of spiders between cropping seasons.