BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Direct and indirect effects of snail herbivory on Spirodela polyrh iza in a two-year outdoor experiment DTSTART;VALUE=DATE-TIME:20260929T155500Z DTEND;VALUE=DATE-TIME:20260929T161500Z DTSTAMP;VALUE=DATE-TIME:20260916T130428Z UID:indico-contribution-2950@cern.ch DESCRIPTION:Speakers: Martin Schäfer (Institute of Organismic and Molecul ar Evolution (iomE)\, Johannes Gutenberg University Mainz)\nPredicting the outcome of species interactions in complex communities requires separatin g the direct effects that organisms have on each other from those that fun ction indirectly through their influence on other community members and th e environment. We performed a two-year outdoor experiment with 14 mesocosm s containing the giant duckweed\, *Spirodela polyrhiza*\, in the presence or absence of its aquatic snail herbivore\, *Lymnaea stagnalis*. We analyz ed the snail effects on the aquatic community and the evolutionary consequ ences for the duckweed. The direct and indirect effects of snails turned o ut to be often antagonistic. In the first year\, snail herbivory reduced t he duckweed abundance by direct grazing but also promoted duckweed growth indirectly by reducing algae competition and increasing phosphate availabi lity\, thereby shifting plant traits and genotype frequencies. In the seco nd year\, the ponds experienced an algae bloom and strong phosphate deplet ion which abolished and reversed various effects and trait-fitness associa tions observed in the previous year. Over the two years\, the direct effec ts were observed to be stronger but fluctuating\, while the indirect effec ts were weaker but more consistent. The results highlight the need for mul tiple season experiments with complex communities to understand the forces in species interactions that drive evolution.\n\nhttps://indico.unina.it/ event/117/contributions/2950/ LOCATION: Sala Monumentini URL:https://indico.unina.it/event/117/contributions/2950/ END:VEVENT END:VCALENDAR