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Nutrient addition extends flowering display, which gets tracked by seed predators, but not by their parasitoids

Authors

  • Benedicte Riber Albrectsen,

  • Lars Ericson,

  • Per Lundberg


B. Riber Albrectsen (benedicte.albrectsen@plantphys.umu.se), Dept of Plant Physiology, SE-901 87 Umeå University, Sweden. – L. Ericson, Dept of Ecology and Environmental Science, SE-901 87 Umeå University, Sweden. – P. Lundberg, Dept of Theoretical Ecology, Lund Univ., SE-223 62 Lund, Sweden.

Abstract

Although phenological matching between two and three trophic interactions has received some attention, it has largely been disregarded in explaining the lack of strong cascade dynamics in terrestrial systems. We studied the response of the specialist seed predator, Paroxyna plantaginis (Tephritidae) and associated generalist parasitoids (Chalcidoidea) to controlled fertilisation of individuals of naturally growing Tripolium vulgare (Asteraceae) on four island populations (Skeppsvik Archipelago, Sweden). We consistently found evidence of nutrient limitation: fertilised plants increased their biomass, produced more capitula (the oviposition units for tephritid flies), were more at risk of attack by the tephritids, and puparia were heavier in fertilised plants. During some parts of the season tephritids became more heavily parasitized, supporting the presence of cascade dynamics, however net parasitism over season decreased in response to nutrient addition. We found no evidence that capitulum size complicated parasitoid access to the tephritids, however the extended bud production prolonged the flowering season. Thus, tephritids utilized the surplus production of capitula throughout the entire season, while parasitoids did not expand their oviposition time window accordingly. Implications for top down regulation and cascade dynamics in the system are discussed.

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