DOI: 10.5061/dryad.g9n85sm
title: Data from: Additive effects of plant chemotype, mutualistic ants and predators on aphid performance and survival

description: 1. Cascading effects in ecological systems acting across three or more
 trophic levels can be either of a resource-based (bottom-up) or natural
 enemy-based (top-down) nature. But, due to their complexity these effects
 are often considered separately and their relative strength, acting
 simultaneously, remains unknown. 2. In a semi-natural field experiment
 using tansy (Tanacetum vulgare L.) and the specialised tansy aphid
 Metopeurum fuscoviride Stroyan as a model system, we compared the effects
 of four distinct plant chemotypes (i.e. bottom-up), defined by the bouquet
 of their volatile terpenoids, on aphid population dynamics by manipulating
 the presence/absence of mutualistic ants and presence/absence of
 naturally-occurring predators (i.e. top-down). 3. Predators reduced aphid
 abundance and colony survival but did not reduce initial growth rate due
 to a time lag until predators arrived on the plants. Ants directly
 benefited initial aphid growth rates and abundance, even in the absence of
 predators, but not the number of days an aphid colony persisted on the
 plant. 4. Plant chemotype directly affected aphid growth rate and final
 abundances across the different plants and indirectly affected the
 abundances of tending ants and predators through effects on aphids. We
 found that tending ants were more abundant on one plant chemotype.
 Although ant abundance did not affect aphid population development, it
 became clear that ants had a preference towards aphids on certain
 chemotypes. However, a higher number of predators led to a lower number of
 aphids. 5. The results confirm the importance of plant chemical variation,
 acting through multiple effects on many species in arthropod communities,
 and support results from field studies. In a natural population, with a
 diverse selection of host-plant variants, aphid populations and their
 interacting species can therefore be structured at the level of an
 individual plant. Specialist aphids on patchily-distributed host plants
 can exhibit metacommunity dynamics at very local scales. Plant
 within-species variation within a local population is often ignored in
 metacommunity ecology, yet our work shows that this can have strong
 effects on insect-ant-natural enemy dynamics and therefore future research
 should incorporate this into current theory and experimental studies.
description: Data
 ExperimentVariable Description -
 Data Experiment. Block: Each of the 16 treatments (four chemotypes; two
 ant treatments (presence and absence); two predator treatments (presence
 and absence) ) was replicated five times: in five blocks. Day: Day of
 observation. Aphids, ants and predators in each cage were counted with a
 mechanical counter on days 0, 2, 4, 6, 8, 11, 14, 17 and 20.
 Plant_Chemotype: Four different chemotypes were tested: chemotypes 2.1,
 2.2, 4.1 and 4.2. Chemotype_Class: The four different chemotypes belonged
 to 2 chemotype classes: 2 and 4. Plant_Identity: This shows the identity
 of each individual plant. Each of the 16 treatments was replicated five
 times resulting in 80 tansy plants (N=80). Biomass: The aboveground
 biomass of each tansy plant was measured by drying plants at 70 °C for
 three days for dry weight determination at the end of the experiment [g].
 Plant_Growth: Plant growth [cm]: Plant height [cm] at the beginning of the
 experiment minus plant height [cm] at the end of the experiment.
 Ant_Treatment: Presence (p) or absence (a). Ant_Abundance: Ant abundance
 at the day of observation. Predator_Treatment: Presence (p) or absence
 (a). Predator_Abundance: Predator abundance at the day of observation.
 Aphid_Abundance: The number of aphids counted on the day of
 observation.DataExperiment.csv