1. How much a plant is attacked by insect herbivores likely depends on its apparency and ability to produce defensive traits, which may be modified by neighbouring plants and abiotic conditions. Yet, how much the direct and trait-mediated effects of neighbours on herbivory is modified by abiotic factors is still unknown. 2. By using a tree diversity experiment in SW France, we measured leaf insect herbivory (chewers and miners), nutritional quality (water content, C/N ratio,...

Flowering plants emit complex bouquets of volatile organic compounds (VOCs) to mediate interactions with their pollinators. These bouquets are undoubtedly influenced by pollinator-mediated selection, particularly in deceptively-pollinated species that rely on chemical mimicry. However, many uncertainties remain regarding how spatially and temporally heterogeneous pollinators affect the diversity and distribution of floral odour variation. Here, we characterized and compared the floral odours of ten populations of deceptively-pollinated Arum maculatum (Araceae), and inter-annual and decadal variation in...

Interactions between ants and plants bearing extrafloral nectaries (EFNs) are among the most common mutualisms in Neotropical regions. Plants secrete extrafloral nectar, a carbohydrate-rich food that attracts ants, which in return protect plants against herbivores. This ant-plant mutualism is subjected to temporal variation, in which abiotic factors can drive the establishment and frequency of such mutualistic interaction. However, studies investigating how abiotic factors (e.g., climate) directly and indirectly influence ant-plant-herbivore interactions are incipient. In this...

Aim: Plants on islands are often subjected to lower levels of herbivory relative to those at mainland sites. As a consequence, island plants are predicted to exhibit lower levels of physical and chemical defences, which renders them more susceptible to introduced herbivores. Yet, instances of high pressure by superabundant herbivores native to islands have been reported in many insular systems, which presumably would result in heightened plant defences. To date, no quantitative review has been...

Previous studies have reported effects of abiotic factors on herbivore-induced plant defences based on effects on single plant traits. However, plants commonly express multiple defences simultaneously and these traits are often correlated. Thus, a fuller understanding of abiotic-context dependency in plant defence requires measuring multiple traits and addressing their patterns of correlated expression. We evaluated the effects of soil salinity on the induction of direct (phenolic compounds, gossypol gland density) and indirect (volatile organic compounds,...

There is increasing evidence that the outcomes of mutualistic interactions between ants and plants bearing extrafloral nectaries (EFNs) is context-dependent. In particular, the total number, density and size of EFNs, as well as the abundance and identity of ants attending host plants, are considered as key factors determining the nature and strength of ant-EFN-bearing plant interaction. Although many previous studies have investigated context-dependency in ant–plant protection mutualisms mediated by EFNs, few have tested whether the...

Airborne plant communication is a widespread phenomenon in which volatile organic compounds (VOCs) from damaged plants boost herbivore resistance in neighbouring, undamaged plants. Although this form of plant signalling has been reported in more than 30 plant species, there is still a considerable knowledge gap on how abiotic factors (e.g., water availability) alter its outcomes. We performed a greenhouse experiment to test for communication between potato plants (Solanum tuberosum) in response to herbivory by the...

While plant diversity is well known to increase primary productivity, whether these bottom-up effects are enhanced by reciprocal top-down effects from the third trophic level is unknown. We studied whether pine tree species diversity, aphid-tending ants and their interaction determined plant performance and arthropod community structure. Plant diversity had a positive effect on aphids, but only in the presence of mutualistic ants, leading to threefold greater number of both groups in the tri-specific cultures than...

1. Plant species allocate resources to multiple defensive traits simultaneously, which often leads to so-called defence syndromes, i.e. suites of traits that are co-expressed. While reports of ontogenetic variation in plant defences are commonplace, no research to date has tested for ontogenetic shifts in defence syndromes. In addition, we still know little about how ecological and evolutionary factors concurrently shape plant defence syndromes via ontogeny. 2. We tested for ontogenetic variation in plant defence syndromes...

Aim: It has been hypothesised that insular plant taxa have evolved reduced defences in response to lower herbivore pressure on islands. However, the few studies testing this hypothesis have addressed variation in individual defensive traits, without paying attention to patterns of correlated trait expression (i.e. defence syndromes). Location: Balearic and Canary Islands. Taxon: Ninety-one woody plant species. Methods: We tested whether plant species with contrasting histories of insularity (namely: endemics, non-endemic natives, and exotics) differed...

Aim: To advance our understanding of how foliar fungal communities are structured and assembled, we assessed to what extent leaf flush and latitude can explain the within- and among-tree variation in the foliar fungal community in a foundation tree species, the pedunculate oak Quercus robur. Location: A latitudinal gradient spanning c. 20 degrees in latitude in Europe. Major taxa studied: The foliar fungal community on Quercus robur. Methods: We examined the main and interactive effects...

The effects of plant species diversity on plant traits conferring herbivore resistance (e.g., chemical defences), as well as the mechanisms underlying such effects, have received little attention. One potential mechanism for diversity effects on plant defences is that increased plant growth at high diversity could lead to reduced investment in defences via growth-defence trade-offs. We measured tree growth (diameter at breast height) and collected leaves for quantification of total phenolics on 2.5-year old plants of...

Aim: One of the main goals of functional biogeography is to examine distribution patterns of trait diversity, and islands provide excellent study cases for this emerging field. We tested the hypothesis that multiple dispersals from a common mainland pool would promote functional similarity among island systems when environmental conditions are similar, but also novel phenotypic traits related to colonization history and exploitation of new habitats. Location: Mediterranean Basin and Macaronesian islands Methods: We used the...

With this dataset, we studied elevational gradients and their underlying climatic factors in constitutive and induced phenolics and volatile organic compounds in Oak trees. Oak defences were measured in leaves in a field study. The dataset includes data for 18 populations of Quercus pyrenaica spanning a 1300 m elevational gradient (from 370 to 1614 m) with their correspondence coordinates. In each population we sampled six saplings that were randomly assigned to one of two treatments:...

The world is rapidly urbanizing, thereby transforming natural landscapes and changing the abundance and distribution of organisms. However, insights into the effects of urbanization on species interactions, and plant-pathogen interactions in particular, are lacking. We investigated the effects of urbanization on powdery mildew infection on Quercus robur at continental and within-city scales. At the continental scale, we compared infection levels between urban and rural areas of different-sized cities in Europe, and investigated whether plant traits,...

Plant diversity has often been reported to decrease insect herbivory in plants. Of the numerous mechanisms that have been proposed to explain this phenomenon, how plant diversity influences plant defences via effects on growth has received little attention. In addition, plant diversity effects may be contingent on abiotic conditions (e.g., resource and water availability). Here, we used a long-term experiment to explore the interactive effects of tree species composition and water availability on growth, direct...