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One of the major concerns of ecological and evolutionary research is the prediction of community function in relation to the degree of biodiversity. To clarify the relationship between biodiversity and the expression of plant defence traits, we investigated ant–plant defensive mutualism in the pioneer plant Mallotus japonicus at several sites across Japan. The plant bears ant‐attracting extrafloral nectar (EFN) and food bodies (FBs) as indirect defence traits.To reveal variations in ant–plant interactions in the field, we measured species richness of nectar‐feeding ants and interaction strength between each ant species and the plant (visiting frequency of each ant species to the plant). We also investigated the expression of EFNs and FBs in natural plant populations at the study sites. To assess the defensive quality of each ant species, we then experimentally estimated the aggressiveness of the dominant ant species. To examine the link between ant species richness and the defensive function of ants, we conducted an ant‐exclusion experiment and a common garden experiment to clarify whether the defence efficacy of ants varied in relation to ant species richness.Ant species richness differed among the study sites. We found negative relationships between ant species richness and the mean interaction strength of ant species, the interaction strength of aggressive ant species and the number of EFNs per leaf. The effectiveness of indirect defence by ants was poor at sites where ant species richness was high. When cultivated in the same environment, plants from sites with low ant species richness developed a larger number of EFNs per leaf than those from sites with high ant species richness.Our results suggest that facultative ant–plant defensive mutualism is weakened at sites where ant species richness is high, resulting in a decrease in the number of EFNs per leaf. Such a link between species richness and an indirect trait function may help us to understand the evolutionary patterns of various species traits in complex biological communities. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Most terrestrial species occur in human‐modified landscapes that are experiencing climate change. In addition to direct impacts on species, both anthropogenic disturbance and climate change can have important effects through changes in species interactions, including the disruption of ecological services provided by them.Here we investigate how chronic anthropogenic disturbance (CAD) and aridity affect the effectiveness of plant protection services provided by ants to plants bearing extrafloral nectaries (EFNs).The study was conducted across 13 01‐ha plots distributed along CAD and aridity gradients in Caatinga vegetation of northeastern Brazil. We focused on Pityrocarpa moniliformis, the most abundant and widely distributed EFN‐bearing tree species occurring in our study area, and we used experimental attack rates on termites as a measure of effectiveness of ant protection services. We investigated the relative roles of nectar production (volume and concentration) and ant species composition in mediating the effects of CAD and aridity on the effectiveness of protection services.Attack rates by ants declined with increasing aridity but were not related to CAD. The volume of extrafloral nectar declined with increasing CAD but was not affected by aridity, whereas the concentration was not related to either CAD or aridity. The composition of attendant ant species varied with aridity but not with CAD.Synthesis. Our findings suggest that CAD does not affect plant‐protection services mediated by EFNs in Brazilian Caatinga. However, ant‐protection services declined with increased aridity, and this occurred through changes in the composition of attendant ant species rather than by changes in the production of extrafloral nectar. Such a response to increasing aridity highlights the vulnerability of EFN‐bearing plants to climate change through decreased predation of herbivores. [ABSTRACT FROM AUTHOR]

Many insects masquerade as parts of plants, such as bark or leaves, or mimic poisonous organisms in order to defend themselves against predators. However, recent studies indicate that plants may mimic insects and other arthropods to deter herbivores. Here, I report visually similar white structures of plants and arthropods in Japan and suggest they are part of a mimicry complex. Young shoots covered with white trichomes or waxy substances may mimic wax-producing insects, such as woolly aphids, coccids and caterpillars, potentially resulting in reduced herbivory. Since wax-producing insects would reduce plant quality and quantity, be distasteful and attract natural enemies, herbivorous insects and mammals may avoid such white shoots. Furthermore, fungus-infected insects, gregarious braconid cocoons, spider egg sacs and froth made by froghopper nymphs or blasticotomid sawfly larvae are also conspicuously white and impose risks for herbivorous insects. Thus, these white structures may be mimicry models for white shoots and are likely to be part of a defensive mimicry complex. Although this study focuses on defence against herbivores, there are simultaneous physiological roles for white colouration that will not be discussed in depth here.

1. Anthropogenic disturbance and climate change might negatively affect the ecosystem services provided by mutualistic networks. However, the effects of such forces remain poorly characterized. They may be especially important in dry forests, which (1) experience chronic anthropogenic disturbances (CADs) as human populations exploit forest resources, and (2) are predicted to face a 22% decline in rainfall under climate change. 2. In this study, we investigated the separate and combined effects of CADs and rainfall levels on the specialization of mutualistic networks in the Caatinga, a seasonally dry tropical forest typical of north-eastern Brazil. More specifically, we examined interactions between plants bearing extrafloral nectaries (EFNs) and ants. We analysed whether differences in network specialization could arise from environmentally mediated variation in the species composition, namely via the replacement of specialist by generalist species. 3. We characterized these ant--plant networks in 15 plots (20 x 20 m) that varied in CAD intensity and mean annual rainfall. We quantified CAD intensity by calculating three indices related to the main sources of disturbance in the Caatinga: livestock grazing (LG), wood extraction (WE) and miscellaneous resource use (MU). We determined the degree of ant--plant network specialization using four metrics: generality, vulnerability, interaction evenness and H2'. 4. Our results indicate that CADs differentially influenced network specialization: we observed positive, negative, and neutral responses along LG, MU and WE gradients, respectively. The pattern was most pronounced with LG. Rainfall also shaped network specialization, markedly increasing it. While LG and rainfall were associated with changes in network species composition, this trend was not related to the degree of species specialization. This result suggests that shifts in network specialization might be related to changes in species behaviour, not species composition. 5. Our study highlights the vulnerability of such dry forest ant--plant networks to climate change. Moreover, dry forests experience highly heterogeneous anthropogenic disturbances, creating a geographic mosaic of selective forces that may shape the co-evolution of interactions between ants and EFN-bearing plants. [ABSTRACT FROM AUTHOR]

Polymorphisms in plants are main factors that determine the diversity of associated animal communities and their population dynamics. Typically, Persicaria lapathifolia var. lapathifolia (Polygonaceae) has no trichomes on leaf surfaces (glabrous type), but a hairy type does sometimes occur. Based on a cultivation experiment, the presence or absence of trichomes is clarified to be under genetic control. To reveal the defensive function of trichomes against herbivores, laboratory experiments were conducted using a major herbivore, Galerucella grisescens (Coleoptera: Chrysomelidae). In both choice and no-choice feeding tests, the glabrous type was significantly more consumed by G. grisescens adults, while the hairy type was not consumed. In the hairy leaf treatment, larval duration tended to become longer, the adult body weight became significantly lower, and adults laid significantly more eggs than in the glabrous leaf treatment. Hairy leaves contained significantly more total phenolics and condensed tannins than glabrous leaves, suggesting that the hairy type allocates more resources for physical and chemical defence. Because no significant differences in leaf consumption were detected in the feeding experiment using powdered host leaves, G. grisescens seems to have adapted to the chemical defences of P. lapathifolia var. lapathifolia. These results clearly indicate that leaf trichomes of P. lapathifolia var. lapathifolia effectively act as a physical defence against G. grisescens. [ABSTRACT FROM AUTHOR]

ABSTRACT Abiotic conditions can increase the costs of services and/or the benefits of rewards provided by mutualistic partners. Consequently, in some situations, the outcome of mutualisms can move from beneficial to detrimental for at least one partner. In the case of protective mutualisms between ant bodyguards and plants bearing extrafloral nectaries ( EFNs), plants from arid environments face a trade-off between EFN production and maintenance and water and carbon economy. This trade-off may increase EFN costs and decrease their value as a defensive strategy to plants in such environments. Despite this, the presence of EFNs is an ubiquitous trait in plants from arid environments, suggesting that they provide greater benefits to plants in these environments to compensate for their higher costs. We used a meta-analysis to investigate if such benefits do increase with decreasing water availability and the possible underlying causes (such as ant behaviour or ant diversity). As predicted, ant effect on EFN plants performance increased as mean annual precipitation decreased. We also found that the frequency of dominant ants on EFN plants increased in drier areas. Due to the more aggressive behaviour of dominant ants, we suggest that they represent an important factor shaping the adaptive value of EFNs to plants in arid environments. [ABSTRACT FROM AUTHOR]

In response to climate change, various organisms tend to migrate to higher elevations and latitudes. Unequal migration rates of plants and animals are expected to result in changes in the type and intensity of their interactions such as plant-herbivore interactions. In the present study, we studied the extent of herbivore damage in Salvia nubicola along an elevational gradient in Manang, central Nepal. A common garden experiment was also carried out by sowing seeds collected from different populations along the elevational gradient. As expected, the extent of herbivore damage in the field was significantly lower at higher elevations, and it increased with the population size and at sites without shrubs. In the common garden experiment, herbivore damage was higher in plants originating from lower elevations and from more open habitats. While higher herbivore pressure in the field at lower elevations may suggest that plants will be better protected against herbivores at lower elevations, the common garden study demonstrated the opposite. A possible explanation could be that plants from higher elevations have to adapt to extreme conditions, and lower palatability is a side effect of these adaptations. Thus, S. nubicola in the Himalayan region is likely to survive the expected higher herbivore pressure caused by an upward shift of herbivores under future climate change. Future studies should attempt to elucidate generality of such a conclusion by studying multiple species along similar gradients. Our results from comparison of the field and common garden study suggest that future experiments need to include comparisons in common environments to understand the expected response of plants to changes in herbivore pressure. [ABSTRACT FROM AUTHOR]

“Plant-ants”, i.e. those symbiotic with myrmecophyte plants, defend their hosts against herbivores. Plant-ants are expected to affect the host-plant ranges of herbivores that feed on myrmecophytes. This study aimed to experimentally determine whether anti-herbivore defences by plant-ants restrict the larval host-plant ranges of fourArhopala(Lycaenidae) butterflies that feed onMacaranga(Euphorbiaceae) trees, some of which are myrmecophytes. We fedArhopalalarvae with the leaves of fiveMacarangaspecies under ant-excluded conditions to examine their potential host-plant ranges. Under ant-excluded conditions, threeArhopalaspecies survived to the pupal stage when fed species not used in the field as well as their normal host species. Our data suggested that the aggressive behaviours of plant-ants towards leaf-feeding insects restrict the potential host-plant ranges of someMacaranga-feedingArhopalabutterflies. [ABSTRACT FROM AUTHOR]

Background and Aims The ecological, evolutionary and genetic bases of population differentiation in a variable environment are often related to the selection pressures that plants experience. We compared differences in several growth- and defence-related traits in two isolated populations of Acacia raddiana trees from sites at either end of an extreme environmental gradient in the Negev desert. Methods We used random amplified polymorphic DNA (RAPD) to determine the molecular differences between populations. We grew plants under two levels of water, three levels of nutrients and three levels of herbivory to test for phenotypic plasticity and adaptive phenotypic plasticity. Key Results The RAPD analyses showed that these populations are highly genetically differentiated. Phenotypic plasticity in various morphological traits in A. raddiana was related to patterns of population genetic differentiation between the two study sites. Although we did not test for maternal effects in these long-lived trees, significant genotype × environment (G × E) interactions in some of these traits indicated that such plasticity may be adaptive. Conclusions The main selection pressure in this desert environment, perhaps unsurprisingly, is water. Increased water availability resulted in greater growth in the southern population, which normally receives far less rain than the northern population. Even under the conditions that we defined as low water and/or nutrients, the performance of the seedlings from the southern population was significantly better, perhaps reflecting selection for these traits. Consistent with previous studies of this genus, there was no evidence of trade-offs between physical and chemical defences and plant growth parameters in this study. Rather, there appeared to be positive correlations between plant size and defence parameters. The great variation in several traits in both populations may result in a diverse potential for responding to selection pressures in different environments. [ABSTRACT FROM AUTHOR]

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. This study examines the effect of ant mutualists on two morphs of the mangrove Conocarpus erectus. 'Silver' C. erectus plants have a dense layer of leaf hairs, or trichomes, while 'green' plants have very few trichomes. Ants are attracted to extrafloral nectaries (EFNs) produced on the foliage of both high- and low-trichome morphs. . High-trichome plants produced fewer and smaller EFNs. Conocarpus erectus plants with fewer and smaller EFNs produced less nectar and attracted fewer ants. . Ant exclusion increased herbivory and decreased growth in low-trichome plants, but had no detectable effect on herbivory and growth in high-trichome plants. Synthesis. This study demonstrates that intraspecific variation in a direct anti-herbivore defence influences the magnitude of the beneficial effect of ants on plants. Individuals with low trichome densities benefitted from ant mutualists while individuals with high trichome densities did not. This likely creates stronger selection for the maintenance of EFN production in low-trichome plants, a conclusion supported by the fact that low-trichome plants produced more and larger EFNs than high-trichome plants, and suggests that the two morphs are on divergent evolutionary trajectories with regard to anti-herbivore defence. [ABSTRACT FROM AUTHOR]

Plant traits have become popular as predictors of interspecific variation in important ecosystem properties and processes. Here we introduce foliar pH as a possible new plant trait, and tested whether (1) green leaf pH or leaf litter pH correlates with biochemical and structural foliar traits that are linked to biogeochemical cycling; (2) there is consistent variation in green leaf pH or leaf litter pH among plant types as defined by nutrient uptake mode and higher taxonomy; (3) green leaf pH can predict a significant proportion of variation in leaf digestibility among plant species and types; (4) leaf litter pH can predict a significant proportion of variation in leaf litter decomposability among plant species and types. We found some evidence in support of all four hypotheses for a wide range of species in a subarctic flora, although cryptogams (fern allies and a moss) tended to weaken the patterns by showing relatively poor leaf digestibility or litter decomposability at a given pH. Among seed plant species, green leaf pH itself explained only up to a third of the interspecific variation in leaf digestibility and leaf litter up to a quarter of the interspecific variation in leaf litter decomposability. However, foliar pH substantially improved the power of foliar lignin and/or cellulose concentrations as predictors of these processes when added to regression models as a second variable. When species were aggregated into plant types as defined by higher taxonomy and nutrient uptake mode, green-specific leaf area was a more powerful predictor of digestibility or decomposability than any of the biochemical traits including pH. The usefulness of foliar pH as a new predictive trait, whether or not in combination with other traits, remains to be tested across more plant species, types and biomes, and also in relation to other plant or ecosystem traits and processes. [ABSTRACT FROM AUTHOR]

Many folivorous insects sever leaf veins, trench across leaf blades, or girdle petioles prior to feeding on leaves. The purpose of these behaviours is generally thought to be sabotage of the anti-herbivore chemical defences of host plants. For insects that construct leaf shelters, these behaviours may make leaves easier to roll or fold. Larvae of the Indian red admiral butterfly,Vanessa indica(Herbst), cut trenches at the base of host plant leaves and construct leaf-fold shelters. I attempted to determine which of the above functions the trenching behaviour ofV. indicalarvae serves. If the function of trenching is to facilitate leaf-folding, then larvae should cut trenches before folding leaves. When the larvae used larger leaves, they tended to trench them prior to folding them. This suggests that the function of trenching behaviour is to make leaves easier to fold. However, larvae sometimes cut trenches after folding the leaves, suggesting that this behaviour has additional functions. When the larvae were about to moult or pupate, they did not cut trenches, suggesting that trenching behaviour may also be involved in feeding. [ABSTRACT FROM AUTHOR]

The optimal defence hypothesis predicts that plant parts characterized by a high value and/or a high risk of being attacked should exhibit the highest level of defence. We tested this hypothesis with Macaranga bancana ant-plants, which are protected efficiently by resident, mutualistic ants from herbivores, parasites and encroaching vegetation. Because cost-effective defence of the host by ants increases ant fitness, selection should act on ant behaviour to produce patterns of distribution of defence as predicted for direct chemical defence traits. Termites and pieces of tape were equally distributed over the uppermost ten leaves and over the leaf-bearing part of the stems (with termites mimicking a transient herbivore, while tape mimics a long-term stress caused by a climber or plant parasite). This arrangement allowed a separation of putative coevolutionary adaptations in the ants' behaviour from other potential sources of spatial patterns in ant defence, such as differences in herbivore pressure, in the vulnerability of different herbivores, or in direct plant defences. Ant activity dropped rapidly at termite baits, but remained high at tapes for at least 5 h, thereby demonstrating adaptive differential responses to the differences between the two stressors. Most importantly, ants preferentially defended young leaves and shoot parts. The temporal and spatial patterns of ant attention to exogenous stressors thus were clearly adaptive, varying with likely costs and benefits of defence as formulated in the optimal defence theory. [ABSTRACT FROM PUBLISHER]

Evidence is presented which suggests that cytochrome P-450, in plants, probably functions as in all other eukaryotic organisms, principally as a detoxification mechanism. In plants this function is largely suppressed during tissue maturation coinciding with cell vacuolation. The consequential accumulation and isolation of potential toxins within vacuoles provides higher plants with an anti-herbivore defence of evolutionary significance. [ABSTRACT FROM AUTHOR]