Search

The disruptive effects of tertiary species on otherwise positive pairwise species interactions (e.g. context-dependent parasitism in pollinator syndromes) is well-known. However, few—if any—studies have investigated how invasive plants affect interactions between facilitative plants and their native plant communities. Further, if tertiary invasive species can change interactions among native species from positive to negative, then a tertiary native should be capable of the same phenom for pairwise interactions between natives and invasives. Our previous research indicates invasive black mustard (Brassica nigra) changes interaction signs for otherwise positive species interactions between the dominant, native facilitator California buckwheat (Eriogonum fasciculatum) and its co-dominant beneficiary California sagebrush (Artemisia californica) in semi-arid California coastal sage scrub habitat. Here, E. fasciculatum and A. californica seedlings increased B. nigra shoot growth in pairwise species interactions in the greenhouse. However, in three-way species interactions, E. fasciculatum and A. californica together reduced B. nigra SLA, height, and reproductive potential while not increasing shoot DW. In three-way species interactions, B. nigra did not significantly reduce E. fasciculatum facilitation of A. californica. Also surprisingly, light competition with B. nigra resulted in an increase in A. californica height, which reduced the negative effects of A. californica light competition on shade-intolerant E. fasciculatum. In an additive field experiment, A. californica protected E. fasciculatum from facilitating germination and growth of B. nigra when water competition was minimized. Taken together, this study demonstrates the importance of studying species interactions between competitive, native perennials in the current ecological context of invaded ecosystems.

The interactions between ants and certain sap-feeding insects in the order Hemiptera are classic examples of food-for-protection mutualisms. In these associations, herbivorous hemipterans use a highly specialized, straw-like mouthpart to consume sap directly from plant phloem and xylem and, as a result, excrete a sugar-rich waste product called honeydew. Ant foragers use specialized adaptations to collect and share honeydew with nestmates and, in exchange, protect hemipterans against predators. The two key innovations underlying this interaction—hemipteran sap feeding and ant harvesting of honeydew—have driven the evolutionary success and ecological dominance of ants. These interactions also carry unique costs and benefits for each partner and are highly context dependent. Understanding the factors mediating this mutualism is critical, as these interactions have broader ecological consequences for the natural and agricultural ecosystems in which they are embedded.

Global declines in bird and arthropod abundance highlights the importance of understanding the role of food limitation and arthropod community composition for the performance of insectivorous birds. In this study, we link data on nestling diet, arthropod availability and nesting performance for the Coastal Cactus Wren (Campylorhynchus brunneicapillus sandiegensis), an at-risk insectivorous bird native to coastal southern California and Baja Mexico. We used DNA metabarcoding to characterize nestling diets and monitored 8 bird territories over two years to assess the relationship between arthropod and vegetation community composition and bird reproductive success. We document a discordance between consumed prey and arthropod biomass within nesting territories, in which Diptera and Lepidoptera were the most frequently consumed prey taxa but were relatively rare in the environment. In contrast other Orders (e.g., Hemiptera, Hymenoptera)were abundant in the environment but were absent from nestling diets. Accordingly, variation in bird reproductive success among territories was positively related to the relative abundance of Lepidoptera (but not Diptera), which were most abundant on 2 shrub species (Eriogonum fasciculatum, Sambucus nigra) of the 9 habitat elements characterized (8 dominant plant species and bare ground). Bird reproductive success was in turn negatively related to two invasive arthropods whose abundance was not associated with preferred bird prey, but instead possibly acted through harassment (Linepithema humile; Argentine ants) and parasite transmission or low nutritional quality (Armadillidium vulgare; "pill-bug"). These results demonstrate how multiple aspects of arthropod community structure can influence bird performance through complementary mechanisms, and the importance of managing for arthropods in bird conservation efforts.

Plant defense against herbivores is multidimensional, and investment into different defense traits is intertwined due to genetic, physiological, and ecological costs. This relationship is expected to generate a trade-off between direct defense and tolerance that is underlain by resource availability, with increasing resources being associated with increased investment in tolerance and decreased investment in direct resistance. We tested these predictions across populations of the shrub Artemisia californica by growing plants sourced from a latitudinal aridity gradient within common gardens located at the southern (xeric) and northern (mesic) portions of its distribution. We measured plant growth rate, resistance via a damage survey, and tolerance to herbivory by experimentally simulating vertebrate herbivory. Plants from more northern (vs. southern) environments were less resistant (received higher percent damage by vertebrate herbivores) and tended to be more tolerant (marginally significant) with respect to change in biomass measured 12 months after simulated vertebrate herbivory. Also, putative growth and defense traits paralleled patterns of resistance and tolerance, such that leaves from northern populations contained lower concentrations of terpenes and increased N, specific leaf area, and % water. Last, plant growth rate did not demonstrate clear clinal patterns, as northern populations (vs. southern populations) grew more slowly in the southern (xeric) garden, but there was no clinal relationship detected in the northern (mesic) garden. Overall, our findings support the prediction of lower resistance and higher tolerance in plant populations adapted to more resource-rich, mesic environments, but this trade-off was not associated with concomitant trade-offs in growth rate. These findings ultimately suggest that plant adaptation to resource availability and herbivory can shape intraspecific variation in multivariate plant defenses.

Species employ multiple strategies to deal with stressful environments, but these strategies often incur costs. Aphids frequently utilize multiple predator avoidance strategies, including attracting mutualist ants for protection and dispersing by producing winged forms. While both strategies can be physiologically costly, the magnitudes of these costs have not been previously compared. In this study, we experimentally manipulated ant attendance in the field and measured the individual and interactive effects of ant attendance and wing formation on body size and reproduction of the ant-tended aphid Cinara schwarzii (Wilson) (Hemiptera: Aphididae). Aphid adult body size was smaller in the presence of ants (18%), but controlling for body size, there were no differences in embryo number or size. In contrast, wing formation did not affect adult body size but strongly reduced embryo number (46%) and size (8%). Although ant attendance reduced C. schwarzii wing formation, ant attendance and wing formation acted independently on aphid body size and reproduction. For comparison, we confirmed that the manipulation of ant presence had no effect on body size or reproduction of the untended co-existing congener Cinara solitaria (Gillette and Palmer) (Hemiptera: Aphididae). Complementing our empirical study, a meta-analysis of 78 responses from 24 publications showed that wing formation consistently and significantly reduces aphid body size and reproduction (37%), while the effects of ant attendance showed a mean positive effect (9%) that did not significantly differ from zero. Together, our empirical study and meta-analysis provide strong evidence for costs of wing formation but not ant attendance for aphids.

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 generalist insect Spodoptera exigua and whether communication was affected by water availability. We paired emitter and receiver potato plants, with half of the emitters damaged by S. exigua larvae and half serving as undamaged controls. Both emitter and receiver plants were factorially subjected to one of two watering treatments: high (i.e. well-watered) vs. low (i.e. reduced watering) availability, thus effectively teasing apart water availability effects on the emission and reception components of signalling. After 4 days of herbivore feeding, we collected emitter VOCs and receivers were subjected to feeding by S. exigua to test for effects of signalling on induced resistance. Herbivory by S. exigua led to increased VOCs emissions as well as changes in VOCs composition in emitter plants. Furthermore, emitters subjected to low water availability exhibited a weaker induction of VOCs in response to herbivory relative to well-watered emitters. Results from the feeding bioassay indicated that receivers exposed to VOCs from herbivore-induced emitters showed lower S. exigua damage (i.e. induced resistance) compared to receivers exposed to undamaged emitters. However, we did not observe a significant effect of water availability in either emitters or receivers on plant signalling effects on receiver resistance. Overall, our study contributes to understanding how the abiotic context affects plant communication by providing evidence of water availability effects on the induction of VOCs that act as airborne signals between plants. The observed changes in induced VOCs due to the water treatment had no detectable consequences for plant communication. Accordingly, the induction of key compounds mediating communication was apparently not compromised by our experimental conditions., This study was supported by a grant from the Spanish Ministry of Science, Innovation and Universities (RTI2018-099322-B-I00) to X.M., a grant from the Spanish National Research Council (2021AEP082) to X.M. and a grant from the Regional Government of Galicia (IN607A2021/03) to X.M. and C.V.-G. C.V.-G was supported by a postdoctoral fellowship from the Xunta de Galicia-GAIN/Fulbright (IN606B2021/004).

Species distributions are driven by abiotic and biotic factors, but the importance of variation in the availability and quality of critical resources is poorly understood. Disentangling the relative importance of these factors—abiotic environment, availability of critical resources, and resource quality—will be important to modeling species current distributions and responses to projected climate change. We address these questions using species distribution models (SDMs) for the western monarch butterfly population (Danaus plexippus), whose larvae feed exclusively on Asclepias species known for their heterogeneous distribution and variation in host quality. We modeled the distribution of 24 Asclepias species to compare three monarch distribution models with increasing levels of complexity: (1) a null model using only environmental factors (climate envelope model), (2) a model using environmental factors and Asclepias availability estimated as species richness, (3) and a model using environmental factors and Asclepias’ availability weighted by host plant quality as assessed through a greenhouse bioassay of larval performance. Asclepias models predicted that half of the Asclepias species will expand their ranges and shift toward higher latitudes, while half will contract. These patterns were uncorrelated with host plant quality. Among the three monarch models, the climate envelope model was the poorest performing. Models accounting for host plant availability performed best, while accounting for host plant quality did not improve model performance. The climate envelope model estimated more restrictive contemporary and future monarch ranges compared to both host plant models. Although all three models predicted future monarch range expansions, the projected future distributions varied among models. The climate envelope model predicted range expansions along the Pacific coast and contractions inland. In contrast, the host plant availability and quality models predicted range expansions in both of these regions and, as a result, 14% and 19% increases in distribution (respectively) relative to the climate envelope model. These models do not include other factors affecting monarch persistence. Nevertheless, our findings suggest that accounting for information on host plant availability and response to climate change is necessary to predict future species distributions, but that variation in the quality of those critical resources may be of secondary importance.

The enemy‐free space hypothesis (EFSH) contends that generalist predators select for dietary specialization in insect herbivores. At a community level, the EFSH predicts that dietary specialization reduces predation risk, and this pattern has been found in several studies addressing the impact of individual predator taxa or guilds. However, predation at a community level is also subject to combinatorial effects of multiple‐predator types, raising the question of how so‐called multiple‐predator effects relate to dietary specialization in insect herbivores. Here, we test the EFSH with a field experiment quantifying ant predation risk to insect herbivores (caterpillars) with and without the combined predation effects of birds. Assessing a community of 20 caterpillar species, we use model selection in a phylogenetic comparative framework to identify the caterpillar traits that best predict the risk of ant predation. A caterpillar species' abundance, dietary specialization, and behavioral defenses were important predictors of its ant predation risk. Abundant caterpillar species had increased risk of ant predation irrespective of bird predation. Caterpillar species with broad diet breadth and behavioral responsiveness to attack had reduced ant predation risk, but these ant effects only occurred when birds also had access to the caterpillar community. These findings suggest that ant predation of caterpillar species is density‐ or frequency‐dependent, that ants and birds may impose countervailing selection on dietary specialization within the same herbivore community, and that contingent effects of multiple predators may generate behaviorally mediated life‐history trade‐offs associated with herbivore diet breadth., This study is an experimental test of the hypothesis that dietary specialization of insect herbivores reduces their predation risk. Unexpectedly, ant predation of caterpillars increased with dietary specialization and depended on bird predation. In this community, dietary specialization was associated with reduced behavioral defenses, which predicted ant predation risk in a way that was also contingent upon bird predation.

10 páginas, 2 tablas y 3 figuras., Terpenoids are secondary metabolites produced in most plant tissues and are often considered toxic or repellent to plant enemies. Previous work has typically reported on intra-specific variation in terpene profiles, but the effects of plant sex, an important axis of genetic variation, have been less studied for chemical defences in general, and terpenes in particular. In a prior study, we found strong genetic variation (but not sexual dimorphism) in terpene amounts in leaves of the dioecious shrub Baccharis salicifolia. Here we build on these findings and provide a more in-depth analysis of terpene chemistry on these same plants from an experiment consisting of a common garden with male (N = 19) and female (N = 20) genotypes sourced from a single population. Our goal in the present study was to investigate quantitative and qualitative differences in terpene profiles associated with plant sex and genotypic variation. For this, we quantified leaf mono- and sesquiterpene amount, richness, and diversity (quantitative profile), as well as the composition of compounds (qualitative profile). We found no evidence of sexual dimorphism in monoterpene or sesquiterpene profiles. We did, however, find significant genotypic variation in amount, diversity, and composition of monoterpenes, but no effects on sesquiterpenes. These findings indicated that genotypic variation in terpene profiles largely surpassed variation due to sexual dimorphism for the studied population of this species., This research was funded by National Science Foundation grants DEB-1354734, DEB-1457029 and DEB-1120794 to KAM. XM was supported by a Spanish National Research Grant (AGL2015-70748-R), a grant from the Regional Government of Galicia (IN607D 2016/001) and the Ramon y Cajal Research Programme (RYC-2013-13230).

Organisms use environmental cues to align their phenology-the timing of life events-with sets of abiotic and biotic conditions that favor the successful completion of their life cycle. Climate change has altered the environmental cues organisms use to track climate, leading to shifts in phenology with the potential to affect a variety of ecological processes. Understanding the drivers of phenological shifts is critical to predicting future responses, but disentangling the effects of temperature from precipitation on phenology is often challenging because they tend to covary. We addressed this knowledge gap in a high-elevation environment where phenological shifts are associated with both the timing of spring snow melt and temperature. We factorially crossed early snow melt and passive warming treatments to (1) disentangle the effects of snow melt timing and warming on the phenology of flowering and fruiting and reproductive success in three subalpine plant species (Delphinium nuttallianum, Valeriana edulis, and Potentilla pulcherrima); and (2) assess whether snow melt acts via temperature accumulation or some other aspect of the environment (e.g., soil moisture) to affect phenological events. Both the timing and duration of flowering and fruiting responded to the climate treatments, but the effect of snow melt timing and warming varied among species and phenological stages. The combined effects of the treatments on phenology were always additive, and the snow melt treatment often affected phenology even when the warming treatment did not. Despite marked responses of phenology to climate manipulations, the species showed little change in reproductive success, with only one species producing fewer seeds in response to warming (Delphinium, -56%). We also found that snow melt timing can act both through temperature accumulation and as a distinct cue for phenology, and these effects are not mutually exclusive. Our results show that one environmental cue, here snow melt timing, may act through multiple mechanisms to shift phenology.

Author(s): Nelson, AS; Pratt, RT; Pratt, JD; Smith, RA; Symanski, CT; Prenot, C; Mooney, KA | Abstract: © 2018 The Authors Although species interactions are often proposed to be stronger at lower latitudes and elevations, few studies have evaluated the mechanisms driving such patterns. In this study, we assessed whether, and by which mechanisms, abiotic changes associated with elevation altered the outcome of an ant–aphid protection mutualism. To do so, we characterized the multi-trophic interactions among the ant Formica podzolica, the aphid Aphis varians, and aphid natural enemies occurring on the plant Chamerion angustifolium within replicate high and low elevation valleys. Low (versus high) elevation sites had longer summers (snowmelt 13 days earlier) and were on average 1.1°C warmer and 41% drier throughout the year. At low elevations, individual ant colonies consumed approximately double the volume of carbohydrate baits, likely due to a higher foraging tempo, and possibly due to a greater demand for sugar- versus protein-rich resources (as indicated by stable isotope analysis). Wild aphid colonies at low elevations were visited by 1.4-fold more natural enemies (controlling for variation in aphid abundance), while experimental aphid colonies on potted plants were tended 52% more frequently by ants. As a result, ants increased aphid colony survival by 66% at low elevations but had no detectable effect at high elevations; at low (versus high) elevations aphid colonies without ants had lower survival, demonstrating stronger predator effects, while aphid colonies with ants had higher survival, demonstrating even stronger ant benefits. Analyses for the effects of mean summer temperature yielded qualitatively identical results to those based on elevation. Collectively, these findings support predictions for a greater sensitivity of higher trophic levels to warming and demonstrate how species interactions can vary across environmental gradients due to simultaneous changes in species traits and abundances across multiple trophic levels.

Classic research on elevational gradients in plant–herbivore interactions holds that insect herbivore pressure is stronger under warmer, less seasonal climates characteristic of low elevations, and that this in turn selects for increased defence in low‐ (relative to high‐) elevation plants. However, recent work has questioned this paradigm, arguing that it overly simplifies the ecological complexity in which plant–insect herbivore interactions are embedded along elevational gradients. Numerous biotic and abiotic factors vary with elevation, and their simultaneous influences are the focus of current work on elevational gradients in insect herbivory and plant defences. The present review 1) synthesizes current knowledge on elevational gradients in plant–insect herbivore interactions; 2) critically analyses research gaps and highlights recent advances that contribute to filling these gaps; and 3) outlines new research opportunities to uncover underlying mechanisms and build towards a unified theory on elevational gradients. We conclude that the next generation of studies should embrace community complexity – including multi‐trophic dynamics and the multivariate nature of plant defence – and to do so by combining observational data, manipulative experiments and emerging analytical tools.

The effects of predator assemblages on herbivores are predicted to depend critically on predator-predator interactions and the extent to which predators partition prey resources. The role of prey heterogeneity in generating such multiple predator effects has received limited attention. Vertebrate and arthropod insectivores constitute two co-dominant predatory taxa in many ecosystems, and the emergent properties of their joint effects on insect herbivores inform theory on multiple predator effects as well as biological control of insect herbivores. Here we use a large-scale factorial manipulation to assess the extent to which birds and ants engage in antagonistic predator-predator interactions and the consequences of heterogeneity in herbivore body size and diet breadth (i.e. the diversity of host plants used) for prey partitioning. We excluded birds and reduced ant density (by 60%) in the canopies of eight northeastern USA deciduous tree species during two consecutive years and measured the community composition and traits of lepidopteran larvae (caterpillars). Birds did not affect ant density, implying limited intraguild predation between these taxa in this system. Birds preyed selectively upon large-bodied caterpillars (reducing mean caterpillar length by 12%) and ants preyed selectively upon small-bodied caterpillars (increasing mean caterpillar length by 6%). Birds and ants also partitioned caterpillar prey by diet breadth. Birds reduced the frequency dietary generalist caterpillars by 24%, while ants had no effect. In contrast, ants reduced the frequency of dietary specialists by 20%, while birds had no effect, but these effects were non-additive; under bird exclusion, ants had no detectable effect, while in the presence of birds, they reduced the frequency of specialists by 40%. As a likely result of prey partitioning by body size and diet breadth, the combined effects of birds and ants on total caterpillar density were additive, with birds and ants reducing caterpillar density by 44% and 20% respectively. These results show evidence for the role of prey heterogeneity in driving functional complementarity among predators and enhanced top-down control. Heterogeneity in herbivore body size and diet breadth, as well as other prey traits, may represent key predictors of the strength of top-down control from predator communities.

Indirect defence, the adaptive top-down control of herbivores by plant traits that enhance predation, is a central component of plant-herbivore interactions. However, the scope of interactions that comprise indirect defence and associated ecological and evolutionary processes has not been clearly defined. We argue that the range of plant traits that mediate indirect defence is much greater than previously thought, and we further organise major concepts surrounding their ecological functioning. Despite the wide range of plant traits and interacting organisms involved, indirect defences show commonalities when grouped. These categories are based on whether indirect defences boost natural enemy abundance via food or shelter resources, or, alternatively, increase natural enemy foraging efficiency via information or alteration of habitat complexity. The benefits of indirect defences to natural enemies should be further explored to establish the conditions in which indirect defence generates a plant-natural enemy mutualism. By considering the broader scope of plant-herbivore-natural enemy interactions that comprise indirect defence, we can better understand plant-based food webs, as well as the evolutionary processes that have shaped them.

Direct and indirect defenses are predicted to trade-off due to costs associated with redundancy in plant defense, but the factors mediating a plant's position along this trade-off axis are unknown. We conducted a bird exclusion experiment of nine sympatric shrub species to assess convergent associations among direct defense, indirect defense from birds, and shrub structural complexity, a trait predicted to influence bird foraging. We found high variation in defense; direct resistance varied four-fold, with indirect defense ranging from a 59% reduction to a 32% increase in herbivore density. These resistance strategies traded off and were mediated by plant structure; high complexity was associated with weaker indirect defense from birds, strong direct defense, and more predatory arthropods. Our findings suggest that species with growth forms that inhibit bird foraging invest more in direct defense and may provide refuge for arthropod predators. Accordingly, we provide evidence for a potentially widespread mechanism underlying the evolution of plant defenses.

It is well known that plant damage by leaf-chewing herbivores can induce resistance in neighbouring plants. It is unknown whether such communication occurs in response to sap-feeding herbivores, whether communication is specific to herbivore identity, and the chemical basis of communication, including specificity. We carried out glasshouse experiments using the California-native shrub Baccharis salicifolia and two ecologically distinct aphid species (one a dietary generalist and the other a specialist) to test for specificity of plant-plant communication and to document the underlying volatile organic compounds (VOCs). We show specificity of plant-plant communication to herbivore identity, as each aphid-damaged plant only induced resistance in neighbours against the same aphid species. The amount and composition of induced VOCs were markedly different between plants attacked by the two aphid species, providing a putative chemical mechanism for this specificity. Furthermore, a synthetic blend of the five major aphid-induced VOCs (ethanone, limonene, methyl salicylate, myrcene, ocimene) triggered resistance in receiving plants of comparable magnitude to aphid damage of neighbours, and the effects of the blend exceeded those of individual compounds. This study significantly advances our understanding of plant-plant communication by demonstrating the importance of sap-feeding herbivores and herbivore identity, as well as the chemical basis for such effects.

10 páginas.-- 3 figuras.-- 2 tablas.-- 45 referencias.-- Additional Supporting Information may be found online in the Supporting Information section at the end of the article, Research Article: Free Access in the publisher https://doi.org/10.1002/ajb2.1210, Premise of the Study: The influence of weather conditions on masting and the ecological advantages of this reproductive behavior have been the subject of much interest. Weather conditions act as cues influencing reproduction of individual plants, and similar responses expressed across many individuals lead to population-level synchrony in reproductive output. In turn, synchrony leads to benefits from economies of scale such as enhanced pollination success and seed predator satiation. However, there may also be individual-level benefits from reproductive responses to weather cues, which may explain the origin of masting in the absence of economies of scale. In a previous study, we found support for a mechanism whereby individual responses to weather cues attenuate the negative autocorrelation between past and current annual seed production—a pattern typically attributed to resource limitation and reproductive tradeoffs among years. Methods: Here we provide a follow-up and more robust evaluation of this hypothesis in 12 species of oaks (Quercus spp.), testing for a negative autocorrelation (tradeoff) between past and current reproduction and whether responses to weather cues associated with masting reduce the strength of this negative autocorrelation. Key Results: Our results showed a strong negative autocorrelation for 11 of the species, and that species-specific reproductive responses to weather cues dampened this negative autocorrelation in 10 of them. Conclusions: This dampening effect presumably reflects a reduction in resource limitation or increased resource use associated with weather conditions, and suggests that responses to weather cues conferring these advantages should be selected for based on individual benefits, This study was supported by a National Science Foundation grant DEB‐1256394 to WDK, by the Ramon y Cajal Research Programme (RYC‐2013‐13230) to XM, by a Spanish National Research Grant (AGL2015‐70748‐R) to XM, by the Spanish MEC projects Heteromed (REN2002‐4041‐C02‐02), Dinamed (CGL2005‐5830‐C03‐01) and Interbos (CGL2008‐04503‐C03‐01) to IMPR, and by the Andalusian Anasinque‐PE2010‐RNM‐5782 project to IMPR.

Ants are ecologically dominant members of terrestrial communities. Ant foraging is often strongly associated with plants and depends upon associative learning of chemicals in the environment. As a result, plant chemicals can affect ant behaviors and, in so doing, have strong multi-trophic indirect effects. Plant chemicals mediate ant behaviors in the contexts of floral visitation, seed dispersal and predation, leaf cutting, interactions with ant-mutualist host plants, interactions with mutualist and prey insects in plant canopies, and plant predation of ants by carnivorous plants. Here, we review what is known about these differing contexts in which plant chemicals influence ant behavior, the mechanisms by which ants are affected by plant chemicals, and future directions within these topics.

Plants are able to adjust their anti-herbivore defenses in response to the volatile organic compounds (VOCs) emitted by herbivore-damaged neighbors, and some of these changes increase resistance against subsequent herbivory. This phenomenon of plant-plant communication is thought to be widespread, but recent investigations have cautioned that it can be context dependent, including variation in the strength of communication based on the identity of plants and their associated herbivores. Here, we performed three greenhouse experiments using multiple male and female genotypes of the dioecious woody shrub Baccharis salicifolia and its specialist aphid Uroleucon macolai to test for specificity of plant-plant communication with respect to plant sex and genotype. Moreover, we evaluated plant sexual dimorphism and genotypic variation in VOC emissions (i.e., the "speaking" side of the interaction) and response of plants to VOC exposure (i.e., the "listening" side of the interaction) in order to identify the chemical mechanisms underlying such specificity. We did not find genotypic specificity of communication; emitter plants damaged by U. macolai significantly reduced subsequent U. macolai performance on receivers, but these effects were indistinguishable for communication within vs. among genotypes. In contrast, we found sex specificity of communication; male emitter plants reduced subsequent U. macolai performance on male and female receiver plants equally, while female emitter plants only did so for female receivers. We found sexual (but not genotypic) dimorphism in speaking but not listening; of the seven compounds induced by U. macolai feeding (speaking), pinocarvone was approximately fivefold greater in female than in male plants, while exposure of plants to pinocarvone emissions (listening) reduced U. macolai performance equally in both male and female plants. Together, our study demonstrates novel evidence for sexually dimorphic specificity of plant-plant communication and the chemical mechanism underlying this effect.

Intraspecific plant trait variation can have cascading effects on plant-associated biotic communities. Sexual dimorphism is an important axis of genetic variation in dioecious plants, but the strength of such effects and the underlying mechanisms relative to genetic variation are unknown. We established a common garden with 39 genotypes of Baccharis salicifolia sampled from a single population that included male and female genotypes and measured plant traits and quantified associated arthropod communities. Genetic variation sensu lato (genotypic variation) had strong effects on most plant traits (flower number, relative growth rate, specific leaf area, percent water content, carbon-nitrogen ratio, monoterpene but not sesquiterpene concentrations) and on herbivore and predator density, and on arthropod community composition (relative abundance of 14 orders). In contrast, sexual dimorphism had weaker effects on only a few plant traits (flower number and relative growth rate), on predator density, and on arthropod community composition, but had no effect on herbivore density. Variation in flower number drove genetic variation sensu lato and sex dimorphism in predator density and arthropod community composition. There was unique genetic variation sensu lato in herbivore density (positively) associated with monoterpene concentration and in arthropod community composition associated with specific leaf area and carbon-nitrogen ratio. There was unique sexual dimorphism in arthropod community composition associated with plant relative growth rate. Together, these results demonstrate that genetic variation sensu lato and sexual dimorphism can shape plant-associated arthropod communities via both parallel and unique mechanisms, with greater overall effects of the former.

Summary Geographic variation in abiotic factors and species interactions is widespread and is hypothesized to generate concomitant patterns of species trait variation. For example, higher rates of herbivory at lower latitudes are thought to select for increased plant defences, although latitudinal variation in defences may also be influenced directly by abiotic factors and indirectly by predators and parasitoids reducing herbivore pressure. We measured defences of the herb Ruellia nudiflora among 30 populations spanning a latitudinal gradient from northern Yucatan to southern Belize that vary substantially in leaf herbivory (fourfold), seed herbivory (25-fold) and seed herbivore parasitism (14-fold). These surveyed populations span one-third of the species’ latitudinal distribution (5° of latitude), the entire precipitation gradient of its distribution, and one-third of the temperature gradient of its distribution. Our prior work showed that leaf herbivory decreased with latitude and that seed herbivory increased with latitude. Here, we measured leaf trichome density and leaf and seed phenolics and tested whether latitudinal variation in climate, herbivory and parasitism explained latitudinal variation in these defensive traits. Patterns of variation in leaf trichomes fully supported predictions, with trichome density increasing with a parallel increase in herbivory towards lower latitudes. While seed phenolics were positively associated with herbivory, and seed herbivory tended to increase with latitude, the predicted (positive) association between latitude and defence was not detectable. There was no detectable association between parasitoids and seed defences. In addition, the association between leaf herbivory and phenolics was weak, and leaf phenolics were not associated with latitude. Importantly, variation in the abiotic environment was associated with plant defence, indicating that abiotic factors can play a major role in shaping plant defences, independently of herbivory. Synthesis. Latitudinal variation in abiotic factors may drive concomitant patterns of variation in plant defences, independently of herbivory. Collectively, these findings highlight the need for assessing geographic variation in plant defences from a multi-factorial perspective, testing for the simultaneous influence of biotic and abiotic factors.

The effects of tree diversity on herbivore-enemy interactions have received relatively little attention and even fewer studies have compared the relative influence of tree intra- versus interspecific diversity on such dynamics. 2 We evaluated the effects of mahogany ( Swietenia macrophylla) genotypic diversity and tree species diversity on parasitoid attack and species richness associated with Phyllocnistis meliacella, a specialist herbivore on mahogany, in a forest diversity experiment consisting of 74 plots (21 × 21 m 2 ; 64 plants/plot). We sampled 34 of such plots classified as: mahogany monocultures of one maternal family (i.e. genotype), mahogany monocultures of four families and polycultures of four species (including mahogany). We surveyed leafminer abundance and collected mined leaves to estimate parasitism and parasitoid species richness. 3 Leafminer abundance was not influenced by either type of diversity. Similarly, there were no effects of genotypic diversity or species diversity on parasitism or parasitoid species richness. Plant diversity effects on parasitoids were probably absent because the species attackingP. meliacella are dietary generalists that likely recruited to multiple host species (in addition to P. meliacella) and their responses to diversity could have cancelled each other out. 4 Future work should explicitly investigate how predator and parasitoid traits mediate the effects of plant diversity on tritrophic interactions.

The abiotic environment drives species abundances and distributions both directly and indirectly through effects on multi-trophic species interactions. However, few studies have documented the individual and combined consequences of these direct and indirect effects. We studied an ant-tended aphid along an elevational gradient, where lower elevations were more arid. Hypotheses of stronger species interactions at lower elevations and a greater sensitivity of higher trophic levels to climate led us to predict increased top-down control of aphids by natural enemies (third trophic level) but even stronger protection from mutualist ants (fourth trophic level) with increasing aridity. As a result, we predicted that mutualism strength and aphid abundance would increase with aridity. We documented patterns of aphid abundance and tested for both the direct and multi-trophic indirect effects of aridity on aphid performance. To do so, we used both observational and manipulative methods across two years in replicate high- and low-elevation valleys, where summer temperatures decreased by 3.7°C and precipitation increased by 27 mm/mo from low to high elevations. Aphid colonies were 75% larger in the most (vs. least) arid sites, and this was best explained by changes in interactions with predators and ants. Aphids were unaffected by the direct effects of the abiotic environment or its indirect effects via host plant quality. In contrast, natural enemy effects increased with aridity; under ant exclusion, natural enemies had no effect on aphids in the least arid sites but depressed colony growth by 252% in the most arid sites. Ant activity also increased with aridity, with ants discovering more aphid colonies and experimental baits and allocating more foragers per aphid, although there was no effect of aridity on ant abundance or community composition. Correspondingly, the mutualist services provided by ants increased with aridity; ants provided no benefits to aphids in the least arid sites but doubled colony growth in the most arid sites. In summary, an elevational cline in herbivore abundance was driven by a monotonic increase in trophic-level sensitivity to aridity. These findings illustrate that predicting species responses to climate change will require a multi-trophic perspective.

8 páginas, 1 figura y 1 tabla., While plant intra-specific variation in the stoichiometry of nutrients and carbon is well documented, clines for such traits have been less studied, despite their potential to reveal the mechanisms underlying such variation. Here we analyze latitudinal variation in the concentration of leaf nitrogen (N), phosphorus (P), carbon (C) and their ratios across 30 populations of the perennial herb Ruellia nudiflora. In addition, we further determined whether climatic and soil variables underlie any such latitudinal clines in leaf traits. The sampled transect spanned 5° latitude (ca. 900 km) and exhibited a four-fold precipitation gradient and 2 °C variation in mean annual temperature. We found that leaf P concentration increased with precipitation towards lower latitudes, whereas N and C did not exhibit latitudinal clines. In addition, N:P and C:P decreased towards lower latitudes and latitudinal variation in the former was weakly associated with soil conditions (clay content and cation exchange capacity); C:N did not exhibit a latitudinal gradient. Overall, these results emphasize the importance of addressing and disentangling the simultaneous effects of abiotic factors associated with intra-specific clines in plant stoichiometric traits, and highlight the previously underappreciated influence of abiotic factors on plant nutrients operating under sharp abiotic gradients over smaller spatial scales., This research was supported by a UC MEXUS-CONACyT collaborative grant (UCM-55592) to LAR, XM, KAM and VPT, a UC MEXUS grant for UC postdocs (UCM-101443), the Ramón y Cajal Research Program (RYC-2013-13230, a grant from the Regional Government of Galicia (IN607D 2016/001), and a Spanish National Research Grant (AGL2015-70748-R) to XM, as well as a grant from the i-COOP+ CSIC program (COOPB20158) to XM and LAR. LAR was also supported by the CONACyT Repatriation Program (#250934).

Supplementary figures S1-S3 and bird functional traits in table S1.

Oikos 000: 001–009, 2015 doi: 10.1111/oik.02033 © 2015 Th e Authors. Oikos © 2015 Nordic Society Oikos Subject Editor: Martijn Bezemer. Editor-in-Chief: Dries Bonte. Accepted 13 January 2015 Comparison of tree genotypic diversity and species diversity effects on different guilds of insect herbivores Luis Abdala-Roberts , Kailen A. Mooney , Teresa Quijano-Medina , Mar i a Jos e Campos-Navarrete , Alejandra Gonz a lez-Moreno and V i ctor Parra-Tabla L. Abdala-Roberts (labdala@uci.edu) and K. A. Mooney, Dept of Ecology and Evolutionary Biology, Univ. of California, Irvine, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA. – LAR, M. J. Campos-Navarrete and V. Parra-Tabla, Depto de Ecolog i a Tropical, Campus de Ciencias Biol o gicas y Agropecuarias, Univ. Aut o noma de Yucat a n, Apartado Postal 4-116, Itzimn a , MX-97000 M e rida, Yucat a n, M e xico. – T. Quijano-Medina, Wageningen Univ., Droevendaalsesteeg 2, NL-6708 PB Wageningen, the Netherlands. – A. Gonz a lez-Moreno, Inst. Tecnol o gico de Conkal, Km. 16.3 Antigua Carretera M e rida-Motul, MX-97345 Conkal, Yucat a n, M e xico. Although the eff ects of plant diversity on herbivores are contingent upon herbivore traits and the source of plant diversity (e.g. intra- and interspecifi c), most studies have analyzed these eff ects separately. We compared the eff ects of genotypic diversity of big-leaf mahogany Swietenia macrophylla with that of tree species diversity on two specialist caterpillars (Hypsipyla grandella stem borers and Phyllocnistis meliacella leaf miners) and three generalist leafhoppers (Cicadellidae) feeding on mahogany in a large-scale (7.2 ha) forest diversity experiment in southern Mexico. Th e experiment consisted of fi fty-nine 21 ! 21-m plots, with 64 tree saplings each (3-m spacing between plants). Plots were either mahogany monocul- tures or species polycultures of four species (including mahogany) and – within each of these two plot types – mahogany was represented by either one or four genotypes. Th roughout a fi ve-month period, beginning six months after planting, we measured mahogany growth and monitored herbivore and predator (spider) abundance. We found no eff ect of mahogany genotypic diversity on either specialist caterpillars or generalist leafhoppers, and this result was consistent across levels of tree species diversity. In contrast, species diversity had signifi cant eff ects on both specialists but neither of the generalist herbivores. Specifi cally, species diversity lowered H. grandella attack at the middle of the sampling season, but increased attack at the end of the season, whereas P. meliacella abundance was consistently reduced. Such eff ects were not mediated by eff ects of species diversity on plant growth (of which there were none), but rather through resource heterogeneity. Diversity did not infl uence spider abundance. Th is study is one of few to directly compare sources of plant diversity, and uniquely compares such eff ects among herbivores with contrasting life histories (e.g. diet breadths). Overall, we demonstrate that plant species diversity eff ects outweigh those of genotypes, and our results suggest that such eff ects are stronger on specialist than generalist herbivores. Evidence has mounted for the eff ects of intra- (reviewed by Bailey et al. 2009) and inter-specifi c (Siemann 1998, Haddad et al. 2009) plant diversity on higher trophic levels. Numerous studies have found eff ects of plant diversity on arthropod species richness and abundance (Koricheva et al. 2000, Crutsinger et al. 2006, Haddad et al. 2009) and on consumptive interactions at higher trophic levels (Moreira and Mooney 2013, Abdala-Roberts and Mooney 2014), with the basis of such eff ects being variation in ecologically important traits among plant species or genotypes within species (Hare 2002, Mooney and Singer 2012). Within this context, a widely documented pattern is that greater plant diversity frequently leads to reductions in herbivory (reviewed by Andow 1991, Barbosa et al. 2009). Two hypotheses have been off ered to explain this phenomenon and invoke the infl u- ence of resource heterogeneity on consumers. According to the ‘ enemies hypothesis ’ (hereafter EH; Root 1973), greater habitat complexity at high plant diversity favors increased predator recruitment (e.g. because of greater availability of shelters or prey) resulting in stronger top – down suppression of herbivore populations and thus lower herbivory (reviewed by Russell 1989). Alternatively, the ‘ resource concentra- tion hypothesis ’ (RCH) (Root 1973) holds that herbivore foraging is density-dependent and increasing plant species diversity at a constant plant density reduces the probabil- ity of fi nding a preferred host plant, which lowers herbivore recruitment and damage on individual plants. While both hypotheses have received considerable attention, evi- dence from natural systems has generated mixed support (Bommarco and Banks 2003, Underwood et al. 2014). Th e inconsistent support for the EH and RCH could be due to unaccounted variation in herbivores traits (Vehvil a inen et al. 2007, Plath et al. 2012). For example, the dynamics predicted by the EH should be more likely to occur for generalist herbivores because they are more sus- ceptible to natural enemies as they frequently lack defense mechanisms found in specialists (e.g. crypsis, sequestration of plant toxic compounds; Mooney et al. 2012, Singer et al. EV-1

9 páginas.-- 4 figuras.-- 2 tablas.-- 44 referencias, The predator satiation hypothesis poses that synchronous and variable seed production during masting events increases seed escape through seed predator satiation. The success of this strategy depends upon the type of consumer functional response, in this case defined as the change in seed consumption rate by a predator as a function of change in seed density. Type II (where the proportion of seed consumed is highest at low levels of seed availability) and type III (where the proportion of seed consumed is highest at some intermediate level of seed availability and then declines towards zero) functional responses describe negative density-dependence and indicate predator satiation. The type of function response should be contingent upon herbivore traits: type II responses are predicted for dietary specialist predators with low mobility, and type III responses are predicted for highly mobile, dietary generalist predators. Surprisingly, most studies have not evaluated whether functional responses vary among seed predator guilds. Here we describe the functional responses at population and individual tree level of highly mobile generalist (birds and rodents) and less mobile specialist (insects) pre-dispersal seed predators attacking acorns of two sympatric oaks (Quercus suber and Q. canariensis) over a 10-year period. Our results showed that in most cases specialist seed predators exhibited the predicted type II functional response at both the individual tree and population level for both oak species. However, generalist seed predators did not exhibit the predicted type III response; instead, they also exhibited a type II response at the individual tree and population level for both oak species. By independently assessing the effects of multiple seed predators associated with the same host tree species, our work highlights the influence of herbivore traits on the outcome of plant–seed predator interactions in masting species, and thus furthers our understanding of the ecological and evolutionary mechanisms underlying masting behaviour., This study was supported by the Ramón y Cajal Research Programme to XM (RYC-2013-13230) and to IMPR (RYC-2013- 13937), by a grant from the Regional Government of Galicia (IN607D 2016/001) to XM, by a Spanish National Research Grant (AGL2015-70748-R) to XM, by the CONACyT Repatriation Programme (no. 250934) to LAR, by the Spanish MEC projects Heteromed (REN2002-4041-C02-02), Dinamed (CGL2005-5830-C03-01) and Interbos (CGL2008-04503-C03-01), and by the Andalusian Anasinque-PE2010-RNM-5782 project. Statement of authorship – XM and IMPR contributed equally to this paper and share the first authorship

A plant's performance and interactions with other trophic levels are recorgnized to be contingent upon plant diversity and underlying associational dynamics, but far less is known about the plant traits driving such phenomena. We manipulated diversity in plant traits using pairs of plant and a substitutive design to elucidate the mechanisms underlying diversity effects operating at a fine spatial scale. Specifically, we measured the effects of diversity in sex (sexual monocultures vs. male and female genotypes together) and growth rate (growth rate monocultures vs. fast- and slow-growing genotypes together) on growth of the shrub Baccharis salicifolia and on above- and belowground consumers associated with this plant. We compared effects on associate abundance (# associates per plant) vs. density (# associates per kg plant biomass) to elucidate the mechanisms underlying diversity effects; effects on abundance but not density suggest diversity effects are mediated by resource abundance (i.e. plant biomass) alone, whereas effects on density suggest diversity effects are mediated by plant-based heterogeneity or quality. Sexual diversity increased root growth but reduced the density (but not abundance) of the dietary generalist aphid Aphis gossypii and its associated aphid-tending ants, suggesting sex mixtures were of lower quality to this herbivore (e.g. via reduced plant quality), and that this effect indirectly influenced ants. Sexual diversity had no effect on the abundance or density of parasitoids attacking A. gossypii, the dietary specialist aphid Uroleucon macolai, or mycorrhizae. In contrast, growth rate diversity did not influence plant growth or any associates except for the dietary specialist aphid U. macolai, which increased in both abundance and density at high diversity, suggesting growth rate mixtures were of higher quality to this herbivore. These results highlight that plant associational and diversity effects on consumers are contingent upon the source of plant trait variation, and that the nature of such dynamics may vary both within and among trophic levels.

The mechanisms by which plant diversity influences consumers are largely unexplored. Plant diversity reduces among-plant competition, and as a result, may have cascading bottom-up effects through altered resource quantity and quality. Less understood are parallel effects of resource heterogeneity on consumer foraging behaviors, and the consequences of such effects for trophic interactions and feedbacks on plant performance. Here, we asked whether genotypic diversity in the herb Ruellia nudiflora influences seed predator (SP) and parasitoid functional responses, and if such effects in turn influence selection on the plant. We established plots with plants of one or five genetic families (pool = 14) and measured fruit, seed predator, and parasitoid abundance. By eliminating direct plant–plant interactions, this experiment explicitly tested for plant diversity effects occurring through altered consumer behaviors (vs. effects through changes in plant quantity or quality). We compared observed plant fitness (under three trophic levels) to projected fitness in the absence of parasitoids (two trophic levels) and in the absence of seed predation (one trophic level) by computing the number of seeds consumed by the SP and the number of seeds rescued from consumption by parasitoids. We then compared the strength and mode of selection on fruit number between levels of diversity, separately under each trophic scenario. Plant diversity did not influence fruit, seed predator, or parasitoid abundance, but did alter plant–SP interactions. SP recruitment resembled a Type II functional response but saturated weakly in polycultures, with fewer SPs at intermediate fruit abundance and more SPs at high fruit abundance relative to monoculture. Parasitoid recruitment was weakly positively density dependent and unaffected by diversity. Importantly, we found that under the bi-trophic scenario, the effect of diversity on SP recruitment altered the mode of selection on fruit number, from directional selection at low diversity to nonlinear (stabilizing) selection at high diversity. In contrast, diversity did not alter selection under mono- or tri-trophic scenarios. Therefore, diversity effects on SP functional responses fed back to alter selection on fruit number, but parasitoids eliminated this linkage by weakening herbivore selection. Collectively, these findings provide novel evidence for the mechanistic basis of eco-evolutionary feedbacks between plant diversity and consumers.

The magnitude of plant intra-specific variation for indirect defence and the underlying plant traits influencing predators remain relatively unstudied, particularly in cultivated plants. 2. We tested whether differences in flower number, pollen production, and leaf trichome density among 17 pepper ( Capsicum annuum Linnaeus) varieties influenced the abundance and predation intensity by the omnivorous mite Amblyseius swirskii Athias-Henriot. 3. A greenhouse experiment was conducted where pepper plants were infested with thrips (Frankliniella cephalica Crawford DL) and subsequently exposed to A. swirskii. We estimated thrips and mite density based on arthropod counts conducted over a 4-week period, and also performed flower and trichome counts, and estimated pollen production per anther. 4. Significant differences were found among varieties for all three traits, as well as mite and thrips density. After accounting for all traits in a multiple regression model, we found that flower and trichome number had significant positive effects on mite density (by providing food and shelter, respectively). Increased mite density was in turn associated with a decrease in thrips density, presumably as a result of mite predation. Moreover, we found that flower number (but not trichome density) increased the strength of thrips suppression and that such an effect was mediated by mite density. 5. These findings suggest that genetic variation for plant traits may indirectly influence herbivore suppression in peppers (although traits may vary in the strength or direction of their effects), and underscore the evolutionary potential and importance of selection not only for direct but also indirect resistance in crops.

Steep climatic gradients may select for clinal adaptation in plant functional traits with implications for interspecifi c interactions and response to future climate change. Terpenes are common in Mediterranean environments and mediate plant interactions with both the abiotic and biotic environment, including herbivores. Clines in traits such as terpenes have received much attention because they are linked to plant fi tness and experience strong selection from the abiotic and biotic environment. In this study, we tested for intraspecifi c variation in Artemisia californica terpene chemistry in a common garden of plants sourced from populations spanning a large precipitation gradient (6 ° latitude) and grown in treatments of high and low precipitation. We found genetic variation in terpene richness, diversity, concentration and composition among A. californica populations spanning this species ’ range. Of these traits, terpene composition and monoterpene concentration varied clinally with respect to source site latitude. Regarding terpene composition, pairwise dissimilarity among populations increased in parallel with geographic distance between source sites. At the same time, monoterpene concentration decreased monotonically from plants of southern origin (source sites with high temperature, aridity, and precipitation variability) to plants of northern origin. Our precipitation manipulation suggests that phenotypic selection by precipitation may underlie this clinal variation in monoterpene concentration, and that monoterpene concentration and other aspects of terpene chemistry are not phenotypically plastic. In summary, this study provides novel evidence for a genetically based latitudinal cline in plant secondary chemistry and suggests that adaptation to a key aspect of the abiotic environment may contribute to this intraspecifi c variation. Accordingly, changes in terpene chemistry under projected future climates will likely occur solely through the relatively slow process of adaptation, with important consequences for plant interactions with the abiotic environment and a diverse community of associates.

Copyright by the Ecological Society of America, Masting is a reproductive strategy defined as the intermittent and synchronized production of large seed crops by a plant population. The pollination efficiency hypothesis proposes that masting increases pollination success in plants. Despite its general appeal, no previous studies have used long-term data together with population- and individual-level analyses to assess pollination efficiency between mast and non-mast events. Here we rigorously tested the pollination efficiency hypothesis in ponderosa pine (Pinus ponderosa), a long-lived monoecious, wind-pollinated species, using a data set on 217 trees monitored annually for 20 years. Relative investment in male and female function by individual trees did not vary between mast and non-mast years. At both the population and individual level, the rate of production of mature female cones relative to male strobili production was higher in mast than non-mast years, consistent with the predicted benefit of reproductive synchrony on reproductive success. In addition, at the individual level we found a higher conversion of unfertilized female conelets into mature female cones during a mast year compared to a non-mast year. Collectively, parallel results at the population and individual tree level provide robust evidence for the ecological, and potentially also evolutionary, benefits of masting through increased pollination efficiency., This research was supported by National Foundation Science grants BMS 75-14050, DEB 78-16798, BSR 8918478, and BSR 912065 to Y. B. Linhart and DEB 1120794 to K. A. Mooney. X. Moreira received financial support from Postdoctoral Fulbright/Spanish Ministry of Education grant program. L. Abdala-Roberts was funded by a GAANN fellowship and a UCMEXUS-CONACyT scholar- ship.

There is increasing evidence that geographic and climatic clines drive the patterns of plant defence allocation and defensive strategies. We quantified early growth rate and both constitutive and inducible chemical defences of 18 Pinaceae species in a common greenhouse environment and assessed their defensive allocation with respect to each species' range across climatic gradients spanning 31o latitude and 2300 m elevation. Constitutive defences traded-off with induced defences, and these defensive strategies were associated with growth rate such that slow-growing species invested more in constitutive defence, whereas fast-growing species invested more in inducible defence. The position of each pine species along this trade-off axis was in turn associated with geography; moving poleward and to higher elevations, growth rate and inducible defences decreased, while constitutive defence increased. These geographic patterns in plant defence were most strongly associated with variation in temperature. Climatic and geographical clines thus act as drivers of defence profiles by mediating the constraints imposed by trade-offs, and this dynamic underlays global patterns of defence allocation., Research was partially founded by the Spanish Ministry of Science and Innovation, projects Consolider-Ingenio MONTES (CSD2008-00040), COMPROPIN (AGL2010-18724) and CSIC (project 200840I153). XM was supported by a Postdoctoral Fulbright/Spanish Ministry of Education fellowship. WKP was supported by a National Science Foundation Graduate Research Fellowship., Ministerio de Ciencia e Innovación (España), Consejo Superior de Investigaciones Científicas (España), Ministerio de Educación y Ciencia (España), National Science Foundation

While invasive plants are widely studied for their effects on native plants, we questioned how plant invasions affect higher trophic levels. We investigated the effects of the invasive plant, Brassica nigra on the multi-trophic arthropod community residing on the native California annual Deinandra fasciculata. In a common garden experiment, we planted D. fasciculata without B. nigra or with one of 45 B. nigra half-sib genetic families. We in turn crossed this B. nigra treatment with the suppression of soil fungi to both test for effects of arbuscular mycorrhizal fungi (AMF) on arthropods, and elucidate the mechanisms of B. nigra’s below ground effects. B. nigra had no effect on D. fasciculata traits (biomass, inflorescence number, root colonization by AMF), arthropod community composition or predator density, but increased herbivore density. While B. nigra families varied 18-fold in size, there was no genetic variation for effects on D. fasciculata or its arthropods. Soil fungi suppression had no effect on D. fasciculata traits, herbivore density or herbivore community composition, but increased predator density and altered predator community composition. While the exact mechanisms of B. nigra effects are unclear, they do not appear to have been mediated by altered plant performance or reductions in root colonization by AMF. Our experiment shows that invasive plants such as B. nigra may affect higher trophic levels even when they do not measurably affect native plant performance.

Local adaptation and plasticity pose significant obstacles to predicting plant responses to future climates. Although local adaptation and plasticity in plant functional traits have been documented for many species, less is known about population-level variation in plasticity and whether such variation is driven by adaptation to environmental variation. We examined clinal variation in traits and performance - and plastic responses to environmental change - for the shrub Artemisia californica along a 700 km gradient characterized (from south to north) by a fourfold increase in precipitation and a 61% decrease in interannual precipitation variation. Plants cloned from five populations along this gradient were grown for 3 years in treatments approximating the precipitation regimes of the north and south range margins. Most traits varying among populations did so clinally; northern populations (vs. southern) had higher water-use efficiencies and lower growth rates, C : N ratios and terpene concentrations. Notably, there was variation in plasticity for plant performance that was strongly correlated with source site interannual precipitation variability. The high-precipitation treatment (vs. low) increased growth and flower production more for plants from southern populations (181% and 279%, respectively) than northern populations (47% and 20%, respectively). Overall, precipitation variability at population source sites predicted 86% and 99% of variation in plasticity in growth and flowering, respectively. These striking, clinal patterns in plant traits and plasticity are indicative of adaptation to both the mean and variability of environmental conditions. Furthermore, our analysis of long-term coastal climate data in turn indicates an increase in interannual precipitation variation consistent with most global change models and, unexpectedly, this increased variation is especially pronounced at historically stable, northern sites. Our findings demonstrate the critical need to integrate fundamental evolutionary processes into global change models, as contemporary patterns of adaptation to environmental clines will mediate future plant responses to projected climate change.

The limiting similarity hypothesis predicts that communities should be more resistant to invasion by non-natives when they include natives with a diversity of traits from more than one functional group. In restoration, planting natives with a diversity of traits may result in competition between natives of different functional groups and may influence the efficacy of different seeding and maintenance methods, potentially impacting native establishment. We compare initial establishment and first-year performance of natives and the effectiveness of maintenance techniques in uniform versus mixed functional group plantings. We seeded ruderal herbaceous natives, longer-lived shrubby natives, or a mixture of the two functional groups using drill- and hand-seeding methods. Non-natives were left undisturbed, removed by hand-weeding and mowing, or treated with herbicide to test maintenance methods in a factorial design. Native functional groups had highest establishment, growth, and reproduction when planted alone, and hand-seeding resulted in more natives as well as more of the most common invasive, Brassica nigra. Wick herbicide removed more non-natives and resulted in greater reproduction of natives, while hand-weeding and mowing increased native density. Our results point to the importance of considering competition among native functional groups as well as between natives and invasives in restoration. Interactions among functional groups, seeding methods, and maintenance techniques indicate restoration will be easier to implement when natives with different traits are planted separately.