Effects Of Herbivory Research Articles

Nectar traits and their responses to herbivory in Solidago altissima as a dominant introduced flowering herb in Japan

AbstractThis study investigates the nectar characteristics of the tall goldenrod (Solidago altissima L.), an introduced dominant fall‐flowering herb in Japan. We found that the nectar volume of S. altissima peaked at approximately 13:00 before decreasing. Glucose and fructose were identified as the primary sugar components, followed by sucrose. The average sugar amount per panicle of naturally growing plants was estimated as 229.0 mg. Herbivory by the exotic lacebug (Corythucha marmorata) reduced the nectar volume per floret but did not affect the total sugar amount per floret. However, the sugar amount per panicle decreased substantially because C. marmorata reduced both the number of disc florets (i.e., nectar‐secreting florets) per head and the number of heads per panicle. Plant genotypes also influenced some nectar traits, interacting with the effects of herbivory. As the distribution of C. marmorata continues to expand across Japan, the nectar resources provided by S. altissima may be diminishing nationwide.

Leaf traits and insect herbivory levels in two Mediterranean oaks and their hybrids through contrasting environmental gradients.

Insect herbivory has attracted enormous attention from researchers due to its effects on plant fitness. However, there remain questions such as what are the most important leaf traits that determine consumption levels, whether there are latitudinal gradients in herbivore pressure, or whether there are differences in susceptibility between hybrids and their parental species. In this work we address all these issues in two species of Mediterranean Quercus (Q. faginea and Q. pyrenaica) and their hybrids. Over two years, we analyzed leaf emergence and 11 leaf traits (biomechanical, chemical and morphological), as well as the levels of herbivory by insects in leaves of the three genetic groups in different locations distributed along a climatic gradient. The hybrids showed intermediate values ​​between both species in leaf emergence, chemical traits and in structural reinforcement. By contrast, they were more similar to Q. faginea in leaf size and shape. Despite their intermediate leaf traits, hybrids always showed lower losses by consumption than both parental species, which suggests that they possess inherent higher resistance to herbivores, which cannot be explained by their dissimilarities in leaf traits. Within each genetic group, differences in leaf size were the most important determinant of differences in herbivory losses, which increased with leaf size. In turn, leaf size increased significantly with the increase in mean annual temperatures across the climatic gradient, in parallel with herbivory losses. In conclusion, contrary to our expectations, hybrids maintained lower levels of herbivory than their parent species. Given the potential negative effect of leaf herbivory on C fixation, this advantage of the hybrids would imply a threat to the persistence of both pure species. More research is needed to elucidate possible alternative mechanisms that allow maintaining species integrity in the absence of reproductive barriers.

Impact of Insect Foliar Herbivory on Soil N₂O Emission and Nitrogen Dynamics in Subtropical Tree Species

Insect foliar herbivory is ubiquitous in terrestrial ecosystems, yet its impacts on soil nitrogen cycling processes remain not yet well known. To examine the impacts of insect foliar herbivory on soil N2O emission flux and available nitrogen (N), we conducted a pot experiment to measure soil available N content and soil N2O emission flux among three treatments (i.e., leaf herbivory, artificial defoliation, and control,) in two broad-leaved trees (Cinnamomum camphora and Liquidambar formosana) and two conifer trees (Pinus massonianna and Cryptomeria fortunei). Our results showed that insect foliar herbivory significantly increased soil inorganic N (i.e., NH4+–N and NO3−–N), dissolved organic nitrogen (DON) and microbial biomass nitrogen (MBN) contents, and urease activity compared to control treatment. However, there were no differences in soil available N contents and urease activity between artificial defoliation and control treatments, implying that insect foliar herbivory had greater impacts on soil available N contents compared to physical damage of leaves. Moreover, soil N2O emission fluxes were increased by insect foliar herbivory in Cinnamomum camphora and Pinus massonianna, but not for the other two tree species, indicating various effect of insect foliar herbivory on soil N2O emission among tree species. Furthermore, our results showed the positive correlations between soil N2O emission flux and soil NO3−–N, DON, MBN, and acid protease activity, and soil inorganic N, pH, and MBN mainly explained soil N2O emission. Our results implied that insect foliar herbivory can speed up soil nitrogen availability in subtropical forests, but the impacts on soil N2O emission are related to tree species.

Herbivory and allelopathy contribute jointly to the diversity-invasibility relationship.

Although herbivory and allelopathy play important roles in plant invasions, their roles in mediating the effect of plant diversity on invasion resistance remain unknown. In a 2-year field experiment, we constructed native plant communities with four levels of species richness (one, two, four, and eight species) and used a factorial combination of insecticide and activated carbon applications to reduce herbivory and allelopathy, respectively. We then invaded the communities with the introduced plant Solidago canadensis L. One year after the start of the experiment, there was no statistically significant net effect of species richness on biomass of the invader. However, a structural equation model showed that species richness had a positive direct effect on invader biomass that was partially balanced out by a negative indirect effect of species richness via increased light interception. In the second year, the relationship between invader biomass and species richness was negative when we analyzed the treatment combination with herbivory and allelopathy separately. Therefore, we conclude that joint effects of herbivory and allelopathy may play major roles in driving the diversity-invasibility relationship and should be considered in future studies.

Effects of foliar herbivory on the vegetative and reproductive traits of Malpighiaceae from Cerrado: when the ontogeny of leaves and flowers matters

Effects of foliar herbivory on the vegetative and reproductive traits of Malpighiaceae from Cerrado: when the ontogeny of leaves and flowers matters

Interactive effects of rhizobia mutualism and herbivory on Vicia faba

ABSTRACT Background Species constantly interact with many organisms simultaneously, and multiple species interactions can have unique effects when combined and potentially cause resource and fitness trade-offs to the host. For example, extrafloral nectar can be an effective defence against herbivory, yet this nectar production can be influenced by abiotic and biotic environmental factors, including other mutualisms. Aims Here, we tested how traits associated with two different types of species interactions, herbivory and rhizobia-induced nodulation, may independently and interactively affect a host plant. Methods We manipulated the presence or absence of rhizobia at two different levels of herbivory in the field. We measured multiple plant growth traits and fitness responses, such as plant height, above- and below-ground biomass, total biomass, the ratio between above- and below-ground biomass, rhizobia nodule number, and average nodule size, extrafloral nectar volume, extrafloral nectar sugar concentration, as well as ant and arthropod visitation to explore the potential ant-plant mutualism. Results Rhizobia inoculation did not affect ant or other arthropod visitation but did alter plant traits associated with growth as well as decreased allocation to sugar concentration within extrafloral nectar. Extrafloral nectar volume remained nearly constant in nearly all treatments, except for a decrease when plants did not have rhizobia and were not subjected to herbivory. Finally, increased herbivory led to reduced nodule size but did not alter nodule number, indicating potential shifts in resource allocation. Conclusions Overall, multiple species interactions have compounding effects when combined, and plant traits alter differentially in response. In particular, we found a substantial benefit of rhizobia to the plants which did not result in either higher ant visitation or herbivory. However, greater herbivory did reduce plant growth, yet these effects varied depending on the presence or absence of rhizobia. This study demonstrates the importance of considering traits associated with multiple diverse species interactions simultaneously to better understand plant responses to environmental conditions.

Biennial Variation and Herbivory Affect Essential Oils of Ipomoea murucoides and Stomata Density of Neighbor Plants.

Essential oils (EOs) are mixtures of volatile organic compounds that mediate plant interactions and are also appreciated for their biological properties in aromatic plants. However, the study of EOs in wild plants with biological activity has been neglected. Ipomoea murucoides is a wild species with allelopathic and insecticide activities; however, the climate factors associated with EOs and their role in intra- and interspecific interactions are still unknown. We investigated the effects of temperature, rain, and solar irradiance for two years on the EOs of I. murucoides and documented the effect of herbivory (without, <20%, >20%, and mechanical damage) on their composition. We evaluated the receptivity to possible infochemicals in conspecific and congeneric neighbors to I. murucoides plants exposed to methyl jasmonate (MeJA), herbivory by Ogdoecosta biannularis and without an elicitor. We measured the stomatal density and aperture in the second leaf generation of the neighbor plants. The year and herbivory >20% affected the composition of EOs. Nerolidol could be a biological marker for herbivory. We concluded that herbivory and rain irregularity contribute to EOs changing. The response in the stomatal density in plants not consumed by I. pauciflora but near I. murucoides under MeJA or herbivory gives evidence of interspecific plant-plant communication.

Mammalian herbivory alters structure, composition and edaphic conditions of a grey‐dune community

AbstractQuestionMammalian herbivory affects the structure and composition of plant communities, soil characteristics and intraspecific leaf traits. Understanding the effects of this type of herbivory is particularly relevant in grey dunes, a priority habitat type of the European Union Habitats Directive.LocationSálvora island (NW Spain).MethodsVegetation surveys and sampling were carried out in a coastal grey‐dune community, comparing the structure and composition of plant communities and soil characteristics in plots with herbivory exclusion and plots with herbivore activity, in autumn and spring. Changes in the specific leaf area (SLA), C/N ratio, δ13C and δ15N of two main plant species were also analysed.ResultsThe differentiation between treatments was low in autumn, in contrast to spring results, which demonstrated seasonal variation in the plant community and herbivore behaviour. Spring results showed lower above‐ground dry mass in plots with herbivory due to defoliation, but greater richness and diversity, indicating that intermediate levels of disturbance reduced competition from dominant species. Herbivory treatments were different in terms of species composition, highlighting the positive effects of herbivory on the development of the threatened species Linaria arenaria. Soil temperature and moisture content were higher in herbivory plots because of the suppression of vegetation cover and the effect of trampling, respectively. No differences were detected in the chemical composition of the soil or the SLA, although the variability of these traits was greater in herbivory plots, indicating spatial heterogeneity generated by the activity of herbivores. No differences between treatments were obtained for % C and δ13C, whereas herbivory plots showed lower values of N content and δ15N as an adaptive response to herbivory pressure at the leaf and root level.ConclusionOur findings show that herbivory effects on plant communities vary by season — stronger in spring and weaker in autumn — emphasising the need for seasonal analysis and highlighting disturbance as a driver of spatial heterogeneity.

Response of Plant Phylogenetic Structure to Plateau Pika (Ochotona curzoniae) Disturbance on Alpine Meadow of Qinghai‐Tibetan Plateau

ABSTRACTPlant community construction is influenced by bottom‐up processes, such as environmental factors, and top‐down processes, such as herbivore disturbances. With climate change and overgrazing, the stability of plant community structure and function decreases, and more land at risk of degradation. However, the response of the plant community to interference from native herbivores under similar environmental conditions remains unclear. Plateau pika (Ochotona curzoniae) is an important small rodent inhabiting the alpine meadow of the Qinghai‐Tibetan Plateau, and its disturbance may accelerate the degradation of grassland ecosystems when its population experiences a burst. In this study, we investigated the plant communities, collected and analyzed the soil samples, to explore the effects of plateau pikas' disturbance intensity on species composition and phylogenetic structure of plant communities on the alpine meadow. We utilized the generalized additive model and structural equation model to explain and predict the response of plant phylogenetic structure and species competition to the disturbance of plateau pikas. Our results indicated that plateau pika disturbance altered the dominance of plant groups, increased species substitution, and facilitated coexistence among different species, and it affected deterministic processes, reduced interspecific competition intensity, and promoted the dispersion of phylogenetic structures. These findings suggested that plateau pika, as a small native herbivore, plays a significant role in fostering multi‐species plant communities. Therefore, it is essential to manage plateau pika disturbance intensity to maintain the stability of alpine meadow plant communities, as well as to influence the long‐term succession of grassland ecosystems. This study provides some new evidence for exploring the effects of native small herbivores on the changes in grassland plant communities.

Effects of multiple mammalian herbivores and climate on grassland-shrubland transitions in the Chihuahuan Desert.

The replacement of grasses by shrubs or bare ground (xerification) is a primary form of landscape change in drylands globally with consequences for ecosystem services. The potential for wild herbivores to trigger or reinforce shrubland states may be underappreciated, however, and comparative analyses across herbivore taxa are sparse. We sought to clarify the relative effects of domestic cattle, native rodents, native lagomorphs, and exotic African oryx (Oryx gazella) on a Chihuahuan Desert grassland undergoing shrub encroachment. We then asked whether drought periods, wet season precipitation, or interspecific grass-shrub competition modified herbivore effects to alter plant cover, species diversity, or community composition. We established a long-term experiment with hierarchical herbivore exclosure treatments and surveyed plant foliar cover over 25 years. Cover of honey mesquite (Prosopis glandulosa) proliferated, responding primarily to climate, and was unaffected by herbivore treatments. Surprisingly, cattle and African oryx exclusion had only marginal effects on perennial grass cover at their current densities. Native lagomorphs interacted with climate to limit perennial grass cover during wet periods. Native rodents strongly decreased plant diversity, decreased evenness, and altered community composition. Overall, we found no evidence of mammalian herbivores facilitating or inhibiting shrub encroachment, but native small mammals interacting with climate drove dynamics of herbaceous plant communities. Ongoing monitoring will determine whether increased perennial grass cover from exclusion of native lagomorphs and rodents slows the transition to a dense shrubland.

Unlocking agro-ecosystem sustainability: exploring the bottom-up effects of microbes, plants, and insect herbivores.

Agricultural ecosystem formation and evolution depend on interactions and communication between multiple organisms. Within this context, communication occurs between microbes, plants, and insects, often involving the release and perception of a wide range of chemical cues. Unraveling how this information is coded and interpreted is critical to expanding our understanding of how agricultural ecosystems function in terms of competition and cooperation. Investigations examining dual interactions (e.g. plant-microbe, insect-microbe, and insect-plant) have resolved some basic components of this communication. However, there is a need for systematically examining multitrophic interactions that occur simultaneously between microorganisms, insects, and plants. A more thorough understanding of these multitrophic interactions has been made possible by recent advancements in the study of such ecological interactions, which are based on a variety of contemporary technologies such as artificial intelligence sensors, multi-omics, metabarcoding, and others. Frequently, these developments have led to the discovery of startling examples of each member manipulating the other. Here, we review recent advances in the understanding of bottom-up chemical communication between microorganisms, plants, and insects, and their consequences. We discuss the components of these "chemo-languages" and how they modify outcomes of multi-species interactions across trophic levels. Further, we suggest prospects for translating the current basic understanding of multitrophic interactions into strategies that could be applied in agricultural ecosystems to increase food safety and security.

Long-term surveys of ungulates' effects on tree and shrub species in mountainous forests -outcomes and potential limits.

Ungulate herbivory might induce different effects on the diversity and growth of trees and shrubs. The density, distribution, and the species of ungulates as well as plant communities' composition and other factors determine whether ungulate herbivory promotes or limits plants' diversity and growth. The impacts of ungulates on woody plants are commonly surveyed with exclosure-control approaches. In practice, such surveys frequently only cover short periods of time, addressing immediate management needs. Long-term surveys, documenting lasting effects of ungulate herbivory, are highly needed, but still rare. However, the general transferability of outcomes of long-term surveys might be limited due to different disturbing factors. This study addresses two basic aspects of long-term monitoring in mountainous forests, based on a unique 30-year data set: (1) Possible long-term effects of herbivores on forest vegetation (e.g., species/structural diversity of woody plants) and (2) potential differences between short-term and long-term surveys in terms of height growth patterns. In our study, diversity of woody plant species showed great variability with no significant impact of ungulate herbivory. The presence of ungulates had a significantly negative effect on the vertical structural diversity and growth of trees. Due to the slower growth on control plots, it took trees longer to reach a 160 cm height-threshold with their terminal shoots than on exclosure plots. Our long-term control-exclosure data set indicated that long-term survey data indeed might differ from growth patterns represented by short-term surveys. This can be induced by several factors, like site-specific growth patterns of trees, occurrences of natural abiotic disturbances that influence the functional life of exclosures, and others.

Impacts of wild herbivores on soil seed banks are explained by precipitation conditions in protected areas across semi‐arid to arid regions

Abstract Protected areas form the backbone of global conservation efforts. Vegetation is the primary foundation for achieving conservation goals, and soil seed banks is a cryptic biodiversity reservoir for recruiting species that may not be represented in above‐ground vegetation. Unfortunately, unmanaged grazing by wild herbivores has led to vegetation degradation in semi‐arid to arid regions. However, experimental evidence on the long‐term impacts of wild herbivores on soil seed banks is largely lacking. Here, with the aim of examining how wild herbivores impact soil seed banks, we investigated the composition of the germinable seed banks in three protected areas (Yathong, Mungo and Boolcoomatta) along a semi‐arid to arid precipitation gradient in south‐eastern Australia. The density and species richness of the soil seed banks increased with increasing aridity, which indicated that the soil seed banks in arid regions is an important biodiversity reservoir. The effects of wild herbivores on soil seed density were strongly dependent on precipitation. Wild herbivores disrupted the soil seed banks at the most arid site but promoted the accumulation of seeds in the soil at the least arid site. Grazing was linked to an increase in the frequency of the seeds of introduced species and decrease in the frequency of the seeds of perennials. Synthesis and applications: Disruption of the soil seed banks by the grazing of wild herbivores could lead to the failure of post‐rain pulses of vegetation growth and hamper efforts to restore vegetation in protected areas. Therefore, suppressing wild herbivore numbers is a strategy that could enhance soil seed bank reserves and revegetation efforts in arid protected areas.

The primacy of density‐mediated indirect effects in a community of wolves, elk, and aspen

AbstractThe removal or addition of a predator in an ecosystem can trigger a trophic cascade, whereby the predator indirectly influences plants and/or abiotic processes via direct effects on its herbivore prey. A trophic cascade can operate through a density‐mediated indirect effect (DMIE), where the predator reduces herbivore density via predation, and/or through a trait‐mediated indirect effect (TMIE), where the predator induces an herbivore trait response that modifies the herbivore's effect on plants. Manipulative experiments suggest that TMIEs are an equivalent or more important driver of trophic cascades than are DMIEs. Whether this applies generally in nature is uncertain because few studies have directly compared the magnitudes of TMIEs and DMIEs on natural unmanipulated field patterns. A TMIE is often invoked to explain the textbook trophic cascade involving wolves (Canis lupus), elk (Cervus canadensis), and aspen (Populus tremuloides) in northern Yellowstone National Park. This hypothesis posits that wolves indirectly increase recruitment of young aspen into the overstory primarily through reduced elk browsing in response to spatial variation in wolf predation risk rather than through reduced elk population density. To test this hypothesis, we compared the effects of spatiotemporal variation in wolf predation risk and temporal variation in elk population density on unmanipulated patterns of browsing and recruitment of young aspen across 113 aspen stands over a 21‐year period (1999–2019) in northern Yellowstone National Park. Only 2 of 10 indices of wolf predation risk had statistically meaningful effects on browsing and recruitment of young aspen, and these effects were 8–28 times weaker than the effect of elk density. To the extent that temporal variation in elk density was attributable to wolf predation, our results suggest that the wolf–elk–aspen trophic cascade was primarily density‐mediated rather than trait‐mediated. This aligns with the alternative hypothesis that wolves and other actively hunting predators with broad habitat domains cause DMIEs to dominate whenever prey, such as elk, also have a broad habitat domain. For at least this type of predator–prey community, our study suggests that risk‐induced trait responses can be abstracted or ignored while still achieving an accurate understanding of trophic cascades.

Assessing climatic conditions and biotic interactions shaping the success of Cystoseira foeniculacea early-life stages.

Early-life stages of canopy-forming macroalgae are critical for the maintenance of natural populations and the success of restoration actions. Unfortunately, the abiotic conditions and biotic interactions shaping the success of these stages have received less attention than the interactions shaping the success of adults. Here, we combined field and mesocosm experiments to explore the effects of temperature, herbivory, and canopy presence on the development of early-life stages of the brown seaweed Cystoseira foeniculacea. We assessed these effects by examining changes in recruit density and size. After recruiting zygotes under laboratory conditions, we conducted one laboratory and three field experiments. In the first field experiment, the density of recruits decreased over time in all rockpools and was negatively affected by rising temperatures and turf cover. Additionally, a marine heatwave (MHW; 11 days >25°C) was recorded in the donor pools, producing strong decay in the density of transplanted recruits and a significant reduction of the mature canopy. The second field experiment tested the survival of recruits based on their positioning within the canopy. We observed a higher density of recruits when placed at the edge or outside the canopy compared to recruits placed under the canopy. In the third field experiment, an herbivory-exclusion experiment, we show how density of recruits decreased in less than 48 h in noncaged treatments. In the laboratory, we conducted a thermotolerance experiment under controlled conditions, exposing the recruits to 19, 22, 25, 28, and 31°C for 7 weeks to assess thermal impacts on their survival and growth. Temperatures above the 25°C threshold reduced the density and size of the recruits. This study sheds light on the performance of the early-life stages of a Cystoseira spp. in Macaronesia, showing a low survival ratio against the current pressures even in the context of the potential refuge provided by the intertidal rockpools.

Contrasting responses of an invasive plant to herbivory of native and introduced insects

BackgroundInteractions between alien plants and insect herbivores in introduced ranges may determine their invasion success. However, few studies have investigated whether alien plants respond differently to native and introduced herbivores in their introduced ranges and whether genotypes of alien plants matter. We conducted a greenhouse experiment to examine the effects of herbivory by a native insect (Spodoptera litura), by an introduced insect (S. frugiperda), and simultaneously by both insect species on growth, morphology, and biomass allocation of 17 genotypes of an invasive alien clonal plant Hydrocotyle verticillata, and used selection gradient analysis to test which herbivory conditions favor selection of a specific leaf or root trait value.ResultsDifferent genotypes of H. verticillata showed significant variation in growth, morphology, and biomass allocation, but their responses to herbivory were relatively consistent. All three herbivory treatments significantly decreased total mass and stolon mass, but herbivory of S. frugiperda increased specific leaf area. Herbivory of S. litura and simultaneous herbivory of both insect species also decreased leaf mass, petiole mass, root mass, and ramet mass. Selection gradient analysis showed that leaf and root traits varied under different herbivory treatments. To achieve greater fitness, as measured by total mass and/or number of ramets, H. verticillata favored larger leaf area under herbivory by S. frugiperda, larger leaf area and lower specific leaf area under herbivory by S. litura, and larger leaf area, lower specific leaf area, and lower root-to-shoot ratio under simultaneous herbivory.ConclusionsH. verticillata demonstrated contrasting responses to herbivory by native and introduced insects, showing a remarkable ability to coordinate leaf trait plasticity and optimize biomass allocation. This strategy allows H. verticillata to achieve greater fitness under various herbivory conditions, potentially contributing to its invasion success. These findings highlight the importance of plant–herbivore interactions in shaping invasion dynamics and underscore the complex adaptive mechanism that enables invasive plants to establish and spread in introduced ranges.

Responses of oak seedlings to increased herbivory and drought: a possible trade-off?

Anthropogenic disturbances are causing a co-occurring increase in biotic (ungulate herbivory) and abiotic (drought) stressors, threatening plant reproduction in oak-dominated ecosystems. However, we wonder whether herbivory could compensate for the adverse impact of drought by reducing evapotranspiration. Thus, we investigate the isolated and joint effects of herbivory and drought on oak seedlings of two contrasting Mediterranean species that differ in leaf habit and drought resistance. California oak seedlings from the evergreen, and more drought-resistant, Quercus agrifolia and the deciduous Q. lobata (n=387) were assigned to a fully crossed factorial design with herbivory and drought as stress factors. Seedlings were assigned in a greenhouse to 3-4 clipping levels simulating herbivory and 3-4 watering levels, depending on the species. We measured survival, growth, and leaf attributes (chlorophyll, secondary metabolites, leaf area and weight) once a month (May-Sep) and harvested above- and below-ground biomass at the end of the growing season. For both oak species, simulated herbivory enhanced seedling survival during severe drought or delayed its adverse effects, probably due to reduced transpiration resulting from herbivory-induced leaf area reduction and compensatory root growth. Seedlings from the deciduous, and less drought-resistant species, benefitted from herbivory at lower levels of water stress, suggesting different response across species. We also found complex interactions between herbivory and drought on their impact on leaf attributes. In contrast to chlorophyll content which was not affected by herbivory, anthocyanins increased with herbivory - although water stress reduced differences in anthocyanins due to herbivory. Herbivory seems to facilitate Mediterranean oak seedlings to withstand summer drought, potentially alleviating a key bottleneck in the oak recruitment process. Our study highlights the need to consider ontogenetic stages and species-specific traits in understanding complex relationships between herbivory and drought stressors for the persistence and restoration of multi-species oak savannas.

Plant community responses to the individual and interactive effects of warming and herbivory across multiple years.

Anthropogenic climate warming affects plant communities by changing community structure and function. Studies on climate warming have primarily focused on individual effects of warming, but the interactive effects of warming with biotic factors could be at least as important in community responses to climate change. In addition, climate change experiments spanning multiple years are necessary to capture interannual variability and detect the influence of these effects within ecological communities. Our study explores the individual and interactive effects of warming and insect herbivory on plant traits and community responses within a 7-year warming and herbivory manipulation experiment in two early successional plant communities in Michigan, USA. We find stronger support for the individual effects of both warming and herbivory on multiple plant morphological and phenological traits; only the timing of plant green-up and seed set demonstrated an interactive effect between warming and herbivory. With herbivory, warming advanced green-up, but with reduced herbivory, there was no significant effect of warming. In contrast, warming increased plant biomass, but the effect of warming on biomass did not depend upon the level of insect herbivores. We found that these treatments had stronger effects in some years than others, highlighting the need for multiyear experiments. This study demonstrates that warming and herbivory can have strong direct effects on plant communities, but that their interactive effects are limited in these early successional systems. Because the strength and direction of these effects can vary by ecological context, it is still advisable to include levels of biotic interactions, multiple traits and years, and community type when studying climate change effects on plants and their communities.

Combined Effects of Heavy Metal and Simulated Herbivory on Leaf Trichome Density in Sunflowers

Trichomes play a key role in both heavy metal tolerance and herbivory defense, and both stressors have been shown to induce increased trichome density. However, the combined effect of these stressors on trichome density in general, and specifically on metal-hyperaccumulating plants, has yet to be examined. The aim of this study was to test the effect of cadmium availability and herbivory on leaf trichome density and herbivore deterrence in the metal hyperaccumulator Helianthus annuus. To test this, H. Annuus plants were grown in control pots or pots inoculated with 10 mg/kg cadmium and were subjected to either no herbivory or simulated herbivory using mechanical damage and foliar jasmonic acid application. Herbivore deterrence was tested in a feeding assay using Spodoptera littoralis caterpillars. Interestingly, while the trichome density of H. annuus increased by 79% or 53.5% under high cadmium availability or simulated herbivory, respectively, it decreased by 26% when the stressors were combined. Furthermore, regardless of cadmium availability, simulated herbivory induced a 40% increase in deterrence of S. littoralis. These findings suggest that the combination of metal availability and herbivory might present excessive stress to hyperaccumulators. Moreover, they suggest that the risk of metal bioaccumulation in phytoremediation can be reduced by simulated herbivory.

Herbivore regulation of savanna vegetation: Structural complexity, diversity, and the complexity–diversity relationship

AbstractLarge mammalian herbivores exert strong top‐down control on plants, which in turn influence most ecological processes. Accordingly, the decline, displacement, or extinction of wild large herbivores in African savannas is expected to alter the physical structure of vegetation, the diversity of plant communities, and downstream ecosystem functions. However, herbivore impacts on vegetation comprise both direct and indirect effects and often depend on herbivore body size and plant type. Understanding how herbivores affect savanna vegetation requires disaggregating the effects of different herbivores and the responses of different plants, as well as accounting for both the structural complexity and composition of plant assemblages. We combined high‐resolution Light Detection and Ranging (LiDAR) with field measurements from size‐selective herbivore exclosures in Kenya to determine how herbivores affect the diversity and physical structure of vegetation, how these impacts vary with body size and plant type, and whether there are predictable associations between plant diversity and structural complexity. Herbivores generally reduced the diversity and abundance of both overstory and understory plants, though the magnitude of these impacts varied substantially as a function of body size and plant type: only megaherbivores (elephants and giraffes) affected tree cover, whereas medium‐ and small‐bodied herbivores had stronger effects on herbaceous diversity and abundance. We also found evidence that herbivores altered the strength and direction of interactions between trees and herbaceous plants, with signatures of facilitation in the presence of herbivores and of competition in their absence. While megaherbivores uniquely affected tree structure, medium‐ and small‐bodied species had stronger (and complementary) effects on metrics of herbaceous vegetation structure. Plant structural responses to herbivore exclusion were species‐specific: of five dominant tree species, just three exhibited significant individual morphological variation across exclosure treatments, and the size class of herbivores responsible for these effects varied across species. Irrespective of exclosure treatment, more species‐rich plant communities were more structurally complex. We conclude that the diversity and architecture of savanna vegetation depend on consumptive and nonconsumptive plant–herbivore interactions; the roles of herbivore diversity, body size, and plant traits in mediating those interactions; and a positive feedback between plant diversity and structural complexity.