Intensity Of Herbivory Research Articles

Passive Recovery Risks Non-native Vegetation Invasion Following Intensive Herbivory by Canada Geese in Two Salish Sea Estuaries

Passive Recovery Risks Non-native Vegetation Invasion Following Intensive Herbivory by Canada Geese in Two Salish Sea Estuaries

Tree growth‐forms reveal dominant browsers shaping the vegetation

Abstract Plants adopt particular growth‐forms when they are exposed to extreme environmental conditions. In this study, we describe a unique woody plant growth‐form induced by large mammalian herbivores and discuss that this growth‐form could have evolved as a strategy for escaping the browser zone in herbivore driven ecosystems. We analysed responses of key architectural and morphological attributes (branching and thorn density, tree dimensions, presence of flowers and fruits) of three Eurasian spiny tree species (Malus sylvestris, Prunus cerasifera and Pyrus communis) to different levels of browsing by large herbivores in the temperate Białowieża Forest, Poland. Under high browsing pressure, studied trees displayed two distinct forms of the crown: a bottom sterile part developing into a densely branched structure with high density of thorns (‘cage‐form’), and an upper reproductive part that escaped from herbivore control (‘escaped‐form’). The size of cage‐form influenced the feeding behaviour of red deer (Cervus elaphus) by increasing the time deer spend foraging and increasing the bite rate. The height at which cages started to escape and their diameter matched with foraging reach of red deer. Synthesis. We argue that the frequency and cage dimensions of this woody growth‐form in the landscape could inform on the type and intensity of recent herbivory. Moreover, its distinctive inducibility suggests that this growth‐form did not emerge recently under anthropogenic pressure but could be the legacy of ancient herbivory effects. Observational evidence suggests that this growth‐form emerged in several herbivore‐driven systems around the globe and may be used to identify the dominant herbivores that control vegetation structure in these ecosystems. Read the free Plain Language Summary for this article on the Journal blog.

Relationships between reproduction, growth, and tolerance to herbivory for the endangered plant clay phacelia (Phacelia argillacea)

The endangered plant clay phacelia (Phacelia argillacea) is endemic to Spanish Fork Canyon, Utah, USA. In addition to habitat loss and abiotic stressors, herbivory is one of clay phacelia's major threats, but negative effects of herbivory have not been quantified. To examine the effects of simulated herbivory by small mammals, we grew 300 clay phacelia plants in a greenhouse (20 replicates of 15 half-sibling families). After six months of growth, half of the plants were randomly assigned to a defoliation treatment that mimicked herbivory from ground squirrels. After providing additional time for growth and natural pollination, we collected seeds and harvested shoots and roots from a subset of the plants. Among the 15 half-sibling families, we found significant genetic variation in shoot mass and a significant correlation between total mass when defoliated and undefoliated, suggesting a strong genetic component to growth. Defoliation significantly reduced seed production, shoot production and root production by 29%, 32%, and 35%, respectively. For these traits, interactions between family (F) and defoliation (D) were not statistically significant, suggesting fixation for tolerance to herbivory. In contrast, for root-to-shoot ratio, there was a statistically significant F × D interaction, revealing genetic variation for tolerance to herbivory. Depending on the type, intensity, and timing of herbivory, clay phacelia may benefit from either increased allocation to shoots or to roots. In fact, tolerance in terms of reproduction was correlated with shoot mass when defoliated, while tolerance in terms of growth was correlated with root mass when defoliated.

The effects of human population density on trophic interactions are contingent upon latitude

AbstractAimGlobal‐scale studies are necessary to draw general conclusions on how trophic interactions vary with urbanization and to explore how the effects of urbanization change along latitudinal gradients. We predict that the intensity of trophic interactions decreases in response to urbanization (quantified by human population density). Since trophic interactions are more intense at lower latitudes, we also expect major impacts of urbanization at higher latitudes, where base levels are essentially lower.LocationGlobal (881 study sites).Time period2000–2021.Major taxa studiedBirds, arthropods and woody plants.MethodsWe compiled global data on insect herbivory and bird predation from studies that employed similar methods and fitted generalized linear mixed models to test how these trophic interactions vary with human population density, latitude and their interactions.ResultsThe intensity of herbivory and predation decreased with an increase in human population density at lower latitudes. Surprisingly, it remained unaffected at intermediate latitudes and even increased at higher latitudes.Main conclusionsThe observed patterns may be attributed to local climate changes in urban areas, such as the Urban Heat Island effect, which disrupts thermal stability in the tropics while increasing niche availability at polar latitudes.

Deep learning‐ and image processing‐based methods for automatic estimation of leaf herbivore damage

Abstract Quantifying the intensity of leaf herbivory pressure is crucial for understanding the interaction between plants and herbivores in both applied and basic science. Visual estimates and digital analysis have been commonly used to estimate leaf herbivore damage but are time‐consuming which limits the amount of data that can be collected and prevent answering big picture questions that require large‐scale sampling of herbivory pressure. Recent developments in deep learning have provided a potential tool for automatic collection of ecological data from various sources. However, most applications have focused on identification and counting, and there is a lack of deep learning tools for quantitative estimation of leaf herbivore damage. Here, we trained generative adversarial networks (GANs) to predict the intact status of damaged leaves and applied image processing technique to estimate the area and percentage of leaf damage. We first described procedures for collecting leaf images, training GAN models, predicting intact leaves and calculating leaf area, with a Python package provided to enable hands‐on application of these procedures. Then, we collected a large leaf data set to train a universal deep learning model and developed an online app HerbiEstim to allow direct use of pretrained models to estimate herbivory damage of leaves. We tested these methods using both simulated and real leaf damage data. The procedures provided in our study greatly improved the efficiency of leaf herbivore damage estimation. Our test demonstrated that the reconstruction of damaged leaf image resembled the ground‐truth image with a similarity of 98.8%. The estimation of leaf herbivore damage exhibited a high accuracy with an averaged root mean square error of 1.6% and had a general applicability to different plant taxa and leaf shapes. Overall, our work demonstrated the feasibility of applying deep learning techniques to quantify leaf herbivory intensity. The use of GANs allows automatic estimation of leaf damage, representing a major advantage of the method. The Python package and the online app with pre‐trained models will facilitate the use of our method for the analysis of large data sets of plant–herbivore interactions.

Phenolic concentrations and carbon/nitrogen ratio in annual shoots of bilberry (Vaccinium myrtillus) after simulated herbivory.

Herbivory can be reduced by the production of defense compounds (secondary metabolites), but generally defenses are costly, and growth is prioritized over defense. While defense compounds may deter herbivory, nutrients may promote it. In a field study in boreal forest in Norway, we investigated how simulated herbivory affected concentrations of phenolics (generally a defense) and the carbon/nitrogen (C/N) ratio in annual shoots of bilberry (Vaccinium myrtillus), a deciduous clonal dwarf shrub whose vegetative and generative parts provide forage for many boreal forest animals. We measured concentrations of total tannins, individual phenolics, nitrogen and carbon following several types and intensities of herbivory. We identified 22 phenolics: 15 flavonoids, 1 hydroquinone and 6 phenolic acids. After high levels of herbivory, the total tannin concentration and the concentration of these 22 phenolics together (called total phenolic concentration) were significantly lower in bilberry annual shoots than in the control (natural herbivory at low to intermediate levels). Low-intensive herbivory, including severe defoliation, gave no significantly different total tannin or total phenolic concentration compared with the control. Many individual phenolics followed this pattern, while phenolic acids (deterring insect herbivory) showed little response to the treatments: their concentrations were maintained after both low-intensive and severe herbivory. Contrary to our predictions, we found no significant difference in C/N ratio between treatments. Neither the Carbon:Nutrient Balance hypothesis nor the Optimal Defense hypotheses, theories predicting plant resource allocation to secondary compounds, can be used to predict changes in phenolic concentrations (including total tannin concentration) in bilberry annual shoots after herbivory: in this situation, carbon is primarily used for other functions (e.g., maintenance, growth, reproduction) than defense.

Large and thin leaves are compromised more by chewers

AbstractA major proportion of primary production is lost to insect herbivory. Leaf functional traits representing defense costs and palatability explain the intensity of herbivory at local scales. However, whether leaf traits explain herbivory at large scales needs clarification. By combining a leaf herbivory database and the TRY plant‐trait database, we compared 190 species from 65 families across 45 sites in nine countries. We hypothesized that defensive and/or nutrient‐poor leaves would compromise herbivory less globally. Both the absolute and percentage of maximum leaf‐area loss were higher in the tropical zone. Larger leaves lost more disproportionate areas to chewer herbivores whenever phylogenetic signals were considered. Thin leaves with low leaf mass per area (LMA) and short lifespan were compromised more by herbivory based on the leaf trait syndrome. Although thin leaves were rich in nitrogen, phosphorus, and calcium, only leaf nitrogen marginally explained the loss of leaf area. The contribution of leaf area dominated the herbivory intensity among all other morphological and chemical traits. Overall, the benefits of chewers on herbivory were based on leaf area, because the loss of leaf biomass and nitrogen increased proportionally with its loss. Leaf construction costs, but not nutrient content, determined the intensity of herbivory globally. However, the overall percentage of loss in leaf area was not high, demonstrating the importance of elucidating the relationship between leaf functional traits and induced defense in future studies.

Leaf defenses of subtropical deciduous and evergreen trees to varying intensities of herbivory.

Generally, deciduous and evergreen trees coexist in subtropical forests, and both types of leaves are attacked by numerous insect herbivores. However, trees respond and defend themselves from herbivores in different ways, and these responses may vary between evergreen and deciduous species. We examined both the percentage of leaf area removed by herbivores as well as the percentage of leaves attacked by herbivores to evaluate leaf herbivore damage across 14 subtropical deciduous and evergreen tree species, and quantified plant defenses to varying intensities of herbivory. We found that there was no significant difference in mean percentage of leaf area removed between deciduous and evergreen species, yet a higher mean percentage of deciduous leaves were damaged compared to evergreen leaves (73.7% versus 60.2%). Although percent leaf area removed was mainly influenced by hemicellulose concentrations, there was some evidence that the ratio of non-structural carbohydrates:lignin and the concentration of tannins contribute to herbivory. We also highlight that leaf defenses to varying intensities of herbivory varied greatly among subtropical plant species and there was a stronger response for deciduous trees to leaf herbivore (e.g., increased nitrogen or lignin) attack than that of evergreen trees. This work elucidates how leaves respond to varying intensities of herbivory, and explores some of the underlying relationships between leaf traits and herbivore attack in subtropical forests.

Foliar herbivory modifies arbuscular mycorrhizal fungal colonization likely through altering root flavonoids

Abstract Insect herbivory may influence arbuscular mycorrhizal (AM) fungal colonisation by changing plant chemistry, and these effects can vary from negative to positive. Yet the underlying mechanisms are unclear. We investigated AM fungal colonization of Chinese tallow tree (Triadica sebifera) after exposing its seedlings to four different foliar‐feeding insects at two levels of herbivory. We then examined the potential role of induced carbon allocation and secondary metabolites, particularly flavonoids, in AM fungal colonization. Light herbivory (ca. 10% leaf area removed) promoted early colonization by AM fungi whereas heavy herbivory (ca. 60% leaf area removed) decreased it. Root flavonoids were increased (in the short‐term) under light herbivory but decreased under heavy herbivory. Further, herbivore‐induced changes to root flavonoids were positively correlated with those of AM fungal colonisation. Moreover, quercitrin, one of the root‐secreted flavonoids, could mediate these AM fungal responses. Surprisingly, however, AM fungal colonization was not correlated with herbivore‐induced carbon allocation in roots or root exudates. We show that AM fungal responses to insect herbivory are at least partially flavonoid‐based and depend on herbivory intensity. Our work highlights the importance of secondary metabolites rather than carbon allocation in interactions between above‐ground herbivory and below‐ground mycorrhiza. Read the free Plain Language Summary for this article on the Journal blog.

Herbivory and elevated levels of CO2 and nutrients separately, rather than synergistically, impacted biomass production and allocation in invasive and native plant species.

Large parts of the Earth are experiencing environmental change caused by alien plant invasions, rising atmospheric concentration of carbon dioxide (CO2 ), and nutrient enrichments. Elevated CO2 and nutrient concentrations can separately favour growth of invasive plants over that of natives but how herbivory may modulate the magnitude and direction of net responses by the two groups of plants to simultaneous CO2 and nutrient enrichments remains unknown. In line with the enemy release hypothesis, invasive plant species should reallocate metabolites from costly anti-herbivore defences into greater growth following escape from intense herbivory in the native range. Therefore, invasive plants should have greater growth than native plants under simultaneous CO2 and nutrient enrichments in the absence of herbivory. To test this prediction, we grew nine congeneric pairs of invasive and native plant species that naturally co-occurred in grasslands in China under two levels each of nutrient enrichment (low-nutrient vs. high-nutrient), herbivory (with herbivory vs. without herbivory) and under ambient (412.9 ± 0.6 ppm) and elevated (790.1 ± 6.2 ppm) levels of CO2 concentrations in open top chambers in a common garden. Elevated CO2 and nutrient enrichment separately increased total plant biomass, while herbivory reduced it regardless of the plant invasive status. High-nutrient treatment caused the plants to allocate a significantly lower proportion of total biomass to roots, while herbivory induced an opposite pattern. Herbivory suppressed total biomass production more strongly in native plants than invasive plants. The plants exhibited significant interspecific and intergeneric variation in their responses to the various treatment combinations. Overall, these results suggest that elevated CO2 and nutrients and herbivory may separately, rather than synergistically, impact productivity of the invasive and co-occurring native plant species in our study system. Moreover, interspecific variation in resource-use strategies was more important than invasive status in determining plant responses to the various treatment combinations.

Seedling responses to moderate and severe herbivory: a field-clipping experiment with a keystone Mediterranean palm.

Plant-ungulate interactions are critical in shaping the structure of Mediterranean plant communities. Nevertheless, there is a dearth of knowledge on how plant intrinsic and extrinsic factors mediate the sign and strength of plant-ungulate interactions. This is most relevant when addressing natural or assisted restoration of plant communities in human-disturbed areas. We conducted field-clipping experiments simulating how different intensities of ungulate herbivory may affect the natural regeneration and establishment of the Mediterranean dwarf palm (Chamaerops humilis), a keystone species in Mediterranean ecosystems. We quantified seedling survival and size in two human-disturbed sites (SW Spain) where wild and domestic ungulates exert high herbivory pressure on vegetation. Severe clipping and seedling aging reduced rates of seedling survival. In contrast, moderate clipping did not affect seedling survival, suggesting a certain degree of C. humilis tolerance to herbivory. Severe clipping reduced seedling height strongly but not seedling diameter, and these effects seem to have decreased seedling survival. Nurse shrubs increased seedling size, which likely improved seedling survival. We also found seedling compensatory growth which varied between study sites. Field-clipping experiments can help disentangle effects of plant extrinsic and intrinsic factors on the sign and strength of plant-ungulate interactions and their ecological consequences on the dynamics of human-disturbed ecosystems. We call attention to the importance of appropriately managing scenarios of severe herbivory and summer droughts, particularly frequent in Mediterranean ecosystems, as synergic effects of such key drivers can negatively affect the structure and dynamics of plant communities and endanger their conservation.

Root traits explain multitrophic interactions of belowground microfauna on soil nitrogen mineralization and plant productivity

Both herbivorous and bacterivorous microfauna have been shown to influence root development, soil nitrogen (N) mineralization, and plant productivity. However, our knowledge of these effects is limited as multitrophic interactions remain largely unexplored. We investigated whether and how herbivorous nematodes (Pratylenchus zeae) and bacterivorous nematodes (Poikilolaimus oxycercus), alone and in combination, affect plant biomass (Lolium multiflorum) through root traits and/or soil N mineralization. Bacterivorous nematodes increased, whereas herbivorous nematodes decreased, plant productivity. We found that root trait coordination in response to soil microfauna was consistent with the concept of root economics space. The negative interaction between herbivorous and bacterivorous nematodes on plant productivity at high herbivorous nematode infestation could be explained by reduced N mineralization and variation in the root nitrogen concentration-root tissue density (RNC-RTD) axis aligned with increased herbivory intensity. This study revealed that herbivorous and bacterivorous nematodes moderated each other's effect on plant productivity via root trait coordination and N mineralization, and suggests, for the first time, the value of the root economics space concept for interpreting phenotypic root plasticity and functioning in response to local biotic factors.

Trade-offs in non-native plant herbivore defences enhance performance.

Non-native plants are typically released from specialist enemies but continue to be attacked by generalists, albeit at lower intensities. This reduced herbivory may lead to less investment in constitutive defences and greater investment in induced defences, potentially reducing defence costs. We compared herbivory on 27 non-native and 59 native species in the field and conducted bioassays and chemical analyses on 12 pairs of non-native and native congeners. Non-natives suffered less damage and had weaker constitutive defences, but stronger induced defences than natives. For non-natives, the strength of constitutive defences was correlated with the intensity of herbivory experienced, whereas induced defences showed the reverse. Investment in induced defences correlated positively with growth, suggesting a novel mechanism for the evolution of increased competitive ability. To our knowledge, these are the first linkages reported among trade-offs in plant defences related to the intensity of herbivory, allocation to constitutive versus induced defences, and growth.

Integrating defense and leaf economic spectrum traits in a tropical savanna plant.

Allocation to plant defense traits likely depends on resource supply, herbivory, and other plant functional traits such as the leaf economic spectrum (LES) traits. Yet, attempts to integrate defense and resource acquisitive traits remain elusive. We assessed intraspecific covariation between different defense and LES traits in a widely distributed tropical savanna herb, Solanum incanum, a unique model species for studying allocations to physical, chemical, and structural defenses to mammalian herbivory. We found that in a multivariate trait space, the structural defenses - lignin and cellulose - were positively related to the resource conservative traits - low SLA and low leaf N. Phenolic content, a chemical defense, was positively associated with resource acquisitive traits - high SLA and high leaf N - while also being associated with an independent third component axis. Both principal components 1 and 3 were not associated with resource supply and herbivory intensity. In contrast, spine density - a physical defense - was orthogonal to the LES axis and positively associated with soil P and herbivory intensity. These results suggest a hypothesized "pyramid" of trade-offs in allocation to defense along the LES and herbivory intensity axes. Therefore, future attempts to integrate defense traits with the broader plant functional trait framework, such as the LES, needs a multifaceted approach that accounts for unique influences of resource acquisitive traits and herbivory risk.

Land-use history, fire regime, and large-mammal herbivory affect deer-preferred plant diversity in longleaf pine woodlands

Since ecological systems often experience multiple disturbances, understanding changes in important ecological interactions, such as plant-herbivore interactions, may require studies capable of disentangling the unique and interactive effects of multiple forms of disturbance. For example, understanding how mammalian herbivores affect plant communities may require understanding how widespread past disturbances, such as agricultural land use, interact with contemporary disturbances, such as prescribed fire. We tested if past agricultural land use and contemporary fire regime modified the effects of mammalian herbivory on focal plant communities by measuring the richness of plant species preferred by deer at 26 longleaf pine woodlands containing paired open and large-mammal exclusion plots. Land-use history significantly affected the community composition of deer-preferred species, and focal species were 8.19 times more likely to be present in post-agricultural sites than non-agricultural sites. Large-mammal herbivory only affected plant species richness in woodlands with low fire frequencies wherein focal species were on average 2.23 times more likely to be present in exclusion plots than open plots. These results suggest that past and present disturbances can mediate contemporary plant-animal interactions and may explain spatial patterns in the intensity of large-mammal herbivory. Our findings also suggest that common management practices, such as use of prescribed burns, may indirectly promote plant species richness by reducing deer herbivory.

Absence of consistent pattern between seasons or among species in effect of leaf size on insect herbivory

Insect herbivory on plant leaves is a major determinant of plant fitness, especially the growth and survival of tree seedlings in forests. Leaf size is believed to significantly affect the intensity of herbivory. Studies often assume the relationship between leaf size and herbivory to be monotonic; however, this relationship is influenced by many factors—the magnitude and direction of which are different—indicating a complex non-monotonic pattern. In this study, we investigated the herbivory of 5754 leaves of 422 seedlings belonging to 42 subtropical tree species over two seasons in southwest China. The effects of leaf size on herbivory differed among seasons; a hump-shaped pattern was detected in December, while a pattern of monotonic increase was detected in September. A variety of patterns, including complex non-monotonic hump-shaped patterns, as well as patterns indicating monotonic decrease and increase existed among species, although most species displayed no significant correlations. The relationship between leaf size and insect herbivory did not follow a constant rule, but differed across species and seasons, indicating that the effects of leaf size on the foraging preferences of insect herbivores may be contingent on both external (e.g., temperature) and intrinsic (e.g., other leaf traits) factors. Therefore, a one-off survey focusing on few species may not provide complete understanding of the overall pattern of the effect of leaf size on herbivory. Similar variations may also exist in other ecological processes, which should be given due consideration in future studies on biotic interactions.

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (SYMP 14) Organized at ESA + CSEE 2022 Joint Meeting

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (<scp>SYMP</scp> 14) Organized at <scp>ESA</scp> + <scp>CSEE</scp> 2022 Joint Meeting

No evident sex-biased herbivory but phenological and interannual variation in Fuchsia parviflora (Onagraceae) a dioecious Neotropical shrub

Herbivory may have a great impact in plants, reducing plant biomass and fitness. Herbivory patterns may differ among genders in dioecious species, affecting male and female plants differentially, and it has been suggested this is a consequence of differences in resource allocation among genders. In this study, we evaluated herbivory intensity and mechanical defenses among genders during two years and during different phenological stages in populations of Fuchsia parviflora, a dioecious shrub. We also evaluated generalist and specialist herbivore gender preferences through a cafeteria experiment. No evident herbivory patterns were detected among genders using both the proportion of leaves affected by herbivory and the proportion of leaf area removed, except during one year in two populations where females had a significantly higher proportion of leaves affected by herbivory. This pattern is similar to the specialist herbivore preference detected in the cafeteria experiment. We also found significant differences in herbivory intensity among phenological stages, populations, and years, highlighting the relevance of continuous sampling to depict the general patterns of herbivory in dioecious plants.

Foliar herbivory affects the rhizosphere microbial assembly processes and association networks

Insect herbivores are prevalent in terrestrial ecosystems, and plants inevitably and continuously suffer damage by insect herbivores. Numerous studies have reported the effect of insect herbivory on plants; however, its effect on the belowground soil microbial community remains understudied. In the present study, using high-throughput sequencing, we investigated the effect of foliar insect herbivory on rhizosphere soil bacterial community. Our results showed that both herbivory intensity and duration after herbivory had no significant effect on the rhizosphere microbial community structure, but microbial assembly processes and association networks were strongly affected by the above two factors. Under moderate and high herbivory and at 6 weeks after herbivory, variable selection explained 55.56% and 51.52% of the community variation indicating that deterministic processes played a dominant role. Network complexity decreased from no herbivory (1.07) to high herbivory (0.97), and network complexity at 2 weeks after herbivory (0.92) was higher than that at 4 and 6 weeks after herbivory (0.79 and 0.84, respectively). The proportion of negative correlations decreased with increasing herbivory intensity and duration after herbivory. The number of keystone species decreased with increasing duration after herbivory but showed no change with increasing herbivory intensity. To our knowledge, this is among the first studies to illustrate the response mechanisms of rhizosphere microbial assembly processes and association networks to foliar herbivory. Our findings suggest that the assembly process and association network patterns of microbes are closely associated with herbivory intensity and duration after herbivory and enhance the understanding of insect-plant-soil microbe interactions.

Meta-analysis of elevational changes in the intensity of trophic interactions: Similarities and dissimilarities with latitudinal patterns.

The premise that the intensity of biotic interactions decreases with increasing latitudes and elevations is broadly accepted; however, whether these geographical patterns can be explained within a common theoretical framework remains unclear. Our goal was to identify the general pattern of elevational changes in trophic interactions and to explore the sources of variation among the outcomes of individual studies. Meta‐analysis of 226 effect sizes calculated from 134 publications demonstrated a significant but interaction‐specific decrease in the intensity of herbivory, carnivory and parasitism with increasing elevation. Nevertheless, this decrease was not significant at high latitudes and for interactions involving endothermic organisms, for herbivore outbreaks or for herbivores living within plant tissues. Herbivory similarly declined with increases in latitude and elevation, whereas carnivory showed a fivefold stronger decrease with elevation than with latitude and parasitism increased with latitude but decreased with elevation. Thus, although these gradients share a general pattern and several sources of variation in trophic interaction intensity, we discovered important dissimilarities, indicating that elevational and latitudinal changes in these interactions are partly driven by different factors. We conclude that the scope of the latitudinal biotic interaction hypothesis cannot be extended to incorporate elevational gradients.