Herbivore Behavior Research Articles

Holling meets habitat selection: functional response of large herbivores revisited

BackgroundHolling (Can Entomol 91(5):293–320, 1959) was the first to describe a functional response between a predator’s consumption-rate and the density of its prey. The same concept can be applied to the habitat selection of herbivores, specifically, the change in relative habitat use with the change in habitat availability. Functional responses in habitat selection at a home-range scale have been reported for several large herbivores. However, a link to Holling’s original functional response types has never been drawn, although it could replace the current phenomenological view with a more mechanistically based understanding of functional responses.MethodsIn this study, discrete choice models were implemented as mixed-effects baseline-category logit models to analyze the variation in habitat selection of a large herbivore at seasonal and diurnal scales. Thus, changes in the use of land cover types with respect to their availability were investigated by monitoring 11 land cover types commonly used by roe deer (Capreolus capreolus) in the Bavarian Forest National Park, Germany. Functional response curves were then fitted using Holling’s formulas.ResultsStrong evidence of non-linear functional responses was obtained for almost all of the examined land cover types. The shape of the functional response curves varied depending on the season, the time of day, and in some cases between sexes. These responses could be referenced to Holling’s types, with a predominance of type II.ConclusionsOur results indicate that Holling’s types can be applied to describe general patterns of the habitat selection behavior of herbivores. Functional responses in habitat selection may occur in situations requiring a trade-off in the selection of land cover types offering different resources, such as due to the temporally varying physiological needs of herbivores. Moreover, two associated parameters defining the curves (prey density and predation rate) can aid in the identification of temporal variations and in determinations of the strength of the cost-benefit ratio for a specific land cover type. Application of our novel approach, using Holling’s equations to describe functional responses in the habitat selection of herbivores, will allow the assignment of general land cover attraction values, independent of availability, thus facilitating the identification of suitable habitats.

Effect of Soy Leaf Flavonoids on Pea Aphid Probing Behavior.

Simple SummaryFlavonoids are plant phenolic compounds whose biological activities include participation in plant responses to various stresses of biological and environmental origins, including protection against insect herbivore attack. We were interested in whether the specific flavonoids detected in soybean leaves have the potential to discourage the pea aphid from infesting other leguminous plants, peas in particular. We immersed the pea leaves in ethanolic solutions of the flavonoids apigenin, daidzein, genistein and kaempferol, offered them to the pea aphids and observed their behavior when they probed plant tissues with their piercing–sucking mouthparts. We discovered that aphids readily probed the pea leaves whether they were treated with flavonoids or not. However, later on, the behavior of the aphids changed depending on the flavonoid applied. Apigenin, daidzein and kaempferol caused a decrease in the intensity of plant sap ingestion. In addition, daidzein and kaempferol made the finding of sap-transporting vessels more difficult for aphids. In contrast, genistein did not affect the pea aphids’ feeding activity. Our findings provide the plant breeders and plant protection services with information on what direction their efforts should take to protect leguminous plants against aphids in a sustainable and environmentally friendly way.Flavonoids detected in soybean Glycine max (L.) Merr. (Fabaceae) cause various alterations in the metabolism, behavior, and development of insect herbivores. The pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) poses potential threat to soybeans, but the effect of individual flavonoids on its feeding-associated behavior is relatively unknown. We monitored probing behavior (stylet penetration activities) of A. pisum on its preferred host plant, Pisum sativum L. untreated (control) and treated with 0.1% ethanolic solutions of flavonoids apigenin, daidzein, genistein, and kaempferol. We applied the electrical penetration graph (electropenetrography, EPG) technique, which visualizes the movements of aphid stylets within plant tissues. None of the applied flavonoids affected the propensity to probe the plants by A. pisum. However, apigenin enhanced the duration of probes in non-phloem tissues, which caused an increase in the frequency and duration of stylet mechanics derailment and xylem sap ingestion but limited the ingestion of phloem sap. Daidzein caused a delay in reaching phloem vessels and limited sap ingestion. Kaempferol caused a reduction in the frequency and duration of the phloem phase. Genistein did not affect aphid probing behavior. Our findings provide information for selective breeding programs of resistant plant cultivars to A. pisum.

Responses to predation risk cues and alarm pheromones affect plant virus transmission by an aphid vector.

Herbivores assess predation risk in their environment by identifying visual, chemical, and tactile predator cues. Detection of predator cues can induce risk-avoidance behaviors in herbivores that affect feeding, dispersal, and host selection in ways that minimize mortality and reproductive costs. For herbivores that transmit plant pathogens, including many aphids, changes in herbivore behavior in response to predator cues may also affect pathogen spread. However, few studies have assessed how aphid behavioral responses to different types of predator cues affect pathogen transmission. Here, we conducted greenhouse experiments to assess whether responses of pea aphids (Acyrthosiphon pisum) to predation risk and alarm pheromone (E-β-Farnesene), an aphid alarm signal released in response to predation risk, affected transmission of Pea enation mosaic virus (PEMV). We exposed A. pisum individuals to risk cues, and quantified viral titer in aphids and pea (Pisum sativum) host plants across several time periods. We also assessed how A. pisum responses to risk cues affected aphid nutrition, reproduction, and host selection. We show that exposure to predator cues and alarm pheromone significantly reduced PEMV acquisition and inoculation. Although vectors avoided hosts with predator cues, predator cues did not alter vector reproduction or reduce nutrient acquisition. Overall, these results suggest that non-consumptive effects of predators may indirectly decrease the spread of plant pathogens by altering vector behavior in ways that reduce vector competence and pathogen transmission efficiency.

Cover Crop Soil Legacies Alter Phytochemistry and Resistance to Fall Armyworm (Lepidoptera: Noctuidae) in Maize.

Plant-soil feedbacks can mediate aboveground plant-herbivore interactions by impacting plant chemistry. Given that soil legacies and agricultural practices are closely tied, a better understanding of soil legacy cascades and their application in pest management are needed. We tested how cover crop legacies alter resistance to fall armyworm (Spodoptera frugiperda Smith, Lepidoptera: Noctuidae) in maize (Zea mays L., Poales: Poaceae). We compared herbivore performance and behavior of fall armyworm larvae on maize grown after four cover crop treatments: a leguminous mycorrhizal cover crop (pea: Pisum sativum L., Fabales: Fabaceae), a nonleguminous mycorrhizal cover crop (triticale: x Triticosecale Wittm. Ex A. Camus, Poales: Poaceae), a nonleguminous nonmycorrhizal cover crop (radish: Raphanus sativus L., Brassicales: Brassicaceae), and no cover crops (fallow). Soil inorganic N was highest in pea treatments and lowest in triticale treatments, while maize AMF colonization was greatest when grown after mycorrhizal cover crops compared to nonmycorrhizal or no cover crops. Cover crop legacies altered the emission of maize volatiles and fall armyworm larvae oriented toward odors emitted by maize grown after radish more frequently than triticale in olfactometer assays. Additionally, larvae performed better and consumed more leaf tissue when feeding on maize grown after radish and poorest on plants grown after triticale. When damaged by fall armyworm, maize grown after triticale expressed higher levels of lipoxygenase-3 (lox3), while plants grown after radish upregulated maize proteinase inhibitor (mpi) gene expression. Our results highlight the importance of appropriate cover crop selection and suggest that triticale could strengthen maize resistance to fall armyworm.

Pans as possible pedological hotspots in an arid African savanna

Vegetation dynamics in savannas are largely determined by water availability as well as soil nutrient dynamics. Species composition differs significantly from nutrient-rich soils to nutrient-poor soils, where the former is dominated by fine-leafed palatable woody species and the latter by broad-leafed and less palatable ones. Whilst this typically occurs at a landscape or catena scale, it is also interestingly observed at a localised and micro scale in areas such as wetlands and termite mounds. Wetlands are important edaphic contrasts in savannas and are paradoxically prevalent in the semi-arid to arid regions. In Southern Africa endorheic (inward draining) wetlands, known as pans, are particularly ubiquitous in arid regions but are not well studied compared to other wetland types. These wetlands were the focus of this study, which took place in the semi-arid savanna of the Limpopo plains, South Africa. The key research aims of this study were to determine how the pans differed from the surrounding terrestrial savanna landscape with respect to soil texture and chemistry, woody plant density and vegetation species composition. Top and sub soil samples were analysed to a depth of 30 and 60 cm and vegetation transects were carried out across three identified ‘hydro-ecological’ zones, i.e. the pan centre, the wooded wetland zone around the pan and representative terrestrial savanna habitat. In addition, drone aerial imagery was utilised to accurately determine woody species density and visually understand habitat changes. As hypothesised, the physiochemical properties of the soils differed along the study gradient from terrestrial to wetland, where in general the soil fertility, clay content and water holding capacity increased. The high clay content of the pans facilitates the surface pooling of rainwater and the possible maintenance of wetland conditions in these depressions which were found to be localised soil nutrient hotspots. The wooded wetland and terrestrial areas differed from each other in woody species composition where the terrestrial areas were largely dominated by broad leafed tree and shrub species and the wooded wetland areas had few to no broad-leafed species present but rather a dominance of fine-leafed Senegalia/Vachelia species. In addition, the Senegalia/Vachelia dominated habitat had a higher tree density than the surrounding bushveld, forming closed canopy patches in some areas. This change in vegetation and soil dynamics are important in savanna ecology as these habitats function quite differently from each other with respect to nutrient cycling, herbivore behaviour and biodiversity. It was concluded that these pans are nutrient-rich hotspots, likely playing an important ecological role in the savanna landscape. Furthermore, as they are likely to be key water sources and preferential forage sites, they could be the first to show signs of degradation and be useful indicators for land managers. These pans should be highlighted as sensitive habitats with regional conservation significance, which are deserving of adequate protection from surrounding threats such as mining.

Plant volatiles as regulators of plant defense and herbivore immunity: molecular mechanisms and unanswered questions.

Plants release distinct blends of herbivore-induced plant volatiles (HIPVs) upon herbivore attack. HIPVs have long been known to influence the behavior of herbivores and natural enemies. In addition, HIPVs can act as physiological regulators that induce or prime plant defenses. Recent work indicates that the regulatory capacity of HIPVs may extend to herbivore immunity: herbivores that are exposed to HIPVs can become more resistant or susceptible to parasitoids and pathogens. While the mechanisms of HIPV-mediated plant defense regulation are being unraveled, the mechanisms underlying the regulation of herbivore immunity are unclear. Evidence so far suggests a high degree of context dependency. Here, we review the mechanisms by which HIPVs regulate plant defense and herbivore immunity. We address major gaps of knowledge and discuss directions for future mechanistic research to facilitate efforts to use the regulatory capacity of HIPVs for the biological control of insect pests.

Variation in herbivore grazing behavior across Caribbean reef sites

Herbivorous fish can increase coral growth and survival by grazing down algal competitors. With coral reefs in global decline, maintaining adequate herbivory has become a primary goal for many managers. However, herbivore biomass targets assume grazing behavior is consistent across different reef systems, even though relatively few have been studied. We document grazing behavior of two scarid species in Antigua, Barbuda, and Bonaire. Our analyses show significant differences in intraspecific feeding rates, time spent grazing, and intensity of grazing across sites, which may alter the ecological impact of a given scarid population. We suggest several hypothesized mechanisms for these behavioral variations that would benefit from explicit testing in future research. As managers set targets to enhance herbivory on reefs, it is critical that we understand potential differences in scarid grazing impact. Our findings demonstrate the variability of grazing behavior across different reef sites and call for further investigation of the drivers and ecological implications of these inconsistencies.

Side Effects of Insecticides on Leaf-Miners and Gall-Inducers Depend on Species Ecological Traits and Competition with Leaf-Chewers.

Internal feeding is considered to shield sessile herbivorous insects from exposure to nonsystemic insecticides aerially sprayed against forest defoliators, although this has not been tested. It is, however, established that leaf damage caused by defoliators affects the survivorship and oviposition behavior of sessile herbivores. Thus feeding ecology and competition may mediate nontarget effects of insecticides on these insects. We tested the ecological sensitivity of 3 guilds of sessile herbivores (upper-surface leaf-miners, lower-surface leaf-miners, and gall-inducers) to the lipophilic larvicides diflubenzuron and tebufenozide aerially applied either at operational rates (12 g active ingredient [a.i.]/ha and 69.6 g [a.i.]/ha, respectively) or at maximum legal rates (60 g [a.i.]/ha and 180 g [a.i.]/ha, respectively), in German oak forests. Diflubenzuron affected leaf-miners at different life stages depending on their position on the leaf but had no effect on gall-inducers. Tebufenozide showed a similar, but not significant, pattern in leaf-miners and did not affect gall-inducers. By reducing the incidence of chewing damage on leaves, both insecticides offset the negative effect of competition on leaf-miner and gall-inducers. The net outcome of insecticide treatment was positive for guilds avoiding exposure, but negative for upper-surface leaf-miners. Exposure to insecticides in situ can be mediated by subtle differences in species biology and species interactions, with potential implications for organisms usually considered safe in risk assessment studies. Environ Toxicol Chem 2021;00:1-17. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Dietary stability inferred from dental mesowear analysis in large ungulates from Rancho La Brea and opportunistic feeding during the late Pleistocene

The Rancho La Brea locality is world famous for asphaltic deposits that trapped and preserved late Pleistocene megafauna over the last 50,000 years. This wealth of paleontological data allows for detailed investigation into paleoecological changes through the last glacial maximum into the Holocene. Here, we used dental mesowear analyses to infer dietary behavior in Bison antiquus, Equus occidentalis, and Camelops hesternus from five deposits (“pits”) spanning the latest Pleistocene: pits 77, 91, 13, 3, and 61/67. Mesowear was compared among pits for each taxon and discriminant function and posterior probability analyses were conducted using a modern dataset to predict dietary categories at Rancho La Brea. Published mesowear scores from late Pleistocene Bison, Equus and Camelops from other localities were included in the discriminant function and posterior probability analyses to assess dietary variability among regions. Mesowear for each taxon did not differ among pits. Posterior probabilities and discriminant function analyses recovered E. occidentalis as a strict grazer with B. antiquus and C. hesternus recovered as mixed feeders. The stability of mesowear scores through the latest Pleistocene suggests average diets of these herbivores did not significantly change at Rancho La Brea. This is in contrast to documented changes in climate and flora proxies of southern California. However, it is unclear whether these proxies are representative of climate and floral changes at Rancho La Brea. Mesowear scores from late Pleistocene populations of Equus, Bison, and Camelops indicate little variability in diet in Equus, modest variability in Bison, and high variability in Camelops. These analyses suggest large ungulates may have been more opportunistic in their feeding strategies and highlights the need for using multiple proxies to clarify dietary behavior of herbivores

Stable isotope evidence for mid-Pleistocene paleoenvironmental conditions at the site of Kathu Pan 1 (central interior, South Africa)

This study investigates the Mid-Pleistocene paleoenvironment and dietary behaviour of ancient herbivores in the South African central interior, today part of the semi-arid Kalahari savanna. Analyses were undertaken of carbon (δ13C) and oxygen (δ18O) stable isotopes in tooth enamel carbonate of twelve fossil herbivore species from Layers 4b and 4a, associated with Earlier Stone Age (ESA) and transitional ESA-Middle Stone Age (Fauresmith) industries respectively, at the archaeological site of Kathu Pan 1. The data are compared with other Eearly to Mid-Pleistocene herbivore assemblages located in the central interior, namely Cornelia-Uitzoek, Wonderwerk Cave and the Florisbad Spring.Results indicate that the median δ13C values for all ungulate taxa at Kathu were >-4‰, indicating predominantly C4 based diets, although in certain taxa, some individuals included a significant C3 component in their diet. The δ18O values of most species at Kathu were relatively low, suggesting a cooler and/or wetter climate. Carbon isotope evidence for C4 dominated habitats at Kathu, but with a larger C3 component amongst grazers than today, resembles the other Early to -Mid-Pleistocene assemblages in the region. Similarly, δ18O values for Kathu supplement existing evidence that the region was substantially wetter than in modern times.

Urbanization as a disrupter and facilitator of insect herbivore behaviors and life cycles.

Insect herbivores require a variety of habitats across their life cycle, with behavior often mediating transitions between life stages or habitats. Human management strongly alters urban habitats, yet herbivore behavior is rarely examined in cities. We review the existing literature on several key behaviors: host finding, feeding, egg placement and pupation location, and antipredator defense. We emphasize that unapparent portions of the life cycle, such as the habitat of the overwintering stage, may influence if urbanized areas act as population sources or sinks. Here, management of the soil surface and aboveground biomass are two areas with especially pressing research gaps. Lastly, high variability in urban environments may select for more plastic behaviors or greater generalism. We encourage future research that assesses both behavior and less apparent portions of insect life cycles to determine best practices for conservation and management.

Plant water stress intensity mediates aphid host choice and feeding behaviour

The effects of drought‐induced changes in plant quality on aphid performance and population growth is well‐studied. The response of aphid behaviour to plant water limitation has received less attention. Water limitation may affect host‐plant colonization by altering the attractiveness of plants. Additionally, plant water limitation may inhibit feeding site establishment and phloem ingestion. Our goal was to examine bird cherry‐oat aphid (Rhopalosiphum padi L.) host selection and feeding behaviour under water limitation. We assessed aphid response to well‐watered, mildly‐stressed, and highly‐stressed wheat (Triticum aestivum L.) by evaluating (i) host‐plant selection through two‐choice assays, (ii) feeding behaviour using the electrical penetration graph technique, and (iii) phloem ingestion by quantifying honeydew production. Aphids were less likely to select highly stressed plants than a mildly stressed or well‐watered alternative. Aphids did not distinguish between mildly stressed and well‐watered plants. Aphid feeding behaviours, including duration of phloem ingestion, were not affected by water availability. However, honeydew production was reduced under both levels of water limitation. These results suggest that the volume of phloem ingested by aphids per unit time declined on stressed plants. The combination of lower colonization and diminished access to food on stressed plants may lead to a reduction in aphid abundance, independent of the direct effects of nutrition on individual aphid performance. This study highlights the potential contribution of herbivore behaviour to documented changes in aphid abundance on stressed plants and underscores the important role of plant water stress intensity in mediating plant‐herbivore interactions.

Effects of species and environmental factors on browsing frequency of young trees in mountain forests affected by natural disturbances

We analyzed the effects of natural disturbances on relationships between forest regeneration and ungulate browsing. Specifically, we asked if natural disturbances affect preferences of ungulate herbivores towards tree species and size classes; and how local and landscape-scale environmental factors affect spatial patterns of ungulate browsing in disturbed forest ecosystems. Our research was conducted in the Tatra National Park, a mountain range affected by large-scale intense disturbances over the last few decades. We used field data collected in a network of regularly distributed 600 circular sample plots where young trees were recorded and examined for browsing signs. Using forage ratio, the Ivlev’s electivity index and chi square tests, we found that the preferences of wild ungulates were similar to those known from undisturbed forests. Our analyses showed preference for deciduous species, especially rowan, sycamore maple and goat willow. The most common species, Norway spruce was strongly avoided by browsing ungulates. Short saplings from 0.5 m to 1.3 m tall were the most browsed size class. Effects of environmental variables on browsing were analyzed with zero-inflated negative binomial models. The occurrence of browsing was positively related to the total number of young trees and mature tree mortality. This suggests the influence of disturbances on spatial patterns of browsing pressure. The browsing frequency (number of browsed individuals per plot) was affected by mature tree mortality and densities of young palatable trees, including silver fir, sycamore maple and rowan. Elevation, geology, soil type, and potential solar radiation did not show any significant influence on the browsing frequency. Browsing frequency was also positively related to the distance to roads and hiking trails, indicating the role of human pressure upon the behaviour of ungulate herbivores. In addition, we analyzed the effects of accumulation of coarse woody debris (CWD) on browsing frequency and found this relationship to be nonlinear. Analysis for all tree species revealed that at low levels of CWD, the browsing frequency increased with CWD accumulation as a consequence of forest regeneration. However, a large amount of CWD (>25 m3) resulted in a decrease in browsing frequency, and this relationship was species-specific.

Feeding and damage-induced volatile cues make beetles disperse and produce a more even distribution of damage for sagebrush.

Induced plant responses to herbivory are common, and we have learned a lot about the mechanisms of induced resistance and their effects on herbivore performance. We know less about their effects on herbivore behaviour and especially on spatial patterns of damage. Theoretical models predict that induced responses can cause patterns of damage to become aggregated, random or even. A recent model predicted that informed herbivore movement coupled with communication between plants would make damage more even within individual plants. We tested these predictions in the field using a specialist beetle Trirhabda pilosa that feeds on sagebrush Artemisia tridentata. Both the beetle and the plant are well-documented to respond to damage-induced volatile cues. Beetle larvae were more likely to move from damaged leaves and leaves that had been exposed to volatiles from nearby damaged leaves compared to undamaged control leaves. Previous laboratory results indicated that beetles were more likely to choose undamaged leaves compared to damaged leaves or those exposed to volatile cues of damage. A comparison of damage patterns early in the season and after completion of beetle feeding revealed that variance in damage among branches decreased as the season progressed; that is, damage became more evenly distributed among the branches within a plant. Larvae damaged many leaves on a plant but removed relatively little tissue from each leaf. Herbivore movement and the spatial patterns of damage that it creates can be important in determining effects on plant fitness and other population processes. Dispersion of damage deserves more consideration in plant-herbivore studies.

Mosquito oviposition and larvae development in response to kairomones originated by different fish.

Predator-released kairomones indicating the presence of predatory fish are known to alter the behaviour and life-history traits of several aquatic herbivores. Culex mosquitoes (Diptera: Culicidae) respond to such cues by altering oviposition habitat selection and larval development time. These responses differ among fish species indicating composition differences among fish-released cues, but the recognition pattern is not clear. This study tested the dependence of fish recognition to co-evolution and the level of threat to larvae. We compared Culex responses to three fish, the invasive larvivorous Gambusia affinis (Cyprinodontiformes: Poeciliidae), the native larvivorous Aphanius mento (Cyprinodontiformes: Cyprinodontidae) and the native algivorous Garra rufa (Cypriniformes: Cyprinidae). The effects of cues released by the three fish on Culex oviposition and life-history shifts were compared in field mesocosms and lab tests. Our results showed that ovipositing females were significantly repelled only by cues originated from G. affinis, while developing larvae response was a more general one. Our results support the idea that fish-released kairomones differ in composition or quantities among different species.

Habitat Use by a Large Herbivore Guild in a Fenced South African Protected Area

In fenced protected areas with limited opportunities to disperse, resources and constraints vary in space and time, affecting herbivore behaviour. The distribution, availability and quality of resources, burnt areas, and potential inter-specific competition all play a role in sustaining populations of large sympatric African herbivores. We investigated the role of resources, constraints and interspecific relationships on habitat use by three ruminants – black and blue wildebeest (Connochaetes gnou, C. taurinus) and red hartebeest (Alcelaphus buselaphus), and a non-ruminant, plains zebra (Equus quagga), across seasons and in different landscape types in a South African reserve. Black wildebeest, blue wildebeest and red hartebeest preferred the open grassland landscape, with homogeneous vegetation, while zebra favoured the wooded grassland landscape, with more heterogeneous vegetation. Burnt areas and vegetation greenness were important for all species, while elevation represented a constraint for black wildebeest only. The presence/absence of other species was important in shaping landscape use for black and blue wildebeest, and this suggests the possibility of competition. Our findings confirm the importance of heterogeneity and, in particular, the important role of a planned burning regime in maintaining such heterogeneity to sustain multi-species herbivore assemblages in small fenced nature reserves, where competition might arise between species using similar resources.

Chemical parameters of decomposing dung in tropical forest as indicators of feeding behaviour of large herbivores: A step beyond classical stoichiometry

• Biomarkers, especially lignin differentiate dung of different herbivores, forest types and seasons. • Gaur and elephant dung show contrasting composition. • After 28 days of field exposure, chemical composition of dung from different herbivores converges. • Sugars and analytical pyrolysis are less suited as indicators of environmental controls of decomposition. Feeding behavior of large herbivores determines the composition of their dung and together with environmental factors the intensity of decomposition processes leading to the recycling of nutrients in tropical forests. Large herbivore dung and its decomposition has so far been characterized by stoichiometric analyses of elements such as C and N. The objective of our study was to examine the suitability of biomarker analyses and analytical pyrolysis to infer large herbivore feeding behavior and the decomposition of their dung in different environments. Our conceptual approach included exposure of fresh dung of a grazing ruminant (gaur, Bos gaurus ) and a non-ruminant mixed-feeder (the Asian elephant, Elephas maximus) in two tropical forest types (dry and moist) and analysis of dung biochemical composition in two seasons (dry and wet). To this end we characterized the dungs’ lignin and carbohydrate (sugar) signatures and pyrolysis products before and after 28 days of exposure. Our results showed that stoichiometric as well as biomarker analyses were able to differentiate gaur and elephant dung independent of season and forest type, while analytical pyrolysis products did not differ between dung types. The lignin signature of fresh dung additionally indicated the forage preference of animals in different forest types and seasons. During decomposition, C and N contents decreased and the chemical composition of both dung types converged. The lignin signature of dung at the end of the experiment showed higher lignin decomposition in moist forest and wet season than dry forest and dry season. We conclude that detailed biochemical analyses can provide deeper insights into the main controls of large herbivore dung and its decomposition in tropical forests than stoichiometric analysis. In particular lignin may be a suitable indicator to investigate large herbivore feeding behavior and the environmental conditions of their habitat.

Biodiversity Survey of Flower-Visiting Spiders Based on Literature Review and Field Study.

Many arthropods exhibit flower-visiting behavior, including a variety of spider species. However, as spiders are assumed to be strictly predatory, flower-visiting spiders are an often neglected group. We conducted a systematic biodiversity study of flower-visiting spiders based on published papers and field surveys. Most previous studies have focused on the herbivorous behavior of flower-visiting spiders (nectivory or pollinivory) and their effects on host flowers (tritrophic interactions with flower-visiting insects). In our field survey, we utilized standard transect walks (active sampling) and colored pan traps (passive sampling) to investigate species occurrence, diurnal and seasonal variation, and flower color preference of flower-visiting spiders. From the transect walks, crab spider species were found to be the dominant flower-visiting spiders and, based on all spider species, juvenile visitors were significantly more common than adults. Furthermore, in terms of spider number and species richness, tulips were the preferred flower to visit. For the pan traps, wolf spiders were found to be the dominant spider species. No significant differences were observed in the number of spiders caught in different colored pans, suggesting that color may not be an important flower trait in regard to spider preference. To the best of our knowledge, this study is the first to propose the term 'flower-visiting spiders' and conduct a systematic investigation of their diversity. However, this is preliminary research and further studies are required, especially as biodiversity is often closely linked to survey sites and ecotopes.

Haliotis tuberculata, a generalist marine herbivore that prefers a mixed diet, but with consistent individual foraging activity

AbstractWhile population foraging behaviour of herbivores has been extensively studied, individual choice is still poorly understood. Very few studies have focused on the individual consistency of foraging behaviour in marine herbivores. Because marine ectotherms are strongly influenced by their environment and because a mixed diet is appropriate for herbivores, we hypothesized that Haliotis tuberculata, a large marine gastropod, would not exhibit significant individual consistency in foraging activity and would display generalist food choices. To test these hypotheses, the behaviour of 120 abalone was studied using a choice test of eight macroalgal species over 3 weeks, with video recording 24 hr a day. In addition, primary components, secondary metabolites and toughness of the eight algae were measured. At the population level, food choice was mainly related to the protein composition and the toughness of the macroalgae. We found that H. tuberculata is a generalist species feeding on a variety of algae (IS = 0.64), even if 21% of the individuals can be considered to be specialists. However, in contrast to our hypothesis, highly consistent between‐individual variation was observed in foraging activity (ICC = 0.81 for time spent feeding and ICC = 0.74 for number of feeding visits per day). The high individual consistency of foraging activity has some ecological and evolutionary implications currently not understood for this marine herbivore.

The Role of Plant-Associated Microbes in Mediating Host-Plant Selection by Insect Herbivores.

There is increasing evidence that plant-associated microorganisms play important roles in shaping interactions between plants and insect herbivores. Studies of both pathogenic and beneficial plant microbes have documented wide-ranging effects on herbivore behavior and performance. Some studies, for example, have reported enhanced insect-repellent traits or reduced performance of herbivores on microbe-associated plants, while others have documented increased herbivore attraction or performance. Insect herbivores frequently rely on plant cues during foraging and oviposition, suggesting that plant-associated microbes affecting these cues can indirectly influence herbivore preference. We review and synthesize recent literature to provide new insights into the ways pathogenic and beneficial plant-associated microbes alter visual, olfactory, and gustatory cues of plants that affect host-plant selection by insect herbivores. We discuss the underlying mechanisms, ecological implications, and future directions for studies of plant-microbial symbionts that indirectly influence herbivore behavior by altering plant traits.