Grasshopper Prey Research Articles

Polistes dominula (Hymenoptera: Vespidae) paper wasps detect native grasshoppers using olfactory cues

AbstractPolistes dominula is an invasive social wasp that preys on the grasshopper Dichroplus elongatus, which constitutes a potential agricultural pest in Northwest Patagonia. This grasshopper feeds on a wide variety of plants, the ‘Dandelion’ (Taraxacum officinale) being one of the main food resources. In this study, by means of a Y‐tube olfactometer, we analysed the use of olfactory cues by P. dominula in the detection of grasshoppers. Specifically, we evaluated the attractiveness of live grasshoppers, their traces (i.e. leaves with herbivory traces + prey faeces or only faeces) and herbivory‐free leaves. The results showed that foragers equally chose olfactory cues emitted by grasshoppers and leaves with herbivory traces + faeces and herbivory‐free leaves, suggesting that the leaves of the host plant also have an important role in the searching behaviour. The current research is the first to demonstrate that the invasive paper wasp orients its search towards either the presence of grasshopper prey or the volatiles of plant leaves. These findings shed new light on predator‐prey interactions mediated by olfactory cues in P. dominula, which may play a biological role as a natural controller of D. elongatus, phytophagous pest in the invaded ecosystems.

Fear of predators alters herbivore regulation of soil microbial community function.

Fear of predation can affect important ecosystem processes by altering the prey traits expression that, in turn, regulates the quantity and quality of nutritional inputs to soil. Here, we aimed to assist in bridging a knowledge gap in this cascading chain of events by exploring how risk of spider predation may affect grasshopper prey performances, and the activity of various microbial extracellular enzymes in the soil. Using a mesocosms field-experiment, we found that grasshoppers threatened by spider predation ate less, grew slower, and had a higher body carbon to nitrogen ratio. Herbivory increased activity of all microbial extracellular enzymes examined, likely due to higher availability of root exudates. Predation risk had no effect on C-acquiring enzymes but decreased activity of P-acquiring enzymes. We found contrasting results regarding the effect of predation on the activity of N-acetyl-glucosaminidase and leucine arylamidase N-acquiring enzymes, suggesting that predation risk may alter the composition of N-inputs to soil. Our work highlighted the importance of soil microbial enzymatic activity as a way to predict how changes in the aboveground food-web dynamics may alter key ecosystem processes like nutritional-cycling.

Woodlice change the habitat use of spiders in a different food chain.

BackgroundIn old field systems, the common woodlouse may have an indirect effect on a nursery web spider. Woodlice and nursery web spiders feed in different food chains, yet previous work demonstrated that the presence of woodlice is correlated with higher predation success by nursery web spiders upon their grasshopper prey. This finding suggested a new hypothesis which links two seemingly disparate food chains: when woodlice are present, the spider predator or the grasshopper prey changes their location in the vegetative canopy in a way that increases their spatial overlap and therefore predation rate. However, warming temperatures may complicate this phenomenon. The spider cannot tolerate thermal stress, meaning warming temperatures may cause the spider to move downwards in the vegetative canopy or otherwise alter its response to woodlice. Therefore, we would expect warming and woodlice presence to have an interactive effect on predation rate.MethodsWe conducted behavioral experiments in 2015, 2017, and 2018 to track habitat domains—the use of the vegetative canopy space by grasshoppers and spiders—in experimental cages. Then, we used three models of spider movement to try to explain the response of spiders to woodlice: expected net energy gain, signal detection theory, and individual-based modelling.ResultsHabitat domain observations revealed that spiders shift upward in the canopy when woodlice are present, but the corresponding effect on grasshopper prey survival was variable over the different years of study. Under warming conditions, spiders remained lower in the canopy regardless of the presence of woodlice, suggesting that thermal stress is more important than the effect of woodlice. Our modelling results suggest that spiders do not need to move away from woodlice to maximize net energy gain (expected net energy gain and signal detection theory models). Instead spider behavior is consistent with the null hypothesis that they move away from unsuccessful encounters with woodlice (individual-based simulation). We conclude that mapping how predator behavior changes across biotic (e.g. woodlouse presence) and abiotic conditions (e.g. temperature) may be critical to anticipate changes in ecosystem dynamics.

Condition-dependent foraging in the wolf spider Hogna baltimoriana

Spiders are major predators of terrestrial arthropods, so understanding the underlying drivers of spider foraging is crucial for understanding how energy and nutrients pass through terrestrial food webs. We tested predictions made by allometric and optimal foraging theory using the wolf spider Hogna baltimoriana and grasshopper prey as a model (Caelifera). Allometric foraging theory predicts that functional response parameters will be dependent on body size, whereas optimal foraging theory asserts the importance of energetic state in determining foraging behaviors. We found that space clearance rate (type II functional response parameter a) was negatively related to the ratio of abdomen width to carapace width (a measure of energetic state) but not to body mass or carapace width. Thus, a key factor in determining the strength of foraging interactions in spiders may be recent energy intake that determines the current body condition of foragers.

Opposite effects of daytime and nighttime warming on top‐down control of plant diversity

Ecological analyses of climate warming explore how rising mean temperature will affect the species composition of communities and their associated functioning. Experimentation usually presumes that warming arises from simultaneous increase in daily maximum (daytime) and minimum (nighttime) temperatures. Yet evidence shows that mean warming arises largely from increasing nighttime temperatures. We report on a 3-yr experiment that compared the effects of daytime and nighttime warming on a community comprising herbaceous plants, grasshopper herbivores and predatory spiders. We warmed experimental mesocosms 3-4°C above ambient control treatments during the daytime (06:00-18:00h) or nighttime (18:00-06:00h). Daytime warming caused spiders to seek a thermal refuge low in the plant canopy and away from grasshopper prey, which allowed grasshoppers to spend more time feeding on a competitively dominant plant species. Nighttime had the opposite effect, where spider activity increased causing grasshoppers to reduce feeding. Two consecutive years of daytime warming resulted in a suppression of the competitive dominant plant and increased the diversity and evenness of the plant community, whereas nighttime warming had opposite effects. These results show that ignoring the nuanced effects of asymmetrical warming may lead to inaccurate conclusions about the net effects of climate change on ecosystems.

A Shift in Escape Strategy by Grasshopper Prey in Response to Repeated Pursuit

We used grasshoppers as a model organism to examine the response of prey to repeated approach from a persistent predator (human observer). We randomly assigned adult Chortophaga australior (Southern Greenstriped Grasshopper) to either low- or highrisk treatments. For both groups, we approached each grasshopper during 15 consecutive encounters and recorded the distance fled (DF) and overall flight path. We approached grasshoppers assigned to the low-risk treatment after a 30-second delay upon landing between each escape flight. Those in the high-risk treatment were approached immediately upon landing and given no opportunity to recover. Grasshoppers assigned to the low-risk treatment exhibited an erratic, or protean flight path to evade detection and traveled shorter distances across consecutive encounters. Those in the high-risk treatment exhibited longer escape flights that were more commonly oriented directly away from the approach of the observer. The results of our study provide additional evidence that prey may shift escape strategies in response to real-time assessment of predation risk.

Prey Luring Coloration of A Nocturnal Semi‐Aquatic Predator

AbstractBody coloration serves a variety of purposes in animals. Diurnal and nocturnal predators such as spiders may use their body coloration to lure prey. We predicted here that the white patches on the forelegs on females of the nocturnal semi‐aquatic spider Dolomedes raptor lure prey, explaining why they are primarily displayed when the spider forages along the water edge. To test our prediction, we developed a color vision model assessing whether the patches are visible to pygmy grasshoppers, the spider's primary prey. We conducted a field experiment using cardboard dummies that resemble D. raptor in size, shape, and color, but with half of them lacking leg patches, and we staged interactions between pygmy grasshoppers and D. raptor with and without leg patches in a greenhouse. We found the white patches to be visible to grasshoppers. The dummies with white patches attracted more grasshopper prey than the dummies without the patches. Moreover, grasshoppers were more attracted to spiders when their white patches were present. Our results supported the hypothesis that the white patches of D. raptor lure prey. Our findings, nevertheless, could not be explained as the spider's body coloration acting as a sensory trap but it should not be ruled out. More studies on a wider range of predators and prey will give more meaningful insights into the co‐evolution of predatory lures and prey sensory modalities.

Fear on the move: predator hunting mode predicts variation in prey mortality and plasticity in prey spatial response

Ecologists have long searched for a framework of a priori species traits to help predict predator-prey interactions in food webs. Empirical evidence has shown that predator hunting mode and predator and prey habitat domain are useful traits for explaining predator-prey interactions. Yet, individual experiments have yet to replicate predator hunting mode, calling into question whether predator impacts can be attributed to hunting mode or merely species identity. We tested the effects of spider predators with sit-and-wait, sit-and-pursue and active hunting modes on grasshopper habitat domain, activity and mortality in a grassland system. We replicated hunting mode by testing two spider predator species of each hunting mode on the same grasshopper prey species. We observed grasshoppers with and without each spider species in behavioural cages and measured their mortality rates, movements and habitat domains. We likewise measured the movements and habitat domains of spiders to characterize hunting modes. We found that predator hunting mode explained grasshopper mortality and spider and grasshopper movement activity and habitat domain size. Sit-and-wait spider predators covered small distances over a narrow domain space and killed fewer grasshoppers than sit-and-pursue and active predators, which ranged farther distances across broader domains and killed more grasshoppers, respectively. Prey adjusted their activity levels and horizontal habitat domains in response to predator presence and hunting mode: sedentary sit-and-wait predators with narrow domains caused grasshoppers to reduce activity in the same-sized domain space; more mobile sit-and-pursue predators with broader domains caused prey to reduce their activity within a contracted horizontal (but not vertical) domain space; and highly mobile active spiders led grasshoppers to increase their activity across the same domain area. All predators impacted prey activity, and sit-and-pursue predators generated strong effects on domain size. This study demonstrates the validity of utilizing hunting mode and habitat domain for predicting predator-prey interactions. Results also highlight the importance of accounting for flexibility in prey movement ranges as an anti-predator response rather than treating the domain as a static attribute.

The many ecologies of behavior

The many ecologies of behavior

Effects of Predator Hunting Mode on Grassland Ecosystem Function

The way predators control their prey populations is determined by the interplay between predator hunting mode and prey antipredator behavior. It is uncertain, however, how the effects of such interplay control ecosystem function. A 3-year experiment in grassland mesocosms revealed that actively hunting spiders reduced plant species diversity and enhanced aboveground net primary production and nitrogen mineralization rate, whereas sit-and-wait ambush spiders had opposite effects. These effects arise from the different responses to the two different predators by their grasshopper prey-the dominant herbivore species that controls plant species composition and accordingly ecosystem functioning. Predator hunting mode is thus a key functional trait that can help to explain variation in the nature of top-down control of ecosystems.

AGGREGATE EFFECTS OF MULTIPLE PREDATOR SPECIES ON A SHARED PREY

We evaluated the potential for emergent nonlinear effects of multiple pred- ators on mortality of a shared prey species by conducting experiments in cages in an old field. We examined interactions among three spider predators, Pisaurina mira, Phidippus rimator, and Rabidosa rabida, and a grasshopper prey Melanoplusfemurrubrum. The pred- ators have disparate hunting behaviors and are located in different parts of the vegetation canopy used by the grasshoppers, suggesting the potential for nonlinear effects. We ex- amined the effects of spider species singly and in all possible combinations using a sub- stitutive design in each of two years. Multiple predator effects on grasshopper mortality were generally the average of the corresponding single-species effects, indicating that the species effects were largely substitutable. This result indicates that it is reasonable to aggregate these predator species into a single functional unit, despite their disparate in- dividual effects on grasshopper prey, when modeling predator-prey interactions for this system.

Effects of Top Predator Species on Direct and Indirect Interactions in a Food Web

Current theory on trophic interactions in food webs assumes that ecologically similar species can be treated collectively as a single functional unit such as a guild or trophic level. This theory implies that all species within that unit transmit identical direct and indirect effects throughout the community. We evaluated this assumption by conducting experiments to compare the direct and indirect effects of three top-predator species, belonging to the same hunting spider guild, on the same species of grasshopper and on old-field grasses and herbs. Observations under field conditions revealed that each spider species exhibited different hunting behavior (i.e., sit-and-wait, sit-and-pursue, and active hunting) and occupied different locations within the vegetation canopy. These differences resulted in different direct effects on grasshopper prey. Grasshoppers demonstrated significant behavioral (diet) shifts in the presence of sit-and-wait and sit-and-pursue species but not when faced with actively hunting species. Grasshopper density was significantly reduced by spider species that occupied lower parts of the vegetation canopy (sit-and-pursue and actively hunting species), but it was not significantly reduced by the sit-and-wait spider species that occupied the upper parts of the canopy. These direct effects manifested themselves differently in the plant trophic level. The sit-and-wait spider caused indirect effects on plants by changing grasshopper foraging behavior (a trait-mediated effect). The sit-and-pursue spider caused indirect effects by reducing grasshopper density (density-mediated effects); the effects of changes in grasshopper behavior were thus not reflected in the plant trophic level. The actively hunting spiders had strictly density-mediated indirect effects on plants. The study offers mechanistic insight into how predator species within the same guild can have very different trophic effects in food webs. Thus classical modeling approaches that treat all predator species as a single functional unit may not adequately capture biologically relevant details that influence community dynamics.

EFFECTS OF TOP PREDATOR SPECIES ON DIRECT AND INDIRECT INTERACTIONS IN A FOOD WEB

Current theory on trophic interactions in food webs assumes that ecologically similar species can be treated collectively as a single functional unit such as a guild or trophic level. This theory implies that all species within that unit transmit identical direct and indirect effects throughout the community. We evaluated this assumption by conducting experiments to compare the direct and indirect effects of three top-predator species, be- longing to the same hunting spider guild, on the same species of grasshopper and on old- field grasses and herbs. Observations under field conditions revealed that each spider species exhibited different hunting behavior (i.e., sit-and-wait, sit-and-pursue, and active hunting) and occupied different locations within the vegetation canopy. These differences resulted in different direct effects on grasshopper prey. Grasshoppers demonstrated significant be- havioral (diet) shifts in the presence of sit-and-wait and sit-and-pursue species but not when faced with actively hunting species. Grasshopper density was significantly reduced by spider species that occupied lower parts of the vegetation canopy (sit-and-pursue and actively hunting species), but it was not significantly reduced by the sit-and-wait spider species that occupied the upper parts of the canopy. These direct effects manifested themselves differ- ently in the plant trophic level. The sit-and-wait spider caused indirect effects on plants by changing grasshopper foraging behavior (a trait-mediated effect). The sit-and-pursue spider caused indirect effects by reducing grasshopper density (density-mediated effects); the effects of changes in grasshopper behavior were thus not reflected in the plant trophic level. The actively hunting spiders had strictly density-mediated indirect effects on plants. The study offers mechanistic insight into how predator species within the same guild can have very different trophic effects in food webs. Thus classical modeling approaches that treat all predator species as a single functional unit may not adequately capture biologically relevant details that influence community dynamics.

Feeding behavior, mastication, and tooth wear in the western tarsier (Tarsius bancanus)

We assessed feeding and masticatory function in western tarsiers, Tarsius bancanus,from field study, from videotaped recordings of the feeding and chewing behavior of wild-caught animals in temporary captivity, from dissections of the muscles of mastication, and from scanning electron microscopic (SEM) examination of wear features of the teeth. Ingestion of large items of animal prey is made possible by the animal’s extremely wide gape. Anterior translation of the knob-like mandibular condyle in the anteroposteriorly elongated mandibular fossa makes possible a gape angle of 60–70‡. We observed two means of ingestion of grasshopper prey: ingestion by mastication, in which the postcanine teeth sever and reduce bites of the food as it is thrust into the mouth cavity, and repeated gape-shove sequences, during which the tarsier pushed grasshoppers of large diameter into the anterior part of its mouth and attempted to sever a bite with its anterior teeth. Morsels were successfully severed after three to five such sequences, and reduced quickly,with relatively few powerful, crushing chews. The insect cuticle was not evenly comminuted during mastication. We observed a marked side-to-side grinding component in the normal chewing cycle of T. bancanuson videotape and confirmed it by SEM. The main jaw adductors are bulky, long-fibered muscles that can accommodate wide grapes and still generate, at wide degrees of gape,the high occlusal pressures necessary to fracture thick chitinous exoskeletons of the scarabid beetles that form a substantial element of the western tarsier’s diet.

The Relationship Between Prey Size and Handling Time and Prey Size and Capture Success in 3 Sympatric Species of Dasyurid Marsupials

Regressions of handling time on prey weight were determined for the dasyurids Srninthopsis hirtipes, S. ooldea and Ningaui spp. preying on grasshoppers and cockroaches in the laboratory. In all cases, a simple linear regression fitted the relationships better than logarithmic models. The slopes of the regression lines were steeper for grasshopper prey than for cockroach prey in all species, and for each prey type the slopes for the predators were ranked in order of predator weight. Capture efficiency, defined as the proportion of successful attacks, did not vary significantly between predator species and prey types, and all predators showed declining capture efficiencies with increasing prey size. Niche separation in these dasyurids does not appear to be based on different optimal prey sizes for each species.

Optimal foraging and intraspecific diet differences in the lizard Cnemidophorus sexlineatus.

Previous studies have shown that adult and juvenile six-lined racerunners, Cnemidophorus sexlineatus, consume different sizes and taxa of arthropod prey. the purpose of this study was to determine if these differences could be explained in terms of energy cost and benefit parameters as related by the optimal diet model. Handling times and encounter rates with each of five categories of prey were determined by direct observation of lizard foraging behavior in the field. Energetic cost of search and energy content of prey were estimated from data in the literature. Mean values of all these parameters were used in the classic optimal diet model to determine which prey types yield the greatest rate of net energy gain for adult and juvenile racerunners. Grasshopper-like insects were the most valuable prey for adults, whereas plant and ground arthropods were the most valuable prey for juveniles. These findings correspond to the age-class specific diet differences.Each age-class adopts foraging tactics that increase the chance of finding the most valuable prey. Adult racerunners move hastily over a large area to find the relatively rare, but large and mobile grasshopper prey. Juveniles move much more slowly, and carefully investigate twigs and leaves to find smaller, cryptic plant and ground arthropods. However these foraging tactics do not preclude the taking of less valuable prey items, should they be encountered. This is because it is energetically better on average to eat the prey item rather than skipping it to search for better prey, except for the case of juvenile racerunners eating grasshoppers. That juvenile racerunners will attempt to capture and consume even very large grasshoppers is contrary to the expectations derived from the optimal diet model. This behavior may be the result of the foraging "rule of thumb" racerunners use to find their prey.