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Anthony Joern - One of the best experts on this subject based on the ideXlab platform.
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Grasshopper Fecundity Responses to Grazing and Fire in a Tallgrass Prairie
Environmental Entomology, 2011Co-Authors: Angela N. Laws, Anthony JoernAbstract:Grasshopper abundance and diversity vary with management practices such as fire and grazing. Understanding how Grasshopper life history traits such as fecundity respond to management practices is key to predicting Grasshopper population dynamics in heterogeneous environments. Landscape-level experimental fire and bison grazing treatments at the Konza Prairie Biological Station (Manhattan, KS) provide an opportunity to examine how management affects Grasshopper fecundity. Here we report on Grasshopper fecundity for nine common species at Konza Prairie. From 2007 to 2009, adult female Grasshoppers were collected every 3 wk from eight watersheds that varied in fire and grazing treatments. Fecundity was measured by examining female reproductive tracts, which contain a record of past and current reproductive activity. Body size was a poor predictor of fecundity for all species. Despite large differences in vegetation structure and composition with management regime (grazing and fire interval), we observed little effect of management on Grasshopper fecundity. Habitat characteristics (Grasshopper density, vegetation biomass, and vegetation quality; measured in 2008 and 2009) were better predictors of past fecundity than current fecundity, with species-specific responses. Fecundity increased throughout the summer, indicating that Grasshoppers were able to acquire sufficient nutritional resources for egg production in the early fall when vegetation quality is generally low. Because fecundity did not vary across management treatments, population stage structure may be more important for determining population level reproduction than management regime at Konza Prairie.
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Grasshopper orthoptera acrididae communities respond to fire bison grazing and weather in north american tallgrass prairie a long term study
Oecologia, 2007Co-Authors: Jayne L Jonas, Anthony JoernAbstract:Because both intrinsic and extrinsic factors influence insect population dynamics, operating at a range of temporal and spatial scales, it is difficult to assess their contributions. Long-term studies are ideal for assessing the relative contributions of multiple factors to abundance and community dynamics. Using data spanning 25 years, we investigate the contributions of weather at annual and decadal scales, fire return interval, and grazing by bison to understand the dynamics of abundance and community composition in Grasshopper assemblages from North American continental grassland. Each of these three primary drivers of grassland ecosystem dynamics affects Grasshopper population and community dynamics. Negative feedbacks in abundances, as expected for regulated populations, were observed for all feeding guilds of Grasshoppers. Abundance of Grasshoppers did not vary in response to frequency of prescribed burns at the site. Among watersheds that varied with respect to controlled spring burns and grazing by bison, species composition of Grasshopper assemblages responded significantly to both after 25 years. However, after more than 20 years of fire and grazing treatments, the number of years since the last fire was more important than the managed long-term fire frequency per se. Yearly shifts in species composition (1983-2005), examined using non-metric multidimensional scaling and fourth-corner analysis, were best explained by local weather events occurring early in Grasshopper life cycles. Large-scale patterns were represented by the Palmer Drought Severity Index and the North Atlantic Oscillation (NAO). The NAO was significantly correlated with annual mean frequencies of Grasshoppers, especially for forb- and mixed-feeding species. Primary grassland drivers-fire, grazing and weather-contributing both intrinsic and extrinsic influences modulate long-term fluctuations in Grasshopper abundances and community taxonomic composition.
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sustainable management of insect herbivores in grassland ecosystems new perspectives in Grasshopper control
BioScience, 2006Co-Authors: David H Branson, Anthony Joern, Gregory A SwordAbstract:Grasshoppers are insect herbivores common to grassland ecosystems worldwide. They comprise important components of biodiversity, contribute significantly to grassland function, and periodically exhibit both local and large-scale outbreaks. Because of Grasshoppers' potential economic importance as competitors with ungulate grazers for rangeland forage, periodic Grasshopper outbreaks in western US rangeland often elicit intervention over large areas in the form of chemical control. Available information combined with alternative underlying conceptual frameworks suggests that new approaches for sustainable management of Grasshopper outbreaks in US rangeland should be pursued. There are many reasons to believe that approaches to Grasshopper management that aim to reduce or prevent outbreaks are possible. These habitat manipulation tactics maintain existing ecological feedbacks responsible for sustaining populations at economically nonthreatening levels. Sustainable strategies to minimize the likelihood and extent of Grasshopper outbreaks while limiting the need for chemical intervention are a rational and attainable goal for managing grasslands as renewable resources.
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Resource-mediated impact of spider predation risk on performance in the Grasshopper Ageneotettix deorum (Orthoptera: Acrididae)
Oecologia, 2003Co-Authors: Bradford J. Danner, Anthony JoernAbstract:In response to increased exposure to predators when searching for food, many prey increase the frequency of antipredator behaviors, potentially reducing foraging rate and food intake. Such direct, nonlethal interactions between predators and prey resulting in reduced food intake can indirectly influence lifecycle development through effects on growth, developmental rate, and survival. We investigated the general hypothesis that individual performance of a herbivorous insect can be negatively affected when exposed to nonlethal predation risk, and that the response can be mediated by food quality. This hypothesis was tested using the common rangeland Grasshopper Ageneotettix deorum with and without exposure to common wolf spider predators (Lycosidae, Schizocosa spp.) on both untreated natural and fertilized vegetation. All spiders were rendered temporarily incapable of direct feeding by restricting function of the chelicerae with beeswax. Detectable responses by Grasshoppers to spiders indicate indirect consequences for lifecycle development. Grasshopper performance was measured as hind femur growth, duration of nymphal lifecycle stages, and survivorship in a caged field experiment conducted over 2 years. Grasshoppers developed faster and grew 3–5% larger when allowed to forage on fertilized vegetation in the absence of risk from a spider predator. Failure-time analysis illustrated enhanced survival probability in response to elevated food quality and the negative effects of Grasshopper susceptibility to nonlethal predation risk. Performance on food of relatively low, ambient quality with no predation risk equaled that of Grasshoppers caged with high quality vegetation in the presence of a modified spider. Increased resource quality can clearly moderate the negative life history responses caused by the behavioral modification of Grasshoppers when exposed to spider predation risk, a compensatory response.
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Biology of Grasshoppers
1990Co-Authors: R. F. Chapman, Anthony JoernAbstract:The Chemoreceptors (W. Blaney & M. Simmonds). Food Selection (R. Chapman). The Pattern of Feeding (S. Simpson). Nutrition (E. Bernays & S. Simpson). Water Regulation (E. Bernays). Grasshopper Thermoregulation (M. Chappell & D. Whitman). Jumping in Orthoptera (H. Bennet--Clark). Hormonal Control of Flight Metabolism in Locusts (G. Goldsworthy). Flight and Migration in Acridoids (R. Farrow). Territory--Based Mating Systems in Desert Grasshoppers: Effects of Host Plant Distribution and Variation (M. Greenfield & T. Shelly). Pheromones and Phase Transformation in Locusts (W. Loher). Grasshopper Chemical Communication (D. Whitman). The Endocrine Basis of Locust Phase Polymorphism (J. Dale & S. Tobe). Population Dynamics and Regulation in Grasshoppers (A. Joern & S. Gaines). Pathogenic Diseases of Grasshoppers (D. Streett & M. McGuire). Color Pattern Polymorphism (J. Dearn). Subject Index. Species Index.
Juergen Langewald - One of the best experts on this subject based on the ideXlab platform.
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field observations of the effects of fenitrothion and metarhizium anisopliae var acridum on non target ground dwelling arthropods in the sahel
Biological Control, 2003Co-Authors: Steven P Arthurs, Matthew B Thomas, Juergen LangewaldAbstract:The effect of the chemical insecticide, fenitrothion, and a mycoinsecticide based on Metarhizium anisopliae var. acridum on the activity of non-target epigeal arthropod scavengers was investigated in areas of open savannah in southeast Niger Republic, West Africa. Both insecticides were applied as full cover sprays to unreplicated 800 ha plots to assess their season-long control of Sahelian Grasshoppers. Compared with control plots, fenitrothion caused an immediate but temporary reduction in Grasshopper numbers, whereas M. anisopliae var. acridum provided delayed but prolonged control. Scavenging rates of pyrethroid-killed Grasshoppers placed along transects in unsprayed plots and those treated with fenitrothion and M. anisopliae var. acridum at various intervals after spraying were assessed. In the fenitrothion plot, an immediate reduction in scavenging activity occurred that was still apparent after 40 days at the plot center, although recovery at the plot edges was more rapid. By contrast scavenging rates remained high over equivalent areas in the M. anisopliae var. acridum and two untreated plots. Concurrent to the scavenging study, counts of Grasshopper cadavers resulting from the spray treatments were conducted. These counts revealed that the density of Grasshopper cadavers remained low throughout the M. anisopliae var. acridum plot and explained 20% in the fenitrothion plot. This shortfall in Grasshopper cadavers resulting from the spray treatment in the M. anisopliae var. acridum plot was unexpected because in a monitoring study, fungus-killed (unlike pyrethroid-killed) Grasshoppers were unattractive to scavengers and readily persisted in this plot, and thus should have become apparent. Given we did not observe significant Grasshopper dispersal, the scarcity of cadavers generated in the M. anisopliae var. acridum plot, together with unquantified visual observations, suggests that predation of infected but living Grasshoppers was high. Our data provide circumstantial evidence that the different effects of chemical and biological Grasshopper control on Grasshopper natural enemies may influence the efficacy of large-scale treatments.
Oswald J. Schmitz - One of the best experts on this subject based on the ideXlab platform.
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Fear on the move: predator hunting mode predicts variation in prey mortality and plasticity in prey spatial response
Journal of Animal Ecology, 2013Co-Authors: Jennifer R. B. Miller, Judith M. Ament, Oswald J. SchmitzAbstract:Summary 1. 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. 2. 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. 3. 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. 4. 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.
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fear of predation slows plant litter decomposition
Science, 2012Co-Authors: Michael S Strickland, Dror Hawlena, Mark A Bradford, Oswald J. SchmitzAbstract:Aboveground consumers are believed to affect ecosystem functioning by regulating the quantity and quality of plant litter entering the soil. We uncovered a pathway whereby terrestrial predators regulate ecosystem processes via indirect control over soil community function. Grasshopper herbivores stressed by spider predators have a higher body carbon-to-nitrogen ratio than do Grasshoppers raised without spiders. This change in elemental content does not slow Grasshopper decomposition but perturbs belowground community function, decelerating the subsequent decomposition of plant litter. This legacy effect of predation on soil community function appears to be regulated by the amount of herbivore protein entering the soil.
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herbivore physiological response to predation risk and implications for ecosystem nutrient dynamics
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Dror Hawlena, Oswald J. SchmitzAbstract:The process of nutrient transfer through an ecosystem is an important determinant of production, food-chain length, and species diversity. The general view is that the rate and efficiency of nutrient transfer up the food chain is constrained by herbivore-specific capacity to secure N-rich compounds for survival and production. Using feeding trials with artificial food, we show, however, that physiological stress-response of Grasshopper herbivores to spider predation risk alters the nature of the nutrient constraint. Grasshoppers facing predation risk had higher metabolic rates than control Grasshoppers. Elevated metabolism accordingly increased requirements for dietary digestible carbohydrate-C to fuel-heightened energy demands. Moreover, digestible carbohydrate-C comprises a small fraction of total plant tissue-C content, so nutrient transfer between plants and herbivores accordingly becomes more constrained by digestible plant C than by total plant C:N. This shift in herbivore diet to meet the altered nutrient requirement increased herbivore body C:N content, the C:N content of the plant community from which Grasshoppers select their diet, and Grasshopper fecal C:N content. Chronic predation risk thus alters the quality of animal and plant tissue that eventually enters the detrital pool to become decomposed. Our results demonstrate that herbivore physiology causes C:N requirements and nutrient intake to become flexible, thereby providing a mechanism to explain context dependence in the nature of trophic control over nutrient transfer in ecosystems.
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BEHAVIORALLY MEDIATED TROPHIC CASCADES: EFFECTS OF PREDATION RISK ON FOOD WEB INTERACTIONS
Ecology, 1997Co-Authors: Oswald J. Schmitz, Andrew P. Beckerman, Kathleen M. O’brienAbstract:Trophic cascades are regarded as important signals for top-down control of food web dynamics. Although there is clear evidence supporting the existence of trophic cascades, the mechanisms driving this important dynamic are less clear. Trophic cascades could arise through direct population-level effects, in which predators prey on herbivores, thereby decreasing the abundance of herbivores that impact plant trophic levels. Trophic cascades could also arise through indirect behavioral-level effects, in which herbivore prey shift their foraging behavior in response to predation risk. Such behavioral shifts can result in reduced feeding time and increased starvation risk, again lowering the impact of her- bivores on plants. We evaluated the relative importance of these two mechanisms, using field experiments in an old-field system composed of herbaceous plants, Grasshopper her- bivores, and spider predators. We created two treatments, Risk spiders that had their che- licerae glued, and Predation spiders that remained unmanipulated. We then systematically evaluated the impacts of these predator manipulations at behavioral, population, and food web scales in experimental mesocosms. At the behavioral level, Grasshoppers did not dis- tinguish between Risk spiders and Predation spiders. Grasshoppers exhibited significant shifts in feeding-time budget in the presence of spiders vs. when alone. At the Grasshopper population level, Risk spider and Predation spider treatments caused the same level of Grasshopper mortality, which was significantly higher than mortality in a control without spiders, indicating that the predation effects were compensatory to risk effects. At the food web level, Risk spider and Predation spider treatments decreased the impact Grasshoppers had on grass biomass, supporting the existence of a trophic cascade. Moreover, Risk spider and Predation spider treatments produced statistically similar effects, again indicating that predation effects on trophic dynamics were compensatory to risk effects. We conclude that indirect effects resulting from antipredator behavior can produce trophic-level effects that are similar in form and strength to those generated by direct predation events.
Steven P Arthurs - One of the best experts on this subject based on the ideXlab platform.
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field observations of the effects of fenitrothion and metarhizium anisopliae var acridum on non target ground dwelling arthropods in the sahel
Biological Control, 2003Co-Authors: Steven P Arthurs, Matthew B Thomas, Juergen LangewaldAbstract:The effect of the chemical insecticide, fenitrothion, and a mycoinsecticide based on Metarhizium anisopliae var. acridum on the activity of non-target epigeal arthropod scavengers was investigated in areas of open savannah in southeast Niger Republic, West Africa. Both insecticides were applied as full cover sprays to unreplicated 800 ha plots to assess their season-long control of Sahelian Grasshoppers. Compared with control plots, fenitrothion caused an immediate but temporary reduction in Grasshopper numbers, whereas M. anisopliae var. acridum provided delayed but prolonged control. Scavenging rates of pyrethroid-killed Grasshoppers placed along transects in unsprayed plots and those treated with fenitrothion and M. anisopliae var. acridum at various intervals after spraying were assessed. In the fenitrothion plot, an immediate reduction in scavenging activity occurred that was still apparent after 40 days at the plot center, although recovery at the plot edges was more rapid. By contrast scavenging rates remained high over equivalent areas in the M. anisopliae var. acridum and two untreated plots. Concurrent to the scavenging study, counts of Grasshopper cadavers resulting from the spray treatments were conducted. These counts revealed that the density of Grasshopper cadavers remained low throughout the M. anisopliae var. acridum plot and explained 20% in the fenitrothion plot. This shortfall in Grasshopper cadavers resulting from the spray treatment in the M. anisopliae var. acridum plot was unexpected because in a monitoring study, fungus-killed (unlike pyrethroid-killed) Grasshoppers were unattractive to scavengers and readily persisted in this plot, and thus should have become apparent. Given we did not observe significant Grasshopper dispersal, the scarcity of cadavers generated in the M. anisopliae var. acridum plot, together with unquantified visual observations, suggests that predation of infected but living Grasshoppers was high. Our data provide circumstantial evidence that the different effects of chemical and biological Grasshopper control on Grasshopper natural enemies may influence the efficacy of large-scale treatments.
Matthew B Thomas - One of the best experts on this subject based on the ideXlab platform.
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field observations of the effects of fenitrothion and metarhizium anisopliae var acridum on non target ground dwelling arthropods in the sahel
Biological Control, 2003Co-Authors: Steven P Arthurs, Matthew B Thomas, Juergen LangewaldAbstract:The effect of the chemical insecticide, fenitrothion, and a mycoinsecticide based on Metarhizium anisopliae var. acridum on the activity of non-target epigeal arthropod scavengers was investigated in areas of open savannah in southeast Niger Republic, West Africa. Both insecticides were applied as full cover sprays to unreplicated 800 ha plots to assess their season-long control of Sahelian Grasshoppers. Compared with control plots, fenitrothion caused an immediate but temporary reduction in Grasshopper numbers, whereas M. anisopliae var. acridum provided delayed but prolonged control. Scavenging rates of pyrethroid-killed Grasshoppers placed along transects in unsprayed plots and those treated with fenitrothion and M. anisopliae var. acridum at various intervals after spraying were assessed. In the fenitrothion plot, an immediate reduction in scavenging activity occurred that was still apparent after 40 days at the plot center, although recovery at the plot edges was more rapid. By contrast scavenging rates remained high over equivalent areas in the M. anisopliae var. acridum and two untreated plots. Concurrent to the scavenging study, counts of Grasshopper cadavers resulting from the spray treatments were conducted. These counts revealed that the density of Grasshopper cadavers remained low throughout the M. anisopliae var. acridum plot and explained 20% in the fenitrothion plot. This shortfall in Grasshopper cadavers resulting from the spray treatment in the M. anisopliae var. acridum plot was unexpected because in a monitoring study, fungus-killed (unlike pyrethroid-killed) Grasshoppers were unattractive to scavengers and readily persisted in this plot, and thus should have become apparent. Given we did not observe significant Grasshopper dispersal, the scarcity of cadavers generated in the M. anisopliae var. acridum plot, together with unquantified visual observations, suggests that predation of infected but living Grasshoppers was high. Our data provide circumstantial evidence that the different effects of chemical and biological Grasshopper control on Grasshopper natural enemies may influence the efficacy of large-scale treatments.
