Effects of grasshoppers on prairies: Herbivore composition matters more than richness in three grassland ecosystems.

Understanding how biodiversity affects ecosystem processes is a key question in ecology. Previous research has found that increasing plant diversity often enhances many ecosystem processes, but less is known about the role of consumer diversity to ecosystem processes, especially in terrestrial ecosystems. Furthermore, we do not know how general biodiversity responses are among ecosystem types. We examined the role of insect herbivore (Orthoptera) diversity on plant production using parallel field experiments in three grassland ecosystems (mixed grass prairie, tallgrass prairie and coastal tallgrass prairie) to determine whether the effects of grasshopper diversity were consistent among sites. Using mesocosms, we manipulated orthopteran species richness (0, 1, 2, 3 or 4 species), functional richness (number of functional feeding groups present; 0, 1 or 2 functional groups) and functional composition (composition of functional groups present; mixed-feeders only, grass-feeders only, both mixed-feeders and grass-feeders). Diversity treatments were maintained throughout the experiment by replacing dead individuals. Plant biomass was destructively sampled at the end of the experiment. We found no effect of species richness or functional richness on plant biomass. However, herbivore functional composition was important, and effects were qualitatively similar across sites: The presence of only grass-feeding species reduced plant biomass more than either mixed-feeding species alone or both groups together. Orthopterans had consistent effects across a range of abiotic conditions, as well as different plant community and orthopteran community compositions. Our results suggest that functional composition of insect herbivores affects plant communities in grasslands more than herbivore species richness or functional richness, and this pattern was robust among grassland types.

Power Bars: Mormon Crickets Get Immunity Boost from Eating Grasshoppers.

In addition to feeding on plants, Mormon crickets Anabrus simplex Haldeman, 1852 predate on invertebrates, including one another, which effectively drives their migration. Carnivory derives from lack of dietary protein, with Mormon crickets deprived of protein having less phenoloxidase (PO) available to combat foreign invaders, such as fungal pathogens. Because Mormon crickets commonly occur with grasshoppers that feed on the same plants, we investigated interactions between grasshoppers and Mormon crickets, and hypothesized that if Mormon crickets are predatory on grasshoppers, grasshopper abundance would influence the protein available to Mormon crickets and their immunity. In a field setting, we varied densities of Mormon crickets (0, 10, or 20 per cage) and grasshoppers Melanoplus borealis (0, 15, 30, or 45) in 68 1-m2 cages. After one month, we measured Mormon cricket dietary preferences and PO activity. As predicted, artificial diet consumption shifted away from protein as grasshopper density increased, and immunocompetence, as measured by PO activity, also increased with grasshopper availability. Although nitrogen availability in the vegetation decreased with increasing insect density, predation became an important source of protein for Mormon crickets that enhanced immunity. Grasshoppers can be an important source of dietary protein for Mormon crickets, with prey availability affecting Mormon cricket immunity to diseases.

Oilfield Reclamation Recovers Productivity but not Composition of Arthropod Herbivores and Predators.

Arthropods are key components of grassland ecosystems. Though arthropod communities are often strongly influenced by plant communities, plants and arthropods may respond differently to disturbance. Studying plant responses alone may, therefore, not fully capture altered ecosystem dynamics; thus multi-trophic approaches are critical to fully understand ecosystem responses to disturbance. Energy development is a large-scale driver of disturbance in northern Great Plains rangelands, and recovery of arthropod communities following reclamation is not well understood. We sampled Orthoptera and spiders in western North Dakota, United States, in 2016. Samples were collected from 14 reclaimed oil well sites ('reclaims') 2-33 yr since reclamation, and native prairie at two distances (50 and 150 m) from reclaim edges. Overall Orthopteran and spider abundances on reclaims and native prairie did not differ; however, Orthopteran community composition and species abundances were distinct on reclaims versus native prairie, including increased abundances of Melanoplus femurrubrum (De Geer) (Orthoptera: Acrididae) (a noted crop pest) on reclaims. In contrast, NMS analyses revealed no differences in spider community composition between reclaims and native prairie, although abundances of one group (Salticidae) strongly decreased on reclaims. We present one of the first studies to investigate impacts of energy development and reclamation on arthropod communities. While reclamation efforts successfully recovered abundances and biomass of arthropod herbivores and predators, Orthopteran (but not spider) community composition on reclaims has not recovered to match that of intact prairie even 30 yr after reclamation. These findings suggest that energy development may have long-term or potentially irreversible impacts to rangeland arthropod communities.

Decoupled recovery of ecological communities after reclamation.

Grassland restoration is largely focused on creating plant communities that match reference conditions. However, these communities reflect only a subset of the biodiversity of grassland systems. We conducted a multi-trophic study to assess ecosystem recovery following energy development for oil and gas extraction in northern US Great Plains rangelands. We compared soil factors, plant species composition and cover, and nematode trophic structuring between reclaimed oil and gas well sites ("reclaims") that comprise a chronosequence of two-33 years since reclamation and adjacent, undeveloped rangeland at distances of 50 m and 150 m from reclaim edges. Soils and plant communities in reclaims did not match those on undeveloped rangeland even after 33 years. Reclaimed soils had higher salt concentrations and pH than undeveloped soils. Reclaims had lower overall plant cover, a greater proportion of exotic and ruderal plant cover and lower native plant species richness than undeveloped rangeland. However, nematode communities appear to have recovered following reclamation. Although total and omni-carnivorous nematode abundances differed between reclaimed well sites and undeveloped rangeland, community composition and structure did not. These findings suggest that current reclamation practices recover the functional composition of nematode communities, but not soil conditions or plant communities. Our results show that plant communities have failed to recover through reclamation: high soil salinity may create a persistent impediment to native plant growth and ecosystem recovery.

Influence of a large late summer precipitation event on food limitation and grasshopper population dynamics in a northern Great Plains grassland.

The complex interplay between grasshoppers, weather conditions, and plants that cause fluctuations in grasshopper populations remains poorly understood, and little is known about the ecological processes that generate grasshopper outbreaks. Grasshopper populations respond to interacting extrinsic and intrinsic factors, with yearly and decadal weather patterns and the timing of precipitation all potentially important. The effects of initial and increasing grasshopper densities on grasshopper survival and reproductive correlates were examined at a northern mixed-grass prairie site through manipulations of grasshopper densities inside 10-m2 cages. High-quality grass growth occurred after a 9.1-cm mid-August rain. Reduced proportional survival was apparent in the two higher density treatments before the rain, indicative of food-limited density-dependent mortality. However, the large late summer rainfall event mediated the effects of exploitative competition on demographic characteristics because of the high-quality vegetation growth. This led to weaker effects of food limitation on survival and reproduction at the end of the experiment. The results indicate a direct link between weather variation, resource quality and grasshopper population dynamics led to a severe grasshopper outbreak and show that infrequent large precipitation events can have significant effects on population dynamics. Additional research is needed to examine the importance of infrequent large precipitation events on grasshopper population dynamics in grassland ecosystems.

Effects of Altered Seasonality of Precipitation on Grass Production and Grasshopper Performance in a Northern Mixed Prairie.

Climatic changes are leading to differing patterns and timing of precipitation in grassland ecosystems, with the seasonal timing of precipitation affecting plant biomass and plant composition. No previous studies have examined how drought seasonality affects grasshopper performance and the impact of herbivory on vegetation. We modified seasonal patterns of precipitation and grasshopper density in a manipulative experiment to examine if seasonality of drought combined with herbivory affected plant biomass, nitrogen content, and grasshopper performance. Grass biomass was affected by both precipitation and grasshopper density treatments, while nitrogen content of grass was higher with early-season drought. Proportional survival was negatively affected by initial density, while survival was higher with early drought than with full-season drought. Drought timing affected the outcome, with early summer drought increasing grass nitrogen content and grasshopper survival, while season-long and late-season drought did not. The results support arguments that our knowledge of plant responses to seasonal short-term variation in climate is limited and illustrate the importance of experiments manipulating precipitation phenology. The results confirm that understanding the season of drought is critical for predicting grasshopper population dynamics, as extreme early summer drought may be required to strongly affect Melanoplus sanguinipes (F.) performance.

Drought Impacts on Competition in Phoetaliotes nebrascensis (Orthoptera Acrididae) in a Northern Mixed Grassland.

Global climate change is predicted to significantly modify patterns of precipitation, making it critical to develop a better understanding of how this will modify biotic interactions. Short-term to decadal-scale weather patterns can impact grasshopper population dynamics, but drought impacts on grasshoppers have rarely been studied in manipulative experiments. A cage experiment was conducted in eastern Montana to examine the impact of intra- and interspecific competition and precipitation manipulation treatments on performance of a common melanopline grasshopper Phoetaliotes nebrascensis (Thomas). High-density and drought treatments had similarly strong negative impacts on food availability. Proportional grasshopper survival did not differ significantly by treatment, but density dependence was evident in both body size and reproductive traits. The impact of precipitation and density treatments on grasshopper body size and reproduction were typically similar in magnitude and much larger than interspecific competition, with the exception of male femur length. Even with high late summer precipitation, drought had strong effects on individual body size and future reproduction. This study provides valuable information on population dynamics of an abundant grasshopper, with moderate precipitation reductions negatively affecting reproduction and body size. No positive impacts of drought as predicted by the plant stress hypothesis were observed. The study reinforces the need to examine drought manipulations to better predict grasshopper population changes due to changing climate conditions.

Density-dependent effects of an early season insect herbivore on a later developing insect herbivore.

Although most North American grasshopper species overwinter as eggs, some species hatch in late summer, overwinter as nymphs, and become adults in late spring. These species periodically reach outbreak densities, but it is unknown if they impact the population dynamics of later developing egg-overwintering grasshopper species. Two experiments were conducted in a northern mixed-grass prairie to examine the effects of herbivory by nymph-overwintering grasshoppers on survival of an egg-overwintering grasshopper, Ageneotettix deorum. When very high densities of nymph-overwintering grasshoppers reduced grass biomass by 80%, survival of A. deorum nymphs was significantly reduced. There was no effect of early season herbivory at a lower density of 16/m(2) on survival of A. deorum nymphs. The effects of early season herbivory appear consistent with exploitative competition. Although a strong reduction in peak grass biomass caused by early season herbivory negatively affected late season grass-feeding grasshopper densities, additional research is needed to examine the potential importance of early summer herbivory on population dynamics of later developing grasshoppers.

An experimental analysis of grasshopper community responses to fire and livestock grazing in a northern mixed-grass prairie.

The outcomes of grasshopper responses to both vertebrate grazing and fire vary across grassland ecosystems, and are strongly influenced by local climactic factors. Thus, the possible application of grazing and fire as components of an ecologically based grasshopper management strategy must be investigated in regional studies. In this study, we examined the effects of grazing and fire on grasshopper population density and community composition in a northern Great Plains mixed-grass prairie. We employed a large-scale, replicated, and fully-factorial manipulative experimental design across 4 yr to examine the separate and interactive effects of three grazing systems in burned and unburned habitats. Grasshopper densities were low throughout the 4-yr study and 1 yr of pretreatment sampling. There was a significant fire by grazing interaction effect on cumulative density and community composition, resulting from burned season long grazing pastures having higher densities than unburned pastures. Shannon diversity and grasshopper species richness were significantly higher with twice-over rotational livestock grazing. The ability to draw strong conclusions regarding the nature of species composition shifts and population changes in the presence of fire and grazing is complicated by the large site differences and low grasshopper densities. The results reinforce the importance of long-term research to examine the effects of habitat manipulation on grasshopper population dynamics.