Recipient Organization
UNIVERSITY OF HOUSTON SYSTEM
4800 CALHOUN ST STE 316
HOUSTON,TX 770042610
Performing Department
Biological Sciences
Non Technical Summary
Sustainable grazing systems that support the production of meat and other products for human consumption depend upon healthy, functioning rangeland ecosystems. Grasshoppers are an important, native component of these rangeland systems, but they compete with livestock for forage. Grasshopper outbreaks often trigger managers to use chemical control measures with the use of broad spectrum pesticides that kill insects indiscriminately. However, most grasshopper species are not pests and may actually be beneficial to rangelands. Individual grasshopper species can increase primary production, nutrient cycling, and influence soil microbial communities. However, we do not understand if the number and composition of grasshopper species present in a rangeland affect how that rangeland functions, or how environmental factors like productivity mediate those responses.Our goals are to determine: (1) the role of grasshopper diversity in rangeland ecosystems and (2) how the effects of grasshopper diversity vary with primary productivity. To achieve these goals, we will conduct a two year field experiment in a grassland in Texas to examine the role of grasshopper diversity in grassland ecosystems. We will manipulate grasshopper diversity (1, 2, 3, or 4 species) in large cages (0.5 m2) placed over native vegetation in a grassland. To test the effects of primary productivity, we will fertilize some of the diversity treatments. We will then measure a suite of important ecosystem processes in each diversity and productivity treatment, including decomposition, nutrient cycling, primary production, as well as responses of plant and soil microbial communities. These data will enable us to determine what role grasshopper diversity plays in grassland ecosystems, and whether the effects of grasshopper diversity vary with productivity.Our research will lead to better understanding of the role of grasshoppers and grasshopper diversity in rangeland ecosystems. This will provide information on insect-plant interactions, mechanisms of plant responses to insects, and improved biologically-based grasshopper management approaches to potentially support sustainable grazing systems. ?
Animal Health Component
40%
Research Effort Categories
Basic
60%
Applied
40%
Developmental
(N/A)
Goals / Objectives
Goal 1: Determine if grasshopper species richness or functional richness (hereafter grasshopper diversity) influence the structure (composition of plant and microbial communities) and functioning (plant productivity, decomposition, nutrient cycling, and microbial functioning) of rangeland ecosystems.Objectives:1. Conduct a two-year field experiment to examine the effects of grasshopper diversity on grassland ecosystem structure and function. The experiment will manipulate grasshopper diversity in field enclosures.Goal 2: Determine if soil nutrient availability mediates the role of grasshopper diversity in the functioning of rangeland ecosystems.Objectives:1. As part of the two-year field experiment described above, we will add a fertilizer treatment, where nitrogen will be added to several of the diversity treatments. We will then examine the effects of grasshopper diversity on grassland ecosystem structure and function in treatments at ambient vs. elevated nutrient availability.Goal 3: Prepare a standard USDA grant to examine the effects of grasshopper diversity on grassland ecosystem processes along a latitudinal gradient of productivity levels, using pilot data from this seed grant.Objectives:1. Conduct a two-year field experiment as described above.2. In year 1, we will conduct a survey of plant and grasshopper communities in 8 grasslands along a latitudinal gradient. We will measure plant quality, plant community species richness, grasshopper density and species richness and look for latitudinal patterns.3. Analyze data from the field experiment and latitudinal survey and form specific hypotheses about the effects of grasshopper diversity on grassland ecosystems, and how those effects will vary with a latitudinal productivity gradient.4. Write a standard USDA grant, using these pilot data and hypotheses as the foundation. This grant will examine the effects of grasshopper diversity on grassland structure and function at four sites along a latitudinal gradient
Project Methods
1. Field ExperimentField experiment. The field experiment will take place at the UHCC, one of the three sites used for our pilot data, and one of the four sites planned for use in future studies. To examine the effects of grasshopper diversity on ecosystem processes, we will create 4 levels of species richness using two functional groups: grass feeders (2 species) and mixed feeders (2 species) in experimental cages. Field cages (basal area: 0.5 m2) will be stocked with 0, 1, 2, 3, or 4 grasshopper species in all possible combinations. To test how the effects of herbivore diversity vary with productivity, we will run all 0-, 1-, and 4-species treatments at two levels of nutrient availability (ambient, fertilized at 10g N/m2). Treatments will be randomly assigned to cages, with 6 replicates each. Grasshoppers for stocking cages will be caught with sweep nets.Grasshoppers in all cages will be counted weekly and identified to species. Dead grasshoppers will be replaced to maintain diversity treatments. The experiment will run long enough to allow all grasshoppers to become adults, which usually takes 7-8 weeks.Plant production and diversity. Plant community composition in each cage will be assessed at the beginning and end of each growing season by counting the number of species present and then visually estimating percent cover of each functional group (grass, forb, shrub). At the end of each growing season, we will destructively sample aboveground plant biomass from all cages to estimate ANPP. Plant biomass from 0.2m2 area in each cage will be clipped 2 cm above the ground, sorted to functional group (grass, forb, shrub), dried at 60°C for 48 hours and weighed. A subsample will be reserved for nutrient analyses. Litter decomposition and microbial community diversity. Litter turnover rates will be measured using decomposition bags with litter from the most common plant species. We will determine bacterial and fungal community composition on a pooled initial sample and again at the end of the second year in the 0, 1, and 4 species, unfertilized treatments. DNA will be extracted from the soil and community composition will be assessed via amplicon sequencing of the V4-V5 region of the bacterial/archeal 16S gene and the fungal ITS1 region. Bacterial and fungal diversity will be determined using Shannon's diversity index and Faith's phylogenetic diversity. Fungal-to-bacterial dominance will be determined via quantitative PCR.We will assess microbial biomass, extracellular enzyme activity, and community level catabolic response profiles (CRP), to examine the effects of grasshopper diversity on microbial function. Microbial biomass will be determined via substrate induced respiration. Extracellular enzyme activity will be determined and will enable us to assess function as well as microbial nutrient demand. CRP will allow us to determine the ability of microbial communities to catabolize various C substrates.Evaluation: Successful completion of the experiment with data on grasshopper effects on primary production, decomposition, microbial communities, and nutrient cycling.2. Latitudinal SurveyIn August of year 1, we will measure grasshopper community density and diversity at eight sites along a latitudinal gradient: (1) the USDA research site, MT (47°28'N, 104°4'W); (2)Thunder Basin National Grassland, WY (43°22'N, 105°6'W); (3) the Central Plains Experimental Range, CO (40o51'N, 104o40'W); (4) Sandhills grasslands, NE (41°50'N, 100°23'W); (5) Konza Prairie Biological Station, KS (39o05'N, 96o35'W) (6) Tallgrass Prairie Preserve, OK (36°22'N, 99°04'W); (7) Caddo National Grassland, TX (33°44'N, 95°58'W); (8)University of Houston Coastal Center, TX (29o23'N, 95o02'W).Grasshopper field densities will be measured using the ring count method. We will place 25 rings (area: 0.1m2) every 2 m along four transects (100 rings/site). Grasshopper species composition will be measured using 200 sweep net samples (4 sets of 25 high/fast sweeps; 4 sets of 25 low/slow sweeps). Plant biomass will be measured by destructively sampling vegetation from 10 plots (10cm x 1m) at randomly chosen points along the transects. C:N analyses will be run on the dried samples of the five most common grass and forb species at each site. We will measure plant diversity in ten 0.1m2 quadrats from random points along each transect (40 total/site). We will count the number of species in each ring and categorize them by functional group (grass, forb, shrub).Evaluation: successfully collect data set on latitudinal patterns in plant and grasshopper communities and plant foliar quality.3. Data analysis and interpretation.Field experiment. We will use repeated-measures ANOVA with sequential sums of squares to assess the effects of species richness and functional richness on response variables. To account for the remaining dependency between species richness and functional richness, we will use models that fit either species richness or functional richness first, and use a contrast to decompose the relative variation of the other term. Multivariate methods, including nonmetric multidimensional scaling and a group separation test such as permutation MANOVA, will be used to determine if grasshopper functional and species richness alters microbial community composition and function and plant community composition.Survey. We will use ANCOVA to assess effects of grasshopper functional richness and latitude on plant diversity, biomass and quality. Data will be assessed to determine whether to use an equal slopes model (indicating no effect of latitude) or an unequal slopes model (indicating these relationships vary with latitude). Where site is significant, pairwise comparisons will be made as appropriate for the model tested.Evaluation: data sets analyzed and prepared for publication4. Efforts and EvaluationResults from our experiments will be disseminated to the scientific and management community through the publication of data in peer reviewed journals. We anticipate at least two peer-reviewed publications from this study focusing on (1) grasshopper diversity effects on grassland ecosystem processes and (2) grasshopper diversity effects on soil microbial communities. We will also present the results of our study at scientific conferences such as the Ecological Society of America and the Entomological Society of America meetings. Evaluation: successful publication of data and presentation of results at two scientific conferences.Results from our experiment will be analyzed and used to create strong hypotheses about the role of grasshoppers in grassland ecosystems, and how those effects are likely to vary along a latitudinal gradient. This will inform a full USDA proposal, which we will begin writing after the second year of the field experiment has been conducted. Evaluation: write and submit a full USDA proposal Educational efforts associated with this grant include classroom instruction that will incorporate data from this research. Laws, Pennings, and Prather currently teach a course on grassland ecology that will discuss the research. Evaluation: Incorporation of data into class materialsEach summer, we will involve undergraduate students in the project. Students will have the opportunity to conduct independent research while learning basic methods for field ecology and scientific inquiry. ?Evaluation: successfully recruiting students to conduct independent research on topics related to the project. This will include successfully gaining funding through university programs aimed at supporting undergraduate research, and the student(s) presenting their research at the annual undergraduate research forum held at the University of Houston.