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Download The THE RELATIONSHIP OF GRAZING TO ORTHOPTERAN DIVERSITY IN THE INTERMONTANE GRASSLANDS OF THE SOUTH OKANAGAN, BRITISH COLUMBIA by PEGGY LIU GRIESDALE B. Sc., The University of British Columbia, 1998 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (ZOOLOGY) THE UNIVERSITY OF BRITISH COLUMBIA September 2005 © Peggy Liu Griesdale, 2005 ABSTRACT The antelope-brush shrub-steppe of the South Okanagan is small in size yet home to many of the unique and endangered flora and fauna of British Columbia and Canada. More insect species are found in this ecosystem than other grassland ecosystems. Antelope-brush ecosystems are dominated by bunchgrasses, antelope-brush, and a well-developed cryptogam crust, owing to the hot and dry summers of the South Okanagan. Urban and vineyard development are the most immediate threat to this fragile ecosystem, followed by unmanaged livestock grazing. Livestock grazing exposes soil, stunts plant growth, and fragments the cryptogam crust. Less than 9% of the antelope-brush ecosystem is relatively undisturbed and only two small ecological reserves exist. Orthopterans are the most important invertebrate herbivore in North American grasslands and are one of the main biotic influences on grasslands. While Orthopterans assist with biomass turnover and nutrient cycling processes of ecosystem functioning, they may add to the effects of livestock overgrazing. Numerous studies have shown contradictory results of the relationship between grasshopper abundances and grazing pressures. As part of a larger study of the biodiversity and impact of grazing on this threatened ecosystem, this study was conducted to determine how livestock grazing in the intermontane grasslands of the South Okanagan of British Columbia influenced the abundance and species assemblage of Orthopterans. Orthopterans were collected with pitfall traps in ten locations in the antelope-brush ecosystem of the South Okanagan over two years. The study sites were of three different grazing levels: 1) non-grazed; 2) moderately grazed; and 3) heavily grazed. Vegetation data were collected with Daubenmire plots at each site. Twenty-four orthopteran species were captured (seventeen grasshopper species and seven cricket species). All seventeen grasshopper species were previously known to occur in British Columbia, but the taxonomies of four of the cricket species are currently being revised. Grazing did not affect orthopteran species abundance or diversity. Regression analyses showed that the number of orthopteran species and Shannon-Wiener Index values increased with increasing bare soil. The effects of grazing on the vegetation community and structure, and its corresponding effects on the orthopteran species assemblage, are discussed. iii TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES ." vi LIST OF FIGURES vii ACKNOWLEDGEMENTS ix 1 INTRODUCTION 1 1.1 The South Okanagan Grassland Conservation Research Project 1 1.2 Grasslands 1 1.2.1 North American Grasslands 1 1.2.2 British Columbian Grasslands 2 1.2.3 Grassland Characteristics 3 1.2.4 Climate 3 1.2.5 Bunchgrass Subzones 4 1.3 Antelope-brush Ecosystem 4 1.3.1 Characteristics and Ecological Significance 4 1.4 Grazing and Grasslands 6 1.4.1 History of Grassland Disturbances in British Columbia 6 1.4.2 Cryptogam Crust 7 1.4.3 Overgrazed Sites 7 1.5 Grasshoppers and Grazing 9 1.6 Objectives 11 2 MATERIALS AND METHODS 12 2.1 Study Location 12 2.2 Overall Study Structure 14 2.3 Grazing Categorization and History 15 2.4 Grazing History by Site 16 2.5 Arthropod Collection 18 2.5.1 Sampling Method 18 2.5.2 Pitfall Trap Design 20 2.5.3 Emptying Trap Contents 21 2.6 Data Processing 21 2.7 Statistical Analysis 23 2.7.1 Data Grouping 23 2.7.2 Data Analysis 24 2.7.3 Biodiversity Measures 24 2.7.3.1 Species Diversity and Heterogeneity Measures 24 2.7.3.2 Analysis of Variance 26 2.7.3.3 Taxonomic Diversity Measures 26 2.7.4 Cluster Analysis and non-metric Multidimensional Scaling 29 2.7.5 Vegetation Data 31 2.7.6 Correlation and Regression Analysis 32 3 RESULTS 33 3.1 Descriptive Statistics and General Observations 33 3.2 Orthopteran Abundance 41 iv 3.3 Site Groupings 44 3.4 Trap Disturbance 46 3.5 Biodiversity Measures 47 3.5.1 Taxonomic Distinctness Measures 48 3.6 Cluster Analysis and non-metric Multidimensional Scaling 51 3.6.1 Vegetation Overlays 56 3.7 Correlation Analysis 63 3.8 Regression Analysis 64 4 DISCUSSION 67 4.1 Trapping Method 67 4.1.1 Sweep Netting 67 4.1.2 Pitfall Trapping 69 4.2 Orthopteran Study in the South Okanagan 71 4.2.1 Orthopteran Species Descriptions 71 4.3 Descriptive Statistics 72 4.4 Biodiversity Measures 74 4.5 Cluster Analysis and non-metric Multidimensional Scaling 75 4.6 Vegetation Overlays, Correlation Analyses and Regression Analyses 75 4.7 Effects of Grazing on Grasshoppers in Different Grassland Types 77 5 CONCLUSION.. 83 LITERATURE CITED 84 v LIST OF TABLES Table 1. The location, latitude, longitude, unofficial name, site label, site label used for vegetation survey, and the grazing category of the ten grassland study sites in the South Okanagan, BC 14 Table 2. The grazing history, definition of grazing history, and grazing history category of the ten grassland study sites in the South Okanagan, BC 16 Table 3. Dates of pitfall trap collections from ten grassland study sites in the South Okanagan, BC 20 Table 4. List of orthopteran species found at ten study sites in the South Okanagan, BC 35 Table 5. Species occurrence at ten grassland study sites in the South Okanagan, BC 37 Table 6. Total catch over the entire collection period from ten grassland study sites in the South Okanagan, BC (missing traps are not accounted for) 39 Table 7. List of orthopteran species captured at all three grazing categories from the ten grassland study sites in the South Okanagan, BC 45 Table 8. The calculated biodiversity indices for each of the ten grassland study sites and the biodiversity indices averaged for each grazing regime from the South Okanagan, BC 48 fable 9. List of percent bare ground, percent plant cover, and plant species richness for the ten grassland study sites in the South Okanagan, BC (raw data provided by Dr. P. Krannitz) 57 Table 10. Correlations between vegetation data and orthopteran data from the ten grassland study sites in the South Okanagan, BC 64 vi LIST OF FIGURES Fig. 1. Map of the ten grassland study sites in the South Okanagan, BC and neighbouring Washington State 13 Fig. 2. Diagram of the layout of pitfall traps at each of the ten grassland study sites in the South Okanagan, BC 19 Fig. 3. The total number of orthopteran species and the total number of orthopteran specimens collected per month from ten grassland study sites in the South Okanagan, BC 41 Fig. 4. The total number of Orthopterans (divided into nymphs and adults, grasshoppers and crickets) summed across all ten grassland study sites per month, captured in the South Okanagan, BC 42 Fig. 5. Average number of Orthoptera per pitfall trap per site (with standard error bars) captured from ten grassland study sites in the South Okanagan, BC, for all collection periods. The number of orthopteran species per site is listed above the standard error bars 43 Fig. 6. Mean number of Orthoptera per grazing category, captured from ten grassland study sites in the South Okanagan, BC (with 95% confidence intervals). Non-grazed (O, V, Z); moderately grazed (S, T, X, Y); and heavily grazed (P, U, W). The number of orthopteran species per grazing category is listed above the confidence intervals 44 Fig. 7. Venn diagram representing grasshopper species presence and absence according to grazing category and the overlap between grazing categories from ten grassland study sites in the South Okanagan, BC 46 Fig. 8. Simulated means (dashed line), 95% probability funnels (continuous line), and measured average taxonomic distinctness (A+) values for each of the ten grassland study sites in the South Okanagan, BC, plotted against the number of species for 1000 random simulations 49 Fig. 9. Simulated means (dashed line), 95% probability funnels (continuous line), and measured variation in taxonomic distinctness (A+) values for each of the ten grassland study sites in the South Okanagan, BC, plotted against the number of species for 1000 random simulations 50 Fig. 10. Fitted 95% probability contours of the joint distribution of A+ and A+, from 1000 random simulations (for species sublist sizes = 5, 10, and 15), calculated for each of the ten grassland study sites in the South Okanagan, BC 51 Fig. 11. Dendrogram for hierarchical clustering of the ten grassland study sites in the South Okanagan, BC, using group-average linking of Bray-Curtis similarities calculated on square root-transformed data 52 vn Fig. 12. Dendrogram for hierarchical clustering of the ten grassland study sites in the South Okanagan, BC, using group-average linking of Bray-Curtis similarities calculated on presence/absence data : ; 53 Fig. 13. MDS of Bray-Curtis similarities from square root-transformed species abundance data from the ten grassland study sites in the South Okanagan, BC 54 Fig. 14. MDS of Bray-Curtis similarities from presence/absence data from the ten grassland study sites in the South Okanagan, BC 55 Fig. 15. MDS of Bray-Curtis similarities from square root-transformed species abundance data from the ten grassland study sites in the South Okanagan, BC, with superimposed circles of increasing size with increasing percent bare soil (arcsine transformed) 58 Fig. 16. MDS of Bray-Curtis similarities from species presence/absence data from the ten grassland study sites in the South Okanagan, BC, with superimposed circles of increasing size with increasing percent bare soil (arcsine transformed) 59 Fig.
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