Abstract Arthropod Community Response to High

ABSTRACT

ARTHROPOD COMMUNITY RESPONSE TO HIGH-INTENSITY, LOW-FREQUENCY CATTLE GRAZING EVENTS AND PASTURE SUCCESSION

by Timothy J. Bankroff

This paper reports on two studies describing responses of abundance, diversity, and functional structure of arthropod communities to high-intensity, low-frequency cattle grazing in eastern North American pastures. The first study assessed the state of arthropod communities before and after discrete grazing events. Grazing negatively affected abundance, diversity, and taxonomic richness, but functional diversity and functional evenness were unaffected. Assemblages of spiders and parasitoid wasps characterized pre-grazing communities, while beetles and flies were common after grazing. The second study assessed how these same properties changed with increasing deferment after grazing, and in response to vegetation structure. Longer deferment periods maximized arthropod abundance. Shorter deferment periods optimized taxonomic and functional diversity. Wasps characterized the most diverse community observed after 32 days of deferment. Vegetation height was important to explaining community composition. Height, biomass, and percent litter cover accounted for 11.8% of variance. Landscape variables may also be important to explaining community composition.

ARTHROPOD COMMUNITY RESPONSE TO HIGH-INTENSITY, LOW-FREQUENCY CATTLE GRAZING EVENTS AND PASTURE SUCCESSION

A Thesis

Submitted to the

Faculty of Miami University

in partial fulfillment of

the requirements for the degree of

Master of Science

Department of Biology

Timothy J. Bankroff

Miami University

Oxford, Ohio

2014

Advisor______Alan B. Cady

Reader______Ann L. Rypstra

Reader______A. John Bailer

Reader______Thomas O. Crist

TABLE OF CONTENTS

List of Tables ……………………………………………………………………...... v

List of Figures……………………………………………………………………………………vi

Acknowledgements…………………………………………………………………………..…vii

Chapter 1: Introduction 1.1 Background and Introduction to the Studies……………………………………...... 1 1.2 Significance………………………………………………………………………...... 3 1.3 Literature Cited…………………………………………………………………...... 3

Chapter 2: Study I, Short-term Effects of Rotational Cattle Grazing on Arthropod Abundance, Diversity, and Composition 2.1 Introduction……………………………………………………………………………5 2.2 Methods 2.2.1 Study sites and experimental units…………………………………………..7 2.2.2 Sampling methods…………………………………………………………...8 2.2.3 Specimen identification and functional group assignment………………….9 2.3 Data Analysis 2.3.1 Arthropod abundance………………………………………………………10 2.3.2 Richness, diversity, and evenness of arthropod communities……………..10 2.3.3 Similarity of community composition before and after grazing…………...11 2.4 Results 2.4.1 Sampling yield……………………………………………………………..12 2.4.2 Arthropod abundance……………………………………………………....12 2.4.3 Diversity, richness, and evenness of arthropod communities……………...13 2.4.4 Community composition…………………………………………………...14 2.5 Discussion……………………………………………………………………………14 2.6 Conclusions…………………………………………………………………………..17 2.7 Future Directions and Research Questions…………………………………………..18 2.8 Literature Cited……………………………………………………………………....18

Chapter 3: Study II, Response of Arthropod Abundance, Diversity, and Composition to Season-long Succession in a Rotationally Grazed Pasture 3.1 Introduction…………………………………………………………………………. 24 3.2 Methods 3.2.1 Study site and experimental units……………………………………….....27 3.2.2 Sampling methods………………………………………………………….27 3.2.3 Measuring structural properties of vegetation…………………………...... 28 3.3 Data Analysis 3.3.1 Sward structure throughout pasture succession…………………………....28 3.3.2 Do abundance, richness and diversity of arthropod communities change with deferment period?...... 29 3.3.3 Functional group distribution……………………………………………...29

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3.3.4 Community dissimilarity…………………………………………………..30 3.4 Results 3.4.1 Sward structure and arthropod community composition…………………..31 3.4.2 Abundance and taxonomic diversity along gradients of grazing deferment.32 3.4.3 Functional composition of communities…………………………………...32 3.5 Discussion……………………………………………………………………………34 3.6 Conclusions…………………………………………………………………………..37 3.7 Future Directions and Research Questions…………………………………………..37 3.8 Literature Cited………………………………………………………………………38

Tables and Figures……………………………………………………………………....….43-78

LIST OF TABLES

Table 2.1………………………………………………………………………………………....45 Table 2.2………………………………………………………………………………………....48 Table 2.3……………………………………………………………………………………...... 51 Table 2.4……………………………………………………………………………………...... 53 Table 2.5……………………………………………………………………………………...... 55 Table 2.6……………………………………………………………………………………...... 58 Table 2.7……………………………………………………………………………………...... 60 Table 3.1……………………………………………………………………………………...... 62 Table 3.2……………………………………………………………………………………...... 65 Table 3.3……………………………………………………………………………………...... 69 Table 3.4……………………………………………………………………………………...... 71 Table 3.5……………………………………………………………………………………...... 72 Table 3.6……………………………………………………………………………………...... 74 Table 3.7……………………………………………………………………………………...... 76

LIST OF FIGURES Figure 2.1………………………………………………………………………………………...44 Figure 2.2……………………………………………………………………………………...... 52 Figure 2.3……………………………………………………………………………………...... 54 Figure 2.4……………………………………………………………………………………...... 56 Figure 2.5………………………………………………………………………………………...57 Figure 2.6……………………………………………………………………………………...... 59 Figure 2.7……………………………………………………………………………………...... 61 Figure 3.1a……………………………………………………………………………………….66 Figure 3.1b…………………………………………………………………………………….....67 Figure 3.1c…………………………………………………………………………………….....68 Figure 3.2……………………………………………………………………………………...... 70 Figure 3.3……………………………………………………………………………………...... 73 Figure 3.4……………………………………………………………………………………...... 75 Figure 3.5……………………………………………………………………………………...... 77 Figure 3.6……………………………………………………………………………………...... 78

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Alan Cady, for supporting my research in so many different ways. Thank you for your dedication to and interest in this project. Thank you for your assistance with planning and executing fieldwork, and for identifying the many spiders collected during our trips to Polyface Farm. I am grateful for the use of your laboratory that became a second home to me. Thank you to Dr. Bruce Steinly for the use of your laboratory space and the use of your dichotomous keys. Thank you to Dr. John Bailer, Mr. Mike Hughes, and Dr. Thomas Crist for your advice on selection of statistical analyses; thank you to Dr. Bailer and Dr. Crist for also serving on my committee. Thank you to Dr. Ann Rypstra for serving on my committee and as the reader of my thesis. Thank you to Dr. Rypstra and to Mr. Rodney Kolb for the use of resources and space at Miami University’s Ecology Research Center to design, assemble, and store my field equipment. Thank you to Miami University and the Department of Zoology (Biology) for the opportunity to pursue this degree. Thank you to Mr. Joel Salatin, the entire Salatin Family, and the Polyface Farm interns for your incredible hospitality during our trips to Polyface Farm. I am deeply grateful to you for allowing me unlimited access to your farm; this project would not have been possible without all of your support. Thank you to Dr. Jonathan Coddington of the Smithsonian Institution for bringing the unique management regime practiced on Polyface Farm to Dr. Cady’s and my attention, and for assisting with fieldwork during our first trip to Polyface. I would like to thank my entire family for their support throughout my graduate studies and this project. Thank you to my parents, Laurie and Tim, for your constant encouragement and support of my passion for the natural world. Thanks to my sister, Taylor, for your words of encouragement. Thanks to my in-laws, Andrea, Attila, Vincent, Carla, and James for all of your support. Thank you to my best friends from all periods of my life: our shared philosophy and adventures were fundamental to my pursuit of this degree. Finally, thank you to my wife, Antonia, for the countless ways you have supported me during my graduate work and helped me see this through. This research was financially supported by the Department of Zoology (Biology) at Miami University.

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Chapter 1: Introduction 1.1 Background and Introduction to the Studies Resource-based management dominates the grazing literature, mainly comprised of studies under agronomic, animal husbandry, or economic themes, which offer management insights mostly relating to the economic productivity of grazing systems. The parameters borne from those investigations, such as primary productivity of the forage crop and mass gains of grazers, have been used regularly to establish performance benchmarks. Due to the varied success of different regimes across spatial and temporal scales, and by region, ecosystem, and climate, the continued practice of alternative grazing regimes, most commonly characterized by periods of pasture rest or deferment, has been attributed to the mere perception that they create more efficient, more productive grazing systems relative to continuous grazing (Briske et al., 2008). This may suggest that the methods we currently use to discriminate grazing regimes may not be adequately sensitive to detect differences in management methods or intensity. The studies herein serve to influence this discussion and to highlight ungulate grazing as an historic landscape management tool. At present, studies that examine the effects of ungulate grazing on localized and rare biodiversity are scarce, and those that highlight shifts in community composition beyond the scope of forage species are even scarcer. Understanding forage community dynamics is inherently fundamental to the longevity of a grazed ecosystem, but in order for one management regime to potentially be differentiated from another, inclusion of higher trophic levels is necessary, especially those that are immediately dependent on pasture vegetation as a habitat or food resource. Animal community dynamics may indicate the state of other ecosystem services and diagnose whether grazing can indeed be sustained locally. Vertebrate responses to grazing management have been documented (herpetofauna: Wilgers et al., 2006, Newbold and MacMahon, 2008; avifauna: Rahmig et al., 2008, Wilcox et al., 2010; and mammals: Schmidt et al., 2004), but the sensitivity of their diversity and functional composition as management tools has not been comprehensively studied. Invertebrates—namely the arthropods—may be especially useful to diagnose the effects of different grazing intensities and manage biodiversity in grazed ecosystems due to their density and abundance. Since arthropods occupy multiple trophic levels and myriad positions in complex food webs, they are vital to nutrient cycling (Reichle, 1977; reviewed in Crist, 2008; Culliney, 2013). Understanding how grazing affects the distribution and functional composition

of arthropod communities is therefore critical to evaluating pasture health. Arthropods are immediately affected by grazing events through incidental consumption or reduction of the standing forage crop. Grazing also reduces habitat availability, food resources, and ambush and oviposition sites, potentially inducing shifts in species dominance or dominance between functional guilds. Arthropod community composition in grazed ecosystems may then be insightful to habitat quality, or to the relative ability of different grazing regimes or intensities to harbor greater biodiversity. Study I (Chapter 2) considers isolated grazing events as discrete environmental perturbations and their effects on the abundance, diversity, and composition of arthropod communities. This is a relatively unexplored perspective to investigating the direction and magnitude of compositional and ecological shifts elicited by ungulate herbivores and arthropod consumer groups. The responses of narrow herbivore assemblages to grazing events have previously been studied (Gómez and González-Megías, 2002, 2007), but not of entire communities. Thus, the responses of arthropod abundance, diversity, and functional composition to single grazing events are examined. High-intensity, low-frequency rotational cattle grazing permits relatively high densities of grazers to spend a small amount of time grazing within a defined area. Grazers then move on to forage elsewhere and may be returned by managers to the area they first grazed after that area has experienced a long period of deferment, or rest. Hypothetically, this occurs infrequently during a growing season. High-intensity, low-frequency grazing modifies an ecosystem such that a mosaic of structurally distinct patches of habitat is produced. The distribution of arthropods among functional groups and the taxonomic identity of those individuals may differ in pastures where grazing has been deferred for different periods of time. Study II (Chapter 3) explores the trajectory of arthropod community succession through time after grazing in a test of Huston’s (1979, 1994) ‘dynamic equilibrium model’, which predicts the biomass, population sizes, and growth rates of primary consumer groups (litter- and plant-feeders) will be greater than that of secondary consumers (predator and parasitoid groups). Physical habitat characteristics naturally vary as pasture vegetation regenerates, so the influence of structural parameters of vegetation—including height, litter cover, and biomass—in shaping arthropod community succession are analyzed in Study II as well.

1.2 Significance Patterns of biodiversity in pastures under various grazing schemes must be understood to facilitate truly holistic resource management and to maximize ecosystem function. Many complex feeding relationships external to ungulate grazers and their forage may support nutrient cycling in grazed systems. Arthropods perform numerous ecosystem services that support the general ecological functioning of productive agricultural systems. If arthropods can be conserved by a management regime that limits exposure to grazing and permits rest following grazing events, such methods may support greater ecological functioning. Understanding the identity and functional role of organisms that sustain ecosystem function can guide decision making from natural resource management and conservation perspectives. Differentiation of arthropod responses to varying deferment periods may produce a spectrum of communities with distinct membership and structure. In turn, this spectrum of community response might be used as an adaptive management tool that allows communities to be benchmarked against other standardized or predicted community profiles in order to prescribe grazing intensity or deferment period. Land managers should implement biological monitoring efforts targeting the arthropod fauna to diagnose the effects of grazing on biodiversity and to formulate sustainable grazing strategies that balance economic and conservation goals. 1.3 Literature Cited Crist, T.O. 2008. Insect Populations, Community Interactions, and Ecosystem Processes in the Shortgrass Steppe, in Ecology of the Shortgrass Steppe: A Long-Term Perspective, W.K. Lauenroth and I.C. Burke, Eds. Oxford University Press, New York, New York, 215- 247. Culliney, T.W. 2013. Role of Arthropods in Maintaining Soil Fertility. Agriculture 3: 629-659. Dennis, P., J. Skartvelt, D.I. McCracken, R.J. Pakeman, K. Beaton, A. Kunaver, and D.M. Evans. 2008. The effects of livestock grazing on foliar arthropods associated with bird diet in upland grasslands of Scotland. Journal of Applied Ecology 45: 279-287. Huston, M. 1979. A General Hypothesis of Species Diversity. The American Naturalist 113(1): 81-101. Huston, M.A. 1994. Biological Diversity: The coexistence of species on changing landscapes. Cambridge University Press.

Newbold, T.A.S. and J.A. MacMahon. 2008. Consequences of cattle introduction in a shrubsteppe ecosystem: indirect effects on desert horned lizards (Phrynosoma platyrhinos). Western North American Naturalist 68(3): 291-302. Rahmig, C.J., W.E. Jensen, and K.A. With. 2009. Grassland Bird Responses to Land Management in the Largest Remaining Tallgrass Prairie. Conservation Biology 23(2): 420-432. Reichle, D.E. 1977. The Role of Soil Invertebrates in Nutrient Cycling. Ecological Bulletins 25: 145-156. Wilgers, D.J, E.A. Horne, B.K. Sandercock, and A.W. Volkmann. 2006. Effects of rangeland management on community dynamics of the herpetofauna of the tallgrass prairie. Herpetologica 62(4): 378-388. Willcox, E.V., G.W. Tanner, W.M. Giuliano, and R. McSorley. 2010. Avian Community Response to Grazing Intensity on Monoculture and Mixed Florida Pastures. Rangeland Ecology & Management 63(2): 203-222.

Chapter 2: Study I, Short-term Effects of Rotational Cattle Grazing on Arthropod Abundance, Diversity, and Composition 2.1 Introduction Grazed lands are estimated to occupy up to 20% of the earth’s land surface (Wood et al., 2000). They may extend over few to many thousands of contiguous hectares, so are in many cases dominant features of terrestrial ecosystems and may span across large geographical regions. In turn, methods of grazing management employed in these expansive agricultural ecosystems influence the ecology of the resident biotic communities. Studies examining the effects of grazing management on biotic communities have traditionally focused on pasture plant species because of their importance as forage, using plant abundance, species richness, or functional diversity as indicators of grazing intensity and ecosystem stress. In general, plant species richness has not conclusively, or consistently, exhibited a directional response to intensified grazing management (Briske et al., 2008); thus plant diversity per se may not be the best indicator of forage condition or ecosystem health (e.g. Rusch and Oesterheld, 1997). Rather, grazing may alter functional composition (Hart and Ashby, 1998; Hart, 2001, but see Derner and Hart, 2007, and Vermeire et al., 2008), sward structure (Mitchley, 1988; Belsky, 1992; Pavlu et al., 2003), and, in turn, palatability (Taylor et al., 1993) of grassland plant communities. Over space and time, grazing elicits responses in such ecological, physical, and chemical properties, which vertebrate grazers accommodate by altering their own distribution and foraging behavior. Shifts in plant community composition are phenomena that occur over long periods of time, influenced by the continuous feedback circuit between forage condition and grazer behavior, so monitoring efforts may detect symptoms of pasture degradation only after longer periods of time. But other taxa whose ecology is closely tied to the availability, structure, and nutrition of grassland flora may experience more rapid declines in abundance or density if any of these factors are diminished, thus altering community-level composition. Grassland invertebrates, particularly arthropods, are among those animals whose close association with vegetation makes them sensitive to grazing perturbations. Those that have studied short- (1 growing season) to long-term (several years) effects of grazing on arthropod communities reported general reductions in arthropod abundance in grazed versus ungrazed plots (Rambo and Faeth, 1999; Gómez and González-Megías, 2002, 2007; González-Megías et al., 2004), or under

intensified grazing management (Gibson et al., 1992; Dennis et al., 1997; Dennis et al., 2001; Littlewood, 2008). Responses of taxonomic richness and community composition varied by season, regional climate, biome and vegetation community, and species of ungulate grazer. There are few arthropods that are encouraged by intensified management (Gibson et al., 1992; Dennis et al., 1997; Dennis et al., 2001); however, Kruess and Tscharntke (2002a) reported consistent declines for all sampled insect taxa with progressive increases in grazing intensity. Investigations of community dynamics across grazing management regimes and intensities are relatively common compared to studies profiling the impact of the grazing event itself on entire communities where the spatial and temporal extent of grazing is controlled. Very few studies have reported the pronounced effects of discrete grazing events. Loeser et al. (2001) reported a 50% decline in arthropod abundance from pre-grazing conditions in a very-high- intensity grazing treatment simulating herd impact, but no comment was made as to changes in diversity or composition. Isolated grazing events occurred only once each year in the two years their experiment was performed. Realistically, domesticated grazers would return to the same site multiple times throughout the growing season, either systematically via rotational grazing management or necessarily in response to depleted forage elsewhere. Gómez and González- Megías (2002) estimated 60-80% of weevils (Ceutorhynchus sp.) were incidentally consumed during grazing in high-mountain scrubland of the Sierra Nevada, Spain, demonstrating that grazing may have a significant impact on grassland arthropod populations. Marked declines in arthropod abundance or richness can be partly attributed to non-trophic effects, but ungulate grazing is indeed a strong mortality factor for arthropods. Studies of the different effects of grazing on functional guilds or groups are also deficient in the literature. On Erysimum mediohispanicum in SE Spain, ungulates incidentally consumed, on average, up to 20% of endophytic taxa, but free-living groups were barely affected (Gómez and González-Megías, 2007). No other such studies were discovered that reported responses of diversity, abundance, and composition of arthropod communities immediately (within 1 day) before and after discrete grazing events; nor have any other such studies been conducted in grazing pastures of the eastern United States that this author was aware of at the time of writing. The focus of this study was to detect and measure shifts in diversity and composition of arthropod communities found in recently grazed paddocks of pasture under a high-intensity, low- frequency rotational management regime. Daily movement of cattle into adjacent, ungrazed

paddocks of pasture presented an opportunity to contrast communities found immediately before and after grazing. One main hypothesis was tested: high-intensity grazing events reduce the abundance and diversity of arthropods, and alter community composition and structure. Responses of the arthropod fauna to discrete cattle grazing events are examined here. 2.2 Methods 2.2.1 Study Sites and Experimental Units Sampling was conducted from 29 to 31 July 2008, and 1 to 2 May 2009 at Polyface Farm (38° 7'6.33" N, 79° 13'38.81" W) near Swoope, Virginia, in the Shenandoah Valley. Elevation at the study site ranged from 500 to 550 m above sea level. The total area of Polyface Farm was was approximately 200 ha; grazing pasture occupied some of this area (below). During the 2008 growing season (~April to November), the area received 374 mm of precipitation, and 417 mm during the same period of 2009 (Weather Underground, 2010). The predominant land use in the region was pasture grazed by cattle. The pasture at Polyface was dominated by non-native, cool- season grasses like tall fescue (Festuca arundinacea) and timothy-grass (Phleum pretense). As a consequence of deforestation to support this land use, the surrounding pastoral landscape was divided by physical property boundaries and sharply contrasting edge habitats (grassland to successional forest). Contiguous forest cover occurred at higher elevations above the valley. Originally, this Appalachian region was characterized by mixed oaks (Quercus spp.); American chestnut (Castanea dentata) was also an important forest species before it was eliminated by blight (Braun, 1950). The pasture was a roughly doughnut-shaped area of 150 ha that extended across hillsides and bottomland bordered by woodland. It was divided into smaller paddocks with electrified wire, and any given paddock was grazed for only one day during one rotation cycle lasting 60 to 70 days. Cattle were moved in a counter-clockwise direction into the next adjacent paddock at the end of each day during the study period (Figure 2.1). Stock rates of cattle in the high- intensity, low-frequency rotation system were equivalent (100 head) between sampling dates at Polyface Farm, but the area of pasture grazed each day changed periodically throughout the growing season (approximately April to November). “Paddock” will hereafter refer to a single, discrete area of pasture. Paddock size decreased from roughly 1 ha early in the season (April) to less than 0.5 ha to match forage production beginning in June. The number of paddocks therefore ranged from about 20, to 60 or more later in the growing season. As part of this

management regime, several hundred laying hens succeeded cattle through rotations; hens were moved into paddocks three days following cattle grazing. Hens were observed searching in and around recently deposited dung, and foraging on arthropods and other organisms in the vicinity. The effect of hen occupation in paddocks is not discussed further in the two following studies but it is mentioned here because no other studies of ungulate-fowl grazing systems were found to exist in the literature. As this management method may be unique to Polyface Farm, the reader is cautioned when drawing comparisons between this system and other rotational grazing schemes. 2.2.2 Sampling Methods Arthropod communities in three paddocks of pasture were sampled before and after cattle grazing to detect immediate effects of the disturbance. Samples were conducted within 24 hours of a grazing event. In 2008, one paddock was sampled on 29 and 30 July, and a second paddock was sampled on 30 and 31 July. Sampling occurred the following spring in a third paddock on 1 and 2 May 2009. Arthropod communities in each paddock were sampled at three sites at least 15 m apart. Two samples no more than 3 m apart were collected at each sample site, for a total of n = 6 samples per paddock before grazing, and n = 6 samples per paddock after grazing. Thus, n = 18 samples were collected both before and after grazing, for an overall total of n = 36 samples. The exact sample site was established by tossing the metal sampling ring a short distance into the area to be sampled. Sampling efforts covered approximately equivalent total areas within paddocks. Areas that were approximately representative of a paddock’s vegetation and topography were selected for sampling. Exposed bedrock or otherwise bare patches without live vegetative cover, woody plants, and recently deposited dung were avoided. For each sample, a 0.25-m2 area was demarcated with a 0.25-m tall cylindrical sample ring. This was performed with great care to avoid disturbing the area. A 25 cc leaf-blower was converted into a vacuum sampler by installing a 1-mm copper mesh across the mid-section of the intake tube (73 cm long, 12 cm diameter) that was used to suction-sample arthropods. The first step when sampling a site was to maneuver the mouth of the intake tube over, into, and through the standing vegetation within the sample ring with the throttle of the apparatus fully engaged for 1 minute. All vegetation was cut to ground level (< 1 cm) and inspected for remaining arthropods on a 1-m2 white nylon beating sheet. Arthropods were gathered by hand or with a handheld aspirator. A second suction sample lasting 1 minute was then initiated to sample the

exposed substrate within the sampling ring. Arthropods collected during suction sampling were stored in 1-gallon zip-top plastic bags at 7º C until sorting occurred in the laboratory, when specimens were transferred to 70% ethyl alcohol. Lastly, the substrate was closely scrutinized by hand, collecting all arthropods with forceps and aspirators for 15 person-minutes. 2.2.3 Specimen Identification and Functional Group Assignment In the laboratory, arthropods were first separated from plant matter and other detritus collected during suction sampling and transferred to 70% ethyl alcohol. Larvae of insect taxa were preserved but not identified, except those of Neuroptera and Coccinellidae (Coleoptera). Orders Coleoptera, Diptera, Hymenoptera, Neuroptera, Odonata, and Orthoptera were identified to family. All Hymenoptera belonged to Suborder Apocrita, including the ants (Vespoidea: Formicidae) and seven superfamilies of parasitoid wasps. In Class Arachnida, the spiders (Order Araneae) were also identified to family, but the mites (Order Acari) were not. Centipedes and millipedes (Classes Chilopoda and Diplopoda, resp.) were identified to level of class, and isopods (Order Isopoda) were identified to level of order. Order Hemiptera refers to the ‘true bugs’ (Suborder Heteroptera) and Order Homoptera refers to Suborders Auchenorrhyncha and Sternorrhyncha; all Hemiptera and Homoptera were identified to family. Most unique taxa, reflecting multiple levels of taxonomic resolution, were also assigned to one of four functional groups (Table 2.1), based on their feeding ecology at the adult life stage. The Parasitic Apocrita were classified as parasitoids even though adults are nectarivorous. Juvenile stages of spiders or nymphs of hemimetabolous insects were assigned to the same functional groups as their adult counterparts. Taxa that could not be assigned to a common functional group without identification to finer taxonomic resolution were excluded from this exercise and thus any analyses concerning functional group responses. The super-abundant ants (Hymenoptera: Formicidae) were the most dominant group excluded. The Geocoris spp. (Hemiptera: Lygaeidae) were the one exception to this protocol because the ‘big-eyed bugs’, as they are commonly known, were easily identified in the laboratory and because they are known to be predators in agricultural systems. The majority of other Lygaeidae are seed predators. Arthropods were classified according to dichotomous keys in the following resources: Araneae (Ubick et al., 2005), Coleoptera (Dillon and Dillon, 1972a 1972b), Diptera (McAlpine et al., 1981, 1987), Hemiptera (Slater and Baranowski, 1978), Homoptera (Arnett, 2000), Hymenoptera (Goulet and Huber, 1993), and Orthoptera (Helfer, 1987). Nymphs of Hemiptera and Homoptera

were identified according to Stehr (1991). Nomenclature for all other taxa followed Arnett (2000). 2.3 Data Analysis Statistical analyses were performed using R version 3.0.2 for Macintosh (R Core Team, 2013). Abundance and diversity data were analyzed at the finest taxonomic resolution achieved except where indicated otherwise; multiple taxonomic levels were thus represented in most analyses. 2.3.1 Arthropod abundance Arthropod count data were analyzed to identify differences between pre- and post- grazing communities using negative binomial mixed effects models (function glmmadmb in R package glmmADMB; Skaug et al., 2013). Treatment (pre- or post-grazing) was a fixed effect and paddock was coded as a random blocking effect to account for the repeated measures error structure. The negative binomial error distribution was used to model count data to control dispersion. A test for each taxon revealed α, the over-dispersion parameter, was always greater than zero, demonstrating the suitability of the selected error distribution. Additionally, goodness of fit for negative binomial models was determined to be superior to that of Poisson models, as evidenced by smaller Akaike information criterion (AIC) values. Counts were sufficiently high at class and order levels (n = 14 taxa) to model the responses of abundance of observed taxa to grazing events. The response of total abundance of each functional group (n = 4) was similarly analyzed. Wald Z-tests tested the null hypothesis of no effect for treatment. 2.3.2 Richness, diversity, and evenness of arthropod communities Observed taxonomic richness of arthropods was rarefied to numbers of individuals collected to differentiate communities present before and after grazing; this analysis was conducted because 34 of the 87 identified taxa from pre-grazing samples were rare (< 2 specimens). Counts of all identified, unique taxa were utilized in these analyses; multiple levels of taxonomic resolution were reflected in the data. The function chosen for rarefaction executes sample-based rarefaction by accumulating individuals instead of samples (function specaccum in R package vegan; Oksanen et al., 2010). Mean expected taxonomic richness was estimated for pre- and post-grazing communities by randomly re-sampling the pool of individuals (N) in each community without replacement at n points, based on n samples (n = 18) each before and after grazing. Therefore, richness was estimated 18 times, once at each addition of approximately

N/18 accumulated individuals. This method was appropriate because the mean number of individuals collected per sample differed and because the sampling order was not recorded (Gotelli and Colwell, 2001). Curves were produced by plotting the average number of taxa represented by a given number of randomly sampled individuals. To facilitate comparisons of richness, curves were fit with lines representing 83% confidence intervals—an 83% confidence level achieved the desired Type I error rate of α = 0.05 based on the standard deviation (σ) of expected taxonomic richness: expected taxonomic richness ± 1.37*σ, where 1.37 is a Z-score. Mean expected richness values and portions of curves were significantly different (p < 0.05) where confidence intervals did not overlap (Austin and Hux, 2002; Payton et al., 2003). The effect of grazing on taxonomic richness of the overall community and within functional groups was modeled using function glmmadmb. Independent variables treatment (i.e. occurrence of grazing) and paddock were coded as fixed and random blocking effects, respectively, in a series of negative binomial mixed effects models. The suitability of the negative binomial error distribution was, as described above, supported by α > 0 and smaller AIC values than those of Poisson models. Family-level richness within orders contributing the majority of taxa to arthropod communities was also analyzed in this way. Wald Z-tests were again used to test the null hypothesis of no grazing effect. The responses of Shannon-Wiener diversity (H’) and Shannon’s evenness (E), and of functional diversity and functional evenness

(denoted as H’FUN and EFUN, respectively) to grazing were modeled using linear mixed effects models (function lme, R package nlme; Pinheiro et al., 2014); fixed and random variables did not differ from those above. Diversity and evenness data were not transformed before analysis. Function anova.lme (R package nlme) was used to conduct Wald F-tests of significance for terms of the fitted model. 2.3.3 Similarity of community composition before and after grazing Permutational multivariate analysis of variance (function adonis in R package vegan) was used to detect differences in community-level taxonomic and functional composition in response to grazing events. Adonis partitions sums of squares of multivariate data sets using matrices of pairwise metric or semi-metric site dissimilarities. The semi-metric Bray-Curtis dissimilarity index was chosen here as the basis for calculating dissimilarities. Log-transformed (log[x+1]) count data by taxon and by functional group were coded as response variables. Permutation tests (n = 999) were constrained to occur within paddocks (n = 3) to account for repeated sampling;

sequential sums of squares from permuted count data were the basis for hypothesis tests (F tests) of significance. Trends of dissimilarity in composition of pre- and post-grazing communities were also analyzed using nonmetric multidimensional scaling (NMDS; default function monoMDS called by function metaMDS in R package vegan; Oksanen et al., 2010). This unconstrained ordination method maximizes the rank-order correlation between calculated pairwise Bray-Curtis dissimilarities and distances plotted in non-Euclidean ordination space by iteratively adjusting plotted positions of samples. The best solution is reached when the discrepancy between calculated and plotted distances—called “stress”—is minimized. Log-transformed (log[x+1]) count data by taxon were supplied to metaMDS to perform ordination. The default number of ordination axes (n = 2) was used. Weighted average ‘species’ scores and site scores on axis 1 and 2 were added to the ordination to facilitate interpretation. 2.4 Results 2.4.1 Sampling yield A total of 2942 specimens were collected in pre- (n = 1952) and post-grazing (n = 990) samples, representing five classes, 12 orders, and 81 families (Table 2.2); 87 unique taxa were identified across all samples. Per-sample arthropod abundance ranged from 28 to 296 before grazing, and from 14 to 172 after grazing, with overall mean abundance of 108.44 ± 17.20 and 55 ± 9.30 (µ ± SE), respectively. The Collembola, Cicadellidae (Order Homoptera), Formicidae (Hymenoptera), and Linyphiidae (Araneae) were ubiquitous and together comprised roughly 59% and 52% of arthropods sampled before and after grazing, respectively. Assignment to a functional group was possible for 2418 arthropods: n = 1642 before grazing, and n = 776 after grazing (Table 2.3). Taxonomic richness per sample ranged from 9 to 35 before grazing, and from 6 to 26 after grazing, with overall mean richness of 21.83 ± 1.52 and 13.72 ± 1.45, respectively. 2.4.2 Arthropod abundance Community arthropod abundance was significantly negatively affected by high-density grazing events (Figure 2.2; Wald Z-test, Z = 3.38, p < 0.001). The main effect of grazing on arthropod abundance was highly significant and negative across a minority of taxa (Table 2.4); mean abundance of most taxa did decline following grazing, however. The abundance of the Araneae was negatively affected by grazing (Wald Z-test, Z = 2.37, p < 0.05), and on average,

Araneae were the most abundant group before (32.28 ± 6.59; µ ± SE) and after grazing (15.33 ± 2.92). All Hymenoptera were significantly negatively affected by grazing events (Wald Z-test, Z = 2.13, p < 0.05); when treated independently of ants, which comprised the vast majority of hymenopterans in pre- and post-grazing communities (82.3% and 90.5%, respectively), the Parasitic Apocrita were significantly reduced by grazing (Wald Z-test, Z = 3.04, p < 0.01). Grazing events significantly and negatively affected abundance of the Hemiptera (Wald Z-test, Z = 2.6, p < 0.01) and the Homoptera (Wald Z-test, Z = 2.5, p < 0.05). Orders Acari and Coleoptera were positively but not significantly affected by grazing (Table 2.4). Mean abundance of Diptera was reduced following grazing events (9.67 ± 3.12 vs. 4.06 ± 1.27), but the main effect was marginally not significant. The effect was also not significant among the least common taxa, including Chilopoda, Neuroptera, Thysanoptera, and Diplopoda. All functional groups exhibited significant and negative responses to the main effect of grazing (Table 2.4). On average, predators and detritivores were the most abundant functional groups before and after grazing (Figure 2.3), but detritivores and parasitoids were more strongly reduced in proportion by grazing disturbances. 2.4.3 Diversity, richness, and evenness of arthropod communities Based on the 83% C.I. of sample-based, individual accumulation curves of taxonomic richness by sampling period (Table 2.5), the richness of arthropod communities sampled before grazing was significantly higher than after grazing events (Figure 2.4). Confidence intervals of each accumulation curve did not overlap; the null hypothesis of no difference was rejected (p < 0.05). The main effect of grazing on overall observed taxonomic richness of arthropods was highly significant and negative (Wald Z-test, Z = 32.71, p < 0.0001). The four richest arthropod taxa—Araneae, Coleoptera, Diptera, Hemiptera (in descending order of mean pre-grazing richness)—contributed the majority of taxa to overall community richness (Figure 2.5). Spiders were the most taxa-rich before grazing events (5.17 ± 0.57) and were the only group for which the main effect was significant (Wald Z-test, Z = 3.52, p < 0.001); only richness of beetles was greater than that of spiders following grazing (3.78 ± 0.45) (Table 2.6). Beetle richness was most resistant to grazing, as there was no difference detected between pre- and post-grazing richness; fly and bug richness declined but the main effect was not significant (Table 2.6). The effect of grazing on richness within each functional group was also significant and negative.

However, numbers of herbivorous and parasitoid taxa were reduced in greater proportions following grazing than detritivorous and predatory taxa (Figure 2.6). Grazing significantly and negatively affected Shannon-Wiener diversity (F1,32 = 6.94, p < 0.05), but Shannon’s evenness, functional diversity, and functional evenness were not affected (Table 2.6). 2.4.4 Community composition Permutation tests of arthropod counts at the paddock level revealed grazing was a highly significant predictor of dissimilarity of taxonomic composition (p = 0.001) and functional composition (p = 0.004) of arthropod communities, though grazing was only a small source of explained variability (Table 2.7), or 9.4% of explained variability. Environmental variables were not available for modeling, so the potential significance of other sources of variation is not reported here. The global solution of the NMDS ordination analysis was reached with a stress of 0.1918809. Pre-grazing sites tended to be characterized by high abundance and richness of parasitoid wasps and spiders. One distinct cluster in the lower left quadrant of the ordination biplot (Figure 2.7) included spider families Araneidae, Corinnidae, Clubionidae, Tetragnathidae, Thomisidae, Lycosidae, and Salticidae. Mimetidae, Gnaphosidae, Oxyopidae, and Pisauridae, all relatively rare taxa, were less closely associated with specific sites in ordination space, but were nearer to pre-grazing than post-grazing sites. Only families Linyphiidae and Theridiidae were in closer association to post-grazing sites. Parasitic Apocrita also clustered near the first pre-grazing spider assemblage mentioned above, including Scelionidae, Pteromalidae, Encyrtidae, Mymaridae, and Torymidae. Carabid and staphylinid beetles were most closely associated with pre-grazing sites, whereas families Chrysomelidae and Phalacridae were in proximity to post-grazing sites. In general, post-grazing sites were characterized by beetle and fly taxa. 2.5 Discussion The results of this study of arthropod communities in grazed lands of the eastern U.S. supported the main hypothesis that cattle grazing disturbances elicit significant community responses, namely declines in local abundance and diversity, and shifts in composition. Total arthropod abundance was significantly affected by grazing events. The main effect was negative and significant for the Araneae, Collembola, Hemiptera, Homoptera, all Hymenoptera, Parasitic Apocrita, and Orthoptera; the effect of paddock was determined to be significant for all groups

except the Hemiptera and Parasitic Apocrita. The effect of grazing on fly abundance was marginally not significant, whereas there was no effect on beetle abundance. On average, beetles actually increased in abundance. In contrast, Woodcock et al. (2005) and Batary et al. (2007a) reported that beetles were unaffected by rotational (i.e. seasonal deferment) or intensified grazing management. Abundance of all functional groups was significantly and negatively affected by grazing events, but numeric responses of a small number of taxa probably drove this trend. The detritivores were dominated by the springtails (Collembola), herbivores by the leafhoppers (Cicadellidae), predators by the money spiders (Linyphiidae) and wolf spiders (Lycosidae), and parasitoids by scelionid wasps. Reduced abundance across all functional groups is consistent with findings of other studies. As cattle and sheep grazing is introduced or as intensity increases, predatory and herbivorous groups have been shown to decline (Woodcock et al., 2005; Dennis et al., 1998), and Cagnolo et al. (2002) reported abundance of secondary consumers was lower under heavy and continuous grazing by horse and cattle. However, Kruess and Tscharntke (2002a) found abundance of Parasitic Apocrita, Coleoptera, Auchenorrhyncha, and Heteroptera did not differ in intensively grazed grasslands. An important caveat to using these studies for comparison is that they occurred in grasslands under continuous grazing management. Continuous grazing maintains a desired sward height (not more than 5.5 cm in the reviewed literature) across an entire pasture. Rotational grazing at Polyface Farm produced a mosaic of paddocks with different vegetation height. Mean sward height—measured after grazing as part of Study II (below)—was 6.8 ± 0.2 cm, and sward height before grazing ranged from 10.4 ± 1.3 cm to 17.7 ± 0.5 cm. The importance of vegetation structure to arthropod communities is discussed in greater detail in Study II. The few studies that have focused on discrete grazing events have reported pronounced declines in arthropod abundance. Loeser et al. (2001) reported a decline of greater than 50% in overall abundance after a single application of very high intensity grazing simulating herd impact in arid grasslands of north-central Arizona. Comparisons of communities in adjacent grazed and ungrazed plots provide an alternative method of “before and after” investigation: Rambo and Faeth (1999) and Dennis et al. (2001) reported that ungulate grazing reduced abundance and species richness of insects and arachnids, respectively. Gómez and González-Megías (2002) reported weevil declines of up to 80% after cattle grazing in scrubland of the Sierra Nevada,

Spain; Gómez and González-Megías (2007) reported average declines of 20% in abundance of endophytic taxa on Erysimum mediohispanicum in SE Spain. Incidental consumption of arthropods by grazers was observed to be a strong mortality factor in both studies. The present study did not attempt to attribute trends in abundance or diversity to trophic interactions, but it is likely that grazers consumed some groups. In particular, species of Linyphiidae spiders are known to stratify across vertical zones of sward vegetation (Cherrett, 1964). The present study characterized neither webs nor the spiders occupying them, but webs were observed throughout the vertical structure of the sward. Direct consumption would more strongly impact taxa or functional groups occupying higher strata defoliated by grazers. The Homoptera, particularly leafhoppers (Cicadellidae), were abundant and also observed throughout the vertical structure of the sward. Their abundance was probably less affected by direct consumption. Adults of many leafhopper species are known to be strong flyers (Waloff, 1973); this trait would permit rapid dispersal away from an area of pasture disturbed by grazers or into pasture vacated by grazers. Of the four most abundant taxa (Collembola, Linyphiidae, Formicidae, and Cicadellidae, in order of declining pre-grazing abundance), cicadellids were least reduced in proportion by grazing events. This could be attributed to their mobility. The same could be true of wolf spiders (Lycosidae), which were reduced even less in proportion, though wolf spiders and other cursorial spiders are closely associated with plant litter (Denno et al., 2002; Wagner et al., 2003) and not necessarily standing vegetation. Their location in litter at the base of the sward would have made them less vulnerable to incidental consumption. Taxonomic and functional composition of communities was different before and after grazing, but the effect of grazing in permutation tests explained only a small amount of variation. Grazing management alone may not be an important predictor of variation in community composition. A combination of local and landscape variables may be necessary to sufficiently account for changes in community structure (Batary et al., 2008; Korosi et al., 2012). In the present study, it was shown that pre- and post-grazing communities were characterized by different taxa. Ordination revealed a high degree of similarity among pre-grazing communities characterized by spider and parasitoid wasp taxa. Relaxation of grazing pressure applied through a regime of systematic pasture deferment may encourage greater richness of predatory and parasitoid taxa (Luff and Rushton, 1989; Tscharntke, 1997; Cagnolo et al., 2002; Kruess and Tscharntke, 2002a; Woodcock et al., 2005). High numbers of beetles and flies belonging to

multiple taxa characterized post-grazing sites; their richness was not affected by grazing. The richness of other abundant orders was reduced. Rarefaction analysis revealed that the taxonomic richness of pre- and post-grazing arthropod communities differed overall. Relaxation of grazing pressure and abatement of grazing has been reported to encourage the accumulation of arthropod taxa (Rambo and Faeth, 1999; Dennis et al., 2001; Cagnolo et al., 2002; Kruess and Tscharntke 2002a, b) in grasslands. Diversity and richness observed at the community and functional group levels were both reduced by grazing events. Evenness and functional evenness were not affected by grazing, findings that are supported in the literature as well as by the results of Study II below. Woodcock et al. (2005) reported that cattle or sheep grazing treatments did not affect species evenness of beetle communities in calcareous grasslands. Predator-prey and primary-secondary consumer ratios have been shown to remain the same as grazing was introduced or intensity increased (Dennis et al., 1998; Cagnolo et al., 2002; Kruess and Tscharntke, 2002b). 2.6 Conclusions High-intensity cattle grazing events negatively affected arthropod abundance and taxonomic richness overall. The effect of grazing was significant and of the same direction for the most common orders, but not for fly or beetle abundance and richness, or for true bug richness. Flies and beetles characterized post-grazing communities, whereas predator (spider) and parasitoid wasp taxa were characteristic of pre-grazing communities. Pre-grazing conditions in paddocks were produced during several weeks of deferment, so these periods of rest without grazing appear to be beneficial to predators and parasitoids. The responses of different groups to grazing and their relative abilities to avoid grazers may be tied to their mobility, foraging behaviors, or vertical location in the sward. Within functional groups, richness was reduced by high-intensity grazing events, but evenness, functional diversity, and functional evenness of arthropod communities were unaffected. These findings suggest that rotational grazing may maintain the functional stability of arthropod communities, which are important to nutrient cycling in ecosystems (Reichle, 1977; Culliney, 2013). Communities having greater evenness may be more resistant to disturbance (Wittebolle et al., 2009). In theory, high richness indicates system function might be preserved after environmental perturbations due to functional redundancy at the species level (Yachi and Loreau, 1999; Ives et al., 2000), but evenness may be a more suitable metric for functional

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Chapter 3: Study II, Response of Arthropod Abundance, Diversity, and Composition to Season-long Succession in a Rotationally Grazed Pasture 3.1 Introduction Grazed lands are among the most important managed ecosystems relative to biodiversity conservation. Estimated to occupy up to 20% of the earth’s land surface (Wood et al., 2000), grazed lands support extensive grazing of ungulates like pigs, sheep, and cattle raised for dietary protein or milk production. Land managers may suppress ecological functioning by allowing too many grazers access to forage resources for too long a period of time. Biotic communities in these agroecosystems may be degraded from habitat and species loss (Green, 1990), species invasions (McIntyre and Lavorel, 1994), soil compaction and reduced water infiltration (Warren et al., 1986; Kumar et al., 2008), and impaired decomposition rates (Shariff et al., 1994) as consequences of overgrazing. Thus, land managers have developed a number of unconventional and innovative grazing strategies to avoid degradation of ecosystems and forage resources, particularly those systems grazed by cattle. Traditional alternative management options have incorporated periods of use and non-use in pastures (Lacey and Van Poollen, 1979). Other strategies apply an advanced rest- rotation system to manage herds of grazers. Most are adaptations of the Savory Grazing Method (Savory and Parsons, 1980), where pastures are subdivided into cells and grazing is restricted to one cell for a short period of time. The time each cell is occupied depends on forage conditions in adjacent cells. Common rotational grazing schemes like short duration grazing (SDG) (Savory, 1978) or Holistic Resource Management (Savory 1983), and high-intensity-low- frequency/non-selective grazing (Acocks, 1966) employ such a systematic redistribution and rotation of cattle in pastures. Redistributing animals and restricting grazing pressure across space and time may realize numerous ecological benefits. Higher densities of ungulate grazers can influence seedling establishment (Hart et al., 1993) and increase organic carbon turnover (McNaughton et al., 1988; Tongway and Ludwig, 1996). Kumar and others (2008) reported enhanced soil infiltration rates following rotational grazing. Grazing uniformity and forage utilization are expected to be greater in rotational grazing systems (Barnes et al., 2008) by decreasing selective grazing of the most palatable species (Hart, 2001). Periods of non-use or deferment also maintain desirable botanical composition by permitting palatable forage species time to recover after grazing (Malechek and

Dwyer, 1983; Heady, 1984). Many studies evaluating the impacts of grazing have focused on animal or forage production, but the effects of grazing on biodiversity have been examined less frequently. We must consider community-level effects of a grazing regime to completely evaluate its merits and importance to biodiversity conservation and maintenance of ecosystem services. Plant species traits strongly influence directional shifts in plant dominance after grazing, and species particularly adapted to frequent defoliation tend to dominate under selective grazing pressure. Selective grazing of C3 grasses under a continuous regime over long periods of time led to dominance of C4 grasses in short-grass steppe (Hart and Ashby, 1998; Hart, 2001). In arid climates, short duration grazing resulted in the dominance of less palatable short grasses (Taylor et al., 1993), but Derner and Hart (2007) and Vermeire and others (2008) found no difference in the standing crops of plant functional groups across grazing treatments in similar climates. However, continuous grazing in the humid Flooding Pampas grasslands increased species richness only by invasion of exotics, prostrate grasses, and low-growing forbs (Rusch and Oesterheld, 1997). Specific plant responses to different grazing regimes also influence sward structure. Tall grasses tend to dominate rotationally grazed paddocks while shorter species usually dominate in continuous treatments. Short or mid grasses may withstand frequent defoliation characteristic of continuous grazing (Mitchley 1988; Belsky, 1992). Pavlu and others (2003) reported that species diversity was not different across grazing treatments, but continuous grazing decreased sward height. Further, higher densities of grazers achieved by rotational grazing removed more standing dead biomass in humid grassland, resulting in increased litter cover and structure at the ground surface (Jacobo et al., 2006). A unifying factor across these various studies in different types of grasslands and climates is the tendency for increased stock rates and grazing intensity to diminish sward structure. Grazers are important mediators of physical and ecological properties of pastures. Arthropods are one animal group strongly affected by vertebrate grazers via direct and indirect effects. Herbivorous insect-plant relationships are disturbed during grazing due to incidental omnivory by grazers (Polis et al., 1989) or in response to decreased availability of food resources and oviposition sites (Gomez and Gonzalez-Megias, 2002). Secondary consumer groups may also be regulated from the bottom-up because of rare prey and hosts (Siemann, 1998), and in the

case of parasitoids, by fewer nectar sources (Jervis et al., 1993). Arthropod diversity is strongly affected by variability in structural diversity and plant architecture (Morris, 1971; Lawton, 1983; Dennis et al., 1998; reviewed in Bell et al., 2001). Arachnid diversity (Dennis et al., 1998) and web building (Dennis et al., 2001) increased with plant litter below leaf strata and vegetation height, respectively, in Nardus stricta pastures. Species richness of Hymenopteran and Lepidopteran taxa (Kruess and Tscharntke, 2002a,b), and Homopteran, Hemipteran, and Coleopteran taxa (Dennis et al., 1998; Kruess and Tscharntke, 2002b) also increased with vegetation height in pastures. Arthropod abundances may be dramatically reduced by grazing (Loeser et al., 2001), but enhanced structural properties of vegetation produced by strategic cycles of pasture grazing and deferment may moderate local species loss or emigration as a result of disrupted trophic and other relationships caused by grazing. This study investigated the relationship between deferment period and vegetation structure, and the succession of arthropod communities in deferred paddocks of a pasture under high-intensity, low-frequency rotational grazing. Two major hypotheses were tested, namely: (a) that arthropods will differ in abundance, diversity, and composition as the deferment period increases, and that longer deferment periods conserve diversity of arthropods; and (b) that structural properties of vegetation—specifically sward height, biomass, and litter cover below leaf level—are important environmental variables influencing succession of arthropod communities in pastures under rotational grazing management. The rotational grazing system implemented at the study site also enabled sequential community sampling in paddocks that had been undisturbed for one day (grazed the previous day) to 105 days. This permitted a test of one of the predictions of Huston’s (1979) “dynamic equilibrium model”, where higher trophic levels are expected to recover more slowly than lower ones following a disturbance of given intensity and frequency (Huston, 1994). Poyry et al. (2006) tested this prediction by measuring differences in species richness of butterflies and moths between pastures of different ages. According to the prediction, biomass, population sizes, and growth rates of predators and parasitoids will be lower than herbivore and detritivore assemblages because only a fraction of the energy available at lower trophic levels is transferred to higher trophic levels. Average daily population growth of primary (litter and plant eaters) and secondary (predators and parasitoids) consumer groups occurring between different deferment periods was computed to test Huston’s model.

3.2 Methods 3.2.1 Study Site and Experimental Units Sampling was conducted in paddocks of grazing pasture from 1 to 2 May 2009, 31 July to 3 August 2009, and 2 to 4 October 2009, at Polyface Farm (38° 7'6.33" N, 79° 13'38.81" W) near Swoope, Virginia, in the Shenandoah Valley. The reader is referred to Study I, Section 2.2.1, for a description of the study site, including details of the high-intensity, low-frequency rotational cattle grazing regime, elevation, precipitation. Non-native, cool-season grasses like tall fescue (Festuca arundinacea) and timothy-grass (Phleum pretense) dominated the pasture at Polyface. 3.2.2 Sampling Methods Two sequences of arthropod community succession following grazing perturbations were achieved by sampling in the spring (early-season, ES), and again in the summer and autumn (late-season, LS). Sampling occurred in discrete paddocks of pasture, where the boundaries were delineated by electric fencing wire. Four paddocks of pasture that had not been grazed for 1, 10, 15, and 20 days were sampled in early May 2009. The paddock that was not grazed for 20 days was re-sampled after grazing to also represent a pasture that had not been grazed for 1 day. In late July 2009, arthropod communities were sampled in an additional five paddocks that had not been grazed for 1, 11, 21, 32, and 42 days by the day of sampling. Four of these were re- sampled in early October 2009 to represent longer periods of succession. Paddocks that had not been grazed for 1 and 42 days were sampled 63 days later, to represent 64 and 105 days of succession, respectively. Paddocks that had not been grazed for 11 and 21 days were sampled 64 days later, to represent 75 and 85 days of succession, respectively. Resampling permitted construction of a sampling sequence (n = 9) spanning up to 105 days of succession. Per Study I, Section 2.2.1, laying hens were permitted to forage in recently grazed paddocks. Paddocks where grazing had been deferred for longer than one day, had therefore been occupied by hens. Bouts of suction sampling, hand-searching of vegetation after it was harvested from the sample ring, and hand-searching the substrate for arthropods were employed to collect specimens within a 0.25-m2 sampling ring at n = 6 different locations in each paddock of pasture. There were n = 54 samples collected overall. The reader is referred to Study I, Section 2.2.2 for a complete description of sample site selection, sampling methods and protocol, and sampling equipment. Each specimen was identified to the finest taxonomic resolution possible; i.e. some

specimens were identified to the level of class or order, while others were identified to the level of family (Table 3.1). Taxonomic data therefore reflected multiple levels of resolution. Of the 11,392 arthropods collected, 1226 were not assigned to a functional group because their feeding behaviors spanned multiple functional groups at the identified level of taxonomic resolution. Identification protocol, nomenclature, and assignment of specimens to functional or trophic groups are described in Study I, Section 2.2.3. A list of dichotomous keys used to identify arthropods is provided therein. 3.2.3 Measuring Structural Properties of Vegetation Plant biomass was estimated using vegetation harvested from within two 10-cm diameter rings within the larger sample ring after the first suction sample was conducted. Samples were dried at 80º C for 72 h; paired dry weights were averaged. Vegetation height was measured at five points within a 1-m radius of the large sample ring using the drop disc method (Holmes, 1974), where a 200-g disk (30-cm diameter, 1 cm thick) was made to slide freely down a metric measuring rod until it came to rest; observations were averaged. Percent litter cover below leaf level inside the sample ring was visually estimated before each second suction sample by estimating coverage of the substrate by dead or living plant matter. 3.3 Data Analysis Statistical analyses were performed using SAS 9.2 for Windows (SAS Institute Inc., Cary, NC, USA), and using R version 3.0.2 for Macintosh (R Core Team, 2013). Abundance and richness data were analyzed at the finest taxonomic resolution achieved except where indicated otherwise; multiple taxonomic levels were thus represented in most analyses. 3.3.1 Sward structure throughout pasture succession Analyses of variability in vegetation height, dry weight, and percent litter cover across all LS paddocks were conducted. Data were distributed normally and were not transformed for these analyses. The effect of deferment period, or number of days since a paddock had been grazed, was determined using mixed-effects standard least squares regression models in JMP (version 8.0; SAS Institute Inc., Cary, NC, USA). In the repeated measures model design, number of days of deferment was coded as a fixed effect and paddock was coded as a random blocking factor. Vegetation dry weight and percent litter cover were weakly correlated with 2 2 vegetation height (R = 0.24, F1,52 = 16.25, p < 0.001, and R = 0.12, F1,52 = 7.11, p = 0.0102,

respectively). Structural variables did not exhibit multicollinearity, so they were used as community predictors in subsequent analyses. 3.3.2 Do abundance, richness and diversity of arthropod communities change with deferment period? Taxonomic richness data from pastures were analyzed using segmented regression in PROC NLIN (SAS Institute Inc., Cary, NC, USA) to determine the point where the relationship between the number of days of deferment and taxonomic richness changed. Observed richness data were pooled at each site (n = 3 per paddock). PROC NLIN selected the time point in paddock succession where there was an optimized difference between slopes of the regression curves to either side of the point estimate. An approximate 95% confidence interval for the change of direction point was also calculated. This analysis only included data from LS paddocks. The taxonomic diversity of arthropod communities was determined using the Shannon-

Wiener diversity index (H’). Shannon’s evenness (E) and functional evenness (EFUN) were also calculated; functional evenness was calculated using counts of functional groups instead of counts of taxa. Mean diversity, evenness, and functional evenness of communities in select paddocks were compared using two sample t-tests (function t.test in R package stats version 3.0.2; R Core Team, 2013); function t.test assumes unequal variances of compared means. Variances were not equal, so variance was estimated separately and the Welch modification to degrees of freedom was applied. Means of resampled paddocks were compared using paired t- tests; variances were again unequal and the Welch modification was applied. 3.3.3 Functional group distribution Examinations of functional group distribution were conducted at two functional levels for early- and late-season sampling periods. Separate analyses for paddocks sampled during the ES and LS grazing rotations were performed using PROC FREQ to investigate shifts in functional composition of arthropod communities. A chi-square test of homogeneity (dfES = 9; dfLS = 24) was first used to test the null hypothesis that the abundance of functional groups did not change with time; this analysis did not necessarily identify only monotonic trends, but general changes in overall group distribution. Abundance data for all four functional groups were arranged in 4 x k matrices, where k = number of time points sampled. A Cochran-Armitage trend test was then used to identify proportional increases within specific groups over time, namely primary and

secondary consumers. This test was limited to matrices with 2 x k dimensions, so counts of detritivores and herbivores, and counts of predators and parasitoids were combined into primary and secondary consumer groups, respectively, to accommodate this limitation. To test the prediction of Huston’s model, the difference in total abundance of each consumer group between paired paddocks (i.e. where repeated sampling had occurred) was computed and divided by the number of intervening days between first- and second-round sampling. The result was effectively the average daily population growth for each consumer group. 3.3.4 Community dissimilarity The multivariate method of constrained analysis of principal coordinates (CAP; function capscale in R package vegan; Oksanen et al., 2010) was used to compute dissimilarities in taxonomic composition among LS arthropod communities along gradients of deferment and of structural properties of vegetation: height, dry weight of standing vegetation, and percent litter cover. Constrained analysis of principal coordinates is an ordination method similar to principal coordinates analysis, only the analysis is constrained by variables of interest and non-Euclidean dissimilarity indices are permitted. The semi-metric Bray-Curtis index was chosen here. A community matrix of arthropod counts by taxon was supplied to capscale as the response variable; square root transformation and Wisconsin double standardization were applied to count data. Deferment period (Days), vegetation height (HT), percent cover (CO), and dry weight (WT) were coded as independent variables in the CAP model. The command term Condition was employed to partial out variance in the count data due to repeated sampling in multiple paddocks, thereby creating a reduced or partial CAP model. An ordination biplot with symmetrically scaled site and species scores was constructed to represent variance in community composition explained by deferment period and structural constraints. Residuals of the reduced CAP model were randomly permuted to test for significance of the joint effect of constraints, residuals of the full model permuted for significance of marginal (Type III) effects, and eigenvalues permuted for significance of each constrained ordination axis. The test of joint effects was based on 200 permutations; separate tests of marginal effects were each based on 199 permutations. Axis tests were each based on different numbers of permutations, reported below.

3.4 Results 3.4.1 Sward structure and arthropod community composition Percent litter cover was significantly but weakly associated with number of days of 2 deferment (Table 3.2; R = 0.23, F1,52 = 18.06, p < 0.001). There were neither strong nor significant relationships between vegetation height and dry weight, and number of days of deferment (Table 3.2). Percent litter cover generally increased with deferment (Fig. 3.1a), reaching a maximum 81.7 ± 4.0% at 105 days. Vegetation height was roughly unimodal (Fig. 3.1b), with approximately equal maxima occurring at 42 and 64 days (17.7 ± 0.5 cm and 17.9 ± 1.5 cm, respectively). Dry weight of vegetation followed a similar trend (Fig. 3.1c) and was, on average, greatest in the pasture where grazing was deferred for 42 days (5.0 ± 1.3 g). A matrix of count data for 98 arthropod taxa across 9 paddocks of grazed pasture, and data describing constraint variables length of deferment period, mean vegetation height, mean percent litter cover, and mean dry weight were used in the constrained analysis of principal coordinates. The first four constrained ordination axes produced a combined eigenvalue of 1.382, and these axes accounted for 11.8% of variance of dissimilarity within taxa count data (Table 3.3). Deferment period was most strongly correlated with axis 1 (CAP1), vegetation height with axis 2 (CAP2), percent litter cover with axis 3, and dry weight of vegetation with axis 4. The conditioned sampling variable explained 14.2% of variance. The joint effect of all constraints under a reduced model was significant (F4,45 = 1.79, p < 0.01). Marginal effects of deferment period (F1,45 = 2.95, p < 0.01) and vegetation height (F1,45 = 1.70, p < 0.01) were significant, but effects of percent litter cover (F1,45 = 0.86, p = 0.71) and dry weight (F1,45 = 1.09, p = 0.31) were not. Most variability in the ordination of taxa occurred along gradients of vegetation height, grazing deferment period, and percent litter cover (Figure 3.2). Assemblages of parasitoid wasps correlated positively with vegetation height and percent litter cover, including families Aphelinidae, Diapriidae, Dryinidae, Pteromalidae, Encyrtidae, Mymaridae, and Ichneumonidae. Eulophid, figitid, braconid, eucoilid, eurytomid, and platygastrid wasps were more closely associated with sites where grazing had been deferred for 32 days. Anyphaenid spiders were correlated with moderate vegetation height; araneid spiders were correlated with longer deferment periods and taller vegetation. Family Lycosidae was correlated with shorter vegetation and moderate litter cover. Spider families Linyphiidae, Theridiidae, Oxyopidae, and Clubionidae were correlated with intermediate deferment periods

and did not occur along other environmental gradients. Alydid bugs, drosophilid flies, and centipedes (Chilopoda) were abundant where litter cover was greatest. Other hemipterans were correlated with less litter cover and shorter vegetation, like families Miridae and Lygaeidae. Fly and beetle families comprised the majority of taxa with negative scores on axes 1 and 2, and were inversely correlated with vegetation height and litter cover. 3.4.2 Abundance and taxonomic diversity along gradients of grazing deferment Results of segmented regression did not identify a LS deferment period that optimized observed taxonomic richness. A single point representing a deferment period where the difference in slope between two regression segments was optimized could not be identified with statistical confidence using PROC NLIN. This difference was maximized at 32 ± 260.9 days, but due to the large standard error of the point of change, the importance of the estimator was ambiguous in terms of the model, and inferential methods like confidence intervals (app. 95% CI: -507.7 to 571.7) were not very useful in its interpretation. In general, observed richness increased both leading up to and after 32 days of deferment, but it increased at a slower rate after 32 days (Formula 3.1). Formula 3.1. S (Taxonomic Richness) = 33.572 + 0.041 * days of deferment, if ≤ 32 days. = 34.407 + 0.015 * days of deferment, if > 32 days. Mean richness was greatest at 32 days (33.2 ± 1.5) of deferment, and it was least at 85 days (15.5 ± 1.1); however, mean diversity (2.71 ± 0.11) and evenness (0.84 ± 0.02) were maximized at a different intermediate deferment period of 21 days (Table 3.4). Mean abundance across all LS paddocks was maximized (406 ± 63) at 105 days of deferment, but later sampling of LS paddocks tended to produce arthropod communities with lower diversity and evenness (Table 3.4). Mean abundance in ES paddocks was also maximized (81 ± 16) by the longest deferment period of 20 days, as were mean diversity and richness (Table 3.5). Maximum evenness (0.84 ± 0.03) was observed at an intermediate ES deferment period of 10 days; it was not significantly different (Welch Two Sample t-test; t8.92 = -0.125, p = 0.903) from maximum LS evenness (Table 3.5). 3.4.3 Functional composition of communities Overall distribution of arthropods among functional groups differed significantly among time points in both ES (X2 = 81.1, p < 0.0001) and LS (X2 = 1168.7, p < 0.0001) grazing

rotations. Cochran-Armitage tests detected significant and directional, consumer group-specific trends in relative abundance over time for both sampling periods (ES: Z = 5.1525, p < 0.0001; LS: Z = 5.8471, p < 0.0001). Functional evenness was maximized in the ES rotation at only 1 day of deferment (0.844 ± 0.03), but it was not different from functional evenness at 10 days (Welch Two Sample t-test; t8.56 = 0.027, p = 0.979; Table 3.5) when most functional groups were least abundant, or at 20 days (paired t-test; t5 = 0.288, p = 0.785; Table 3.5). Detritivores increased in relative abundance with length of deferment period, while herbivores and predators declined (Fig. 3.3). The relative abundance of parasitoids remained low, ranging from 1.2 to 3.4% of the overall community, while herbivores consistently comprised the largest functional group, ranging between 46.1% and 50.8% of functional composition (Table 3.6). The ratio of primary to secondary consumers remained approximately constant (2.3:1) to 15 days of deferment, but the distribution was most skewed after 20 days of deferment (Fig. 3.4), when numbers of detritivores and herbivores increased by 140% and 29%, respectively, from levels observed at 15 days. Functional groups were least abundant after 10 days of deferment, except for parasitoids; functional groups were most abundant at 20 days, with the exception of predators (Fig. 3.4). All functional groups declined in abundance from 1 to 11 days of deferment, and detritivores and predators were present in even lower numbers after 21 days in the LS rotation (Table 3.7). Relative abundance of herbivores was more variable in LS communities than in ES communities and reached a maximum at 42 days (Fig. 3.5), but herbivores were more abundant in observed numbers, especially at 42 (N = 767) and 105 (N = 1324) days of deferment. The distribution of arthropods among consumer groups fluctuated throughout the sampling period, but the distribution was most skewed at 42 days of deferment (Fig. 3.6), where the ratio of primary to secondary consumers was 3.8:1. In most cases, observed abundance within functional groups and consumer groups was greater in later samples (i.e. October 2009), and LS functional evenness was maximized at 32 days of deferment (0.91 ± 0.02), but it was not different from functional evenness at 1 day (Table 3.4; Welch Two Sample t-test; t8.71 = -1.883, p = 0.094). Average daily population growth (dN) of primary consumers and secondary consumers were compared as a test of Huston’s (1994) dynamic equilibrium model. When positive population growth occurred between repeated samples of communities in LS paddocks, average

daily growth of primary consumer populations was greater than that of secondary consumers. The greatest average daily population growth for both primary and secondary consumers occurred between deferment periods of 42 and 105 days (Table 3.7). 3.5 Discussion This study illuminated the magnitude and direction of effects that grazing deferment period can produce in arthropod communities. Population, composition, and diversity of arthropods in paddocks of rotationally grazed pasture differed with length of deferment period. This supported the hypothesis that increasing deferment period would conserve these community properties, but different properties were maximized by different deferment periods. However, the findings of this study did not support the second major hypothesis concerning the relationship and predictive power of structural properties to explain arthropod community composition. Through ordination methods, structural properties were revealed to only explain a small amount of variance in composition. Overall, deferment encouraged population growth, though, on average, populations of primary consumers increased in greater numbers each day than secondary consumers. This lends support to Huston’s dynamic equilibrium model and its applicability to arthropod communities subjected to grazing management. Higher trophic levels may be slower to respond in number following grazing events. Monitoring and management efforts should consider the disparate effects of grazing on trophic or consumer groups over time if an objective of conservation is to optimize the evenness of membership among groups. Constrained analysis of principal coordinates was useful in assessing the variability in community composition explained by deferment period and measured structural properties of vegetation; these included height, biomass (dry weight), and percent litter cover. Two constrained axes, correlated with deferment period (DAYS) and vegetation height (HT), were significant and together accounted for 82.1% of the explained variance in computed dissimilarities of composition. However, explained variance only accounted for 11.8% of overall variance in arthropod composition. A combination of local and landscape variables may be required to account for differences in composition. Local variables like vegetation height and litter cover have been shown to promote richness and abundance of parasitoids (Kruess and Tscharntke, 2002b), true bugs (Korosi et al., 2012), arachnids (Dennis et al., 2001; Batary et al., 2008), and the Orthoptera (Batary et al., 2007b), especially where grazing was abated or reduced in intensity. Variables describing landscape configuration and composition were important

predictors of species composition of hunting and web-building spiders (Korosi et al., 2012). The conditioned source of variance attributed to repeated sampling accounted for 14.2% of overall variance. This may indicate that the variables included in the CAP model were, on their own, not good predictors of variability of community composition when sampling along a successional gradient occurs in different paddocks. However, it may also indicate that variability of composition in late successional (≥ 64 days) paddocks may have been more dependent on the composition of communities and condition of vegetation structure that existed during sampling and measurement earlier in the same paddocks. Even though the intensity and uniformity of grazing events were not observed to differ between paddocks, the convenience of sampling arthropods and measuring vegetation properties in different paddocks to assemble a sequence of successional communities may not be an acceptable tradeoff for a genuine sequence achieved through repeated sampling. The magnitude and statistical significance of taxon-level responses to the analyzed constraints were not examined here, but other studies have reported the benefits of enhanced vegetation structure to arthropod communities. Arachnid diversity has been shown to increase with litter cover (Dennis et al., 2001) and litter may even mediate trophic interactions between predatory arthropods and their prey (Denno et al., 2002), but excessive trampling of litter under high stocking rates may reduce open spaces available for spiders and disrupt these interactions (Duffey, 1975). At the spatial scale of daily grazing events in the present study, stocking rates in individual paddocks were high. Litter depth could have added important information about the effects of vegetation structure because different spider taxa have been shown to occur at different litter strata (Wagner et al., 2003, in deciduous forest). Taller vegetation near dung deposited by grazers and apertures of hoofprints may also promote web-building by spiders when stocking rates are high (Dennis et al., 2001). Sensitivity of grazers to tussocks of relatively dense and tall vegetation—common features of grazing pastures—may maintain community structure (Luff and Rushton, 1989), and promote arthropod richness (Cherrett, 1964; Dennis et al., 1998) and abundance (Woodcock et al., 2005). During bouts of hand-searching in the present study, an abundance of various insects and spiders was observed at the base of tussocks where there were open spaces in the loose topsoil around plant stems. Finally, taller vegetation, not necessarily associated with tussocks, has been shown to promote species richness of spiders, beetles, true bugs, parasitoid wasps, and the Auchenorrhyncha (Dennis et al., 1998; Kruess and Tscharntke,

while foraging in paddocks; many beetle and fly taxa are coprophagous as adults or larvae, so their specific responses could have been tied to the introduction of new fecal material. Arthropod diversity and richness were maximized by similar deferment periods in LS (late-season) and ES (early-season) rotations. In the ES rotation, this was the longest deferment period (20 days); diversity and richness were maximized by intermediate deferment periods in the LS rotation (21 and 32 days, respectively). LS taxonomic evenness and functional evenness were greatest at 21 and 32 days of deferment, respectively, in paddocks with intermediate height and biomass of standing vegetation, and with intermediate litter cover. Ordination of site and species (taxa) scores was useful in representing the correlation of arthropod taxa to sites of differing deferment periods, and to sites where communities differed in diversity. Taxa scores of parasitoid wasps, in particular, tended to be most similar to site scores of diverse and even communities that occurred in paddocks with enhanced structural qualities. No difference was found between the functional evenness of the earliest (just grazed) successional communities and later successional communities in the ES or LS rotations, even where taxonomic richness was maximized. This suggests that arthropod community structure and function may be stable and resistant to high-intensity, low-frequency grazing events. Average daily population growth of primary consumers was greater than that of secondary consumers during succession following grazing. Huston’s (1979) dynamic equilibrium model more directly refers to populations of species and their biomass, but if arthropods of higher trophic levels recover in number more slowly after grazing, then it is possible their diversity will also recover more slowly and will be reduced by grazing events that are too frequent or intense. Tscharntke (1997) reported that species richness of insect parasitoids decreased more than herbivore species richness from ungrazed to grazed reeds, supporting Huston’s model. In a test of Huston’s model, Poyry et al. (2006) found that richness of insect herbivores was highest in older successional (abandoned) pastures, whereas richness of vascular plants peaked in younger pastures with higher intensity or frequency of disturbance. These findings confirmed that higher trophic levels are slower to recover from environmental disturbances and supported Huston’s model. Monitoring and management efforts should consider the disparate effects of grazing on trophic or consumer groups over time if an objective of conservation is to optimize the evenness or diversity of members among and within groups.

3.6 Conclusions Arthropod communities differed in abundance, composition, and diversity along a successional gradient after high-intensity, low-frequency cattle grazing. The local management and vegetation variables accounted for roughly one-tenth of the overall variance in community composition, so it is clear communities are likely also responding to landscape-level variables as has been demonstrated in the literature. Enhanced structure of vegetation has been shown to promote arthropod richness and abundance, and to maintain community structure, and the present study confirms via ordination methods the importance of vegetation structure to certain taxa. On the whole, taxonomic and functional evenness were maximized from 20 days of paddock deferment (early season) to 32 days of paddock deferment (late season), but functional evenness did not differ during paddock succession. Daily rates of population growth were greater for primary consumers than for secondary consumers, indicating that predators and parasitoids may be more sensitive to grazing disturbances and that they are important groups deserving attention from conservation managers. These findings suggest that applying a management regime that targets a particular deferment period to produce an architecturally complex sward can optimize arthropod diversity, community structure, and potentially community function. Conservation of diverse and even arthropod communities is vital to nutrient cycling (Reichle, 1977; Culliney, 2013), and it may improve and stabilize ecosystem function (Yachi and Loreau, 1999; Ives et al., 2000; Wittebolle et al., 2009). 3.7 Future Directions and Research Questions • Is litter depth more important than litter cover to conserving arthropod diversity? • Which trophic relationships are quickest to develop during succession? Do local environmental and structural properties of vegetation influence when these relationships form? • How do feeding guilds within functional groups change during pasture succession? • Which landscape variables are important to arthropod community composition? Are different variables important at different stages of succession? • How does the introduction of cattle dung affect arthropod community structure? Which groups directly utilize this resource, and how do those groups change during succession and interact with others not tied to the resource?

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TABLES AND FIGURES

Figure 2.1 A diagrammatic representation of high-intensity, low-frequency rotational cattle grazing at Polyface Farm in Swoope, Virginia, USA. Cattle spent one day grazing in each paddock of pasture before being moved to the adjacent paddock. Paddocks are represented by subdivisions of the ellipse in the figure. Arrows indicate the general counter-clockwise movement of the herd around the pasture during the growing season.

Table 2.1 Taxonomy, adult feeding ecology, functional group assignment, and number of arthropods collected in three paddocks of pasture before and after high-intensity, low-frequency cattle grazing events at Polyface Farm in Swoope, Virginia, USA (July 2008 and May 2009). Overall abundance (N) is the yield of all sampling efforts (n = 36) for a given taxon. Arthropods were collected using a vacuum sampling apparatus, handheld aspirators, and a nylon beating sheet. Taxa were not assigned to a functional group wherever one is not listed.

Order/Class Family Feeding Ecology Functional Group N Acari Many 85 Araneae Araneidae Predaceous Predator 41 Araneae Clubionidae Predaceous Predator 24 Araneae Corinnidae Predaceous Predator 2 Araneae Gnaphosidae Predaceous Predator 1 Araneae Linyphiidae Predaceous Predator 486 Araneae Lycosidae Predaceous Predator 190 Araneae Mimetidae Predaceous Predator 1 Araneae Oxyopidae Predaceous Predator 14 Araneae Pisauridae Predaceous Predator 2 Araneae Salticidae Predaceous Predator 29 Araneae Tetragnathidae Predaceous Predator 12 Araneae Theridiidae Predaceous Predator 4 Araneae Thomisidae Predaceous Predator 51 Chilopoda Predaceous Predator 1 Coleoptera Anthicidae Phytophagous Herbivore 8 Coleoptera Anthribidae Saprophagous Detritivore 1 Coleoptera Carabidae Predaceous Predator 12 Coleoptera Chrysomelidae Phytophagous Herbivore 30 Coleoptera Coccinellidae Predaceous Predator 8 Coleoptera Curculionidae Phytophagous Herbivore 21 Coleoptera Elateridae Phytophagous Herbivore 39 Coleoptera Erotylidae Mycophagous Detritivore 10 Coleoptera Histeridae Predaceous Predator 6 Coleoptera Lathridiidae Mycophagous Detritivore 15 Coleoptera Meloidae Phytophagous Herbivore 2 Coleoptera Phalacridae Mycophagous Detritivore 20 Coleoptera Scaphidiidae Saprophagous Detritivore 2 Coleoptera Scarabaeidae Saprophagous Detritivore 2 Coleoptera Staphylinidae Predaceous Predator 86 Collembola Saprophagous Detritivore 458 Diplopoda Saprophagous Detritivore 25 Diptera Anthomyzidae Phytophagous Herbivore 15 Diptera Cecidomyiidae Mycophagous Detritivore 2 Diptera Ceratopogonidae Pollinators Herbivore 9 Diptera Chloropidae Saprophagous Detritivore 107

Diptera Drosophilidae Saprophagous Detritivore 8 Diptera Empididae Predaceous Predator 23 Diptera Ephydridae polyphagous Detritivore 6 Diptera Lonchopteridae Nectarivorous Herbivore 3 Diptera Muscidae Saprophagous Detritivore 6 Diptera Mycetophilidae Mycophagous Detritivore 1 Diptera Phoridae Saprophagous Detritivore 7 Diptera Pipunculidae Endoparasitic Predator 1 Diptera Psychodidae Saprophagous Detritivore 2 Diptera Scathophagidae Coprophagous Detritivore 2 Diptera Sciaridae Saprophagous Detritivore 6 Diptera Sepsidae Saprophagous Detritivore 13 Diptera Sphaeroceridae Saprophagous Detritivore 35 Diptera Tipulidae Nectarivorous adults Herbivore 1 Hemiptera Alydidae Phytophagous Herbivore 1 Hemiptera Berytidae Phytophagous Herbivore 6 Hemiptera Coreidae Phytophagous Herbivore 7 Hemiptera Dipsocoridae Predaceous Predator 5 Hemiptera Lygaeidae Phytophagous, granivorous Herbivore 31 Hemiptera Miridae Phytophagous Herbivore 12 Hemiptera Pentatomidae Phytophagous Herbivore 11 Hemiptera Reduviidae Predaceous Predator 3 Hemiptera Rhopalidae Phytophagous Herbivore 1 Hemiptera Thyreocoridae Phytophagous Herbivore 1 Homoptera Aphididae Phytophagous Herbivore 24 Homoptera Cercopidae Phytophagous Herbivore 1 Homoptera Cicadellidae Phytophagous Herbivore 317 Homoptera Delphacidae Phytophagous Herbivore 23 Hymenoptera Bethylidae Parasitoid Parasitoid 1 Hymenoptera Braconidae Parasitoid Parasitoid 4 Hymenoptera Ceraphronidae Parasitoid Parasitoid 3 Hymenoptera Diapriidae Parasitoid Parasitoid 12 Hymenoptera Encyrtidae Parasitoid Parasitoid 1 Hymenoptera Eucoilidae Parasitoid Parasitoid 1 Hymenoptera Eurytomidae Parasitoid Parasitoid 8 Hymenoptera Formicidae Many 404 Hymenoptera Ichneumonidae Parasitoid Parasitoid 1 Hymenoptera Mymaridae Parasitoid Parasitoid 2 Hymenoptera Platygastridae Parasitoid Parasitoid 1 Hymenoptera Pteromalidae Parasitoid Parasitoid 6 Hymenoptera Scelionidae Parasitoid Parasitoid 29 Hymenoptera Torymidae Parasitoid Parasitoid 1 Hymenoptera Trichogrammatidae Parasitoid Parasitoid 1 Isopoda Saprophagous Detritivore 40 Neuroptera Hemerobiidae Predaceous Predator 1

Orthoptera Acrididae Phytophagous Herbivore 4 Orthoptera Gryllidae Saprophagous Detritivore 26 Orthoptera Rhaphidophoridae Saprophagous Detritivore 2 Orthoptera Tetrigidae Saprophagous Detritivore 2 Orthoptera Tettigoniidae Phytophagous Herbivore 5 Thysanoptera Many 9 Total 2942

Table 2.2 Taxonomy, abundance, and frequency of arthropods collected before (n = 18) and after (n = 18) high-intensity, low-frequency grazing in paddocks of pasture grazed by cattle in Swoope, Virginia, USA (July 2008 and May 2009). Overall abundance (N) is the yield of all sampling efforts for a given taxon. Frequency is the proportion of all samples in which a given taxon was counted at least once. Maximum abundance is the greatest number of a taxon counted in one sample. Before After N Frequency (%) Max. N Frequency (%) Max. Order or Class Family Acari 27 56 7 58 72 33

Araneae Araneidae 36 56 6 5 11 4

Clubionidae 21 56 3 3 17 1

Corinnidae 1 6 1 1 6 1

Gnaphosidae 1 6 1 0 0 0

Linyphiidae 329 94 60 157 94 25

Lycosidae 116 89 23 74 89 12

Mimetidae 1 6 1 0 0 0

Oxyopidae 14 28 9 0 0 0

Pisauridae 2 11 1 0 0 0

Salticidae 27 61 7 2 6 2

Tetragnathidae 10 39 3 2 11 1

Theridiidae 2 11 1 2 11 1

Thomisidae 21 56 7 30 33 24

Chilopoda 1 6 1 0 0 0

Coleoptera Anthicidae 1 6 1 7 22 4

Anthribidae 1 6 1 0 0 0

Carabidae 6 28 2 6 22 2

Chrysomelidae 21 56 7 9 39 3

Coccinellidae 7 33 2 1 6 1

Curculionidae 8 28 3 13 61 2

Elateridae 11 39 4 28 44 11

Erotylidae 8 33 3 2 11 1

Histeridae 0 0 0 6 22 3

Lathridiidae 8 33 2 7 28 3

Meloidae 2 6 2 0 0 0

Phalacridae 10 44 2 10 33 2

Scaphidiidae 1 6 1 1 6 1

Scarabaeidae 1 6 1 1 6 1

Staphylinidae 25 56 5 61 78 11

Collembola 362 89 151 96 72 28

Diplopoda 15 22 5 10 22 5

Diptera Anthomyzidae 15 28 6 0 0 0

Cecidomyiidae 2 11 1 0 0 0

Ceratopogonidae 5 17 3 4 11 3

Chloropidae 86 50 45 21 39 7

Drosophilidae 5 6 5 3 17 1

Empididae 20 44 7 3 11 2

Ephydridae 6 22 2 0 0 0

Lonchopteridae 2 11 1 1 6 1

Muscidae 3 17 1 3 17 1

Mycetophilidae 1 6 1 0 0 0

Phoridae 1 6 1 6 17 4

Pipunculidae 1 6 1 0 0 0

Psychodidae 2 11 1 0 0 0

Scathophagidae 2 6 2 0 0 0

Sciaridae 6 17 4 0 0 0

Sepsidae 1 6 1 12 17 8

Sphaeroceridae 15 33 6 20 50 7

Tipulidae 1 6 1 0 0 0

Hemiptera Alydidae 0 0 0 1 6 1

Berytidae 4 22 1 2 11 1

Coreidae 7 6 7 0 0 0

Dipsocoridae 2 11 1 3 17 1

Lygaeidae 28 50 14 3 11 2

Miridae 5 17 2 7 28 3

Pentatomidae 10 39 2 1 6 1

Reduviidae 2 11 1 1 6 1

Rhopalidae 1 6 1 0 0 0

Thyreocoridae 0 0 0 1 6 1

Homoptera Aphididae 23 33 8 1 6 1

Cercopidae 1 6 1 0 0 0

Cicadellidae 196 94 59 121 61 44

Delphacidae 23 61 9 0 0 0

Hymenoptera Bethylidae 0 0 0 1 6 1

Braconidae 2 11 1 2 11 1

Ceraphronidae 2 11 1 1 6 1

Diapriidae 7 39 1 5 28 1

Encyrtidae 1 6 1 0 0 0

Eucoilidae 0 0 0 1 6 1

Eurytomidae 8 11 7 0 0 0

Formicidae 261 100 78 143 89 35

Ichneumonidae 1 6 1 0 0 0

Mymaridae 2 11 1 0 0 0

Platygastridae 0 0 0 1 6 1

Pteromalidae 5 17 3 1 6 1

Scelionidae 26 61 11 3 17 1

Torymidae 1 6 1 0 0 0

Trichogrammatidae 1 6 1 0 0 0

Isopoda 20 44 7 20 17 13

Neuroptera Hemerobiidae 1 6 1 0 0 0

Orthoptera Acrididae 4 17 2 0 0 0

Gryllidae 23 39 9 3 11 2

Tetrigidae 2 11 1 0 0 0

Tettigoniidae 5 28 1 0 0 0

Rhaphidophoridae 2 6 2 0 0 0

Thysanoptera 6 28 2 3 11 2

Total 1952 990

Table 2.3 Functional group, abundance, and frequency of arthropods collected before (n = 18) and after (n = 18) high-intensity, low-frequency grazing in paddocks of pasture grazed by cattle in Swoope, Virginia, USA (July 2008 and May 2009). Overall abundance (N) is the yield of all sampling efforts for a given functional group. Frequency is the proportion of all samples in which a given functional group was counted at least once. Maximum abundance is the greatest number of a functional group counted in one sample.

Before After N Frequency (%) Max. N Frequency (%) Max.

Functional Group Detritivore 566 94 161 205 89 56

Herbivore 367 100 68 198 94 47

Predator 652 100 90 358 100 55

Parasitoid 57 78 14 15 44 4

Total 1642 776

140

120

100

60 Abundance

0 Before After Sample Period

Figure 2.2 Abundance of arthropods collected within 24 hours before (n = 18) and after (n = 18) high- intensity, low-frequency cattle grazing in paddocks of pasture at Polyface Farm in Swoope, Virginia, USA (July 2008 and May 2009). Data were means and one Standard Error of the Mean.

Table 2.4 Responses of abundance of arthropod taxa and functional groups to high-intensity, low- frequency cattle grazing events in paddocks of pasture in Swoope, Virginia, USA (July 2008 and May 2009). Before After Z p µ SE µ SE Taxon or Functional Group Acari 1.5 0.47 3.22 1.78 2.11 0.17 Araneae 32.28 6.59 15.33 2.92 2.37 0.018* Chilopoda 0.06 0.06 0 0 0.05 0.96 Diplopoda 0.83 0.40 0.56 0.32 0.62 0.53 Coleoptera 6.11 0.77 8.44 1.28 -1.49 0.14 Collembola 20.11 8.14 5.33 1.80 3.55 0.0004* Diptera 9.67 3.12 4.06 1.27 1.93 0.053‡ Hemiptera 3.28 1.06 1.06 0.37 2.6 0.0093* Homoptera 13.5 3.92 6.78 2.80 2.5 0.012* Hymenoptera 17.61 4.86 8.78 2.17 2.13 0.033* Parasitic Apocritaa 3.11 0.86 0.83 0.28 3.04 0.0024* Isopoda 1.11 0.42 1.11 0.76 0.72 0.47 Neuroptera 0.06 0.06 0 0 0.005 0.96 Orthoptera 2 0.72 0.17 0.12 3.53 0.0004* Thysanoptera 0.33 0.14 0.17 0.12 0.9 0.3696

Total Count 108.44 17.20 55 9.30 3.3 8 0.0007* Detritivores 31.44 8.60 11.39 3.19 3.5 0.0005* Herbivores 20.39 4.23 11 2.88 2.77 0.0056* Predators 36.22 7.01 19.89 3.08 2.1 0.036* Parasitoids 3.17 0.86 0.83 0.28 3.1 0.002* Negative binomial mixed effects models were fit to counts of each taxon, total count, and counts of each functional group yielded by sampling arthropods before (n = 18) and after (n = 18) grazing to detect a response to the fixed effect of grazing. Wald Z-tests tested the null hypothesis of no grazing effect. Italicized Z-scores indicate a significant random effect of paddock; same paddocks were sampled before and after grazing. Mean abundance of taxa and functional groups, and one Standard Error of the Mean are given. aParasitic Apocrita were a subset of Hymenoptera that did not include the ants. *Statistically significant value. ‡ Marginally not statistically significant.

Abundance 20

0 Detritivores Herbivores Predators Parasitoids Functional Group

Figure 2.3 Abundance of arthropods by functional group collected within 24 hours before (n = 18; dark gray bars) and after (n = 18; light gray bars) high-intensity, low-frequency cattle grazing in paddocks of pasture in Swoope, Virginia, USA (July 2008 and May 2009). Data were means and one Standard Error of the Mean.

Table 2.5 Rarefied taxonomic richness of arthropod communities sampled before (n = 18) and after (n = 18) high-intensity, low-frequency cattle grazing of pastures in Swoope, Virginia, USA (July 2008 and May 2009). Mean expected taxonomic richness of each arthropod community was estimated once at each addition of individuals; the pool of individuals was randomly re-sampled without replacement each time. Intervals of 83% confidence were computed based on the sample standard deviation to compare taxonomic richness of communities before and after grazing. Richness was based on the number of unique taxa at multiple levels of taxonomic resolution.

Before After Sample Individuals Richness SD 83% C.I. Individuals Richness SD 83% C.I. 1 108 28.5 3 24.4 32.6 55 18.4 2.3 15.2 21.6 2 217 39.8 3.2 35.5 44.2 110 25.3 2.6 21.8 28.9 3 325 46.9 3.2 42.5 51.2 165 30.2 2.7 26.5 34.0 4 434 52 3.2 47.7 56.3 220 34 2.7 30.2 37.8 5 542 56 3.1 51.7 60.3 275 37.1 2.7 33.4 40.8 6 651 59.4 3.1 55.2 63.5 330 39.7 2.7 36.0 43.4 7 759 62.2 3.0 58.1 66.3 385 42 2.6 38.4 45.5 8 868 64.7 2.9 60.8 68.7 440 43.9 2.5 40.5 47.4 9 976 67 2.8 63.1 70.8 495 45.7 2.4 42.4 49.0 10 1084 69.0 2.7 65.3 72.7 550 47.3 2.3 44.1 50.4 11 1193 70.9 2.6 67.4 74.5 605 48.7 2.2 45.7 51.7 12 1301 72.7 2.4 69.4 76.0 660 50 2.0 47.2 52.8 13 1410 74.3 2.2 71.3 77.4 715 51.2 1.9 48.6 53.8 14 1518 75.8 2.0 73.1 78.6 770 52.3 1.7 49.9 54.6 15 1627 77.3 1.8 74.9 79.7 825 53.3 1.5 51.2 55.3 16 1735 78.6 1.5 76.6 80.6 880 54.2 1.2 52.5 55.9 17 1844 79.9 1.0 78.4 81.3 935 55.1 0.9 53.9 56.4 18 1952 81 0 990 56 0

Figure 2.4 Sample-based rarefaction curves and corresponding 83% C.I. (faint dotted lines) of arthropod taxonomic richness in paddocks of pasture before and after high-intensity, low-frequency cattle grazing in Swoope, Virginia, USA (July 2008 and May 2009). Richness was based on the number of unique taxa at multiple levels of taxonomic resolution. Sampling effort encompassed n =18 pre-grazing and n = 18 post-grazing samples.

$!!"#

,!"#

+!"#

*!"#

)!"#

(!"#

'!"#

&!"# % of Overall Richness Overall of %

%!"#

$!"#

!"# Before After Sample Period

Figure 2.5 Relative contributions to arthropod community taxonomic richness by the four most family-rich orders (Araneae, Coleoptera, Diptera, and Hemiptera; hatched bars) and by all other taxa (solid) collected before (n = 18) and after (n = 18) high-intensity, low-frequency cattle grazing in paddocks of pasture in Swoope, Virginia, USA (July 2008 and May 2009). Overall mean richness is represented by 100% of each bar: 21.8 and 13.7 before and after grazing, respectively.

Table 2.6 Responses of richnessa, and of Shannon-Wiener diversityb and evennessb of arthropod taxa

(H’ and E, resp.) and functional groups (H’FUN and EFUN, resp.) to high-intensity, low-frequency cattle grazing events in paddocks of pasture in Swoope, Virginia, USA (July 2008 and May 2009).

Before After Z or F p µ SE µ SE Taxon or Functional Group Araneae 5.17 0.57 2.78 0.22 3.52 0.0004* Coleoptera 3.78 0.45 3.78 0.45 0 1 ‡ Diptera 3 0.72 1.83 0.35 1.74 0.083 ‡ Hemiptera 2.83 0.34 1.72 0.30 1.91 0.057 Homoptera 1.61 0.31 0.89 0.28 3.2 0.0014* Hymenoptera 1.94 0.22 0.67 0.14 2.18 0.029* Detritivores 4.94 0.64 3.39 0.55 2.26 0.024* Herbivores 5.72 0.54 3.11 0.44 3.65 0.0003* Predators 7.28 0.74 4.44 0.45 3.45 0.0006* Parasitoids 1.89 0.35 0.83 0.28 2.37 0.018* Community Taxonomic Richness 21.83 1.52 13.72 1.45 32.71 <0.0001*

H' 2.31 0.08 1.95 0.11 6.94 0.0129* E 0.76 0.02 0.78 0.02 0.21 0.65

H'FUN 0.99 0.04 0.89 0.06 1.7 0.2019

EFUN 0.76 0.03 0.76 0.03 0.0002 0.9878 aNegative binomial mixed effects models were fit to counts of arthropod families belonging to each order, and to counts of unique taxa belonging to each functional group collected before (n = 18) and after (n = 18) grazing to detect responses to the fixed effect of grazing. Wald Z-tests tested the null hypothesis of no effect. Italicized Z-scores indicate a significant random effect of paddock; paddocks sampled before and after grazing were the same. bLinear mixed effects models were fit to taxonomic and functional diversity and evenness data to detect responses of those measures to the fixed grazing effect. Taxonomic diversity and evenness data were based on counts of arthropods belonging to unique taxa; functional diversity and evenness data were based on counts of arthropods within each functional group. Wald F-tests (on 1 and 32 degrees of freedom) were conducted to determine significance of the fixed effect. Mean counts of families within arthropod orders, mean counts of unique taxa within functional groups, mean diversity and evenness, and one Standard Error of the Mean are given. *Statistically significant value. ‡ Marginally not statistically significant.

Number of Taxa NumberTaxa of 3

0 Detritivores Herbivores Predators Parasitoids Functional Group

Figure 2.6 Taxonomic richness of arthropods by functional group collected within 24 hours before (n = 18; dark gray bars) and after (n = 18; light gray bars) high-intensity, low-frequency cattle grazing in paddocks of pasture in Swoope, Virginia, USA (July 2008 and May 2009). Richness was based on the number of unique taxa; multiple levels of taxonomic resolution are represented. Data were means and one Standard Error of the Mean.

Table 2.7 Contribution and significance of high-intensity, low-frequency cattle grazing events to explaining variation in taxonomic and functional composition of arthropod communities in grazed paddocks of pasture in Swoope, Virginia, USA (July 2008 and May 2009).

Taxonomic Functional df SS MS F R2 p df SS MS F value R2 p Grazing 1 0.62 0.62 3.53 0.09 0.001* 1 0.21 0.21 5.50 0.14 0.004* Residuals 34 5.96 0.18 0.91 34 1.32 0.04 0.86

Matrices of Bray-Curtis dissimilarities based on arthropod count data by taxon and by functional group were ‘partitioned’ among sources of variation in community composition, namely occurrence of grazing. Sequential sums of squares from randomly permuted (n = 999) count data were the basis for F tests of significance; permutations were constrained within each paddock to account for repeated sampling before and after grazing. Count data from n = 18 pre-grazing and n = 18 post-grazing samples were log-transformed (log [x+1]). Multiple levels of taxonomic resolution were represented in count data; counts at the finest level of resolution (i.e. counts of unique taxa) were included in this analysis.

Figure 2.7 Nonmetric multidimensional scaling of mean arthropod taxon abundances before and after high-intensity, low-frequency cattle grazing in paddocks of pasture in Swoope, Virginia (July 2008 and May 2009). Multiple levels of taxonomic resolution are represented; counts at the finest level of resolution (i.e. counts of unique taxa) were included in this analysis. Plotted ‘species’ (taxon) scores are labeled with respective taxon names. Lines drawn from each group’s centroid indicate site scores for n = 18 pre-grazing and n = 18 post-grazing samples.

Table 3.1 Taxonomy, adult feeding ecology, functional group assignment, and number of arthropods collected paddocks of pasture under a high-intensity, low-frequency cattle grazing management scheme at Polyface Farm in Swoope, Virginia, USA. Arthropods were collected using a vacuum sampling apparatus, handheld aspirators, and a nylon beating sheet from paddocks where grazing had been deferred for 1 to 105 days. Sampling occurred in May, July, August, and October 2009. Taxa were not assigned to a functional group wherever one is not listed.

Order/Class Family Feeding Ecology Functional Group Number Collected Acari Many 662 Araneae Anyphaenidae Predaceous Predator 1 Araneae Araneidae Predaceous Predator 8 Araneae Clubionidae Predaceous Predator 6 Araneae Corinnidae Predaceous Predator 2 Araneae Dictynidae Predaceous Predator 1 Araneae Gnaphosidae Predaceous Predator 1 Araneae Linyphiidae Predaceous Predator 1565 Araneae Lycosidae Predaceous Predator 210 Araneae Oxyopidae Predaceous Predator 8 Araneae Salticidae Predaceous Predator 15 Araneae Tetragnathidae Predaceous Predator 73 Araneae Theridiidae Predaceous Predator 19 Araneae Thomisidae Predaceous Predator 66 Araneae Uloboridae Predaceous Predator 1 Chilopoda Predaceous Predator 41 Coleoptera Anthicidae Phytophagous Herbivore 7 Coleoptera Anthribidae Saprophagous Detritivore 3 Coleoptera Carabidae Predaceous Predator 45 Coleoptera Chrysomelidae Phytophagous Herbivore 184 Coleoptera Coccinellidae Predaceous Predator 17 Coleoptera Curculionidae Phytophagous Herbivore 71 Coleoptera Elateridae Phytophagous Herbivore 55 Coleoptera Erotylidae Mycophagous Detritivore 50 Coleoptera Histeridae Predaceous Predator 6 Coleoptera Lathridiidae Mycophagous Detritivore 50 Coleoptera Leiodidae Saprophagous Detritivore 1 Coleoptera Melandryidae Mycophagous Detritivore 1 Coleoptera Phalacridae Mycophagous Detritivore 102 Coleoptera Scaphidiidae Saprophagous Detritivore 3 Coleoptera Scarabaeidae Saprophagous Detritivore 5 Coleoptera Scolytidae Phytophagous Herbivore 3 Coleoptera Staphylinidae Predaceous Predator 411 Coleoptera Throscidae Phytophagous, pollenivorous Herbivore 9

Collembola Saprophagous Detritivore 1996 Dermaptera Saprophagous Detritivore 1 Diplopoda Saprophagous Detritivore 27 Diplura Saprophagous Detritivore 2 Diptera Agromyzidae Leaf-miners, phytophagous Herbivore 7 Diptera Anthomyzidae Phytophagous Herbivore 39 Diptera Calliphoridae Coprophagous Detritivore 1 Diptera Cecidomyiidae Mycophagous Detritivore 15 Diptera Ceratopogonidae Saprophagous, pollinators Herbivore 68 Diptera Chamaemyiidae Predaceous Predator 1 Diptera Chironomidae Nectarivorous adults Herbivore 1 Diptera Chloropidae Saprophagous Detritivore 203 Diptera Drosophilidae Saprophagous Detritivore 41 Diptera Empididae Predaceous Predator 13 Diptera Ephydridae Polyphagous Detritivore 57 Diptera Lonchopteridae Nectarivorous Herbivore 49 Diptera Muscidae Saprophagous Detritivore 3 Diptera Mycetophilidae Mycophagous Detritivore 6 Diptera Phoridae Saprophagous Detritivore 55 Diptera Psychodidae Saprophagous Detritivore 1 Diptera Sciaridae Saprophagous Detritivore 19 Diptera Sepsidae Saprophagous, coprophagous Detritivore 4 Diptera Sphaeroceridae Saprophagous, coprophagous Detritivore 83 Diptera Strongylophthalmyiidae Unknown 1 Diptera Syrphidae Pollinators Herbivore 2 Hemiptera Alydidae Phytophagous Herbivore 6 Hemiptera Anthocoridae Predaceous Predator 10 Hemiptera Berytidae Phytophagous Herbivore 4 Hemiptera Lygaeidae Phytophagous, granivorous Herbivore 27 Hemiptera Miridae Phytophagous Herbivore 175 Hemiptera Nabidae Predaceous Predator 71 Hemiptera Pentatomidae Phytophagous Herbivore 5 Hemiptera Saldidae Predaceous Predator 8 Hemiptera Thyreocoridae Phytophagous Herbivore 1 Homoptera Aphididae Phytophagous Herbivore 189 Homoptera Cercopidae Phytophagous Herbivore 17 Homoptera Cicadellidae Phytophagous Herbivore 2984 Homoptera Delphacidae Phytophagous Herbivore 453 Hymenoptera Aphelinidae Parasitoid Parasitoid 3 Hymenoptera Bethylidae Parasitoid Parasitoid 2 Hymenoptera Braconidae Parasitoid Parasitoid 64 Hymenoptera Ceraphronidae Parasitoid Parasitoid 22 Hymenoptera Diapriidae Parasitoid Parasitoid 46 Hymenoptera Dryinidae Parasitoid Parasitoid 1 Hymenoptera Encyrtidae Parasitoid Parasitoid 5

Hymenoptera Eucoilidae Parasitoid Parasitoid 41 Hymenoptera Eulophidae Parasitoid Parasitoid 9 Hymenoptera Eurytomidae Parasitoid Parasitoid 6 Hymenoptera Figitidae Parasitoid Parasitoid 1 Hymenoptera Formicidae Many 516 Hymenoptera Ichneumonidae Parasitoid Parasitoid 2 Hymenoptera Megaspilidae Parasitoid Parasitoid 2 Hymenoptera Mymaridae Parasitoid Parasitoid 19 Hymenoptera Platygastridae Parasitoid Parasitoid 6 Hymenoptera Pteromalidae Parasitoid Parasitoid 29 Hymenoptera Scelionidae Parasitoid Parasitoid 122 Isopoda Saprophagous Detritivore 31 Lepidoptera Many 1 Neuroptera Hemerobiidae Predaceous Predator 6 Odonata Coenagrionidae Predaceous Predator 1 Orthoptera Acrididae Phytophagous Herbivore 12 Orthoptera Gryllidae Saprophagous Detritivore 48 Orthoptera Tetrigidae Saprophagous Detritivore 1 Orthoptera Tettigoniidae Phytophagous Herbivore 2 Psocoptera Polypsocidae Saprophagous Detritivore 1 Thysanoptera Many 46 Total 11 392

Table 3.2 Responses of height, dry weight, and percent litter cover to number of days grazing was deferred in paddocks of rotationally grazed pasture at Polyface Farm in Swoope, Virginia, USA.

Vegetation Parameter Deferment Period (days) R2 F p 1 11 21 32 42 64 75 85 105 Sward Height (cm) 6.8 ± 0.2 11.7 ± 0.6 10.7 ± 0.6 10.2 ± 1.4 17.7 ± 0.5 17.9 ± 1.5 11.9 ± 0.7 10.4 ± 1.3 12.4 ± 0.4 0.19 2.91 NS Dry Weight (g) 0.8 ± 0.2 4.0 ± 0.8 1.8 ± 0.3 2.8 ± 0.6 5.0 ± 1.3 2.6 ± 0.4 3.7 ± 0.6 2.8 ± 0.7 3.5 ± 0.5 0.27 0.61 NS % Litter Cover 49.2 ± 6.1 51.7 ± 4.8 61.7 ± 7.0 60.0 ± 10.3 71.7 ± 4.0 66.7 ± 3.3 80.0 ± 6.8 65.0 ± 5.6 81.7 ± 4.0 0.23 18.06 < 0.001*

Linear mixed effects models were fit to vegetation measurements to detect responses to the effect of deferment period. F tests (on 1 and 52 degrees of freedom) were conducted to determine significance of the effect of deferment period. Data were not transformed for these analyses. Means are reported with Standard Error of the Mean. Asterisk indicates statistically significant value. NS indicates not significant.

100

40 % Litter Cover Cover Litter %

0 1 11 21 32 42 64 75 85 105 Deferment Period (days)

Figure 3.1a Percent litter cover observed in paddocks of rotationally grazed pasture under different deferment periods at Polyface Farm in Swoope, Virginia, USA. Percent litter cover was visually estimated for the area within a 0.25-m2 sampling ring. Data were means and one Standard Error of the Mean.

25.0

20.0

15.0

10.0 Height (cm) Height

5.0

0.0 1 11 21 32 42 64 75 85 105 Deferment Period (days)

Figure 3.1b Vegetation height observed in paddocks of rotationally grazed pasture under different deferment periods at Polyface Farm in Swoope, Virginia, USA. Height was measured at five points within a 1-m radius of the large sample ring using Holmes’ (1974) drop disc method. Data were means and one Standard Error of the Mean.

7.0

6.0

5.0

4.0

3.0 Dry Weight (g) Dry Weight

2.0

1.0

0.0 1 11 21 32 42 64 75 85 105 Deferment Period (days)

Figure 3.1c Dry weight of vegetation in paddocks of rotationally grazed pasture under different deferment periods at Polyface Farm in Swoope, Virginia, USA. Dry weight was measured using dried samples of vegetation harvested from within two 10-cm diameter rings within the larger sample ring; these samples were harvested prior to harvesting all vegetation to hand search for arthropods. Data were means and one Standard Error of the Mean.

Table 3.3 Correlation coefficients between environmental variables and four ordination axes produced by constrained analysis of principal coordinates for arthropod communities sampled from paddocks of pasture under a high-intensity, low-frequency cattle grazing regime at Polyface Farm in Swoope, Virginia, USA, in 2009. Italicized numbers highlight the largest correlation coefficients. Significance of constrained axes was determined by permutation tests (test statistic in parentheses). Environmental variables are abbreviated: percent litter cover as CO, days of deferment as Days, vegetation height as HT, and dry weight of vegetation as WT.

Variable Axis 1 Axis 2 Axis 3 Axis 4 CO 0.48 0.15 -0.62 -0.46 Days 0.84 -0.27 -0.07 0.10 HT 0.43 0.52 0.42 -0.42 WT 0.10 -0.22 0.24 -0.78

% Variance/axis 8.1% 3.2% 1.4% 1.0% % Contribution to explained variance 59.2% 22.9% 10.5% 7.5% a b c c Constrained eigenvalues 0.8166 (4.25**) 0.3163 (1.64*) 0.1455 (0.75) 0.1031 (0.54)

Different superscripts indicate different numbers of permutations: a, n = 199; b, n = 399; c, n = 99 **p < 0.01 for 1 and 45 degrees of freedom *p < 0.05 for 1 and 45 degrees of freedom

Figure 3.2 Ordination of site and arthropod taxa scores based on constrained analysis of principal coordinates. Directional arrows represent constraints HT (mean vegetation height), CO (mean percent litter cover), Days (length of deferment period), and WT (mean dry weight of vegetation). Site and taxa scores were symmetrically scaled, and are represented by numbers and taxa names in ordination space, respectively. Gray crosses were used to represent less abundant taxa. Numbers incidentally represent the deferment period. Arthropods were sampled (n = 54) and vegetation data were collected in paddocks of rotationally grazed pasture at Polyface Farm in Swoope, Virginia, USA, in 2009.

Table 3.4 Abundance (N), taxonomic richness (S), Shannon-Wiener diversity index (H'), Shannon's evenness (E), and functional evenness

(EFUN) of arthropods in late season (LS) paddocks of rotationally grazed pasture, reported by days of grazing deferment, at Polyface Farm, Swoope, Virginia, USA, in 2009. Means reported with Standard Error of the Mean in parentheses for n = 6 samples per paddock. Taxonomic diversity, richness, and evenness data were based on counts of arthropods belonging to unique taxa; multiple levels of taxonomic resolution are represented. Functional evenness data were based on counts of arthropods within each functional group.

Deferment Period (days) 1 11 21 32 42 64 75 85 105 N 134 (21) 90 (14) 90 (10) 219 (38) 223 (38) 298 (90) 182 (17) 91 (12) 406 (63) S 26.7 (2.5) 21.2 (0.7) 25 (1.5) 33.2 (1.5) 24.7 (1.5) 25.3 (2.7) 28.7 (1.3) 15.5 (1.1) 27 (0.9) H' 2.58 (0.09) 2.45 (0.10) 2.71 (0.11) 2.70 (0.07) 1.98 (0.08) 2.01 (0.14) 2.37 (0.05) 2.02 (0.11) 1.68 (0.06) E 0.79 (0.02) 0.80 (0.03) 0.84 (0.02) 0.77 (0.02) 0.62 (0.03) 0.63 (0.05) 0.71 (0.01) 0.74 (0.02) 0.51 (0.02)

EFUN 0.87 (0.01) 0.83 (0.02) 0.85 (0.02) 0.91 (0.02) 0.67 (0.02) 0.82 (0.03) 0.80 (0.03) 0.84 (0.05) 0.74 (0.02)

Table 3.5 Abundance (N), taxonomic richness (S), Shannon-Wiener diversity index (H'), Shannon's evenness (E), and functional evenness (EFUN) of arthropods in early season (ES) paddocks of pasture, reported by days of grazing deferment, at Polyface Farm in Swoope, Virginia, USA, in 2009. Taxonomic diversity, richness, and evenness data were based on counts of arthropods belonging to unique taxa; multiple levels of taxonomic resolution are represented. Functional evenness data were based on counts of arthropods within each functional group. Means reported with Standard Error of the Mean in parentheses for n = 6 samples per paddock.

Deferment Period (days) 1 10 15 20 N 57 (14) 37 (4) 72 (14) 81 (16) S 13.8 (0.5) 12.8 (0.7) 17 (1.6) 19.7 (2.3) H' 2.04 (0.09) 2.13 (0.07) 2.24 (0.06) 2.27 (0.13) E 0.78 (0.04) 0.84 (0.03) 0.80 (0.03) 0.78 (0.05)

EFUN 0.844 (0.03) 0.843 (0.02) 0.835 (0.03) 0.823 (0.04)

60%

50%

40% Detritivores Herbivores 30% Predators Parasitoids

% Abundance% 20%

10%

0% 1 10 15 20 Deferment Period (days)

Figure 3.3 Distribution of early season (ES) arthropod abundance among functional groups as deferment period lengthened in paddocks of rotationally grazed pasture at Polyface Farm in Swoope, Virginia, USA, in 2009. The proportional abundance of each functional group is based on its overall abundance and the abundance for all groups in n = 6 samples at each deferment period. Abundance across all groups was N = 260, 155, 325, and 438, in order of increasing deferment period.

Table 3.6 Distribution of arthropod abundance (N) and percent of total abundance in parentheses by functional group and consumer group by early season (ES) grazing deferment period for arthropod communities sampled in paddocks (n = 6 samples/paddock) of rotationally grazed pastures at Polyface Farm, Swoope, Virginia, USA, in 2009. 1Functional group distributions significantly different (p < 0.0001) as determined by Chi-square test of homogeneity. 2Positive, group-specific trend in proportion over time determined to be significant (p < 0.0001) by Cochran-Armitage trend test.

Deferment Period (days) 1 10 15 20 N (%) N (%) N (%) N (%) 1 Functional Group Detritivores 48 (18.5) 35 (22.6) 75 (23.1) 180 (41.1) Herbivores 132 (50.8) 78 (50.3) 157 (48.3) 202 (46.1) Predators 77 (29.6) 38 (24.5) 82 (25.2) 44 (10.0) Parasitoids 3 (1.2) 4 (2.6) 11 (3.4) 12 (2.7)

Consumer Group2 Primary Consumers 180 113 232 382 Secondary Consumers 80 42 93 56

Total 260 155 325 438

100%

90%

80%

70%

60%

2º Consumers 50% 1º Consumers 40% % Abundance%

30%

20%

10%

0% 1 10 15 20 Deferment Period (days)

Figure 3.4 Distribution of early season (ES) arthropod abundance among primary and secondary consumer groups by days of deferment of rotationally grazed pastures at Polyface Farm in Swoope, Virginia, USA. Sampling occurred in 2009. The proportional abundance of each consumer group is based on its overall abundance and the total abundance for both groups in n = 6 samples at each deferment period. Total abundance across both groups was N = 260, 155, 325, and 438, in order of increasing deferment period.

75 Table 3.7 Distribution of arthropod abundance (% of total in parentheses) by functional group and consumer group by late season (LS) grazing deferment period for arthropod communities sampled in paddocks of pasture (n = 6 samples/paddock) grazed by cattle at Polyface Farm in Swoope, Virginia, USA, in 2009. Average daily population growth (dN) between paired paddocks are given for functional and consumer groups (pairs are indicated with same superscript letters). 1Functional group distributions significantly different (p < 0.0001) as determined by Chi-square test of homogeneity. 2Positive, group-specific trend in proportion over time determined to be significant (p < 0.0001) by Cochran-Armitage trend test.

Deferment Period (days) 1a 11b 21c 32 42d 64a 75b 85c 105d N (%) N (%) N (%) N (%) N (%) N (%) dN N (%) dN N (%) dN N (%) dN 1 Functional Group Detritivores 282 (39.4) 103 (25.6) 96 (21.1) 392 (31.7) 156 (13.4) 816 (49.4) 8.48 180 (17.9) 1.20 97 (22.2) 0.02 515 (21.2) 5.70 Herbivores 200 (27.9) 134 (33.3) 189 (41.4) 388 (31.4) 767 (65.8) 429 (26.0) 3.63 388 (38.7) 3.97 172 (39.4) -0.27 1324 (54.6) 8.84 Predators 188 (26.3) 146 (36.3) 134 (29.4) 374 (30.3) 216 (18.5) 360 (21.8) 2.73 386 (38.5) 3.75 156 (35.7) 0.34 541 (22.3) 5.16 Parasitoids 46 (6.4) 19 (4.7) 37 (8.1) 81 (6.6) 26 (2.2) 47 (2.8) 0.02 49 (4.9) 0.47 12 (2.7) -0.39 45 (1.9) 0.30

2 Consumer Group Primary Consumers 482 237 285 780 923 1245 12.11 568 5.17 269 -0.25 1839 14.54 Secondary Consumers 234 165 171 455 242 407 2.75 435 4.22 168 -0.05 586 5.46

Total 716 402 456 1235 1165 1652 1003 437 2425

70%

60%

50%

40% Detritivores Herbivores Predators 30% Parasitoids % Abundance%

20%

10%

0% 1 11 21 32 42 64 75 85 105 Deferment Period (days)

Figure 3.5 Distribution of late season (LS) arthropod abundance among functional groups as deferment period lengthened in paddocks of rotationally grazed pasture at Polyface Farm in Swoope, Virginia, USA, in summer and autumn 2009. The proportional abundance of each functional group is based on its overall abundance and the total abundance for all groups in n = 6 samples at each deferment period. Total abundance across all groups was N = 716, 402, 456, 1235, 1165, 1652, 1003, 437, and 2425, in order of increasing deferment period.

100%

90%

80%

70%

60% 2º Consumers 50% 1º Consumers 40% % Abundance% 30%

20%

10%

0% 1 11 21 32 42 64 75 85 105 Deferment Period (days)

Figure 3.6 Distribution of late season (LS) arthropod abundance among primary and secondary consumer groups by days of deferment of rotationally grazed pastures at Polyface Farm in Swoope, Virginia, USA. Sampling occurred in summer and autumn of 2009. The proportional abundance of each consumer group is based on its overall abundance and the total abundance for both groups in n = 6 samples at each deferment period. Total abundance across both groups was N = 716, 402, 456, 1235, 1165, 1652, 1003, 437, and 2425, in order of increasing deferment period.