Seasonal Patterns of Arthropod Diversity and Abundance on Big Sagebrush, Artemisia Tridentata Author(S): Monte P
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Seasonal Patterns of Arthropod Diversity and Abundance on Big Sagebrush, Artemisia tridentata Author(s): Monte P. Sanford and Nancy J. Huntly Source: Western North American Naturalist, 70(1):67-76. 2010. Published By: Monte L. Bean Life Science Museum, Brigham Young University DOI: http://dx.doi.org/10.3398/064.070.0108 URL: http://www.bioone.org/doi/full/10.3398/064.070.0108 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Western North American Naturalist 70(1), © 2010, pp. 67–76 SEASONAL PATTERNS OF ARTHROPOD DIVERSITY AND ABUNDANCE ON BIG SAGEBRUSH, ARTEMISIA TRIDENTATA Monte P. Sanford1,2 and Nancy J. Huntly1,3 ABSTRACT.—The sagebrush biotype is the largest in the western United States. This vast sagebrush community is thought to harbor equally vast and diverse arthropod communities, but these remain little explored. Our objective was to examine the diversity, abundance, and seasonal phenology of arthropod taxa found on the dominant shrub of the sage- brush ecosystem, big sagebrush (Artemisia tridentata). We wanted to improve understanding of this little-studied arthro- pod assemblage that may play significant roles in the dynamics of sagebrush populations and the sagebrush ecosystem. We sampled free-living and gall-forming arthropods from a stratified random sample of sagebrush plants at the Barton Road Ecological Research Area, Idaho, resulting in a sample of over 8000 individuals and 232 morphospecies. Species richness and abundance declined from May to August, and abundance of most taxa similarly declined over the summer. A few taxa, including Acari (mites), were notably more abundant in August. Fluid feeders were the most diverse and abundant free-living feeding guild during all months and comprised up to 79% of morphospecies. The gall formers included 4713 individuals of 12 species of gall flies (Rhopalomyia spp.), primarily (97%) R. ampullaria. Abundance of galls increased from small to large (presumably young to old) plants. Overall, A. tridentata was host to a high diversity of arthropods, some of which have potential to cause or mitigate significant damage to their host plant. Arthropods seem likely to have the greatest impact on sagebrush early in the growing season, when they are most diverse and abundant. Documentation of the full diversity of arthropods associated with sagebrush required samples taken throughout the growing season, but a single sample early in the growing season captured a high proportion of taxa. Key words: Artemisia tridentata, big sagebrush, Rhopalomyia, arthropod, insect, biodiversity, phenology. Sagebrush steppe is the largest temperate abundance, and seasonal phenology of the semidesert ecosystem in North America, com- arthropods associated with sagebrush are large ly prising an area of about 44.8 × 106 km2 (West unexplored, despite the large spatial extent 1983). The Columbia and Snake River plateaus and economic importance of sagebrush. Welch contain 4.48 × 105 km2 of sagebrush commu- (2005) reviewed the literature to assemble a list nities (West 1983), and the Great Basin desert of arthropods associated with sagebrush and includes over 2.06 × 105 km2 (Brussard et reported that 72 spider and 237 insect species al. 1998). This vast sagebrush community is are documented associates of sagebrush, includ- thought to harbor a similarly vast and diverse ing 42 gall-forming insects, 52 aphids, and 23 arthropod fauna (Horning and Barr 1970, Tingey beetles. However, the typical arthropod fauna et al. 1972, Gittins et al. 1976, Jones et al. 1983, of an individual Artemisia shrub and the fau- Stafford et al. 1986, Stafford 1987, Hampton nal variation over the growing season have not 2005, Welch 2005). However, little is known been documented. about the sagebrush-associated arthropods of Sagebrush steppe is one of North America’s the cold-desert regions of North America. endangered ecosystems and is strongly affected Most research on sagebrush arthropods has by land uses, such as livestock grazing, and by focused either on a single taxon known to defo- exotic species invasions (Knick and Rotenberry liate sagebrush (e.g., Aroga moths; Gates 1964, 1997, Dobkin and Sauder 2004, Welch 2005, Hanson et al. 1982) or on the broad biology of Bangert and Huntly 2009, Prevey et al. 2010, a single genus (e.g., gall-forming Rhopalomyia in press). The arthropods of sagebrush ecosys- flies; Jones et al. 1983). These studies have tems are likely to affect the population dynamics made significant contributions to our under- of sagebrush because they are major parts of standing of the life cycles and distributions of the food webs of sagebrush steppe, they influ- the focal taxa, but overall patterns of diversity, ence ecosystem functioning, and they provide 1Center for Ecological Research and Education, Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007. 2Present address: Biology Department, MS 315, University of Nevada, Reno, NV 89557. 3Corresponding author. Present address: National Science Foundation, 4201 Wilson Blvd., Arlington, VA 22230. E-mail: [email protected] 67 68 WESTERN NORTH AMERICAN NATURALIST [Volume 70 ecosystem services, such as pollination and seed The progression of summer involves increas- dispersal (e.g., Pringle 1960, Banham 1961, ing temperature and decreasing pre cipitation. Christiansen et al. 1989a, Dobkin and Sauder Annual average precipitation at the Pocatello 2004, Welch 2005, Shiojiri and Karban 2008). Airport (17 km from the site and at 1359 m Thus, efforts to conserve and restore sagebrush elevation) averages 30.8 cm, with July–Octo- steppe require an understanding of the associ- ber being driest. We calculated average tem- ated arthropods. perature and precipitation for +–5 days from Our research objective was to examine the sample dates using weather data from the diversity, abundance, and seasonal phenology Pocatello Airport Weather Station. Average high of arthropod taxa associated with big sagebrush temperatures increased from 78 °F (25.6 °C) in (Artemisia tridentata). We posed 4 questions: late May to 97 °F (36.1 °C) in late June and (1) What are the patterns of diversity and abun- dropped to 88 °F (31.1 °C) in late August. Mean dance of arthropods on A. tridentata during precipitation dropped from 3.03 mm in May to the spring/summer growing season? (2) What 0.04 mm in July and 0.21 mm in August. Evap- feeding guilds are associated with A. tridentata, oration typically exceeds precipitation from and how do their diversity and abundance vary late May through early October (Anderson and over the summer months? (3) What is the tax- Inouye 2001). onomic composition of the fauna of A. triden- tata? (4) What species comprise the gall-form- Free-living Arthropods ing guild of A. tridentata, and how are galls We sampled arthropods from sagebrush distributed within the canopy of A. tridentata? located on 100 permanent plots that were Our research provides a basis for identifying 10 m × 10 m and separated by 2-m aisles. time frames and target taxa for future research The A. tridentata plant located nearest to the on sagebrush-arthropod interactions and can point 4 m north and 6 m east of the south- be used to more fully understand sagebrush west corner of each plot was selected to be ecosystem dynamics. sampled. Arthropods were sampled in late May (28 May–1 June), late June (28 June), METHODS and mid- to late August (23 and 24 August) of 2000. Plants were divided into cardinal quad- Study Site rants (NE, NW, SE, SW) and one quadrant, This study was conducted in a sagebrush- selected at random for each shrub, was sam- steppe community at the Barton Road Ecolog- pled each month; no quadrant on the same ical Research Area. The study site was located plant was sampled twice. Arthropods were at 1450 m elevation in the foothills at the east- collected by beating sagebrush foliage of a ern edge of Pocatello, Idaho, at roughly the selected quadrant 10 times with a stick and border of the hydrographic Great Basin and collecting the dislodged arthropods in a 60- the Snake River Plateau. Soils at the site are cm-diameter sweep net held below the deep, well-drained calcareous silt loams that branches. The arthropods were separated are moderately alkaline near the surface and from vegetation and kept frozen until processed moderately to strongly alkaline at depths of and identified. 20–150 cm (McGrath 1987). Shrub cover on We identified and enumerated arthropods the 27-ha research area ranges from 25% to from a randomly selected subset of 50 of the 35%, perennial grass cover from 20% to 27%, 100 samples from each sample period. Speci- and forb cover from 1% to 3.7% (Inouye 2002). mens were identified to family using Borror et Artemisia tridentata is the clear vegetative al. (1989), noted as adult or immature, and fur- dominant, comprising more than 95% of total ther sorted to recognizable taxonomic units shrub cover and 30% of total cover. Other (RTUs; Oliver and Beattie 1996, Kerr et al. abundant grasses and shrubs include Elymus 2000). Voucher specimens were deposited at lanceolatus, Stipa comata, several species of Idaho State University.