Composition and Seasonal Abundance of Hover Flies (Diptera: Syrphidae) at a Midelevation Site in Central Utah

Home , Blera nigra, Chrysotoxum, Eristalis anthophorina, Eupeodes luniger, Eupeodes volucris, Paragus haemorrhous

Western North American Naturalist

Volume 77 Number 4 Article 8

1-12-2018

Composition and seasonal abundance of hover flies (Diptera: Syrphidae) at a midelevation site in central Utah

Tyson J. Terry Brigham Young University, Provo, UT, [email protected]

C. Riley Nelson Brigham Young University, Provo, UT, [email protected]

Follow this and additional works at: https://scholarsarchive.byu.edu/wnan

Recommended Citation Terry, Tyson J. and Nelson, C. Riley (2018) "Composition and seasonal abundance of hover flies (Diptera: Syrphidae) at a midelevation site in central Utah," Western North American Naturalist: Vol. 77 : No. 4 , Article 8. Available at: https://scholarsarchive.byu.edu/wnan/vol77/iss4/8

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 77(4), © 2017, pp. 487–499

COMPOSITION AND SEASONAL ABUNDANCE OF HOVER FLIES (DIPTERA: SYRPHIDAE) AT A MIDELEVATION SITE IN CENTRAL UTAH

Tyson J. Terry 1,2 and C. Riley Nelson 1

ABSTRACT .—Dipteran pollinators are important in the successful reproduction of many plants, yet are less studied than other groups. We know that these insects affect the biodiversity of natural landscapes, yet much remains unknown about the extent of their influence in pollination systems and flight seasons. In this study, we collected hover flies (Diptera: Syrphidae) with 3 Malaise traps at a midelevation site in central Utah throughout the flies’ flight season of 2015. We collected 27 genera and 48 species in our traps. We determined seasonal flight times by collecting at weekly intervals throughout the frost-free year. Abundance of all hover flies peaked twice, in June and September, showing a bimodal distribution. We noted a drop in overall abundance during the hottest months of July and August. Species diversity and richness also peaked in June and September. We calculated species richness estimators, which suggest that more than 60 species make up the total assemblage at the study site. Local museum records show 28 species caught in similar locations near the sample site before the year 2000 that were not collected during our study.

RESUMEN .—Los polinizadores dípteros son cruciales para la reproducción exitosa de muchas plantas, sin embargo, son menos estudiados que otros grupos. Sabemos que tienen impacto en la biodiversidad de los entornos naturales, aún así queda mucho por conocer sobre la magnitud de su influencia en los sistemas de polinización y en las temporadas migratorias. En este estudio se colectaron moscas voladoras (Diptera: Syrphidae) a lo largo de la temporada migratoria del año 2015, mediante el empleo de tres trampas para insectos voladores, en una zona de mediana elevación en el centro de Utah. Mediante esta técnica, colectamos 27 géneros y 48 especies. Determinamos las épocas de temporadas migratorias mediante colectas en intervalos semanales, durante el año libre de heladas. La abundancia de las moscas voladoras alcanzó su pico máximo dos veces (en junio y en septiembre) mostrando una distribución bimodal, a la vez que notamos una caída en su abundancia general durante los meses más calurosos (en julio y en agosto). La diversidad y la riqueza de las especies también alcanzaron su punto máximo en junio y en septiembre. Calculamos, también, los estimadores de riqueza de especies, que sugirieron que más de 60 especies forman el grupo total en el área de estudio. Los registros de los museos locales muestran 28 especies en sitios similares (cercanos al sitio de prueba) capturadas antes del año 2000 y que no fueron colectadas durante nuestro estudio.

Hover flies are a diverse group of pollina - information on the contributions of syrphids tors in the dipteran family Syrphidae. In the in their native environments is sparse (Ssy - Nearctic region alone, there are 812 species mank et al. 2008). The vital role of hover (Miranda et al. 2013). Often referred to as flies in maintaining ecosystem health goes flower flies, they feed on pollen and nectar beyond pollination services, as some taxa as adults (Holloway 1976, Kevan and Baker also prey on aphids and other soft-bodied 1983). In some species, females require plant pests (Thompson and Vockeroth 1989). pollen during stages of ovarian development, Many hover flies are likely to be bioindica - although both males and females (before and tors of community health in their ecosystems after oogenesis) consume large amounts of because they integrate their life history nectar and pollen (Holloway 1976, Haslett across diverse feeding strategies, but more 1989, Inouye et al. 2015). Although syrphids intensive studies are needed to fully under - have been recognized in several studies to stand this role (Kevan 1999). Moreover, the be significant pollinators across diverse sys - diverse habits of syrphid larvae (phytophagy, tems, much of their basic biology has yet to mycophagy, saprophagy, and zoophagy) sug - be discovered (Larson et al. 2001, Ssymank gest that lowered syrphid diversity could et al. 2008, Stanley et al. 2013). Many stud - reflect environmental stress and loss of land - ies identify the importance of a few taxa to scape diversity (Thompson and Vockeroth cultivated crops (such as sweet peppers), but 1989, Sommaggio 1999).

1Department of Biology and Monte L. Bean Life Science Museum, Brigham Young University, Provo, UT 84602. 2E-mail: [email protected]

487 488 WESTERN NORTH AMERICAN NATURALIST [Volume 77

Fig. 1. Location of study site in central Utah.

Pollinating flies have a significant effect on is nearly impossible to track changes and the biodiversity of plants in natural landscapes. responses of syrphids to new ecological stresses. Gaps in knowledge of pollinating flies and Size and diversity of hover fly populations can their reactions to climate change prevent be difficult to quantify because of the short more effective conservation plans (Ssymank et flight season of some species (Speight 1986, al. 2008). Floral constancy is thought to be very Speight and Castella 1993) and lack of focused high among the Syrphidae due to preference attention from the scientific community. The in flower height, color, and type (Ssymack ease of use of passive Malaise traps to sample 2003), which likely created close evolutionary the flies can alleviate many of these concerns. relationships of syrphid species with specific We conducted our study to more fully angiosperms (Inouye et al. 2015). Dipteran understand the composition of hover fly species pollinators are thought to be especially and their changes in abundance throughout the important in Arctic and montane-alpine envi - flight year. Though recent review papers such ronments because of their active foraging in as Inouye et al. (2015) give us a great back - wetter and colder climates (Kearns 1990), ground on the ecology of syrphids, this paper matched with the limited availability of flow - attempts to fill some of the voids in knowledge ering species (Kevan 1972). The availability of of this important group of insects. only a couple of flowering plant species at a time forces pollinators to visit conspecific METHODS plants, thereby increasing the likelihood of Study Site successful pollination (Kevan 1972). Analysis in some parts of Europe suggest We sampled syrphids during the generally hover fly decline and shifts in distribution frost-free months of April through November (Biesmeijer et al. 2006). In the Rocky Moun - in 2015 at a midelevation site (1820 m +– 45 m) tains, very few studies have been done in central Utah (39.95864 ° N, 111.26742 ° W; specifically on this group of Diptera beyond +–400 m) (Fig. 1). Our study site was in a moun - basic taxonomic works, and few of these have tainous region where the Colorado Plateau been conducted in recent years. Much infor - and Central Basin ecoregions overlap (EPA mation on hover fly distribution and abun - 2006). The canyon is flanked by steep slopes. dance remains unknown (Sedman 1952). With On our site the riparian vegetation is domi - little data on abundance and flight season, it nated by willows and cottonwoods, with a 2017] HOVER FLY ABUNDANCE AND COMPOSITION IN UTAH 489 diversity of smaller flowering plants. Beyond small spring-fed waterfall. The rock face the riparian corridor, dominant vegetation where the waterfall occurs is covered in moss includes rubber rabbitbrush ( Ericameria nau - and sediment buildup with significant hygro - seosa ), big sagebrush ( Artemisia tridentata ), petric habitats. We chose these 3 locations to Gambel oak ( Quercus gambelii ), bigtooth maple represent diverse terrain in close proximity, (Acer grandidentatum ), Canada goldenrod thereby maximizing potential plant and syrphid (Solidago canadensis ), and thistle ( Carduus diversity in the area. sp.). Most precipitation (65%) occurs from Collection and Analysis October through April in the form of snow, and 35% occurs as rain from May through We visited the traps on a weekly basis to September (EPA 2006). Water flow exhibits a collect samples and to maintain the traps in normal snowmelt-dominated flow pattern and good working condition. We collected a total peaks in May and June. The driest months of of 90 week-long samples, which we then the year are July and August (EPA 2006). combined over the 3 traps by week to provide Water in western canyons is extremely impor - 30 one-week samples spanning the flight tant for general biodiversity, as wetter canyons period at the study site. Townes-style Malaise support a broader spectrum of plants (Schoene- traps collected insects in 500-mL bottles of berger 1992). The largest water source in the 70% ethanol. We sorted the samples to family canyon, Soldier Creek, fulfills that need, but is in the laboratory at Brigham Young University on the Utah 303(d) list of impaired waterbod - (BYU) in Provo, Utah, using an Olympus SZ61 ies for high total phosphorus and heavy sedi - stereo microscope. Families were placed in mentation/siltation (Division of Water Quality individual 10- or 50-mL plastic capped vials, 2014) for use by aquatic life. Unstable vertical with vial size dependent on the number and banks and high soil erosion contribute to the bulk of specimens. The senior author sorted sedimentation of the waterway (EPA 2006). all specimens belonging to Syrphidae to genus We selected our sampling location in using the key by Miranda et al. (2013). We Spanish Fork Canyon 12 miles east of Thistle used specimens from the Monte L. Bean Life near Highway 89 (Fig. 1). The segments of Science Museum (MLBM) at Brigham Young waterways on the sample site are on private University (BYU) identified by prominent land and are inaccessible to the public, and authorities to confirm and clarify our generic thus remain less disturbed at the riparian identifications. All specimens were dried border and in the immediate surroundings. before being identified to the genus and The 3 trap sites have an elevation difference species levels. To dry the specimens, we sub - of <45 m and are within 300 m of each merged them in ethyl acetate for 15 min and other. We deployed one Malaise trap at each then pinned or point mounted them. We placed site throughout the sampling period. We the drying specimens in an undisturbed cabi - chose sites to represent diversity in terrain net for 48 h before further identification. The and vegetation over a localized area. We specimens were then identified to species chose locations having rather low apparent using several dichotomous keys that were human/agricultural impact, along with exten - chosen from references in Miranda et al. sive vegetation and good apparent riparian (2013). We also used the species lists from health. We placed the traps over small creeks Miranda et al. (2013) to verify that names were because vegetation was denser and more those most currently used. diverse along these water sources. This had We searched the extensive insect collection the secondary advantage of funneling flying at the MLBM to find historic records of hover insects into the traps. Trap 1 was placed over a fly specimens found within 50 km of the first-order spring-fed stream in a narrow side sample site and at a similar elevation (within canyon, 50 m below the source. This location 200 m). These specimens were reexamined to is well shaded for a good portion of the day. confirm that names were those most currently Trap 2 was placed over a second-order stream used (Miranda et al. 2013). Names were (Soldier Creek) in an open meadow within the checked against the species lists, generic key, larger canyon (Spanish Fork Canyon). This and listed-species keys from the publication location was in full sunlight throughout the used to identify the collected samples from day. We placed trap 3 near the base of a the study site (Miranda et al 2013).

490 WESTERN NORTH AMERICAN NATURALIST [Volume 77

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2017] HOVER FLY ABUNDANCE AND COMPOSITION IN UTAH 491

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S P P P S S S S S T S X T fier. Syrphidae in this study were considered 492 WESTERN NORTH AMERICAN NATURALIST [Volume 77

160

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0 April May June July August Sept Oct Nov

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consistent, a nd their presence in multiple yielded 27 genera and 48 species collected samples was detectable. Our use of sample- during the trapping period. Overall abundance based rarefaction from several trap locations curves (Fig. 2) are dominated by the genera overcame sm all-scale sampling bias. Sampling Paragus and Eupeodes, which were the most methods wer e random and approximately inde - abundant taxa (Table 1, Fig. 3). These 2 genera pendent beca use collection was via consistently accounted for 44% of the total number of syr - run Malaise traps over the flight season of phids and 21% of the species collected. The Syrphidae in Utah. Collection likely did not driest months of the year on average (July affect the large assemblage of the population, and August) showed a lower total abundance and thus, collections approximated results than the earlier and subsequent months. Thus, using random replacement. we see bimodal distribution for abundances. We determined temperature averages from Despite the lower abundances of July and recorded data that was measured at the mouth August, these months exhibited diversity val - of the canyon during the year of the study ues close to those of wetter months (Table 2). (40.0797 ° N, 111.604 ° W; U.S. Climate Data During the study, we noticed large varia - 2016). This location is 15 miles down-canyon tion in yield from the different trap locations. from our study site, and though the numbers Trap 1 (wooded area, over first-order stream, may not reflect exact temperatures, we believe small canyon) produced more consistent yields they are representative of temperature trends than the other 2 traps. Trap 2 (second-order for our site. stream, larger canyon, little to no shade) pro - duced yields consistent with trap 3 (base of RESULTS first-order stream waterfall, little shade, hygro - petric environments); both traps had large We identified a total of 404 hover fly speci - spikes in yield during the spring and late fall. mens to the species level (Table 1). This The abundant and diverse taxon Eupeodes 2017] HOVER FLY ABUNDANCE AND COMPOSITION IN UTAH 493

Rank Abundance 0.2 0.18 0.16 0.14 n o

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r 0.08 P 0.06 0.04 0.02 0 01020304050 Rank (Abundance High to Low)

Fig. 3. Rank abun da nce c urve that sho ws the dis tributio n an d rarity of s yrph id tax a c aught at ttaxahe st ucaughtdy site at in study centr asitel in central Utah. The mUost abund ant s pecies was Eupeod es vo lucris, follo wed by Paragus h aem orrhous, Chrysotoxum derivatum, Platycheirus stegnus, an d Eupeodes lu niger, res pect ively.

TABLE 2. D iversity, richness, and abundance of hover flies (Diptera: Syrphidae) at a midelevation central Utah study site summari zed by month, along with monthly averages of temperature and precipitation from historic data retrieved from U.S. Cl imate Data (2016). Diversity values are calculated according to the Shannon’s diversity index formula: Hj = −∑pijlog e(pij). Total individuals is the total number of specimens caught during the month. Total species present is the total number of distinct species caught during the month at the study site. Apr May Jun Jul Aug Sep Oct Nov

Diversity (Shannon’s index) 1.79 1.83 2.58 2.33 2.12 2.84 2.32 1.61 Total individ uals 18 30 139 51 27 109 24 5 Total species present 10 10 29 19 10 25 12 5 Precipitation (cm) 5.9 8.7 0.3 1.5 4.0 0.91 1.4 3.6 Average high ( °C) 19.4 21.0 33.2 32 32.4 29.1 21.6 9.2 Average low ( °C) 3.1 8.2 14.7 15.2 15.6 12.4 8.3 −1.4

(Metasyrp hus ) was collected mostly from the fall (Fig. 4). Though they exhibit different trap 2, whereas the other subgenus, Eupeodes peak abundance patterns, both taxa exhibit (Eupeodes ), was collected more in the small small peaks during the larger peaks of the canyon at traps 1 and 3. The abundant taxon other species. Paragus was caught mostly at trap 1. The second most abundant species at the The most abundant genera collected dur - study site, Paragus haemorrhous, rose sharply ing the study belong to the tribes Syrphini, in abundance at the end of the month of Paragini, and Melanostomini. Syrphini (47%) June, then slowly declined throughout the were by far the most abundant. Within this rest of the flight season, with only a slight tribe, genera such as Eupeodes show diversity increase during the late fall (Fig. 5). During and abundance of many species with over - the decline and lower abundances of P. haem - lap ping flight seasons. It is surprising that orrhous, another member of its genus, P. this genus with aphidophagous behavior in bicolor, appeared in low abundances. its immature stages is so diverse despite Sphaerophoria spp. exhibited high abun - requiring specific larval resources (Sedman dances in the spring, but decreased abruptly 1952, Henderson 1982). during the month of July (Fig. 6). Lower The 2 subgenera of the genus Eupeodes abundances remained until the end of fall. overlap in their flight seasons, yet peak Platycheirus spp. and Chrysotoxum sp. exhib - abundances occur in different seasons. Eu - ited higher abundances in the fall (Figs. 7, 8). peodes (Eupeodes ) peaks in the late spring, Records from the MLBM indicate that whereas Eupeodes (Metasyrphus ) peaks in another 28 species have been collected in close 494 WESTERN NORTH AMERICAN NATURALIST [Volume 77

Eupeodes 18 16 14 Eupeodes( Metasyrphus) Eupeodes (Eupeodes) 12 10 8 6 4 2 0 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / 3 0 7 2 9 6 5 5 8 8 0 7 3 2 9 5 0 7 3 7 5 0 2 9 5 7 4 6 4 8 1 / / / / / / / / 1 2 2 1 1 2 2 1 2 2 1 2 2 1 2 2 1 1 2 1 2 2 1 / / / / / / / / / / / / / / / / / / / / / / 0 / 1 5 6 7 8 9 9 0 0 0 1 1 1 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 1 9 1 1 1 1 1 1 1

Fig. 4. Number of spec imens belongi ng to Eupeodes (Metasyrphu s ) and Eupeodes (Eupeodes ) caught over the frost-free year at the study site in Spanish Fork Canyon, Utah.

Paragus

14 12 Paragus bicolor Paragus haemorrhous 10 8 6 4 2 0

Fig. 5. Total number of specimens belonging to Paragus haemorrhous and Paragus bicolor caught over t he frost-free year at the study site in Spani sh Fork C a nyon, Utah. proximity t o the study area in years before family Syrphidae from a single locality. Thor - 2000 (Table 3). From the 28 missing species, 11 ough sampling was done during the flight genera were not observed at the sample site. season of one year. We identified and sum - Cole rare faction calculations reflect a diver - marized all records of distribution and abun - sity level c lose to what was observed in our dance for these syrphids (Table 1). We now catch, while richness estimators reflect a gap of have a much better understanding of the diver - 10–12 missi ng species. The Michaelis–Menten sity of this local system. richness est imator indicates that with 30 sam - We determined that the basic biology (flight ples, the com munity should contain 58 species, seasons, biodiversity, and general abundances) and Cole rarefaction indicates that 50 species of the hover fly community in this system can should be present with 30 samples (Fig. 9). be addressed with thorough sampling over a single full flight season. We would prefer to DISCUSSION have more years of data, but that is not possible at this time. This study provides information about the The drop in total abundance and species species composition and flight season of the richness during July and August reflects a 2017] HOVER FLY ABUNDANCE AND COMPOSITION IN UTAH 495

Sphaerophoria 18 16 14 12 10 8 6 4 2 0

Figure 6. Total number of specimens caught over frost-free year at the Spanish Fork Canyon, Utah study site Fig. 6. Totalb number o f s pec imens belongi ng to 3 species on s ite o f the g enus Sphaeroph oria caught over frost-free year at the study site in Spanish Fork Canyon, Utah.

Platycheirus

5 4

2 1

Fig. 7. Total number o f sp eci men s belong ing to the 5 s pecies of the g enus Platycheirus caught over the frost-free year at the study site in Spanish Fork Canyon, Utah. possible res ponse of Syrphidae to drier condi - saw a dramatic drop in the abundance of many tions during those months (Fig. 2). Although taxa. It appears that high temperatures may the respons e of hover flies to drier and hotter have a strong effect on hover fly abundance months is un clear in the literature, their abun - and that low precipitation levels don’t present dance patte rns seem to be affected more by large immediate effects (Table 2). The factors high temperatures when historic temperatures that shape the abundance curves and life his - are examined. On average, the hottest months tory strategies of hover flies are difficult to during the p ast 5 years were July and August determine from our data. We speculate that (U.S. Clima te Data 2016), but according to hover flies are likely adapted to the more available te mperature data, June was the productive vegetation of the spring and fall, hottest mon th during the study year. Despite which was still present in the hotter month of having the h ighest average monthly tempera - June. Further studies are needed to determine ture, June exhibited the highest number of the accompanying change in plant resources total individuals and species (Table 2, Fig. 2). during the drop in hover fly abundance to Once the historically hotter months began, we determine whether the effect of heat on 496 WESTERN NORTH AMERICAN NATURALIST [Volume 77

Chrysotoxum derivatum 7

Fig. 8. Total number of Chrysotoxum derivatum specimens caught over the frost-free year at the study site in Spanish

Fork Canyon, Utah.

TABLE 3. Historic species of Syrphidae deposited in the abundance and hotter months, we do see that Monte L. Bean Life Science Museum that were collected within 40 km and 500 m elevation of the study site in many taxa seem less able to cope with hotter Spanish Fork Canyon, Utah, that were missing from our and drier months within our study (Fig. 2). study. Paragus is an exception (Fig. 5). Sphaerophoria Species Author and Eupeodes accounted for the most indi - viduals at our study site, and were found Blera nigra (Williston, 1887) Brachyopa flavescens Shannon, 1915 throughout the flight season. They were pres - Brachyopa ferruginea (Fallen, 1817) ent in moderately high numbers in the early Brachypalpus femorata (Williston, 1882) spring and persisted in small numbers until Brachypalpus oarus (Walker, 1849) late November. Sphaerophoria and Eupeodes Ceriana tridens (Loew, 1872) Cheilosia pikei (Shannon, 1922) show resilience to cold temperatures, with Copestylum marginatum Say, 1892 high abundances in almost freezing condi - Copestylum satur (Osten Sacken, 1877) tions, yet exhibited a sharp decrease in total Didea fuscipes Loew, 1863 abundance during the hotter months (on aver - Eristalis anthophorina (Fallen, 1817) Eristalis brousii Williston, 1882 age) of July and August (Figs. 4–6). This result Eristalis flavipes Walker, 1849 fits data from other studies showing a sharp Eristalis hirta Loew, 1866 drop in fitness at higher temperatures (Deutsch Eristalis tenax (Linnaeus, 1758) et al. 2008). If the indicated trend of intoler - Helophilus obscurus Loew, 1863 Lejops curvipes (Wiedemann, 1830) ance to higher temperatures (on average) is Lejops polygrammus (Loew, 1872) sig nificant, then there is potential concern Microdon baliopterus (Loew, 1872) that climate change would result in shifts of Microdon xanthopilis Towsend, 1895 flight season toward cooler months for these Neoascia sphaerophoria Curran, 1925 Scaeva pyrastri (Linnaeus, 1758) sensitive taxa and possibly reduce total abun - Sericomyia militaris Walker, 1849 dance as populations respond to higher tem - Spilomyia liturata Williston, 1887 peratures year-round. Syritta pipiens Linnaeus, 1758 Analyses of the species richness indicator Toxomerus marginatus (Say, 1823) Tropidia quadrata (Say, 1824) Chao 1, the coverage indicator ACE, and the Volucella spp. Geoffroy, 1762 Michaelis–Menten richness estimator (asymp - tote of species accumulation curve) reveal that several more species likely exist at the study hover fly abundance is physiological or whether site that were not collected (Fig. 9). Both rar - it is indirect through its effect on vegetation. efaction and richness estimators indicate more Although we cannot determine an un - species, but the missing historic taxa support equivocal relationship between hover fly the diversity indicators over the rarefaction

2017] HOVER FLY ABUNDANCE AND COMPOSITION IN UTAH 497

50 S E I C E

P 40 S

F O

R E

B 30 M U N

0 05101520253035 NUMBER OF SAMPLES

S(est) ACE Mean Chao 1 Mean MMMeans Cole Rarefaction

Fig. 9. Comparison of s pec ies accu mula tion curve s us ing raref action and ric hness e sti mators . S(est ) = the expected number of species of Sy rphidae f rom the stud y site in S panish F ork C anyon, Utah, in t poole d sample s, given the refer - ence sample (analytic a l) . ACE mean = ACE abunda nce cove ra ge-ba sed es timator of species richness (mean among runs). Chao 1 mean = Chao 1 richness estimator (mean among runs), MMMeans = Michaelis–Menten richness estima - tor; both are e stimators computed once for the analytical rarefaction curve. Cole rarefaction = Coleman rarefaction (number of sp ecies expected in t pooled samples, assuming that individuals are distributed at random among samples).

estimate in the scope of how many more We do not know how the several species species are in the study area or its environs belonging to Eupeodes interact on a limited (Table 3). This may indicate that richness resource (such as aphids or pollen) on the genus, estimators are more representative of actual subgenus, and species level. Taxa belonging to population composition than rarefaction. Our the tribe Syrphini were very abundant and are study seem s to suggest that the richness indi - likely to exhibit an interesting interaction as cators are m ore accurate than rarefaction as they conceivably compete for pollen and larval we compared our year’s catch with the historic resources. Future research could focus on taxa. Rank abundance curves show a relatively niche breadth of these taxa. It is possible that standard pattern, indicating that the remain - diversity of aphids is a significant driver of ing taxa that we didn’t collect during the study speciation and diversity within the system at are likely rare species (Fig. 3) our test site, but due to the diverse nature of Successful future studies would likely be aphids and their complex life cycle (Knowlton able to approach a full sample of the popula - 1924, 1983), a specific study would be needed tion with more traps in more diverse locations. to determine relationships. It would be inter - We estimate that with 2 traps in each type of esting to determine whether larval feeding terrain, yields would closely approximate habits of aphidophagous Syrphidae are conspe - richness estimators. Each designated repre - cific or whether different Syrphidae species sentative zone could be sampled with 2 traps feed on different life stages of aphids. in diverse locations within the same terrain With regards to Eupeodes, it is surprising type. With emphasis on size and extent of to see this genus so abundant, diverse, and collection, rarefaction and richness estimators overlapping in species flight seasons because give accurate representations of the system of its aphidophagous behavior in its immature (Chao and Jost 2012). stages (Sedman 1952, Henderson 1982). There During the study we identified many taxa of is likely an interesting interaction on the the same tribe, genus, and subgenus level that species level as individuals compete for proper overlap in their flight seasons. This is espe - egg-laying habitat and pollen as adults and cially apparent for Eupeodes and Platycheirus. aphid prey as immatures. We caught 7 species 498 WESTERN NORTH AMERICAN NATURALIST [Volume 77 of Eupeodes (Metasyrphus ) during the study, Version 9. User’s guide and application. http://purl along with 1 species of the closely related .oclc.org/estimates COLWELL , R.K., A. C HAO , N.J. G OTELLI , S.Y. L IN , C.X. subgenus Eupeodes (Eupeodes ). Both subgen - MAO , R.L. C HAZDON , AND J.T. L ONGINO . 2012. Models era overlap in flight season, and at the species and estimators linking individual-based and sample- level we see many overlaps. Within the sub - based rarefaction, extrapolation and comparison of genus Metasyrphus, the species ochrostomus, assemblages. Journal of Plant Ecology 5:3–21. COLWELL , R.K., C.X. M AO , AND J. C HANG . 2004. Interpo - luniger, and snowi overlap in the early season. lating, extrapolating, and comparing incidence-based In the late season, luniger, snowi, perplexus, species accumulation curves. Ecology 85:2717–2727. vanblesi, gentneri, and subsimus occur (all DEUTSCH , C.A., J.J. T EWKSBURY , R.B. H UEY , K.S. S HELDON , members of Metasyrphus ). This overlap in the C.K. G HALAMBOR , D.C. H AAK , AND P.R. M ARTIN . late season involves 8 species of Eupeodes 2008. Impacts of climate warming on terrestrial ectotherms across latitude. Proceedings of the within a period of 10 weeks (Table 1). We do National Academy of Sciences 105:6668–6672. see a slight difference as the Metasyrphus DIVISION OF WATER QUALITY . 2014. Utah’s Year 2002 subgenus peaks more in the fall, whereas the 303(d) list of waters submitted in fulfillment of Eupeodes subgenus peaks in the late spring. Section 303(d) of the Clean Water Act, Department Rising summer temperatures may have played of Environmental Quality, Salt Lake City, UT. [EPA] E NVIRONMENTAL PROTECTION AGENCY . 2006. Total a role in the separation of these 2 subgenera. maximum daily load (TMDL) water quality analysis We see a similar pattern on the subgenus level of Soldier Creek Watershed, Utah, EPA, Utah. http:// with the Paragus taxa. www.deq.utah.gov/ProgramsServices/programs/water/ We conducted this study to understand watersheds/docs/2007/08Aug/Soldier_Creek_TMDL .pdf the composition of hover fly species and their GOTELLI , N.J., AND R.K. C OLWELL . 2011. Estimating changes in abundance throughout the flight species richness. Frontiers in Measuring Biodiver - year. This study has revealed an incredible sity 12:39–54. diversity and variation within the Syrphidae. HASLETT , J.R. 1989. Adult feeding by holometabolous insects: pollen and nectar as complementary nutri - Sampling from several sites has allowed us to ent sources for Rhingia campestris (Diptera: Syrphi - see a large variation in flight seasons between dae). Oecologia 81:361–363. species. With use of richness indicators and a HENDERSON , D.H. 1982. Fine structure and neurophysi - rarefaction curve, we were able to more fully ol ogy of a gustatory sensillum on the ovipositors of Metasyrphus venablesi and Eupeodes volucris (Dip - determine the richness of the system. Many tera: Syrphidae). Canadian Journal of Zoology 60: interesting questions and relationships were 3187–3195. exposed. We now understand the main com - HOLLOWAY , B.A. 1976. Pollen feeding in hover flies position of Syrphidae in respect to this sys - (Diptera: Syrphidae). New Zealand Journal of Zool - tem, and we hope that this study aids future ogy 3:339–350. INOUYE , D.W., B.M.H. L ARSON , A. S SYMANK , AND P.G. research in determining drivers and main - KEVAN . 2015. Flies and flowers III: ecology of forag - tainers of biodiversity, richness, and flight ing and pollination. Journal of Pollination Ecology seasons of hover flies in Utah and throughout 16:115–133. the world. KEARNS , C.A. 1990. 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