Status and Ecology of a Rare Gomphid Dragonfly at the Northern Extent of its Range Jeffrey D. Corser* Abstract - New records of a rare dragonfly, Stylurus plagiatus, are described from the Hudson River estuary in eastern New York State. Breeding occurred primarily in tidal mudflats; however, in other parts of its range, this species is known to use a broader array of habitat types. As a southerly species at its northern range margin, populations of S. plagiatus in eastern New York are likely to be temperature-limited, although other factors, such as shoreline habitat integrity and dispersal behavior, may also play a role in defining its range limits. The range of the riverine dragonfly Stylurus plagiatus Selys (Russet-tipped Clubtail) is centered along the Oklahoma/Kansas border, with a northern range boundary around 43° to 44°N latitude in both the Northeast and upper Midwest (Craves 2001, Donnelly 2004). This species is generally regarded as being common in the southern and midwestern United States but rare in the north. At its northern extent, in New York, Pennsylvania, and New Jersey, it is listed as critically imperiled (NatureServe 2005), and has never been reported from states or provinces further to the north and east. Prior to the early 1990s, it was known north of the Long Island/ New Jersey area from a single historical record at Lake George in northeastern New York (Needham 1928), although the validity of this record is questionable (T. Donnelly, SUNY Binghamton, Binghamton, NY, pers. comm.). The species was then rediscovered in September 1991 by Ken Soltesz on the Hudson River estuary (HRE) in Dutchess County and is currently found northward along the Hudson to the Mohawk River (Table 1, Fig. 1). In this note, I describe new records of S. plagiatus from HRE, highlight certain aspects of its ecology and life history, and ask what factors may potentially limit its geographic distribution at its northern range margin. Stylurus plagiatus was found breeding primarily in freshwater tidal mudflats and tidally influenced tributaries along the HRE. Specimens were not found in apparently suitable non-tidal habitats to the north on the Hudson, the Champlain Canal, or lower Lake Champlain, nor further west along the Mohawk River (Fig. 1). Estuarine mudflat communities in New York are confined to the lower Hudson River and are characterized by emergent and submerged aquatic vegetation, high productivity, and adaptation to tidal disturbance. About 80% of this habitat has been lost to Notes of the Northeastern Nat u ral ist, Issue 17/2, 2010 341 Table 1. Summary of Stylurus plagiatus (Russet-tipped Clubtail) records in New York State. # = number of new site records. Time period # Location (county) Source(s) 1920s 2 Suffolk, Warren* Needham 1928 1990–2004 5 Columbia, Dutchess, Putnam, Donnelly 1999, Donnelly 2004, Rockland NYNHP 2008b 2005–2009** 9 Albany, Columbia, Greene, White et al. 2010, this study Rensselaer, Saratoga, Ulster *Owing to labeling inaccuracies, this record is of questionable validity (T. Donnelly, pers. comm.). **Period of Odonata Atlas efforts in New York (White et al. 2010). *New York Natural Heritage Program, 625 Broadway, 5th Floor, Albany, NY 12233; jdcorser@ gw.dec.state.ny.us. 342 Northeastern Naturalist Notes Vol. 17, No. 2 urbanization along the Hudson’s riparian zone (NYNHP 2008a). The species likewise did not turn up elsewhere in New York during extensive statewide Odonata surveys during 2005–2009 (White et al. 2010). However, other large rivers in New York may have been under-surveyed, and the species’ late flight season and cryptic behavior could have led to under-reporting. In other parts of its range, S. plagiatus appears less habitat specific, occurring on large rivers, creeks, and even lakes with silty and/ or sandy bottoms (Dunkle 2000). The larvae of S. plagiatus exhibit microhabitat selection, burrowing deeply into sand/gravel substrates while feeding on chironomids, tubificid worms, and Figure 1. The extent of the Hudson River estuary (HRE) in eastern New York. The dot (•) on the Mohawk River near its confluence with the Hudson represents the northernmost occurrence of Stylurus plagiatus in the Northeast. Shed skins (exuviae), but not adults, were found at this non-tidal locale in summer 2007 (Hemeon 2007) and 2008. The dashed line (---) represents the approximate location of a major topographic/ climatic boundary (Pederson et al. 2004). 2010 Northeastern Naturalist Notes 343 burrowing mayflies, living for one to two years, or possibly longer (Cannings 2003, Corbet 1999). They emerge at mid-day from late June to early July, the final instar larvae clinging just above the waterline to emergent vegetation, tree roots, rocks, and embankments, often in rather residential riverside locations (Hemeon 2007). The nature of shoreline habitat is critical for S. plagiatus because the newly-emerged adults fly immediately up to trees and shrubs bordering the riverbank and for the next couple of months they are seldom observed, presumably (Cannings 2003, Corbet 2006) seeking shelter in mature riparian forests along tidal mudflats. Along the HRE, breeding commenced the first week of September, and during this time, adults could often be found in sheltered, forested coves, but activity ceased by late September as nighttime temperatures cooled. Many other riparian dragonfly species (Samways and Steytler 1996), including the close relative S. olivaceus (Selys) (Olive Clubtail), are known to benefit from the maintenance of natural shorelines and the ecological processes that maintain functioning tidal wetland communities (Cannings 2003). Butler and deMaynadier (2008) also found that shoreline habitat integrity played an important role in the diversity of lacustrine damselfly assemblages. Perching dragonfly species such as S. plagiatus must spend long periods suspended vertically from tall trees and shrubs as they absorb heat in order to power their flight (Corbet 1999). The growth and development of egg and larval stages is also strongly temperature dependent, requiring threshold amounts of heat input (i.e., growing degree days) for developmental processes to occur (Pritchard 1982, Pritchard and Leggott 1987). Therefore, the geographic distribution of these species is known to be strongly temperature limited (May 1991). Based on an ecological niche model (e.g., Guisan and Zimmerman 2000, Prasad et al. 2006) that used known S. plagiatus occurrences in New York and 47 different environmental variables (see Howard 2006), several different thermal variables such as elevation, growing degree days, and monthly minimum temperatures (May–July) were found to be key factors in defining suitable habitats. This finding helps explain why a southerly species like S. plagiatus would find favorable microclimates along the mild HRE. The northernmost known occurrence of S. plagiatus (Fig. 1) lies just south of a well-defined northern range limit of many southerly distributed plant and animal species (e.g., Pederson et al. 2004, Stewart and Rossi 1981). Dragonfly populations are known to shift their ranges in response to regional temperature changes (Hickling et al. 2005), and Ott (2001) documented the expansion of more southerly distributed Odonata species into northern Europe as the climate warmed. Increasing temperatures lead to more rapid development rates (voltinism) of Gomphid larvae (Braune et al. 2008) and thus earlier emergence of adults, leading to longer flight seasons (Hassall et al. 2007) and a corresponding extension of northern range limits. Although the distribution of currently occupied S. plagiatus habitats in New York appears to be quite restricted, the stability of this northern range margin over the past 80+ years is in doubt because of the uncertain status of the historical record in Lake George, Warren County (Table 1). As a result, it is not clear whether the species’ range has contracted or, more likely, has been expanding northward as the climate has warmed in the Hudson Valley (Pederson et al. 2004). If S. plagiatus in New York is characteristic of other range-margin insect species (Thomas et al. 2001), its potential to further expand its range beyond HRE will depend on both larvae and adults responding to novel environments far from the center of their distribution, and incorporating ecological (habitat) as well as evolutionary (dispersal) adaptations. 344 Northeastern Naturalist Notes Vol. 17, No. 2 Acknowledgments. Erin White helped with the Figure and offered suggestions which improved earlier drafts of the manuscript, as did Paul Novak, Nick Donnelly, Matt Schlesinger, Tim Howard, Jason Bried, and two anonymous reviewers. Kevin Hemeon generously contributed his collection of exuviae and provided helpful feedback. Paul Novak verified adult specimens. Survey work was supported by the Biodiversity Research Institute and the NYS Department of Environmental Conservation. Literature Cited Braune, E., O. Richter, D. Söndgerath, and F. Suhling. 2008. Voltinism flexibility of a riverine dragonfly along thermal gradients. Global Change Biology 14:470–482. Butler, R.G., and P.G. deMaynadier. 2008. The significance of littoral and shoreline habitat integrity to the conservation of lacustrine damselflies (Odonata). Journal of Insect Conservation 12:23–36. Cannings, S.G. 2003. Status of Olive Clubtail (Stylurus olivaceus) in British Columbia. BC Ministry of Water, Land, and Air Protection, Biodiversity Branch, Victoria, BC, Canada. Wildlife Bulletin No. B-112. Corbet, P.S. 1999. Dragonflies: Behavior and Ecology of Odonata. Cornell University Press, Ithaca, NY. 829 pp. Corbet, P.S. 2006. Forests as habitats for dragonflies (Odonata). Pp. 13–36, In A.C. Rivera (Ed.). Forests and Dragonflies. Fourth WDA Symposium of Odonatology, Pensoft Publishers, Sofia, Bulgaria. 299 pp. Craves, J.A. 2001. Notable new dragonfly records. Williamsonia 5:5–6. Donnelly, T.W. 1999. The Dragonflies and Damselflies of New York. Prepared for the 1999 International Congress of Odonatology and 1st Symposium of the Worldwide Dragonfly Association. July 11–16, 1999. Colgate University, Hamilton, NY. 39 pp. Donnelly, T.W. 2004. Distribution of North American Odonata. Part I: Aeshnidae, Petaluridae, Gomphidae, Cordulegasteridae. Bulletin of American Odonatology 7:61–90. Dunkle, S.W. 2000. Dragonflies Through Binoculars: A Field Guide to Dragonflies of North America. Oxford University Press, New York, NY. 266 pp. Guisan, A., and N.E. Zimmerman. 2000. Predictive habitat distribution models in ecology. Ecological Modelling 135:147–186. Hassall, C., D.J. Thompson, G.C. French, and I.F. Harvey. 2007. Historical changes in the phenology of British Odonata are related to climate. Global Change Biology 13:933–941. Hemeon, K. 2007. Gimme some skin (Exuviae). Vermont Entomological Society News 57:10–11. Hickling, R, D.B. Roy, J.K. Hill, and C.D. Thomas. 2005. A northward shift of range margins in British Odonata. Global Change Biology 11:502–506. Howard, T.G. 2006. Salmon River watershed inventory and landscape analysis. New York Natural Heritage Program. Albany, NY. 177 pp. Available at http://www.tughill.org. May, M.L. 1991. Thermal adaptations of dragonflies, revisited. Advances in Odonatology 5:71–88. NatureServe. 2005. NatureServe Explorer: An online encyclopedia of life. Available online at http://www.natureserve.org/explorer. Accessed 20 October 2008 Needham, J.G. 1928. Odonata. Pp. 45–56, In M.D. Leonard (Ed.). A List of the Insects of New York. Cornell University Press, Ithaca, NY. NYNHP. 2008a. Online conservation guide for freshwater intertidal mudflats. Available online at http://guides.nynhp.org/guide.php?id=9870. Accessed 5 November 2008. NYNHP. 2008b. Online conservation guide for Stylurus plagiatus. Available online at http:// guides.nynhp.org/guide.php?id=8361. Accessed 5 November, 2008. NYNHP. 2009. New York dragonfly and damselfly survey database. New York Natural Heritage Program, Albany, NY. 2010 Northeastern Naturalist Notes 345 Ott, J. 2001. Expansion of Mediterranean Odonata in Germany and Europe—Consequences of climatic changes. Pp. 89–111, In G.R. Walther, C.A. Burga, and P.J. Edwards (Eds.). “Fingerprints” of Climate Change: Adapted Behavior and Shifting Species Ranges. Plenum Publishers, New York, NY. Pederson, N., E.R. Cook, G.C. Jacoby, D.M. Peteet, and K.L. Griffin. 2004. The influence of winter temperatures on the annual growth of six northern range-margin tree species. Dendrochronologia 22:7–29. Prasad, A.M., L.R. Iverson, and A. Liaw. 2006. Newer classification and regression tree techniques: Bagging and random forests for ecological prediction. Ecosystems 9:181–199. Pritchard, G. 1982. Life-history strategies in dragonflies and the colonization of North America by the genus Argia (Odonata: Coenagrionidae). Advances in Odonatology 1:227–241. Pritchard, G., and M.A. Leggott. 1987. Temperature, incubation rates, and origins of dragonflies. Advances in Odonatology 3:121–126. Samways, M.J., and N.S. Steytler. 1996. Dragonfly (Odonata) distribution patterns in urban and forest landscapes, and recommendations for riparian management. Biological Conservation 78:279–288. Stewart, M.M., and J. Rossi. 1981. The Albany Pine Bush: A northern outpost for southern species of amphibians and reptiles in New York. American Midland Naturalist 106:282–292. Thomas, C.D., J. Bosworth, R.J. Wilson, A.D. Simmons, Z.G. Davies, M. Musche, and L. Conradt. 2001. Ecological and evolutionary processes at expanding range margins. Nature 411:577–581. White, E.L., J.D. Corser, and M.D. Schlesinger. 1010. The New York Dragonfly and Damselfly Survey 2005–2009: Distribution and Status of the Odonata of New York. Department of Environmental Conservation, New York Natural Heritage Program, Albany NY.