«THE BIOGEOGRAPHY AND ECOLOGY OF EUPHYES DUKESI (HESPERIIDAE) IN FLORIDA JOHN V. CALHOUN l 1731 San Mateo Drive, Dunedin, Florida 34698, USA ABSTRACT. ...»
Journal of the Lepidopterists' SOciety
49(1), 1995, 6-23
THE BIOGEOGRAPHY AND ECOLOGY OF EUPHYES DUKESI
(HESPERIIDAE) IN FLORIDA
JOHN V. CALHOUN l
1731 San Mateo Drive, Dunedin, Florida 34698, USA
ABSTRACT. A distinctive endemic phenotype of Euphyes dukesi (Lindsey) was first
discovered in Florida in 1971. The endemic nature of Floridian populations was only
recently recognized, and the populations currently remain undescribed. Pleistocene glacial events probably contributed to the isolation of these populations from populations on the North American mainland. The species has been found in at least five types of forested wetlands in Florida. The primary hostplant is Rhynchospora inundata (Oakes) Fern (Cyperaceae), but Rhynchospora miliacea (Lam.) A. Gray (Cyperaceae) and a species of Carex (Cyperaceae) also are utilized. Euphyes dukesi is bivoltine in Florida, with adults active primarily during May-June and September-October. Adults frequent sunlit patches of hostplants within swamps and visit a variety of nectar sources. The alteration and destruction of forested wetlands threaten populations of this species. Euphyes dukesi has a limited distribution and is considered rare in Florida.
Additional key words: endemic, swamps, hostplants, energy resources, behavior.
Since its description, Duke's skipper, Euphyes dukesi (Lindsey), has remained an enigmatic and poorly understood North American mem- ber of the genus Euphyes. This species generally is considered rare and known from only a few widely separated localities (e.g., MacNeill 1975, Pyle 1981, Opler & Krizek 1984). In Michigan, E. dukesi is a state- listed threatened species (Haack 1992). Owing to this perceived rarity, a number of distributional and ecological discoveries have been doc- umented in detail (Pliske 1957, Mather 1963,1966, Price & Shull 1969, Irwin 1969, 1972, Covell et al. 1979). The known range of E. dukesi extends from Virginia, southward along the Atlantic coast to Florida, west to southeastern Texas and northward in the Mississippi drainage to Indiana, Ohio, Michigan, and southern Ontario (Opler & Krizek 1984, HoI es et al. 1991, Stanford & Opler 1993) (Fig. 1). The species is represented in Florida by a recently recognized, but undescribed endemic subspecies (Shuey 1993). Throughout its range, this species is associated primarily with the interiors of swamps, habitats that char- acteristically support few butterfly species. Because of this extraordinary habitat affinity, E. dukesi remained undiscovered until 1922 (Lindsey 1923).
In common with most other North American members of the genus, E. dukesi has been recorded in association only with Carex (Cyperaceae) sedge hostplants (Shuey 1986). In the Great Lakes region, the only reported host is Care x lacustris Willd., a broad-leaved species fre- 1 Research Associate, Florida State Collection of Arthropods, Division of
quently found within swamp forests and partially shaded drainage ditches (Pliske 1957, Shuey 1985, Iftner et al. 1992). In the Gulf States (e.g., Louisiana and Texas), E. dukesi has been found in association with Carex hyalinolepis Steud. (Irwin 1972) and Carex lurida Wallenb.
(Rickard & Knudson 1980). Carex lacustris was once considered conspecific with C. hyalinolepis (=G.lacustris var.laxiflora Dewey). These species are very similar and it is possible that some Great Lakes populations of E. dukesi actually utilize G. hyalinolepfs. The only other reported host is Carex walteriana Bailey which Scott (1986) listed withJOURNAL OF THE LEPIDOPTERISTS' SOCIETY out reference. At least two additional Carex species are utilized in Texas (M. A. Rickard pers. comm.). Alternate common names for E. dukesi allude to these habitat and hostplant preferences (e.g. scarce swamp skipper [Pyle 1981] and brown sedge skipper [Scott 1986]).
For nearly twenty years following its original description, E. dukesi was known only from the type locality of Mobile, Alabama (Mather 1963). Although Holland (1931) predicted that E. dukesi would eventually be found "elsewhere along the Gulf," it was not until 1971 that the species was recorded in Florida. Until recently, the entire known Florida distribution of E. dukesi was limited to nine locations within six counties (Fig. 1). This species was considered very rare in Florida and records consisted of single or few individuals. In most cases, the species was encountered only once or twice at a given locality. Minno and Calhoun (in press) stress the need for surveys and ecological studies to properly determine the status of E. dukesi in Florida. Similar studies have led to the discovery of at least 30 populations in Ohio alone (Shuey 1985, Iftner et al. 1992). The purpose of this paper is to present the results of a detailed examination of the distribution, habitat, hostplants, and behavior of E. dukesi in Florida. Potential threats to Floridian populations also are identified.
Shapiro (1971) remarked that E. dukesi possesses "the most extraordinary distribution of any North American butterfly," exhibiting a Coastal Plain-Great Lakes distribution pattern. He proposed that this pattern may be at least partially explained by the displacement of populations during Pleistocene glacial intervals, followed by the dispersal of the species through suitable vegetational corridors (e.g., the Mississippi and Mohawk Valleys) when the ice sheets retreated. Although Shapiro (1971) stated that E. dukesi is not phenotypically differentiated, the species does exhibit morphological differences to varying degrees (Mather 1963, Shuey 1994).
Remington (1968) observed that many plants and animals in peninsular Florida differ from their respective mainland populations. He identified a narrow zone of transition in northern Florida, across which little or no clinal trends exist. He attributed this to a combination of glacial and postglacial episodes, especially during the late Pleistocene.
Shuey (1993) suspected that vegetational changes associated with glacial events contributed to the fragmentation and eventual divergence of peripheral populations of several species of Euphyes, including E. dukesi.
During Pleistocene glacial maxima, boreal forests penetrated far into 49, 1 9
VOLUME NUMBERthe southeastern United States (Webb 1990) and may have displaced populations of E. dukesi into refugia located in the Florida peninsula.
During the Wisconsinan glacial maxima (approx. 20,000 YBP), Florida's land area was much larger, extending outward to the edge of the continental shelf (Florida Plateau). At this time, swamps may have occupied bottomland and low-lying areas in northern Florida where mesic and riparian forests dominated (Webb 1990). The general climate of northern Florida appears to have remained relatively constant over the last 20,000 years (Platt & Schwartz 1990), suggesting that conditions were well suited for such refugia. Boreal forests may have acted as effective barriers, isolating populations of E. dukesi in Florida. Endemic populations of sand pine (Pinus clausa [Chapm. ex. Engelm.]) are believed to have been confined to Florida in this manner (Webb 1990).
It is possible that populations of E. dukesi became isolated in Florida by a similar process during a glacial event prior to the Wisconsinan.
Euphyes dukesi has probably been present continuously in Florida many millennia longer than in the Great Lakes region where current populations could not have become established until after the Wisconsinan glaciers had retreated (approx. 12,000 YBP). The species presumably populated present day forested wetlands during the last seve ral thousand years in a manner consistent with island colonization.
Euphyes dukesi currently is found in Florida between the latitudes 300 20'N and 28°N, representing the southernmost populations of the species. Populations in Hillsborough County, Florida are located nearly 350 km further south than those in Texas and Alabama. Where E.
dukesi occurs in Florida, average annual temperatures range from IS. 9°C to 22.8°C (Fernald 1981). Many Florida populations are found within the Ocala Uplift physiographic district (Fig. 2) which is a highly diverse region with a relatively wide range of elevations an.d botanical communities (Brown et a1. 1990). The remaining populations are found within the northern portion of the Eastern Flatwoods District (a low, flat region composed primarily of pine flatwoods communities), the Central Lake District (karst terrain with numerous lakes and sandhills) and the Sea Island District (pine flatwoods, dunes and salt marshes).
The species probably occurs southward into the central portion of the Eastern Flatwoods District and the northern portion of the Southwestern Flatwoods District (another low, flat region dominated by pine flatwoods communities) (Figs. 1 & 2). A number of temperate species reach their southern range limit in this area (roughly 27°30'N), apparently due to decreasing habitat availability. Euphyes dukesi is undoubtedly absent from the Gold Coast-Florida Bay District of subtropical southern Florida. This district is low-lying and consists largely of marshes, dwarf cypress communities, and mangrove swamps (Brown et a1. 1990). The
10 JOURNAL OF THE LEPIDOPTERISTS' SOCIETY
F. Ocala Uplift District G. Tifton Upland District H. Dougherty Karst District
1. Apalachicola Delta District J. Southern Pine Hills District FIG. 2. Physiographic districts of Florida (adapted from Brown et al. 1990). Dots denote E. dukesi populations.
ecological characteristics of forested wetlands in this region differ from those elsewhere in the State.
Populations of E. dukesi almost certainly inhabit swamps within the various physiographic districts of the Florida panhandle. This portion of Florida lies only 48 km east of mainland E. dukesi populations in Alabama. As a result, populations of the mainland phenotype could inhabit the western counties of the Florida panhandle and intermediate populations may extend eastward. However, if sympatric populations of these subspecies are located, with no evidence of intergradation, their taxonomic relationship should be re-evaluated. Other butterflies that share the basic distribution pattern of E. dukesi in Florida include Wallengrenia egeremet (Scudder) (Hesperiidae), Poanes zabulon (Bois.
& LeConte) (Hesperiidae), Satyrium c. calanus (Hubner) (Lycaenidae), 11 49, NUMBER 1 VOLUME Incisalia henrici margaretae dos Passos (Lycaenidae), Anthanassa texana seminole (Skinner) (Nymphalidae), Satyrodes appalachia (R. L.
Chermock) (Satyridae), and Cyilopsis gemma (Hubner) (Satyridae).
With the exception of S. calanus, these taxa are associated primarily with forested wetland habitats in Florida.
HABITAT In August 1990, a large population of E. dukesi was discovered along a branch of the Big Cypress Swamp in southern Pasco County, Florida.
The swamp is part of a forested wetland complex extending from central Pasco County southward into northern Hillsborough County. It supports an abundance of water ash (Fraxinus caroliniana Mill., Oleaceae), southern red maple (Acer rubrum var. trilobum K. Koch., Aceraceae), sweetgum (Liquidambar styraciflua L., Hamamelidaceae), water oak (Quercus nigra L., Fagaceae), cabbage palm (Sabal palmetto (Walt.) Lodd. ex Schultes, Arecaceae), and bald cypress (Taxodium distichum (L.) Rich., Taxodiaceae). Buttonbush (Cephalanthus occidentalis L., Rubiaceae) occurs locally throughout the swamp. Arrowroot (Thalia giniculata L., Marantaceae), dotted smartweed (Pol!/gonum punctatum Elliot, Polygonaceae) and pickerelweed (Pontederia cordata L., Pontederiaceae) grow within many sunlit wet depressions. The swamp is seasonally flooded and becomes dry during the spring and autumn when precipitation levels are low. During the wet season (June-September), water levels may reach 0.5 m or more in the deeper depressions.
It is within these water-filled depressions that Rhynchospora and Carex sedges form impressively large patches, sometimes dozens of square meters in size and consisting of thousands of individual plants. These sedge patches are common throughout the open understory where they grow to approximately 1 m in height and conceal many cypress aerial roots or "knees," making travel through the swamp very treacherous (Figs. 3-4). Euphyes dukesi is found in close association with these sedges.
Based on this initial discovery, other forested wetlands in central Florida were surveyed in 1991 for E. dukesi. Swamps were selected that consisted of hardwoods with interior stands of cypress, suggesting that water levels were sufficient to support an abundance of sedges.
Consequently, six additional populations of E. dukesi were found in Hillsborough, Pasco, Polk, and Sumter counties (Fig. 1).
Invertebrate diversity is high within swamps where E. dukesi occurs.
Spiders are abundant, including Nephila clavipes (L.) (Araneidae), which constructs webs measuring 1 m or more in diameter. Large mosquitoes of the genus Aedes (Culicidae) are particularly troublesome. Dragonflies, such as Epiaeschna heros (Fab.) (Aeshnidae), patrol sunlit clearJOURNAL OF THE LEPIDOPTERISTS' SOCIETY ings. Species of Lepidoptera inhabiting swamps with E. dukesi include Callosamia securifera (Massen) (Saturniidae), Catocala spp. (Noctuidae), Oligoria maculata (W. H. Edwards) (Hesperiidae), Problema byssus (W. H. Edwards) (Hesperiidae), Wallengrenia egeremet, Hermeuptychia sosybius (Fab.) (Satyridae), C. gemma and S. appalachia.
Calpodes ethlius (Stoll) (Hesperiidae) frequents sunlit patches of its host plant (T. giniculata) and Papilio glaucus (L.) (Papilionidae) is a common canopy species in many swamps dominated by hardwoods.
Species of sedge moths (Glyphipterigidae) undoubtedly occur in these swamps as well. A number of vertebrates also occupy these habitats.
The eastern diamondback rattlesnake (Crotalus adamanteus Beauvois, Viperidae) and Florida cottonmouth (Agkistrodon piscivorus conanti Gloyd, Viperidae) are occasionally encountered. Many species of migrating songbirds utilize the swamps as important food sources.