Academic journal article The American Midland Naturalist

Distribution, Population Structure and Habitat Use of the Endangered Saint Francis Satyr Butterfly, Neonympha Mitchellii Francisci

Academic journal article The American Midland Naturalist

Distribution, Population Structure and Habitat Use of the Endangered Saint Francis Satyr Butterfly, Neonympha Mitchellii Francisci

Article excerpt


The endangered St. Francis Satyr (Neonympha mitchellii francisci) is a small sedentary butterfly and one of the rarest in North America. Our study examined various quantitative aspects of this butterfly's biology, including the distributional range, habitat associations, population size and trends, demographic parameters and spatial aspects of population structure. The range of N.m. francisci distribution is restricted to DoD lands at Ft. Bragg, North Carolina, where the butterfly utilizes wetland habitats, predominantly those that have previously been impounded by beaver. In situ habitat associations and captive rearing experiments indicate that multiple sedges in the genus Carex, particularly C. mitchelliana, may be important larval food plants. Subpopulation estimates range between 49-739 individuals at any one site, while cumulative population estimates range between 700-1400 individuals for all accessible areas on Ft. Bragg. Habitats occupied by N.m. francisci are frequently subject to burning or flooding and thus butterfly subpopulations are extremely dynamic, fluctuating in response to these disturbances. This regular disturbance regime dictates that dispersal is necessary for population persistence. Several inter-colony movements were measured during capture-recapture studies and we observed both subpopulation extinctions and colonization of new habitat through the period of our studies. Conservation of N.m. francisci depends on accommodating unique aspects of its populations, including its dependence on beaver and its multi-tiered metapopulation structure.


St. Francis' satyr, Neonympha mitchellii francisa, is one of the most imperiled butterflies in North America. First discovered in 1983, its range is restricted to Ft. Bragg, North Carolina (NC), where several small subpopulations persist in glades along streams (Parshall and Krai, 1989; Hall, 1993; Hall and Hoffman, 1994).

Neonympha mitchellii francisci is currently considered a subspecies of Mitchell's satyr (N. mitchellii mitchellii), which is also endangered. Neonympha m. mitchellii populations in the Great Lakes region have been the subject of detailed investigations (McAlpine et al., 1960; Ledge and Rabe, 1996; Shuey, 1997; Darlow, 2000; Kost, 2000; Szymanski et al., 2004; Barton and Bach, 2005). Since 1988 southern populations of N.m. mitchellii have also been discovered in Virginia, Alabama and Mississippi (Roble et al, 2001; Hart, 2004). A phylogenetic analysis indicates that these southern populations are more closely related to the nominate N.m.mitchellii than to N.m.francisci (Goldstein et al, 2004).

Neonympha mitchellii francisa exhibits several morphological and behavioral similarities with N. m. mitchellii (Parshall and Krai, 1989). These butterflies share similar wingspans, coloration and flight behavior, and both utilize wetland grasses or sedges as larval food plants. Like N.m. mitchellii, N.m. francisa appears to be imperiled due to habitat loss (Hall, 2003; Szymanski et al., 2004). However, they differ markedly in terms of their ecology and life history, reflecting adaptations to very different environments (Table 1). In particular, northern populations of N.m. mitchellii in the Great Lakes region occupy relatively longlasting fen habitats, are relatively sedentary and often have large populations with little or no evidence of subdivision (MacAlpine et al., 1960; Szymanski et al., 2004). In contrast, N.m, francisa inhabits a shifting mosaic of early successional wetland habitats and occupies relatively small subpopulations across the landscape. More specifically, N. m. francisa persist in a multi-tier metapopulation structure that appears to be influenced by disturbance dynamics associated with beaver activity. This complicated population structure and association with beavers is novel in studies of Lepidoptera and provides a unique case study in butterfly conservation.

Understanding the population structure, population dynamics, habitat requirements, and basic life history of Neonympha mitchellii francisa is critical for its management and potential delisting. …

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