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Butterflies of Glacier National Park, Montana

Discussion


Species Richness Through Time

Approximately 86% of the previously recorded butterflies were observed during the 3 yr of sampling and the total number of species observed increased each year. Two butterfly species were added to the Park lists in 1987, four in 1988, and three in 1989. Unfortunately, a comparison between the number of species found using the more extensive sampling scheme of 1987 relative to that of the more intensive design of 1988 and 1989 was not possible. Several factors confounded this comparison. For example, sampling in 1987 started 3 wk later than it did during the next 2 yr, so several of the early-emerging species were missed. In addition, some of the biennial species will be missed during any one year.

Lycaena hyllus was found in 1987, but not seen again. Nymphalis californica was found in both 1987 and 1988. Callophrys sheridanii and Satyrium saepium, Vanessa carye annabella, and Neophasia menapia were found in 1988, but not in 1989. In 1989, I identified Callophrys polios, Speyeria aphrodite, and Danaus plexippus as new listings for the park. The sitings of Lycaena hyllus, Callophrys sheridanii, and Danaus plexippus can be considered as small range expansions (one county) relative to Ferris and Brown (1981), but the remainder of the species is known to exist in at least one of the two counties in which Glacier National Park resides.

As noted above, three species have not been sighted for many years. Colias pelidne occurs in Montana, Idaho, Wyoming, and Oregon (Ferris and Brown, 1980). Given that this species occurs in the two counties (Glacier and Flathead) that comprise Glacier National Park, it should occur in the Park. Although Papilio bairdii occurs in many Rocky Mountain states, it is not known to occur outside the park in either Flathead or Glacier counties. Everes comyntas is an eastern species that does not occur in Montana. Prior to 1964, authors associated the Montana subspecies Everes amyntula albrighti Clench 1944, with E. comyntas. Everes amyntula albrighti is common in Glacier National Park and surely is the taxon which Garth referred to as E. comyntas. Papilio bairdii probably is limited in the park owing to the limited occurrence of its foodplant, Artemesia dracunculus. Both the plant and the butterfly are found in drier, lower elevation habitats; the butterfly probably strays into the park on occasion from areas in Montana such as western Flathead County, and Sanders, Lake, Missoula, and Ravalli counties.

Other species of concern are those with specific habitat requirements. For example, Colias nastes is an arctic species and Glacier National Park may be at the southernmost limit of its range. Because Colias nastes occurs only at high elevations within the park, loss of such habitats might reduce the total range of this species. Successional habitats are also important to monitor. Species such as Euphydryas gillettii depend on wet meadows where this species deposits eggs on the host plant, Lonicera involucrata. These types of meadows are often in the early stages of succession. If large trees begin to encroach, blocking the sun, the habitat may no longer be suitable for the host plant on which the larvae of E. gillettii depend. Management that would preserve the meadow and prevent succession may be called for in this case.


Monitoring

There were significant changes in the occurrences of 24 of the butterfly species found between 1988 and 1989. However, butterfly populations normally fluctuate in size (Scott, 1986); thus, these changes may not be ecologically significant. Nonetheless, 15 species were found in more sites in 1988 than in 1989 and nine were found in more sites in 1989 than in 1988. Three of these species are biennial (Vanessa cardui, Nymphalis vau-album, and N. californica); thus, one would expect marked fluctuations in their occurrences from year to year. The putative changes in occurrence of Papilio glaucus rutulus and Plebejus icariodes may be attributed to misidentification during 1987 and 1988. The reasons for changes in the others are unknown.

Acknowledgements: This research was supported by the National Park Service (at Glacier National Park, Montana). I thank Tom Vawter, Craig Odegard, Steve Bracken, and Tom Jacobsen for their assistance in the fieldwork, and Philip Humphrey and George Byers for their critical review of early drafts of this manuscript.


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