Grand Canyon Butterflies Article

On Jeweled Wings: Distribution and Ecosystem Management Implications of Butterflies and Skippers in the Grand Canyon Lauren K. McLain, Grand Canyon Honors Semester Participant Lawrence E. Stevens, Ecologist In the fall of 1999 I participated in the Grand Canyon Honors Semester, sponsored by the National Collegiate Honors Council, Northern Arizona University, Grand Canyon National Park, and the Grand Canyon Trust. One of the requirements for completion of the semester was an undergraduate research project related to the Grand Canyon. A river trip was also part of the semester. Larry Stevens joined our trip as boatman and lecturer. He introduced me to the invertebrates of Grand Canyon and asked if I would like to assist with an inventory of butterflies in the Grand Canyon. What follows is the result of our collaboration. – Lauren McLain Butterflies are good candidates as indicators of Grand Canyon ecosystem health for several reasons. They are highly visible. Different species tend to prefer specific host plants. They play a primary role as consumers and pollinators. They have a tendency to display endemic morphological traits. And they exhibit unique dispersal and migratory behaviors. J.S. Garth completed the last inventory of butterflies in the Grand Canyon in 1950. A more recent inventory was needed to determine the status of butterfly species in the Grand Canyon so that they could be used as indicators of ecological health. Data from Garth’s inventory was combined with collections from the Museum of Northern Arizona and Northern Arizona University (Stevens 1976). Taxonomy of all specimens was updated using the nomenclature of J.A. Scott (1986). Additional specimens were collected and identified as part of this study. A total of 673 butterfly and skipper specimens or observations were identified in the Grand Canyon region from this limited study. They comprised six families with 62 genera, 112 species and 121 subspecies. No new species were added to Garth’s 1950 inventory. For the purpose of this study the Grand Canyon area was divided into five landscape zones: 1) South Rim, 2) slopes between South Rim and the river, 3) river corridor, 4) North Rim slopes, and 5) North Rim. The number of species occurring in each of these zones was determined and data compiled on diversity in relation to elevation. The results were contradictory to the researchers’ expectations. For most types of insects, diversity declines with distance from the equator, with the highest diversity in the tropics (Lackner in prep.). Diversity for most species also declines at higher elevations, because of the cooler temperatures and greater precipitation, conditions similar to those at higher latitudes. Grand Canyon is different. Butterfly diversity appears to increase at higher elevations, with the most diversity found on the North Rim. (Graph, Figure 3, placed near this paragraph) The positive relationship between diversity and elevation may be a function of increased habitat area at higher elevations within Grand Canyon. The Grand Canyon region lies on the strongly uplifted southern Colorado Plateau, with extensive habitat at and above 6000 feet elevation. The low-level deserts of the river corridor make up only a small portion of the entire region. Environmental harshness may also play a role in this matter. The proximity of high plateau tablelands creates colder wintertime temperatures, and the extensive south-facing dark slopes of the inner canyon are far hotter than flat lands at equivalent elevations. Geologic time may be a factor as well. Desert vegetation has expanded into Grand Canyon only in the past 12,000 years. This is a sufficiently brief period to potentially limit butterfly diversity to the more actively dispersing species, such as some Nymphalidae (the brush-footed butterflies), and restricts the distribution of those that are highly host specific. Skippers are a separate but related group of butterfly-like insects, characterized by stouter bodies and differences in wing venation and form of the antennae. Microhabitat plays a role in skipper distribution. Skipper diversity was greatest on the south side of Grand Canyon, reaching maximum diversity on south-side slopes. These north-facing slopes are remarkably cool and wet, compared to the hot, dry south-facing slopes on the north side of the Grand Canyon. Skipper diversity on the north side was positively related to elevation, showing the greatest number of species in the cool, moist forests of the North Rim. Four endemic (found only in the park) butterfly subspecies have been identified in Grand Canyon National Park: Cercyonis sthenele damei Coenonympha tullia furcae Papilio indra kaibabensis Speyeria atlantis schellbachi Scrub wood nymph Grand Canyon ringlet Kaibab swallowtail Schellbach’s Atlantis fritillary All occur predominately on the rims. This pattern further supports the idea that time and habitat area plays major roles in regional biodiversity, as isolation and the resultant evolution of distinct subspecies have occurred on the rims, but apparently not in the geologically-recent desert of the inner canyon. This was the second inventory of butterflies in the Grand Canyon in fifty years, and the first attempt to understand patterns of butterfly distribution across elevation. Current collections are sufficient to support the positive correlation between diversity and elevation for butterfly species in the Grand Canyon. Other collections may have been made and the search continues for additional data. More observations and collections from intermediate elevations in the remote upper and lower Grand Canyon would strengthen the understanding of this pattern, as would further collection on the rims in the western canyon. Many species, including endemic species, are located in potentially high impact areas on the North and South Rims where visitation is concentrated. It appears that of the endemic species only P.i. kaibabensis has been collected since Garth completed his inventory in the 1950s. However, the status of the other endemic butterfly populations is largely unknown. Several management implications arise from this preliminary study. To protect biodiversity in the park, the National Park Service can benefit by understanding the distribution of invertebrates. The relationships between butterflies and other invertebrates remains largely unexplored in the Grand Canyon. Other invertebrates may show different distribution patterns from those found for butterflies and skippers. Such groups deserve at least inventory attention, if not more thorough analysis. Invertebrate distribution studies could be related to patterns of occurrence and change at isolated and highly productive microhabitats such as caves and desert springs. Even if monitored only once a decade, the NPS may be able to relate changes in butterfly and skipper distribution to human impacts or environmental change. Due to their visibility, butterflies and skippers may prove to be a useful indicator of changes in Grand Canyon invertebrate populations and climate, as well as an excellent educational tool for public interpretation. References Garth, J.S. 1950. Butterflies of Grand Canyon National Park. Grand Canyon: Grand Canyon Natural History Association. Lackner, T. In preparation. Patterns of tenthredinid gallfly diversity across elevation and latitude in western North America. Flagstaff: Northern Arizona University MS Thesis. Scott, J.A. 1986. The butterflies of North America: a natural history and field guide. Stanford: Stanford University Press. Stevens, L.E. 1976. An insect inventory of Grand Canyon. Pp. 141-145 & appendix in Carothers, S.W. and S.W. Aitchison (eds.). An ecological survey of the riparian zone of the Colorado River between Lees Ferry and the Grand Wash Cliffs, Arizona. Grand Canyon: National Park Service, Colorado River Research Series Technical Report No.10. Figure 1. Grand Canyon Honors Semester students Michelle Zajac (left) and Lauren McLain examine a monarch butterfly (Danaus plexippus). Figure 2. A sister butterfly (Limenitis bredowii) on the mud along the Colorado River near Kanab Creek. Figure 3. Comparison of numbers of species of butterflies and skippers in various habitats at Grand Canyon National Park. Word count (including citations and captions): 1254