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COSEWIC Assessment and Update Status Report on the Poweshiek Skipperling (Oarisma Poweshiek) in Canada

Habitat

Habitat requirements

O. poweshiek is an obligate resident of wet to mesic tall-grass prairies in Canada (Catling and Lafontaine 1986). The habitat of this skipper in Michigan is alkaline-fen-like, with Shrubby Cinquefoil, Pentaphylloides floribunda (Pursh), as a common shrub (Holzman 1972). However in the Dakotas, Minnesota, and Iowa, this skipper was more common in drier, mesic prairies (Swengel and Swengel 1999).

The wet-mesic tall-grass prairies where O. poweshiek occurs in Manitoba, are small (0.4 ha) to large (300 ha), more or less elongated openings among Bur Oak, Quercus macrocarpa Michx., and Trembling Aspen, Populus tremuloides Michx., groves (Catling and Lafontaine 1986) (Figure 5). These prairies are characterized by low relief (at most one or two metres), and most have alternating lower, periodically wetter, and higher drier sections, each with a distinctive plant community. The lower wetter areas are often dominated by species such as willow species, Salix sp., Tufted Hair Grass, Deschampsia caespitosa (L.) Beauv, Redtop, Agrotis stolonifera L., Mat Muhly, Muhlenbergia richardsonis (Trin.) Rydb., (all Gramineae), Carex species, Slender Spike Rush, Eleocharis elliptica Kunth (Cyperaceae), Baltic Rush, Juncus balticus Willd. (Juncaceae), Four-flowered Loosestrife, Lysimachia quadriflora Sims, (Primulaceae), and Heal-all, Prunella vulgaris L. (Labiatae). The endangered Western Prairie Fringed Orchid, Platanthera praeclara Sheviak and Bowles, and the Small White Lady’s Slipper, Cypripedium candidum Willd., are present in some of the wetter areas of the prairies. The higher and drier areas are often dominated by Big Bluestem, A. gerardii Vitman, Prairie Dropseed, Sporobolus heterolepis A. Grey (Gramineae), and various forbs, such as Smooth Camas or Alkali Grass, Zigadenus elegans Pursh (Liliaceae), Solidago rigida L., Black-eyed Susan, Rudbeckia serotina Nutt., and Blazingstar, Liatris ligulistylis (A. Nels.) (Compositae). Pale-spike Lobelia, Lobelia spicata (Lobeliaceae), was often present in the transition areas between the mesic and drier prairie. Shrubby Cinquefoil, P floribunda, was a common small shrub in these habitats. Z. elegans is considered to be a calciphile and requires a soil pH above 7.0 (Sheviak 1974), indicating that the soils of these prairies are alkaline. At most sites O. poweshiek was generally most common on or near the margin of the higher, drier sections of the prairie where A. gerardii was common. One of the larval host plants of O. poweshiek, E. elliptica (McAlpine 1972, Holzman 1972), occurs in the wetter areas of the prairie habitat (Catling and Lafontaine 1986).

Figure 5. Habitat of Oarisma poweshiek. Tall-grass/bluestem prairie near Tolstoi, Manitoba (Photo by R.P. Webster).

 Figure 5. Habitat of Oarisma poweshiek. Tall-grass/bluestem prairie near Tolstoi, Manitoba(Photo by R.P. Webster).

Trends

The historical distribution of O. poweshiek in North America will never be precisely known as much of the tall-grass prairie habitat had been converted to row-crop agriculture or severely degraded by overgrazing before any surveys for this and other prairie insects were initiated. At one time, there were approximately 34,000,000 ha (340,000 km²) of tall-grass prairie in North America (Samson and Knopf 1994). Much of this habitat was lost between 1850 and 1920. Now, only about 500,000 ha are left, a decline of over 99%. In Manitoba, 600,000 ha of tall-grass prairie once existed (Samson and Knopf 1994). Now only about 5,000 ha (this includes sites that are under a late fall mowing regime) are left, a decline of 99.5%. O. poweshiek populations have presumably declined in proportion to the loss of tall-grass prairie habitat in North America. Most populations of O. poweshiek in North America are now highly fragmented and restricted to the few isolated prairie remnants (Royer and Marrone 1992a).

It is not known how widespread O. poweshiek once was in Canada. A number of suitable tall-grass prairie habitats (total of about 3,000 ha) are still present in the inter-lake region of Manitoba between LakeS Manitoba and Winnipeg. No populations of O. poweshiek are known to occur on any of these prairies, although the related O. garita is still common on many of them. It is possible that O. poweshiek always had a limited distribution in Canada.

The shallow, rocky, highly calcareous soils in the areas where O. poweshiek now occurs in Canada are unsuitable for most agricultural uses. The small size (0.4 to 0.8 ha) of many the prairie openings, coupled with the presence of plant species that are often unsuitable for forage, particularly on the higher ground, make these sites generally unsuitable for grazing (Catling and Lafontaine 1986). As a result, the flora of these sites has not been significantly altered by agriculture. However, many sites in the U.S.A. have been lost as a result of various anthropogenic activities (Royer and Marrone 1992a).

Protection/ownership

Most populations of O. poweshiek are currently protected (at least nominally) in the 2,200-ha Tall-grass Prairie Preserve through The Critical Wildlife Habitat Program. A few additional sites outside the preserve are privately owned.