Old- Ij\iiif; Rfsoii/ve.s — Imcrichniles 



175 



unit) to identify wiiicii units had relatively 

 greater densities of particular species and which 

 factors might account for this variation. Details 

 regarding the survey and statistical methodolo- 

 gies are provided elsewhere (A.B. Swengel. 

 unpublished data). 



Management and Distribution 



The overwhelming destruction of prairie 

 habitat has had disastrous consequences for 

 prairie-specialist butterflies, not just because of 

 the outright loss of appropriate living space but 

 also because of habitat fragmentation. Because 

 prairie-specialist butterflies are rarely encoun- 

 tered outside of these fragmented prairie patch- 

 es, populations at different sites may have min- 

 imal gene flow and are rarely able to recolonize 

 sites of local extinctions. For example, the regal 

 fritillary is the most widespread prairie butterfly 

 species, but it requires larger habitat patches or 

 connected networks of habitat patches to main- 

 tain populations. The arogos skipper (Arntoue 

 arogos icnva) and ottoe skipper (//cv/^^^Wfl ottoe) 

 also occur widely in the prairie biome but arc 

 more restricted in their habitat requirements, 

 resulting in more localized and spotty distribu- 

 tions. The Dakota skipper and poweshiek skip- 

 per (Oarisimi poweshiek) are most restricted in 

 range, occuning only in northern prairie, and 

 have further habitat restrictions within that 

 range. As a result, the northern Midwest (north- 

 western Iowa, western Minnesota, and the east- 

 ern Dakotas) is the region where tall-grass 

 prairie conservation has the most potential for 

 maintaining the greatest diversity of prairie-spe- 

 cialist butterflies. 



Regal fritillaries (.S'/iivc/vt; idulia) mating on pale purple 

 coneflower (Echimiceii pallida). 



Our surveys show that the management 

 occuning at a prairie critically affects whether 

 prairie-specialist butterflies exist at the site and 

 at what abundance. Although each butterfly 

 species has its own response to fire, the prairie 

 specialists show a pronounced and statistically 

 significant decline after fire; this decline per- 

 sists 4 or more years (A.B. Swengel, unpub- 

 lished data). Species with the broadest habitat 

 adaptation (invaders) are most abundant in 

 recently burned units and least abundant in units 

 left unburned the longest. Species of intermedi- 

 ate adaptations (grasslands, generalists) showed 

 milder, intermediate trends. 



Unintensive haying management (a single 

 annual or biennial cutting with removal of the 

 clipped vegetation) is more favorable for butter- 

 fly diversity. Such haying is more beneficial for 

 butterflies sooner after treatment and causes a 

 less pronounced variation in butterfly abun- 

 dance between different treatment years. In 

 general, butterflies are more abundant in the 

 first years after haying than after burning; spe- 

 cialists account for much of this difference (Fig. 

 2). Our limited opportunities to test light graz- 

 ing show that it may also serve specialist butter- 

 flies better than fire. 



Prairie-specialist butterflies apparently 

 respond to different management types because 

 of varying degrees of mortality (e.g.. fire causes 

 more direct mortality than haying or grazing) 

 and because of differences in continuity of 

 required habitat resources (e.g.. fire removes all 

 cover but is followed by regrowth of thick 

 cover, while unintensive haying and grazing can 

 more consistently maintain moderate cover). 

 Management also indirectly affects butterfly 

 populations by altering the abundance and 

 occurrence of plants they depend on as well as 

 the vegetational structure and physical features 

 they require. 



These results are consistent with butterfly 

 conservation experience around the world, par- 

 ticulariy in Europe and Australia (Butterflies 

 Under Threat Team 1986; Kirby 1992; New 

 1993). Thus, simply preserving habitat is not 

 sufficient to conserve insect biodiversity; suit- 

 able management approaches and land uses 

 compatible with the habitat's native biodiversi- 

 ty must be preserved. It is possible to maintain 

 plants successfully without protecting the asso- 

 ciated animals, but it is impossible to maintain 

 the associated animals successfully without 

 protecting the plants. 



It appears desirable for managers to aim for 

 diversity and patchiness in prairie-management 

 approaches within and among sites rather than 

 broadly applying a single management formula 

 for prairie everywhere. Whether or not a site is 

 managed specifically to conserve insects, 

 declines and extirpations of insects specialized 



■ burn-year 

 D burn-y ear 1 



■ hay-year 

 B hay-year 1 



Nonspecialisi Specialist 



Fig. 2. Abundance of all. non.spe- 

 cialist (grassland, generalists. and 

 invaders), and piairie-specialisi 

 study species in the first years of 

 fire and hay management. 

 Missouri study sites. 



