Lycaeides melissa samuelis Nabokov, the Karner blue butterfly, is a federally endangered species that has two generations per year in oak savanna habitats. The significance of “subhabitat” variation, formed by variable tree canopy cover, in creating high-quality habitat for this butterfly was evaluated. Subhabitats were characterized by percent canopy cover as open (0–15%), partial (16–75%), and closed (76–100%). Habitat quality was assessed by measuring egg distribution and larval and pupal survival, in each subhabitat at sites in Wisconsin and Minnesota for as long as 3 yr. Estimates of mortality rates were used to project adult production for each subhabitat in each generation at the two Wisconsin sites (Sawyer and Fishery). At the Sawyer site, the largest number of eggs tended to occur in open subhabitats, ranging in number from 16,460 to 665,860. Similarly, during the second flight at the Fishery site, a greater number of eggs were observed in the open subhabitat; for two of the five sample periods, egg numbers ranged from 61,470 to 173,430. However, in other years and/or broods, partial subhabitats had greatest number of eggs at the Fishery site, ranging from 24,850 to 88,160 eggs. The fewest total eggs were laid in closed subhabitat, ranging from 20 to 12,740, where larval survival rates were the highest. Therefore, the subhabitat with the highest immature survival rates typically received the lowest total number of eggs. However, we predicted greater adult production per stem to occur in partial and closed subhabitats. The unique attributes of all three subhabitats and their potential influences on population dynamics suggest that all subhabitats studied may be essential for the long-term persistence of healthy L. m. samuelis populations.
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Vol. 96 • No. 6