Geographic distribution, habitat association, and the importance of host quality for one of the rarest butterflies in North America: Thorne's hairstreak (Mitoura thornei)
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Authors
Lucas, Amy M.
Issue Date
2012
Type
Thesis
Language
Keywords
conservation , habitat characterization , H. forbesii , Lycaenidae , management , Tecate cypress
Alternative Title
Abstract
Mitoura thornei, Thorne’s hairstreak butterfly, is endemic to a single mountain in
south-western North America. The extremely small geographic range of this species
coupled with threats to its host plant, Hesperocyparis forbesii, motivated a study of
habitat association and fine-scale mapping of both butterfly and host distributions. Often
the study of habitat associations for rare or threatened species is complicated by habitat
loss. In the case of M. thornei, the range is naturally small, which provides an opportunity
to investigate small scale variation in vegetation and geographic features as they may
affect larval and adult butterflies. Specifically, the following questions were posed: How
much of the range of the host plant is occupied by M. thornei within the focal geographic
area? What biotic and abiotic features predict the presence and abundance of M. thornei?
How does tree age affect larval performance? These questions were addressed with a
combination of field observations and laboratory experiments involving caterpillars. H.
forbesii size (diameter at breast height) was found to have a significant association with
the presence and absence of larval M. thornei, while slope, density of herbaceous plants
and density of H. forbesii were found to be the factors most strongly associated with adult
M. thornei. Laboratory experiments with larvae showed no effect of tree age on larval
survival, but a slight reduction in adult size for individuals reared on foliage from the
oldest trees. From a conservation perspective, the most important result is the widespread
occurrence (greater than previously reported) of M. thornei throughout the study area.
However, I caution that spatial factors (such as fragmentation, isolation and perimeter to
ii
interior ratios) could be important for M. thornei, though these factors were not addressed
directly in this study. In other words, while the presence of the host plant is essential, we
do not yet understand how the spatial arrangement of this resource might affect the
butterflies. In general, results illustrate the challenges of understanding habitat
association for a geographically-restricted species, and the utility of studying larval and
adult life history stages, both in the field and in the laboratory.
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In Copyright(All Rights Reserved)