Landscape-Level Phenology of a Threatened Butterfly: A GIS-Based Modeling Approach |
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Authors: | Stuart B Weiss Andrew D Weiss |
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Institution: | (1) Center for Conservation Biology, Department of Biological Sciences, Stanford University, Stanford, California 94305, USA , US |
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Abstract: | Phenology of organismal development varies between growing seasons according to the weather and also varies within growing
seasons across topoclimatic gradients. Combining these factors is necessary to predict landscape-level patterns of phenology
and their consequences for population dynamics. We developed a model on a Geographic Information System (GIS) that predicts
phenology of adult emergence of the threatened Bay checkerspot butterfly across complex terrain under variable weather. Physiological
time was modeled by accumulated slope-specific direct insolation. Insolation sums through growing seasons were calculated
for each cell of a digital terrain model (skipping over cloudy days) until a threshold for adult emergence was reached. Emergence
times of adult butterflies for a given year were then mapped out across a 100-ha area. To generate predicted emergence curves
for the population in a given year, these maps ofemergence times were then modified by incorporating microdistributions of
postdiapause larvae. Different larval microdistributions changed both the magnitude and shape of emergence curves under the
same yearly weather and could change mean population-wide emergence dates by 11 days. Reproductive success in this butterfly
is strongly dependent on the timing of adult emergence, and these models provide insights into the effects of weather, topography,
and population history on population dynamics. Because adult emergence phenology is often a key component of reproductive
success for insects, understanding the components of phenological variation in space and time in complex terrain may provide
insights into population dynamics for management of pests and conservation of rare species.
Received 2 December 1997; accepted 24 March 1998. |
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Keywords: | : butterfly phenology topoclimate insolation Geographic Information System (GIS) spatially explicit weather insect |
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