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Variation among populations of Clarkia Unguiculata (Onagraceae) along altitudinal and latitudinal gradients¹

Section of Ecology and Systematics, Corson Hall, Cornell University, Ithaca, New York 14853

We investigated phenotypic variation in 15 traits in greenhouse-grown plants from 16 populations of Clarkia unguiculata from three elevational habitats and six latitudinal transects. Populations from the lowest and highest elevations were geographically and ecologically marginal within the species' range. We (1) describe patterns of trait variation with elevation and latitude; (2) compare latitutidinal variation between marginal and central areas of the species' range; and (3) compare patterns of variation within C. unguiculata to interspecific patterns within the genus. Although there was some evidence that traits varied clinally (i.e., increased/decreased monotonically) along environmental gradients, interaction effects between altitude and latitude dominated patterns of variation. For most traits, latitudinal trends at the low-elevation margin of the species' range differed from trends at mid- and high-elevation areas. Based on interspecific comparisons, populations at the hotter, more arid ends of both environmental gradients were expected to have rapid development, small flowers and vegetative size, low levels of herkogamy and protandry, and high rates of gas exchange. Instead, we found that while some traits were correlated with one gradient in the expected way (e.g., development time with elevation, gas-exchange physiology with latitude), all traits were not consistently associated with each other along both gradients, and intraspecific patterns of variation differed from interspecific patterns.

Key Words: altitude • Clarkia unguiculata • elevation • floral traits • geographic variation • marginal and central populations • morphology • Onagraceae • phenology • physiology

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