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Distributions and light adaptations in a set of forest violets (Viola).
Adkison, Greg*,1, Gleeson, Scott2, 1 Western Carolina University, Cullowhee, NC2 University of Kentucky, Lexington, KY
ABSTRACT- A species′ distribution is a pattern of abundance that reflects the match between trait values and the environment. Limiting trait theory predicts that a species′ abundance peaks in habitats where traits that potentially limit fitness are optimal and that it declines as these traits become suboptimal. This prediction was studied in the understory of an eastern deciduous forest by examining four traits in several violets (Viola), a group that stood out in prior community-level work because of their striking range of distributions. V. blanda and V. sororia span much of the primary gradient in this forest, whereas V. hirsutula, V. triloba, and V. canadensis have rather narrow distributions. V. pubescens and V. rostrata were particularly interesting because their distributions overlap along much of the gradient but peak at opposite ends. Individuals were randomly sampled in six distinct sites along a transect that spanned the forest′s primary environmental gradient. Several intriguing patterns were detected, especially in V. pubescens and V. rostrata. First, the trait values for these two species fall fairly close to the community mean trait values along the gradient. Second, in four cases (V. pubescens SLA; V. rostrata leaf size, etiolation, leaf:shoot) the traits are fixed across the gradient. In the other four cases (V. pubescens leaf size, etiolation, leaf:shoot; V. rostrata SLA) trait values change across the gradient, presumably due to phenotypic plasticity or ecotypic differentiation. In each case the shift is in the same direction as the community mean and generally with lower slope. Interestingly, the one trait that is fixed in V. pubescens is the only trait that is variable in V. rostrata. Third, except for leaf:shoot in V. pubescens, all patterns of deviation from the community mean across the gradient are consistent with trait limitation: deviation increases away from the peak niche position.
Key words: light adaptations, distribution limits, forest herb community