Effects of population, latitude, and individual tree to leaf variation in oaks: An empirical study and simulation of sampling strategies in bur oak (Quercus macrocarpa, Fagaceae)

PREMISEOaks are notoriously variable in leaf morphology, but little is known regarding the partial contributions of climate, population, latitude, and individual tree to total variation in leaf morphology. This study examines the contributions of within-tree, among-tree, and among-site variation to the total variation in leaf morphology in bur oak (Quercus macrocarpa), one of North Americas most geographically widespread oak species. METHODSSamples were collected from four sites each at northern, central, and southern latitudes of the bur oak range. Ten leaf size traits were measured, and variance in these traits and eight ratios was partitioned into tree, population, and latitude components. We then parameterized a series of leaf collections simulations using empirical covariance among leaves on trees and trees at sites. KEY RESULTSLeaf size measurements were highly responsive to latitude. Site contributed more than tree to total variation in leaf morphology. Simulations suggest that power to detect among-site variance in leaf morphology increases with either increases in leaves per tree (10-11 leaves from each of 5 trees) or trees per site (5 leaves from each of 10+ trees). CONCLUSIONSOur study demonstrates the utility of both simulating sampling and controlling for variance in sampling for leaf morphology, whether the questions being addressed are ecological, evolutionary, or taxonomic. Simulation code is provided to help researchers plan sampling strategies to maximize the ability to detect among-site variance in leaf morphology.