Adaptations of Andropogon gerardii and Schizachyrium scoparium in disjunct populations northeast of their contiguous range

Geographically and/or ecologically isolated populations are considered to be biological units just below the species level. They are of particular importance because they are often the potential forerunners of new species. These populations often exhibit unique adaptations to the to extreme and often fluctuating environmental conditions in which they typically occur. In this study, the adaptations of northern disjunct populations of two warm-season grasses. Andropogon gerardii Vitman and Schizachyrium scoparium (Michx.) Nash. were compared with populations located in the once-contiguous grassland biome. Existing studies of the ecology of these species was summarized. The genetic variation between disjunct and central-range populations of these species (as expressed by phenotypic expression in morphology, physiology, and phenology) was examined for three life-stages: seed, young plants, and mature plants.;Germination of seed from disjunct populations of S. scoparium exhibited little evidence of differentiation from central-range populations. Disjunct populations of A. gerardii maintained viability for a longer duration and exhibited greater germination than central-range populations in the northern climate.;Disjunct populations of S. scoparium had greater vigor while disjunct populations of A. gerardii had reduced vigor in a northern climate compared to central populations. Plants decreased in phenologic fitness, but increased in vegetative (A. gerardii) and reproductive (S. scoparium) vigor with increased environmental distance between their source and the common garden site near Rapid River, Michigan.;Northern populations of both species initiated flowering and entered dormancy earlier than southern populations. The inability of the southern source plants to consistently produce viable seeds in a northern location was the result of delayed phenology in combination with the short northern growing season.;Leaf morphology of S. scoparium was distinctly different for central and disjunct populations. Andropogon gerardii leaf morphology was less distinct.;For both species, the spatial pattern of plant variations on the landscape is better represented by environmental distance and grouping measures than by geographical distance. The Ecological Classification System shows potential for use in developing guidelines for plant transplantation.