Distribution patterns of genetic variation across landscapes at multiple scales: Empirical and modelling approaches with organisms from 10(-6) to .10 meters in size

I explored the effects of landscape structure on the distribution of genetic diversity at multiple scales by pursuing diverse empirical and modelling studies. I investigated the scaling patterns of soil properties across an elevational gradient of changing vegetative communities and soil types in the Front Range of Colorado using a multiscale nested systematic sampling scheme that covered five orders of magnitude. Using semivariograms on log-log plots I observed consistent and general scaling patterns across diverse sites for soil pH, water content, and organic matter content, while I observed no significant patterns for soil biomass. Using the same soil samples generated with the multi-scale sampling scheme, I investigated the diversity and distribution of soil Crenarchaeota, a newly discovered group of microorganisms which are ubiquitous in soil and aquatic habitats. I used a dilution technique to identify the most abundant lineages of soil Crenarchaeota, as defined by 16S rRNA sequence, and found that most fall within a few clusters of closely related lineages, a pattern which is in agreement with theoretical predictions, and I hypothesize that these distinct clusters are different functional groups. I investigated general properties of four existing neutral landscape models and two cellular automata-based models which I developed by using several landscape metrics: the contagion index, the scaling exponent, semivariograms and patch size distributions. I describe the possible ranges of these metrics based on empirical data and theory, and conclude that those models which incorporate cellular automata rules and explicitly i incorporate multiple scales reproduce more of the full range of behavior exhibited by natural landscapes than those which do not. I investigated the distribution of genetic diversity of the allopatrically distributed foxtail pine (Pinus balfouriana) at the subspecific and population levels. While differentiation between the two subspecies is small but significant, interpopulation differentiation within the northern subspecies is markedly higher. I suggest that the strong genetic homogenizing forces typically operating in conifers have been overcome by a strong mountain island effect in which historical effects have been amplified in small and ecologically marginal populations at the extreme lower limit of the species' elevational distributions.