Premise of the study:Low-elevation surveys with small aerial drones (micro–unmanned aerial vehicles [UAVs]) may be used for a wide variety of applications in plant ecology, including mapping vegetation over small- to medium-sized regions. We provide an overview of methods and procedures for conducting surveys and illustrate some of these applications.Methods:Aerial images were obtained by flying a small drone along transects over the area of interest. Images were used to create a composite image (orthomosaic) and a digital surface model (DSM). Vegetation classification was conducted manually and using an automated routine. Coverage of an individual species was estimated from aerial images.Results:We created a vegetation map for the entire region from the orthomosaic and DSM, and mapped the density of one species. Comparison of our manual and automated habitat classification confirmed that our mapping methods were accurate. A species with high contrast to the background matrix allowed adequate estimate of its coverage.Discussion:The example surveys demonstrate that small aerial drones are capable of gathering large amounts of information on the distribution of vegetation and individual species with minimal impact to sensitive habitats. Low-elevation aerial surveys have potential for a wide range of applications in plant ecology.

Cities and adjacent regions represent foci of intense human activity and provide unique opportunities for studying human-mediated dispersal and gene flow. We examined the effect of landscape features on gene flow in the invasive grass across an urban-rural interface at the edge of its expanding range. We used genome-wide single-nucleotide polymorphism surveys of individuals from 22 locations. Resistance surfaces were created for each landscape feature, using ResistanceGA to optimize resistance parameters. Our Structure analysis identified three distinct clusters, and diversity analyses support the existence of at least three local introductions. Multiple regression on distance matrices showed no evidence that development, roads, canopy cover or agriculture had a significant influence on genetic distance in Geographical distance was a mediocre predictor of genetic distance and reflected geographical clustering. The model of rivers acting as a conduit explained a large portion of variation in genetic distance, but the lack of evidence of directional gene flow eliminated hydrochory as a dispersal mechanism. These results and observations of the distribution of populations in disturbed sites indicate that the influence of rivers on patterns of dispersal of probably reflects seed dispersal due to human recreational activity.

The potential for rapid evolution in invasive species makes them useful for studying adaptive responses of populations to novel environments. However, phenotypic divergence during invasion is not necessarily due to selection, but may be a product of neutral processes resulting from population bottlenecks during colonization and range expansion. We investigated phenotypic adaptation during the establishment and range expansion of the invasive bunchgrass, slender false brome (Brachypodium sylvaticum; Poaceae). Utilizing a novel approach, we made robust comparisons of functional traits using genetic similarity based on unique alleles to determine the genetic probability of contribution from native source regions and integrated these probabilities into our Q -F comparisons for 12 physiological and anatomical traits associated with drought stress in the introduced range. Our results indicate phenotypic divergence greater than neutral expectations in five traits between native and invasive populations, indicating selective divergence occurred during invasive species establishment. The results indicate that the majority of divergence in B. sylvaticum occurred after introduction to the novel environment, but prior to invasive range expansion. This study provides evidence for adaptive genetic differentiation during the establishment of an invasive species, while also describing a robust method for the detection of selective processes after species introduction to a novel environment.

Rapid range expansion of newly invasive species provides a unique opportunity for studying patterns of dispersal and gene flow. In this thesis, I examined the effect of landscape features on gene flow in the invasive grass Brachypodium sylvaticum at the edge of its expanding range. I used genome-wide Single Nucleotide Polymorphism (SNP) surveys of individuals from 22 locations in the Clackamas Watershed in the Portland, Oregon metropolitan region to assess genetic diversity and structure, to identify putative source populations, and to conduct landscape genetic analyses. Resistance surfaces were created for each landscape feature, using ResistanceGA to optimize resistance parameters. My STRUCTURE analysis identified three distinct clusters, and diversity analyses support the existence of at least two local introductions. Multiple Regression on distance Matrices (MRM) showed no evidence that development, roads, canopy cover, or agriculture had a significant influence on genetic distance in B. sylvaticum. The effect of geographic distance was marginal and reflected geographic clustering. The model of rivers acting as a conduit explained a large portion of variation in genetic distance. Results indicate that rivers influence patterns of dispersal of B. sylvaticum by human recreational activity centering on use of rivers, and possibly due to movement of deer.