Spatial Population Genomics and Landscape Ecology of Urban Brown Rats (Rattus norvegicus)

Spatial patterns of genetic variation provide a lens into the ecological and evolutionary responses of wildlife populations to landscape heterogeneity, though our understanding of urban landscapes remains limited. Further, it remains unclear whether species exhibit parallel responses to independent landscapes. Commensal rodents are widely distributed within cities and around the world, offering a useful model for understanding the influence of cities on gene flow, genetic drift, and habitat distribution. Here I study the population genetics and landscape ecology of brown rats (Rattus norvegicus) in four urban landscapes, New York City (NYC), New Orleans (NOL), Salvador (SAL), Vancouver (VAN), using genome-wide SNPs to understand the influence of urban landscapes on eco-evolutionary processes governing their distribution and functional connectivity.Rat populations in each city exhibited significant genetic discontinuities that coincide with landscape features, despite widespread isolation-by-distance processes. Genetic variation in NYC and SAL rats was clinal, but I identified genetic clusters separated by areas with lower genetic diversity and reduced migration. Rats in NOL and SAL exhibited stark genetic structure that coincided with a canal and major roadways, respectively. I identified spatially restricted dispersal in all populations leading to parallel decays in spatial autocorrelation with increased distance. Habitat suitability modeling revealed a consistent response of rat distribution to human population density, income, and building characteristics. Landscape genetic modeling indicated that models incorporating features of the built physical environment consistently predict gene flow processes, though unique landscape effects were identified in each city, particularly at local spatial scales. Further, I found that habitat suitability and genetic connectivity were uncoupled (i.e., driven by different factors) and habitat is rarely the best predictor of gene flow for urban rats. My results demonstrate the utility of multi-landscape studies in identifying generalized trends across populations, with implications for the management of invasive pest populations. Ultimately, this dissertation improves our understanding of the influence of urban landscapes on neutral evolutionary processes in widely distributed species and the ecology of commensal rodents