Rats About Town: A Systematic Review of Rat Movement in Urban Ecosystems

Abstract

Norway and black rats (Rattus norvegicus and Rattus rattus) are ubiquitous urban pests, inhabiting cities worldwide. Despite their close association with people, urban rats remain difficult to control. This can be partly attributed to a general lack of information on basic rat ecology to inform management efforts. In this systematic review and narrative synthesis, we collate the published literature to provide a comprehensive description of what is known about urban rat movement, including information on home range, site fidelity, dispersal, movement patterns, barriers to, and factors impacting, movement. We also discuss the methodologies used to track and infer rat movement, as well as the advantages and limitations of employing these techniques. Our review suggests that the distances traveled by urban rats are location-specific, determined by both local resource availability and barriers to movement such as roadways. Although roads may impede rat movement, genetic techniques suggest that rats traverse roadways more often than revealed by capture-based tools, while long-distance dispersal events by either natural migration or facilitated by humans (i.e., as stowaways in transport vehicles) can maintain connectivity among distant populations. Because rat movement patterns are related to the transmission of rat-associated pathogens and the success of rodent control programs, these results have implications for city planners, pest control efforts, and public health. Therefore, we emphasize the importance of understanding local rat movement patterns in order to devise and deploy efficient and effective rat mitigation initiatives in urban centers.

Interplay between historical and current features of the cityscape in shaping the genetic structure of the house mouse (Mus musculus domesticus) in Dakar (Senegal, West Africa)

“…Deviations from the main genetic pattern resulting from historical processes can be attributed to the current heterogeneity of the cityscape in terms of habitat quality for the house mouse (Adrichem et al, 2013;Byers et al, 2019;Combs et al, 2018a,b;Lambert et al, 2017;Lucaccioni et al, 2016;Masi et al, 2010;Santos et al, 2017). Spatial variations in the level of genetic differentiation are often interpreted as reflecting the presence of physical barriers to individual dispersal, while they may actually result from variations in effective population size, i.e.…”

“…Such a demographic process can be especially relevant for commensal rodents as natural dispersal distances (i.e. not human-mediated) of these species are generally short ranged (< 1 km) and mainly prompted by the lack of feeding and harborage sites (Byers et al, 2019;Pocock et al, 2005). In a very large and spatially continuous population, gene flow will occur through step-by-step migration over generations (IBD).…”

“…In these areas, the presence of numerous warehouses to stock different food products such as groundnuts, rice, sugar and flour (Ba et al, 2013) would allow to sustain large and continuous population of mice. The second situation could explain why high-standing residential areas, which are already known to be less prone to commensal rodent infestations (Adrichem et al, 2013;Byers et al, 2019;Combs et al, 2018a,b;Lambert et al, 2017;Masi et al, 2010), are characterized by low levels of genetic diversity (H s ) and high levels of differentiation.…”

“…Rodent control actions are costly, and classical control protocols, relying mostly on poisoning, have proven to be quite inefficient in reducing urban rodent densities in the long term (Parsons et al, 2017;Richardson et al, 2017). It is now recognized that the development of more efficient management strategies requires a better understanding of urban rodent evolutionary ecology (Byers et al, 2019;Combs et al, 2018a;Feng and Himsworth, 2014;Makundi and Massawe, 2011;Parsons et al, 2017;Singleton et al, 1999) and notably of variations in gene flow (Combs et al, 2018a,b;Gardner-Santana et al, 2009;Johnson and Munshi-South, 2017;Kajdacsi et al, 2013;Parsons et al, 2017;Richardson et al, 2017). For instance, identifying genetic clusters can allow defining meaningful spatial units for control actions (Combs et al, 2018a;Kajdacsi et al, 2013;Richardson et al, 2017).…”

“…Such genetic breaks have been attributed to physical barriers to dispersal (waterway in Baltimore, USA -Gardner-Santana et al, 2009; roads and topography in Pau de Lima, Salvador, Brazil -Kajdacsi et al, 2013;Richardson et al, 2017) or spatial heterogeneity in habitat quality that impacts local population size (resource availability varying with socioeconomic features of urban infrastructures, Manhattan, USA -Combs et al, 2018b). The need to integrate socioeconomic features of the urban environment in population dynamic and genetic studies of commensal rodents is advocated by previous works that have shown that areas with poor housing conditions (including building material quality, sanitation status within and outside the houses) and commercial premises are more prone to rodent infestations than high-standing residential or touristic areas (Adrichem et al, 2013;Byers et al, 2019;Combs et al, 2018a;Jassat et al, 2013;Lambert et al, 2017;Lucaccioni et al, 2016;Masi et al, 2010;Santos et al, 2017). In addition to current features, spatial genetic patterns may also reflect past demographic events related to cityscape evolution during the historical timeframe of urbanization Lourenço et al, 2017).…”