Mapping the Emotional Landscapes of the Holocaust: Visualizing Space and Place in Survivor Trajectories

<p>Urban water demands vary across multiple spatio-temporal scales, driven by population growth, climate change, and urbanization. Demand-side management emerged as an important complementary measure to supply-side interventions to address urban water scarcity, foster water conservation, and inform water governance. Moreover, rapid development and deployment of Advanced Metering Infrastructure (AMI) and so-called digitalization in the water sector unfold new opportunities to uncover water demand patterns and model water demands at increasingly high spatial and temporal scales. However, challenges to modelling water demands arise from the uncertainties of water demands under abrupt environmental and societal change. The current Covid-19 Pandemic with the Stay-at-Home order is an example of such sources of uncertainty because it rapidly and unexpectedly changed people’s working patterns and lifestyles. Understanding and modelling water demands across spatial and temporal scales considering an uncertain world is, thus, key to designing robust demand management strategies.</p><p>In this work, we investigate urban water demand changes at multiple spatio-temporal scales in Milan (Italy). We combine different state-of-art data-driven models (i.e., Ruptures breakpoint detection framework, LightGBM, Hierarchical clustering, and Recurrent Neural Networks) to extract water demand characteristics from heterogeneous data sources, including historical time series of water consumption recorded with AMI, drinking water volumes pumped in the water distribution network, and socio-demographic characteristics of different urban districts. At the city scale, we found that a significant declining trend in water consumption occurred in 2017-2020, especially during the Pandemic and the first lockdown measures. At the sub-city scale, we explored the relationships between water demand and different socio-demographic, economic, and urban form features with data from 2004 to 2020. Finally, we analyzed AMI data collected at the water account level in 2019-2021 to assess the effect of Pandemic on demand pattern change and cross-correlate it with spatial heterogeneity of neighborhood features. While the investigation of historical demand pattern change gives insights to design long-term demand management strategies, accurate prediction of future demand can help improve short-term operational efficiency for water utilities. In this regard, in the last phase of this work, we compare state-of-art predictive models to explore how accurately machine learning/deep learning models can predict water demand at city and sub-city scales. Preliminary prediction results show that advanced models like Long Short Term Memory networks (LSTM) with wavelet transform technique can attain model accuracies (R<sup>2</sup>) of 0.80 to 0.95 for 1-day ahead prediction. </p>

Landscape structures affect pests, depending on compositional heterogeneity (the number and proportions of different habitats), configurational heterogeneity (spatial arrangement of habitats), and spatial scales. However, there is limited information on the relative effects of compositional and configurational heterogeneity on invasive pests and their associates (species that can benefit from invasive pests), and how they vary across spatial scales. In this study, we assayed the invasive pest Bactrocera dorsalis (Hendel) and its associated fly Drosophila melanogaster in 15 landscapes centered on mango orchards. We calculated landscape composition (forest percentage, mango percentage, and Shannon's diversity) and configuration (edge density) using two methods: spatial distance scales and combined scales. Spatial distance scales included buffer rings with radii of 0.5, 1.0, and 1.5 km, and combined scales referred to cutting or not cutting a smaller ring from larger ones. Our results shown that compositional heterogeneity positively affected B. dorsalis and D. melanogaster due to forest cover percentage, whereas configurational heterogeneity with high edge density negative effect on B. dorsalis. Forest cover had less of an effect on B. dorsalis than configurational heterogeneity, but the opposite effect was observed for D. melanogaster. Importantly, the direction and strength of forest cover and configurational heterogeneity to species did not vary with spatial distance scales or spatial combined scales. Thus, compositional and configurational heterogeneity exhibit differential effects on this invasive pest and its associator, and revealed that the relative effects of landscape structures are consistent across multiple scales. These results provide new insights into landscape effects on interconnected species using a diverse spatial-scale approach.

Climate factors, considered significant factors in regulating soil organic carbon (SOC), are not equally important at all spatial scales. However, the scale which provides the optimal relationship between climate and SOC and how that relationship varies at multiple scales are still unclear. Thus, it is crucial to study the relationship between climate factors and SOC at multiple scales when attempting to accurately predict the SOC pool and evaluate the influence of climate change on global carbon cycling. The objective of this research is to examine the scale effect of climate factors on SOC content in the Uplands of Northeast China. The relationship between climate factors and SOC content at the regional, provincial, city, and county scales was evaluated at 0–20 and 0–100 cm using correlation and regression analysis. Data for the study in the Uplands of Northeast China were examined using 1,022 profiles obtained from the Second National Soil Survey of China. A nested sampling scheme was adopted at four scales for this research. Differences exist in the degree of correlation and relative importance of temperature and precipitation at different scales. Temperature is the main climate factor controlling SOC content at the regional scale. At the provincial scale, temperature is also the main climate factor controlling SOC content in the Uplands of Heilongjiang and Eastern Inner Mongolia. SOC content in Jilin and Liaoning is influenced jointly by temperature and precipitation. Additionally, obvious regional differences occurred in the relationship between climate factors and SOC content at the provincial scale. Although this scale differs from those by other researchers, similar results have been reported in China, Spain, and the USA. The reasons might be attributed to the differences in soil type, ecosystem, and topographic position. At both the city and county scales, weak or no relation was observed between climate factors and SOC content. Climate factors have limited ability to explain SOC content variability given that SOC is affected by multiple factors which were not taken into account by this research. Therefore, multiple scales should be considered when the feedback relationship between global climate change and SOC content is studied. The relationship between climate factors and SOC content weakens with decreasing scale, especially from the provincial to city scale. The main climate factors controlling SOC content vary with different scales. The provincial scale is optimal for studying the relationship between climate factors and SOC content in the Uplands of Northeast China. Seasonal change of temperature and precipitation may also influence SOC. Thus, it is necessary to consider climate factors at multiple timescales. Moreover, further studies focusing on the scale effect of other factors (including climate) on SOC content variability will be carried out at different scales to determine the main factors controlling SOC content.

Reviewed by: Holocaust Survivors: Resettlement, Memories, Identities ed. by Dalia Ofer, Françoise S. Ouzan, and Judy Tydor Baumel-Schwartz Beth Cohen Holocaust Survivors: Resettlement, Memories, Identities Edited by Dalia Ofer, Françoise S. Ouzan, and Judy Tydor Baumel-Schwartz. New York: Berghahn Books, 2011. 306pp. As scholars recognize the importance of the postwar era and the aftermath of the Holocaust, the canon of the genocide’s literature has expanded in the twenty-first century to include the period after 1945. Studies of the displaced person camps and reception of survivors in Europe, Israel, and abroad are now respected topics of scholarly analysis. With the publication of Holocaust Survivors: Resettlement, Memories, Identities, editors Dalia Ofer, Françoise Ouzan, and Judith Tydor Baumel-Schwartz contribute a welcome and nuanced volume on survivors’ lives after the Holocaust to this growing area of Holocaust studies. Holocaust Survivors begins with an overview by Zeev Mankowitz in which he asks the reader to consider the Hebrew term She’erit Hapletah as “Saving Remnant” rather than the commonly accepted “Surviving Remnant.” The former suggests survivor agency and renewal, an interpretation that echoes throughout the book. Judith Tydor Baumel-Schwartz’s, “The Identity of Women in the She’erit Hapletah” follows, which raises the question of gender and survivors’ postwar choices. After these two essays, the collection is organized loosely around geography, with three chapters situated in Europe followed by four chapters on Israel and one each on the United States, Buenos Aires, and Australia. The final chapter explores the demographics of the worldwide survivor population. While the individual essays are generally thought provoking and well researched, it is the sum total that offers a sweep of survivor experience and provides the framework for a rich comparative analysis. Over the course of the collection certain themes emerge and recur that connect the individual studies. One, for example, is gender, which is not surprising given Baumel-Schwartz’s and Ofer’s previous work. This is the starting point for Baumel-Schwartz’s “The Identity of Women in the She’erit Hapletah: Personal and Gendered Identity as Determinants in Rehabilitation, Immigration, and Resettlement,” where she explores the lives of three women, all avowed Zionists during the war, and scrutinizes the role gender played in the postwar choice of two to remain in Europe. Micha Balf’s contribution, “Holocaust Survivors on Kibbutzim: Resettling Unsettled Memories,” looks at collective and individual memory in three kibbutzim, noting the role of women in creating more personal connections to memory, for example, memorial stones in their kibbutz cemeteries with [End Page 146] family names. While not the main thrust of her chapter, Ofer also notes the role of gender in the work that female adolescents on kibbutzim eschewed. The subject of postwar silence and commemoration is key to Balf’s work as well as Hana Jablonka’s “Holocaust Survivors in Israel: Time for an Initial Taking of Stock,” in which she challenges the conventional wisdom that survivors in Israel chose to remain silent after the war. Balf also acknowledges the role that myth making played in early commemorations. He quotes kibbutz lore that recalls Antek Zuckerman’s insistence as a surviving leader of the Warsaw Ghetto Uprising and founding member of Kibbutz Lochamei Ha-gheta’ot (“Ghetto Fighters’ Kibbutz”) that the revolt be the focus of the annual Holocaust commemoration, even though the majority of members were not ghetto survivors and did not necessarily share his feelings. Both Balf and Yablonka note the linking of Holocaust commemorations to displays by the fledgling state’s military that encouraged Holocaust memory as part of a new Israeli identity. In “New Roots for the Uprooted: Holocaust Survivors as Farmers in America,” Françoise Ouzan also points out that survivors held early memorial programs in their US farming communities. Although the authors cast a wide net, four of the contributors explore the experience of survivors in Israel. On the one hand, this feels somewhat unbalanced; on the other, it gives the reader a deeper understanding of the complexity of survivors’ resettlement in Eretz Yisrael. Yablonka, for example, argues that survivors shaped national culture while Ofer’s “Mending the Body, Mending the Soul” highlights the importance of the Zionist...

The four essays assembled in this issue of Kritika bring together a number of interesting points about the Holocaust in the USSR. The authors pose different research questions, use distinct methodologies to collect empirical evidence, write about specific demographic groups (Zeltser studies the Red Army personnel, for example), and offer commentary on a range of issues. Anna Shternshis's essay, because of its methodology, is among the last of its kind. Soon there will be no more Holocaust survivors for scholars to interview. The author managed to speak with 200 Jews who were Soviet citizens before 1939 and were evacuated from their place of residence in the western USSR into the Soviet interior. Technically, since they never came into contact with the Nazis, they should not be considered Holocaust survivors, but the matter has not been sorted out in the historical literature. Polish Jews deported into the Soviet interior in 1939-41--victims of Soviet repression to which they inadvertently owed their lives, and numerically the largest group of Polish Jews to survive the war--are automatically included among Holocaust survivors. They were allowed to return to their country after liberation and then, already after the war, massively fled from life-threatening Polish antisemitism to displaced persons (DP) camps in the American occupation zone in Germany. Only in 2007 did Attina Grossman begin to puzzle over why their status was not problematized in the literature. (1) Their recollections--including what they learned during the stopover in Poland about their families' deaths under Nazi occupation--are abundant in the archives of Holocaust testimonies, both in the Jewish Historical Institute in Warsaw and in Yad Vashem. In Shternshis's article a single pre-Holocaust finding ominously stands out. When queried about what motivated their evacuation decision before the Nazis' arrival her respondents quoted fear of neighbors--of pogroms, in other words--as the most important factor that induced them to flee. Memory of the German occupation from the time of World War I, which lingered among local residents, was benign. And since Soviet propaganda muted criticism of anything untoward that the Third Reich did after the Ribbentrop-Molotov Pact, there was no information about anti-Jewish Nazi policies in occupied Poland. People did, however, remember well the wave of pogroms that swept the area in the aftermath of the October Revolution and during the Civil War. With the prospect of collapse of the Soviet state authority as the front was rapidly approaching, many Jews fled, mindful of their neighbors' aggression a generation earlier. The study by Vladimir Solonari is grounded in the most promising sources of all those drawn upon in these essays. The historiographical breakthrough in Holocaust studies that we have observed in Poland in the last decade came through the systematic exploration of court files produced, for the most part, in the late 1940s when people were brought to justice for alleged wartime collaboration with the Germans. Solonari's essay demonstrates that similar materials--postwar trials and investigations--provide rich details about the mechanism of, and personnel involved in, killings of Jews in southern Ukraine. His study is limited to the area occupied by the Romanians, but there is no reason, it seems to me, why a similar quality of evidence could not be culled from the Soviet-era secret police archives about other regions of Ukraine and Belorussia. Anika Walke's article about Jewish youth in the Minsk ghetto makes in passing an interesting point that Soviet Jews were the most impoverished (542-43). They had no personal property to speak of, which in itself adversely affected their chances of survival in hiding compared to Jews from capitalist Eastern Europe. Among young Jewish boys raised in the Soviet Union, however, only some of them were circumcised (551), which gave them as a cohort more survival chances outside the ghetto. …

Conspicuous expansion and intensification of impervious surfaces accompanied by rapid urbanization are widely recognized to have exerted evident impacts on the urban thermal environment. Investigating the spatially and temporally varying relationships between Land Surface Temperature (LST) and impervious surfaces (IS) at multiple scales is of great significance for steering IS expansion and intensification. This study proposes an analytical framework to investigate the spatiotemporal variations of LST and its responses to IS in Wuhan, China at both city scale and sub-region scale. The summer LST patterns in 2002–2017 are extracted by Multi-Task Gaussian Process (MTGP) model from raw 8-day synthesized MODerate-resolution Imaging Spectroradiometer (MODIS) LST data. At the city scale, the weighted center of LST (LSTWC) and impervious surface fraction (ISFWC), multi-temporal trajectories and coupling indicators are utilized to comprehensively examine the spatial and temporal dynamics of LST and IS within Wuhan. At the sub-region scale, urban heat island ratio index (URI), impervious surfaces contribution index (ISCI) and sprawl rate are introduced for further quantifying the relationships of LST and IS. The results reveal that IS and hot thermal landscapes expanded by 407.43 km2 and 255.82 km2 in Wuhan in 2002–2017 at city scale. The trajectories of LSTWCs and ISFWCs are visually coherent and both heading to southeast direction in general. At the sub-region scale, the specific cardinal directions with the highest ISCI variations are examined to be the exact directions of ISFWC trajectories in 2002–2017. The results reveal that the spatiotemporal variations of LST and IS are highly correlated at both city and sub-region scales within Wuhan, thus testifying the significance of steering IS expansion and renewal for controlling urban thermal environment deterioration.

Summary1. Grazing by large ungulates may affect plant species richness and diversity at multiple spatial and/or temporal scales, because grazing affects small‐scale resource heterogeneity and plant interactions at the local scale, while effects at the landscape scale are related to grazing intensity and timing.2. We used diversity partitioning to analyse long‐ and short‐term effects of cattle grazing on plant species richness and diversity in an experimental spatial hierarchy in Mediterranean annual grassland. Short‐term changes during secondary succession in grazed plots (2003–2005) at two grazing intensities (heavy and moderate) were analysed and compared with long‐term protected vegetation. We applied Hill’s q‐diversity metrics at q = 0 (species richness) and q = 2 (reciprocal Simpson diversity) to examine the partitioning of species richness and diversity between their alpha (α) and beta (β) components in the different treatments at four spatial scales: quadrats, within exclosures, within plots, within treatments.3. At q = 0, α‐diversity was always significantly lower, and β‐diversity significantly higher, than predicted by the randomised null model. Diversity partitioning at q = 2 showed a similar trend at the quadrat scale. At the exclosure scale, partitioning exhibited a similar trend during the first 2 years of secondary succession but did not deviate from the null model in the third year, as observed in protected vegetation in all years.4. At q = 0, diversity decreased across all treatments in the short term. At q = 2, diversity was initially higher in grazed plots than in protected vegetation; α and β components both decreased during secondary succession, to the levels observed in the protected vegetation.5. Synthesis and applications.. Lower dominance in grazed vegetation indicates that grazing affects competitive exclusion at the local, small scale and accentuates natural heterogeneity (e.g. patchiness of soil resources, presence of rocks in the landscape) at a larger scale. The results of this study emphasise the importance of grazing as a management tool for maintaining plant diversity at multiple scales. This is a major concern worldwide, as the area covered by natural ecosystems continues to dwindle, necessitating management of grasslands for multiple functions such as animal production, resource protection and wildlife enhancement.

Evaluating land and runoff variations caused by urbanization is crucial to ensure the safety of people living in highly developed areas. Based on spatial scales, runoff analysis involves different methods associated with the interpretation of land cover and land use, the application of hydrological models, and the consideration of flood mitigation measures. Most studies have focused on analyzing the phenomenon on a certain scale by using a single data source and a specific model without discussing mutual influences. In this study, the runoff changes caused by urbanization are assessed and cross-analyzed on three sizes of study areas in the Zhuoshui River Basin in Taiwan, including basin (large), watershed (medium), and city (small) scales. The results demonstrate that, on the basin scale, land-cover changes interpreted from satellite images are very helpful for identifying the watersheds with urbanization hotspots that might have larger runoff outputs. However, on the watershed scale, the resolution of the land-cover data is too low, and land-cover data should be replaced by investigated land-use data for sophisticated hydrological modeling. The mixed usage of land-cover and land-use data is not recommended because large discrepancies occur when determining hydrological parameters for runoff simulation. According to present and future land-use scenarios, the influence of urbanization on runoff is simulated by HEC-1 and SWMM on watershed and city scales, respectively. The results of both models are in agreement and show that runoff peaks will obviously increase as a result of urbanization from 2008 to 2030. For low return periods, the increase in runoff as a result of urbanization is more significant and the city’s contribution to runoff is much larger than its area. Through statistical regression, the watershed runoff simulated by HEC-1 can be perfectly predicted by the city runoff simulated by SWMM in combination with other land/rainfall parameters. On the city scale, the installation of LID satisfactorily reduces the runoff peaks to pre-urbanization levels for low return periods, but the effects of LID are not as positive and are debatable for higher return periods. These findings can be used to realize the applicability and limitations of different approaches for analyzing and mitigating urbanization-induced runoff in the process of constructing a sponge city.

Measuring genetic diversity requires selection of a spatial scale of analysis. Different levels of genetic structuring are revealed at different spatial scales, however, and the relative importance of factors driving genetic structuring varies along the spatial scale continuum. Unequal gene flow is a major factor determining genetic structure in plant populations at the local level, while the effect of selection imposed by environmental heterogeneity increases with the spatial scale of analysis. At a continental and global scale genetic structure of invasive plant populations is significantly affected by founder effect and propagule transport via human vectors. Although genetic analysis at one spatial scale provides only partial information about the invasion process, little published research reports such data for the same species at multiple scales. A multi-faceted approach to investigating the genetic structure of invasive plant species that incorporates sampling at different spatial and temporal scales would provide a more complete picture of the role of genetic forces in invasion.

Studies on riparian buffers have usually focused on the amount of land needed as habitat for the terrestrial life stages of semiaquatic species. Nevertheless, the landscape surrounding wetlands is also important for other key processes, such as dispersal and the dynamics of metapopulations. Multiple elements that influence these processes should therefore be considered in the delineation of buffers. We analyzed landscape elements (forest cover, density of roads, and hydrographic network) in concentric buffers to evaluate the scale at which they influence stream amphibians in 77 distinct landscapes. To evaluate whether our results could be generalized to other contexts, we determined whether they were consistent across the study areas. Amphibians required buffers of 100-400 m of suitable terrestrial habitat, but interspecific differences in the amount of habitat were large. The presence of amphibians was related to roads and the hydrographic network at larger spatial scales (300-1500 m), which suggests that wider buffers are needed with these elements. This pattern probably arose because these elements influence dispersal and metapopulation persistence, processes that occur at large spatial scales. Furthermore, in some cases, analyses performed on different sets of landscapes provided different results, which suggests caution should be used when conservation recommendations are applied to disparate areas. Establishment of riparian buffers should not be focused only on riparian habitat, but should take a landscape perspective because semiaquatic species use multiple elements for different functions. This approach can be complex because different landscape elements require different spatial extents. Nevertheless, a shift of attention toward the management of different elements at multiple spatial scales is necessary for the long-term persistence of populations.

BackgroundThe movement behavior of an animal is determined by extrinsic and intrinsic factors that operate at multiple spatio-temporal scales, yet much of our knowledge of animal movement comes from studies that examine only one or two scales concurrently. Understanding the drivers of animal movement across multiple scales is crucial for understanding the fundamentals of movement ecology, predicting changes in distribution, describing disease dynamics, and identifying efficient methods of wildlife conservation and management.MethodsWe obtained over 400,000 GPS locations of wild pigs from 13 different studies spanning six states in southern U.S.A., and quantified movement rates and home range size within a single analytical framework. We used a generalized additive mixed model framework to quantify the effects of five broad predictor categories on movement: individual-level attributes, geographic factors, landscape attributes, meteorological conditions, and temporal variables. We examined effects of predictors across three temporal scales: daily, monthly, and using all data during the study period. We considered both local environmental factors such as daily weather data and distance to various resources on the landscape, as well as factors acting at a broader spatial scale such as ecoregion and season.ResultsWe found meteorological variables (temperature and pressure), landscape features (distance to water sources), a broad-scale geographic factor (ecoregion), and individual-level characteristics (sex-age class), drove wild pig movement across all scales, but both the magnitude and shape of covariate relationships to movement differed across temporal scales.ConclusionsThe analytical framework we present can be used to assess movement patterns arising from multiple data sources for a range of species while accounting for spatio-temporal correlations. Our analyses show the magnitude by which reaction norms can change based on the temporal scale of response data, illustrating the importance of appropriately defining temporal scales of both the movement response and covariates depending on the intended implications of research (e.g., predicting effects of movement due to climate change versus planning local-scale management). We argue that consideration of multiple spatial scales within the same framework (rather than comparing across separate studies post-hoc) gives a more accurate quantification of cross-scale spatial effects by appropriately accounting for error correlation.

Getting a grip on hydrological and sediment connectivity

This comparative study involves the influence of the Xiongnu on Han China and of the Scythians on Rome, focusing on military, cultural, economic, and political dimensions. Drawing on the Han Shu, Roman annals, and recent frontier studies, it shows that each empire responded to steppe threats by militarizing frontiers (Han fortifications and cavalry) and adapting mobile warfare. Economically, both engaged in trade and tribute. Politically, Han emperors used treatiesand tributary demands to pacify the Xiongnu; likewise, Roman emperors negotiated with steppe princes. Culturally, mutual perceptions and borrowings appear in both cases: Chinese histories emphasize Xiongnu barbarians yet Xiongnu tombs yield Chinese-style artifacts, while Greco-Roman accounts conflated Scythians with Celts and exoticized them as wandering horse nomads. Situated in the late Western Han and the late Republic/early Empire, the paper demonstrates that the Huns prompted Han centralization and frontier militarization, whereas Scythian contacts led Rome to deepen economic integration of steppe networks. This juxtaposition illuminates divergent imperial responses to nomadic pressures and advances our understanding of ancient statecraft under external threat.

PurposeThis viewpoint adds context and variety to the “decolonizing international business” debate by engaging in a discussion of the decolonial thinking approach and proposing a broader framework for analysing the link between international business (IB) activities on the one hand and colonisation and decolonisation on the other. The purpose of this paper is to inspire a more intensive engagement of IB scholarship with issues related to colonisation and decolonisation.Design/methodology/approachThis paper involves taking a reflexive review on recent calls to decolonise IB, contextualising and extending the decolonisation debate in the academic field of IB.FindingsThis paper argues that the current discussion of decolonisation should be extended beyond the decolonial thinking approach and its focus on knowledge and the cultural dimension towards a broader framework that covers both colonisation and decolonisation as well as the respective economic, political, social and cultural dimensions. It introduces the varieties of colonisation and decolonisation approach, which considers the complexities of the phenomenon and covers the economic, social, political and cultural dimensions.Research limitations/implicationsThrough its focus on foreign market expansion, international trade, global value chains and formal and informal institutions in the business environment, the academic field of IB provides several starting points for research on the link between IB activities and colonisation and decolonisation. The decolonisation debate can be used to inspire future research in IB, for example, with respect to the role of multinational corporations in colonisation and neo-colonisation processes and the implications of the emerging multipolar world order for IB.Practical implicationsIB scholars will be better informed when engaging in discussions on decolonisation and the decolonise IB project. This paper suggests considering both colonisation and decolonisation processes as well as the respective economic, political, social and cultural dimensions in research and teaching. The varieties of colonisation and decolonisation approach provides a comprehensive and flexible alternative framework to analyse issues related to colonisation and decolonisation.Social implicationsA balanced view of the implications of colonisation and decolonisation with respect to economic, political, social and cultural dimensions may suitably be incorporated in the field of IB and contribute to tackling grand societal challenges. This applies likewise to past, current and future processes of colonisation and decolonisation.Originality/valueThis paper contextualises and adds a new perspective and variety to the current debate on decolonising IB. This is valuable for engaging in discussions on decolonisation and future conceptual and empirical research on the topic.

The factors driving β-diversity (variation in community composition) yield insights into the maintenance of biodiversity on the planet. Here we tested whether the mechanisms that underlie bacterial β-diversity vary over centimeters to continental spatial scales by comparing the composition of ammonia-oxidizing bacteria communities in salt marsh sediments. As observed in studies of macroorganisms, the drivers of salt marsh bacterial β-diversity depend on spatial scale. In contrast to macroorganism studies, however, we found no evidence of evolutionary diversification of ammonia-oxidizing bacteria taxa at the continental scale, despite an overall relationship between geographic distance and community similarity. Our data are consistent with the idea that dispersal limitation at local scales can contribute to β-diversity, even though the 16S rRNA genes of the relatively common taxa are globally distributed. These results highlight the importance of considering multiple spatial scales for understanding microbial biogeography.