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The coronavirus disease 2019 (COVID-19) pandemic is straining public health systems worldwide, and major non-pharmaceutical interventions have been implemented to slow its spread.sup.1-4. During the initial phase of the outbreak, dissemination of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was primarily determined by human mobility from Wuhan, China.sup.5,6. Yet empirical evidence on the effect of key geographic factors on local epidemic transmission is lacking.sup.7. In this study, we analyzed highly resolved spatial variables in cities, together with case count data, to investigate the role of climate, urbanization and variation in interventions. We show that the degree to which cases of COVID-19 are compressed into a short period of time (peakedness of the epidemic) is strongly shaped by population aggregation and heterogeneity, such that epidemics in crowded cities are more spread over time, and crowded cities have larger total attack rates than less populated cities. Observed differences in the peakedness of epidemics are consistent with a meta-population model of COVID-19 that explicitly accounts for spatial hierarchies. We paired our estimates with globally comprehensive data on human mobility and predict that crowded cities worldwide could experience more prolonged epidemics. Analysis of spatial heterogeneity of crowding in China and Italy, together with COVID-19 case data, show that cities with higher crowding have longer epidemics and higher attack rates after the first epidemic wave., Author(s): Benjamin Rader [sup.1] [sup.2] , Samuel V. Scarpino [sup.3] [sup.4] [sup.5] , Anjalika Nande [sup.6] , Alison L. Hill [sup.6] [sup.7] , Ben Adlam [sup.6] , Robert C. Reiner [...]

The context of mass gatherings Mass gatherings--which include major sporting tournaments, and political, cultural, religious and artistic events--are attended by a sufficient number of people to strain the planning and [...]

Most marine populations are sustained by the entry of juveniles that have survived the larval phase, during which time most die. The number of survivors depends strongly on the quality of the eggs produced by spawning females, but it is not known how the social conditions under which breeding occurs influence the quality of larvae produced. Here I show that the density of females interacting with breeding mothers directly influences the size of larvae produced, through a stress-related mechanism. On the Great Barrier Reef of Australia, breeding pairs of a damselfish, Pomacentrus amboinensis, were isolated on habitat patches, and additional females that could not access the spawning site were added at four densities (0, 1, 3, or 6 females). Additional females increased aggressive interactions by mothers and increased the levels of the stress hormone, cortisol, in their ovaries, leading to reduced larval size. Neither egg output nor yolk size of the larvae was influenced by female density. Pairs breeding in isolation produced the largest larvae; current theory suggests that these larvae should contribute most to subsequent population replenishment events. This social mechanism may influence which females effectively contribute to the next generation and may promote resilience in patchy or isolated populations. Key words: Allee effects; damselfish; density dependence; Great Barrier Reef Australia; larval size, maternal effects; offspring quality; Pomacentrus amboinensis; silver-spoon effect; social interactions; stress.